Phylum Arthropoda
PHYLUM ARTHROPODA
This is the phylum with the most number of animals (arthras-jointed ,pod-feet.
Characteristic features
Have jointed appendages which include legs and other body out growths e.g antennae
Have an open blood circulatory system
Have bodies which are segmented i.e with distinct divisions
Have a bilateral symmetry
Have a developed nervous system located ventrally on the body
They shed off their exo skeleton to allow growth
This phylum is divided into four classes basing on;
Number of limbs
Number of body divisions
Presence of antennae
Number of antennae
The four classes of this phylum are;
Insecta
Arachnida
Myriapoda
Crustacea
CLASS EXAMPLES NUMBER OF BODY DIVISIONS NUMBER OF LEGS NUMBER OF ANTENNAE
Insecta Grasshoppers ,housefly, bees ,beetles 3 6 2
Arachnida Spiders, ticks, mites, scorpions 2 8 None
Crustacea Woodlice, crayfish, lobsters, water flea 2 10 or more 4
Myriapoda Centipedes, millipedes Many body segments with head Many 2
CLASS INSECTA
Insects have the following characteristics
The body is divided into three body parts, namely; head, thorax, and abdomen
They have three pairs of legs on the thorax
They have a pair of compound eyes except the soldier termites
Adults have one or two pairs of wings except some few members
They breath through the spiracles and gases reach the body cells through the tracheal system
The thorax is divided into three main parts i.e. prothorax, mesothorax, and metathorax
CLASS ARACHNIDA
Arachnids have the following characteristics
They do not have wings
Its body is divided into two parts i.e cephalothorax and abdomen
It has four pairs of legs attached to the cephalothorax
It has no antennae
It has simple eyes
It breathes by means of the lung book located in the abdomen
Its mouth parts are segmented and end in
CLASS CRUSTACEA
They have the following characteristics
They are aquatic or live in damp places
They use the gills and body surface for breathing
They have two pairs of antennae
They have two body divisions namely; cephalothorax and abdomen
CLASS MYRIAPODA
They contain the following characteristics
It has an elongated body with many legs
It has one pair of antennae
It breathes through the spiracles
It lives on land
It has many body segments
It has simple eyes
DIFFERENCES BETWEEN CENTIPEDES &MILLEPEDES
CENTIPEDES MILLEPEDES
Have fewer body segments Have many body segments
Have one pair of legs per segment Have two pairs of legs per segment
Have poison claws Have no poison claws
Are carnivorous Are herbivores
Do not coil They coil
Thursday 18 September 2014
ecological succession o level notes
ECOLOGICAL SUCCESSION
ECOLOGICAL SUCCESSION
Is the gradual replacement of the community of organisms in one area or another. It may take millions of years . Once the plant have qst themselves eg will attract animals since they are the producers . succession occurs in stages known as SERAL STAGES .
The first community of plants is refered to as the PIONEER COMMUNITY . This keeps its self under harsh conditions . this place has very low rainfall very high temperature nutrients are scarce and the surface on which it grows lacks soil (rocks) eg lichens which are highly adopted to these un favourable conditions .As the successive communities colonise the area in the prvious community has made the conditions more favourable for for growth.
It weathers the surface to form soil ,it conserves and traps moisture and as they die ,they decay and contributes nutrients to the soil. In the process of succession there is a transition from simpler communities to more complex communities and this occurs through the process of colonization.
Colonization is mainly by disposal of seeds, spirals ,fruits and any vegetative part of a plant.
Types of succession
1) Primary succession
The primary community colonizes and establishes on a bare surface which has never had any community existing. It has got several stages
First stage (Gutose lichen’s stage). It is a thin layer of lichens on the surface.
Stage two. (Foliase lichen) .This means leafy
Stage three. (The moss). It is plenty with a lot of rain
Stage four (Herb) it’s anon woody eg dood
Stage five (shrub) it’s made up of woody plants.
Stage six (climax forest community) it’s made up of highly developed big trees. It starts in a few trees which are scattered and have started growth due to unfertile soils. Their leaves fall and decay and this increase the soil fertility. The forests trap rain water using their leaves. Invertebrates and rodents are attracted hence braking down the little. New species of trees colonise the area and have a faster rate of growth. The trees grow closer to form a forest. A typical forest has got a number of layers. The big trees form the emergent layer followed by the canopy layer and then the under growth (shrubs and herbs).
The temperatures are moderate with enough rainfall and high humidity. The litter becomes a habitat for invertebrates e.g. earth worms and termites which improve the soil with their droppings. When they die, decay and add humus to the soil. They create tunnels in the soil improving the soil drainage and aeration. They mix the soil, earth worms break down plant materials as they feed.
2) Secondary Succession:
It occurs when a previously existing community is completely destroyed and a new community re-establish its self.
Natural pests attacks, fire out break, volcanic eruption, flooding, droughts.
Human hazards include; – Bush clearing and burning
Wars,
Deforestation
Excavations (mining and constructions)
ECOLOGICAL SUCCESSION
Is the gradual replacement of the community of organisms in one area or another. It may take millions of years . Once the plant have qst themselves eg will attract animals since they are the producers . succession occurs in stages known as SERAL STAGES .
The first community of plants is refered to as the PIONEER COMMUNITY . This keeps its self under harsh conditions . this place has very low rainfall very high temperature nutrients are scarce and the surface on which it grows lacks soil (rocks) eg lichens which are highly adopted to these un favourable conditions .As the successive communities colonise the area in the prvious community has made the conditions more favourable for for growth.
It weathers the surface to form soil ,it conserves and traps moisture and as they die ,they decay and contributes nutrients to the soil. In the process of succession there is a transition from simpler communities to more complex communities and this occurs through the process of colonization.
Colonization is mainly by disposal of seeds, spirals ,fruits and any vegetative part of a plant.
Types of succession
1) Primary succession
The primary community colonizes and establishes on a bare surface which has never had any community existing. It has got several stages
First stage (Gutose lichen’s stage). It is a thin layer of lichens on the surface.
Stage two. (Foliase lichen) .This means leafy
Stage three. (The moss). It is plenty with a lot of rain
Stage four (Herb) it’s anon woody eg dood
Stage five (shrub) it’s made up of woody plants.
Stage six (climax forest community) it’s made up of highly developed big trees. It starts in a few trees which are scattered and have started growth due to unfertile soils. Their leaves fall and decay and this increase the soil fertility. The forests trap rain water using their leaves. Invertebrates and rodents are attracted hence braking down the little. New species of trees colonise the area and have a faster rate of growth. The trees grow closer to form a forest. A typical forest has got a number of layers. The big trees form the emergent layer followed by the canopy layer and then the under growth (shrubs and herbs).
The temperatures are moderate with enough rainfall and high humidity. The litter becomes a habitat for invertebrates e.g. earth worms and termites which improve the soil with their droppings. When they die, decay and add humus to the soil. They create tunnels in the soil improving the soil drainage and aeration. They mix the soil, earth worms break down plant materials as they feed.
2) Secondary Succession:
It occurs when a previously existing community is completely destroyed and a new community re-establish its self.
Natural pests attacks, fire out break, volcanic eruption, flooding, droughts.
Human hazards include; – Bush clearing and burning
Wars,
Deforestation
Excavations (mining and constructions)
o level notes on mutation
Mutation
MUTATION. Is a sudden change in the gene or chromosome structure or the number of chromosomes In an organism (sudden change in the genetic make up of an organism) and such a change may lead to new characters appearing in organisms or the formation of a complete new specie of organisms. It may have undesirable effects especially on humans or it may have benefits to man e.g. production of crops with desirable characteristics. It can occur naturally but there are factors which can induce mutation and these include;
Use of chemicals e.g. mustard gas and colchicines.
Use of radioactive substances e.g. X rays, ultra violet radiations, etc.
Types of Mutation.
It’s grouped according to whether the change has occurred in the gene or the chromosome.
Therefore, there are two types of mutation;
Gene mutation and Chromosomal mutation. Chromosomal mutation is more common than gene mutation. The later is mainly concerned with D.N.A and it’s not common because D.N.A is very stable and can not easily be changed. Chromosomal mutation;
Causes.
Deletion: vital genetic information may be deleted from the chromosome
A
B
C
D
E
A
B
C
D
Translocation: Part of the chromosome with vital information breaks off and joins another.
A
B
C
D
E
Part F joins
A
B
C
D
E
F
Inversion: Genetic message is reversed or when a section of chromosome breaks off and turns through 180o and attaches its self.
A
B
C
D
E
E
D
C
B
A
Duplication: it’s the doubling of the genetic information
A A
B B
C C
D D
A
B
C
D
EXAMPLES OF CHARACTERISTICS RESULTING FROM MUTATION IN MAN
Albinism: This is a result of the recessive mutant gene which prevents formation of normal skin colour/pigmentation.
Sickle cell anaemia: Presence of a recessive gene responsible for formation of abnormal haemoglobin.
Mongolism: There is an extra chromosome in the cells of mongo people. They have no resistance to diseases and therefore hardly survive. They are mentally retarded and this condition is known as Down’s syndrome.
Turner’s syndrome: is when either the X chromosome or the Y chromosome is missing in the gametes and gives the genetic constitution of XO. They are normally females who are infertile and can not get pregnant. They have under developed sex characteristics.
Achondroplasia: is dwarfism due to a dominant mutant gene. It’s a rear condition since most homozygotes die off.
Cystis fibrisis: Mucus containing cells of the pancreas and other 0rgans do not function normally. Its due to a recessive mutant gene.
XXY: is acondition which occurs when a Y sperm fertilizes an XX diploid egg. Its referred to as Klinefelter’s syndrome. Externally, this person is a male but can not produce sperms (sterile) and has some feminine features.
XXX : is a female who is mentally retarded.
Its now possible to detect that the baby will be a mutant with extra/less chromosomes before its born by a process known as amniocentesis. Some amniotic fluid is examined since it has cells from which are peeled off from the skin of the embryo. Such cells will show any defects in the chromosomes. In case of mutant signs, the pregnancy may be terminated by abortion.
Haemophilia: Is as a result of a mutant recessive gene carried on the X chromosome which prevents easy clotting of blood from even a simple wound.
Other organisms
Resistance of mutant mosquitoes to DDT
Resistance of mutant bacteria to penicillin
Polyploidy
When a cell undergoes meiosis, complete separation of chromosomes may fail. This means that some gametes are diploid and others are empty. There at fertilization one gets conditions like, i) 2n + n = 3n (triploid)
ii) 2n + 2n = 4n (tetraploid)
After fertilization, in formation of new body cells by mitosis, the chromosome set doubles meaning that the cells will be tetraploid. Its common in plants and results into varieties with desirable characteristics eg resistance to diseases, resistance to bad environmental conditions, varieties which give off very high yield and varieties which mature fast.
MUTATION. Is a sudden change in the gene or chromosome structure or the number of chromosomes In an organism (sudden change in the genetic make up of an organism) and such a change may lead to new characters appearing in organisms or the formation of a complete new specie of organisms. It may have undesirable effects especially on humans or it may have benefits to man e.g. production of crops with desirable characteristics. It can occur naturally but there are factors which can induce mutation and these include;
Use of chemicals e.g. mustard gas and colchicines.
Use of radioactive substances e.g. X rays, ultra violet radiations, etc.
Types of Mutation.
It’s grouped according to whether the change has occurred in the gene or the chromosome.
Therefore, there are two types of mutation;
Gene mutation and Chromosomal mutation. Chromosomal mutation is more common than gene mutation. The later is mainly concerned with D.N.A and it’s not common because D.N.A is very stable and can not easily be changed. Chromosomal mutation;
Causes.
Deletion: vital genetic information may be deleted from the chromosome
A
B
C
D
E
A
B
C
D
Translocation: Part of the chromosome with vital information breaks off and joins another.
A
B
C
D
E
Part F joins
A
B
C
D
E
F
Inversion: Genetic message is reversed or when a section of chromosome breaks off and turns through 180o and attaches its self.
A
B
C
D
E
E
D
C
B
A
Duplication: it’s the doubling of the genetic information
A A
B B
C C
D D
A
B
C
D
EXAMPLES OF CHARACTERISTICS RESULTING FROM MUTATION IN MAN
Albinism: This is a result of the recessive mutant gene which prevents formation of normal skin colour/pigmentation.
Sickle cell anaemia: Presence of a recessive gene responsible for formation of abnormal haemoglobin.
Mongolism: There is an extra chromosome in the cells of mongo people. They have no resistance to diseases and therefore hardly survive. They are mentally retarded and this condition is known as Down’s syndrome.
Turner’s syndrome: is when either the X chromosome or the Y chromosome is missing in the gametes and gives the genetic constitution of XO. They are normally females who are infertile and can not get pregnant. They have under developed sex characteristics.
Achondroplasia: is dwarfism due to a dominant mutant gene. It’s a rear condition since most homozygotes die off.
Cystis fibrisis: Mucus containing cells of the pancreas and other 0rgans do not function normally. Its due to a recessive mutant gene.
XXY: is acondition which occurs when a Y sperm fertilizes an XX diploid egg. Its referred to as Klinefelter’s syndrome. Externally, this person is a male but can not produce sperms (sterile) and has some feminine features.
XXX : is a female who is mentally retarded.
Its now possible to detect that the baby will be a mutant with extra/less chromosomes before its born by a process known as amniocentesis. Some amniotic fluid is examined since it has cells from which are peeled off from the skin of the embryo. Such cells will show any defects in the chromosomes. In case of mutant signs, the pregnancy may be terminated by abortion.
Haemophilia: Is as a result of a mutant recessive gene carried on the X chromosome which prevents easy clotting of blood from even a simple wound.
Other organisms
Resistance of mutant mosquitoes to DDT
Resistance of mutant bacteria to penicillin
Polyploidy
When a cell undergoes meiosis, complete separation of chromosomes may fail. This means that some gametes are diploid and others are empty. There at fertilization one gets conditions like, i) 2n + n = 3n (triploid)
ii) 2n + 2n = 4n (tetraploid)
After fertilization, in formation of new body cells by mitosis, the chromosome set doubles meaning that the cells will be tetraploid. Its common in plants and results into varieties with desirable characteristics eg resistance to diseases, resistance to bad environmental conditions, varieties which give off very high yield and varieties which mature fast.
o level notes for genetics
Genetics
GENETICS
Is the study of inheritance of characteristics or the study of transmission of characteristics/traits from the parents to the off springs.
Simplified illustrations:
sexual union
parents Male X female
↓ ↓
Gametes sperms eggs
↘ ↙
fertilization (Zygote)
↓ Growth and development
Off springs (sexually mature individual
Transmission of characters from the parents to off springs is by gametes. The male organism if animal contributes sperms and in plants pollen grains
The Female animal contributes ova and in plants it will contribute ovules. Animals have to mate to bring the two gametes together.
In human beings, they have sexual intercourse, in plants the two gametes come together by pollination (self/cross pollination). When the female and male gametes fuse, fertilization is said to have occurred. Fertilization is the fusion of the male and female nuclei to form a zygote.
In animals the zygote is formed in the fallopian tube and it begins to undergo growth (growth is an irreversible increase in the size of an organism.) Growth occurs by cell division.
The type of cell division which leads to growth is mitosis. The zygote also undergoes development. Development is the change in shape and form. Growth and development eventually lead to a sexually mature organism.
Sexual maturity in flowering plants is evidenced by the on set of flowering. In female animals its evidenced by ovulation and in male animals by sperm development.
Gametes are formed by meiosis (meiosis is the type of cell division resulting in formation of gametes and takes place in the reproductive cells while mitosis is the cell division that leads to growth of an organism and occurs in the non reproductive cells/somatic cells/body cells
Examples of somatic cells;
Liver cells, check cells, ovary cells, testis cells etc
Examples of reproductive cell;
Sortollic cells in the testis which form sperms
Follicles in the ovary that give rise to ova
The cell
With in the cell nucleus is the observable genetic material known as the chromosomes. In body cells chromosomes are found in pairs (Half from the female parent and half from the male parent.) In reproductive cells/gametes, they occur in a single set called haploid and represented by n but in body cells they occur in a double set called diploid and represented by 2n.
Chromosomes
These are threadlike structures found in the nucleus of the cell and they contain the genetic material responsible for inheritance. They form the physical basis for inheritance since their structure can be observed under a high power microscope.
Simplified structure
Each chromosome is made up of two longitudinal strands called the chromatids.
Each chromatid has a double helical DNA molecule. The two chromatids are held together by a structure called the centromere. During cell division, the spindle fibres are attached to the centromeres.
The chromosomes are present in pairs. The pairs are called the homologous pairs (they must be similar in structure and also have the same chemical composition). A species will always have the same number of chromosomes. This is called the chromosome number and it will always be an even number. This number is called the diploid number. During gamete formation, the homologous chromosomes separate and the gametes will have only half the number of chromosomes. This number is called the haploid number. Thus the somatic or the vegetative cells of all organisms are diploid and the gametes are haploid.
Number of chromosomes per cell nucleus varies from species to species. In man there are 46 chromosomes per nucleus (23 pairs) of somatic cells and 23 chromosomes in the gametes.
DNA
Is the chemical compound responsible for inheritance of characters.
DNA is one of the nucleic acids and the other is RNA.
IN FULL
DNA: Deoxyribo nucleic acid (less oxygen)
RNA: Ribo nucleic acid (more oxygen)
Both are similar in composition but different in structure.
Chemical composition of DNA
Contains a 5 carbon sugar (ribose sugar) in its structure and there fore has five corners.
It has a nucleic acid. An example is the phosphoric acid
Nitrogen/organic base is also present. There are four types namely
i) Adenine ii) Thymine iii) Cytosine iv) Guanine.
In both DNA and RNA adenine, Cytosine and Guanine are found.
Thymine is found in DNA while Uracil is found in RNA.
The following combine;
Adenine (A) + Thymine (T) for DNA or Adenine (A) + Uracil (U) in case of RNA.
Cytosine (C) + Guanine (G)
Always the pairing of bases as indicated above is due to the matching of their structure (i.e complimentary base pairing rule)
Formation of the DNA molecule
Formed from nucleotide units to form long chains
DNA replication
It’s the ability of DNA to produce a copy of its self.
DNA replication occurs in three stages and its catalyzed by a series of enzymes.
i) Twisted strands un wind giving two strands. The strands are still joined.
ii) Weak bonds between the nitrogen bases will be broken down to give two separate strands.
iii) One strand will induce the formation of another strand which is complimentary to it and the same thing will happen to the other strand.
After replicating, two new DNA molecules similar to the original DNA molecule are formed.
Why is DNA suitable for inheritance?
i) Because of its ability to replicate
ii) DNA is capable of carrying large a mount of genetic information
iii) DNA is a very stable chemical and therefore can not easily be changed.
Cell division
Cell division is a process which leads to cell multiplication.
It occurs in both plants and animals. Original cells which undergo division are known as parent cells and the new on ones resulting from division are known as daughter cells.
There are two types of cell division i.e Mitosis (mitotic cell division) which occurs in somatic cells and Meiosis (meiotic cell division) which occurs in reproductive cells.
MITOSIS
Stages of mitosis
1) Interphase (resting stage of the parent cell) During this stage the following happens to prepare a cell for nuclear division)
In this stage the cell builds up energy reserve in form of ATP
It also builds up food/nutrient reserve
Replication of DNA also takes place in the chromosomes. i.e the amount of DNA is doubled
There is synthesis/replication of new cell organelles/structures eg mitochondria, endoplasmic reticulum, centrioles, chloroplasts etc
prophase
Chromosomes become visible as long thin entangled threads.
The nucleolus begins to shrink and centrioles move to the opposite ends of the cell
Chromosomes shorten and they can be seen to comprise of 2 chromatid joined at the centromere
Nucleolus disappears
Nuclear membrane breaks up
Mendel’s contribution in genetics:
He was an Austrian and by practice he was a monk. He carried out experiments about inheritance in plants over 120 years ago.
The 1st experiment he carried out was referred to as monohybrid inheritance. The experiment considered one type of contrasting characters at a time. Hybrid is as a result of crossing between two different characteristics. In the first experiment mendel used pure breeding seeds
E.g tall plants crossed with tall plants Tall off springs only (no short plants)
He planted garden pea (Pisum sativum). The garden pea showed a variety of characteristics e.g colour of flowers, colour of pods, height of stems, nature and texture of pods, and shaped of pods.
The pattern of transmission of different characteristics was interesting eg when a plant showing one set of characteristic is cross pollinated with that showing opposite characteristic, the first generation off spring will be showing one parent’s characteristic.
When the first generation plants are self pollinated, a mixture of both parental characteristics is shown.
For example:
Parents: Tall cross pollinated with short
1st generation off springs: All tall
1st generation off springs self pollinated
2nd Generation off springs: ¾ tall and ¼short.
For colour of pods
Parent plants Green pods X Yellow pods
Gametes pollen grains ovules
Fertilization
1st Generation off springs green coloured pods
The seeds from the first generation are planted again and after flowering, self pollination was carried out.
1st Generation off springs Green pods X (self pollinated) green pods
Gametes pollen grains ovules
Fertilization
2nd Generation off springs ¾ green pod ¼ yellow pod plants
A mixture of green poded and yellow poded plants was got.
Mendel referred to what is responsible for the characteristic as genes carried by chromosomes.
A gene is a unit of inheritance:
There fore, A gene responsible for green pods is dominant (green pod is a dominant character) and is represented by letter G and yellow pod is a recessive character and the gene is represented by letter g.
Green pods X yellow pods
Parents GG gg
Gametes
Random fertilization
1st gen Gg Gg Gg Gg All off springs green poded
1st generation off springs self pollinated.
Parents Green pods X Green pods
Genotype Gg Gg
Gametes
Random fertilization
2nd gen GG gg Gg Gg
(GG, Gg, Gg) = ¾ 2nd generations plants with greens pods and (gg) = ¼ 2nd generation plants with yellow pods.
For height:
Tallness is dominant character and shortness is recessive character.
There fore;
Let the gene for tallness be T
Let the gene for shortness be t
There fore the genotype for the tall plant is TT and for the short plant is tt
Parents Tall plant X Short plant
Genotype T T t t
Gametes
Random fertilization
1st generation Tt Tt Tt Tt First generation plants, all tall
First generation off springs self pollinated
1st generation Tall plant X Tall plant
Genotype Tt Tt
Gametes
Random fertilization
2nd gen TT tt Tt Tt
(TT, Tt, Tt) = ¾ 2nd generation off springs tall and tt = ¼ 2nd generation off springs short.
Working out fertilization using the punnet/chi square
Pollen
ovules
T
t
T TT Tt
t Tt tt
Genetic terms
1. Genotype: is the genetic make up of an organism. From the illustrations above (Tallness), we see 3 genes TT, Tt and tt which gives 1:2:1 as the genotypic ratio.
TT and tt are known as homozygous genes
They are called so because they were formed from fusion of the same gene.
TT is homozygous dominant (tall) and tt is homozygous recessive (short)
TT and tt are pure breeds.
Tt is known as heterozygous (tall) created from different genes fusing together. Its not a pure breed.
2. Phenotype: is the external expression of a gene present in an organism. When expressing its self its known as an allele which is a short of allelomorph.
When not expressing its self, its simply termed as agene.
A dominant gene is one that over shadows a weaker gene known as a recessive gene.
A recessive gene is one that is over shadowed by a dominant gene.
This happens when both the recessive and dominant genes for a particular trait/ characteristic are present in an organism i.e heterozygous (Tt )
3. Filial generation: The off springs that result from fusion of gametes in various generations eg
F1 Generation 1st generation.
F2 Generation 2nd generation.
F3 Generation 3rd generation.
Test/back cross
Its used to determine the genotype of either homozygous dominant (TT, GG, HH) or Heterozygous (Tt, Gg, Hh). Since genotypes TT and Tt both produce tall plants, its not possible to know from the phenotype whether the tall plants are homozygous dominant or heterozygous.
The test or back cross is done by crossing the tall plants from the F1 generation with a true recessive plant (tt).
The proportion of tall and short off springs in F2 will determine the genotype in the tall F1 plants.
In case of homozygous dominant (TT), when crossed with homozygous recessive, the off springs are 100%tall
Parents (F1) Tall plant X Short plant
Genotype T T t t (Homozygous recessive)
Gametes
Random fertilization
2nd generation Tt Tt Tt Tt 2nd generation plants, all tall
An in case of Heterozygous (Tt)
Parents (F1) Tall plant X Short plant
Genotype T t t t (homozygous recessive)
Gametes
Random fertilization
2nd generation Tt tt tt Tt F2 generation plants, 50% tall and 50% short
Incomplete dominance/partial/co-dominance
This is a condition where genes controlling contrasting characteristics have equal influence when in heterozygous genotype. Such gene are said to be co-dominant genes.
E.g in hibiscus plants genes responsible for the red and white flower colours are co-dominant.
If a plant with red flowers is cross pollinated with that of white flowers, what are the possible genotype and phenotype of the F1 off springs?
Let the gene responsible for red flower colour be R and the gene for white flower colour be W. There fore the Genotype for plant with red flowers is RR and for the plant with white flowers is WW
Parents Red flower X White flower
Genotype R R W W
Gametes
Random fertilization
1st generation RW RW RW RW First generation: all pink flowered plants
F1 off springs are self pollinated, state the possible genotype, phenotype, genotypic ratio and phenotypic ratio
F1 off springs Pink flowered plant X Pink flowered plants
Genotype R W RW
Gametes
Random fertilization
2nd generation RR WW RW RW
Genotype = RR, RW and WW
Genotypic ratio= 1:2:1
Phenotype = Red flower plant (RR), Pink Flower Plants (RW and RW) and white Flower plant (WW)
Phenotypic ratio 1:2:1
Blood groups in human beings
A and B are co-dominant genes but dominant over O
Genes Possible genotype Phenotype
A AA or AO Blood group A
B BB or BO Blood group B
O O Blood O
A and B AB only Blood group AB
What is the possible genotype of off springs from a marriage between a man of blood group A and a woman of blood group B?
Possible genotype of the father: AA and AO and that of the mother: BB and BO
Parents Mother X father
Genotype B B A A
Gametes
Random fertilization
F1generation AB AB AB AB
Blood group B Blood group A
Parents Mother X Father Off springs
BB AA → all AB
BO AA → AB, AB, AO,AO
BB AO → AB, AB, BO, BO
BO AO → AB, BO, AO, O
There fore the possible blood groups of the F1 children are: A, B, AB and O
In a mixed day school, Angela got pregnant and she is of blood group B, Kapere a fellow student was accused to be responsible for her condition, which he denied. Angela gave birth to bouncing baby boy of blood group O. As an investigation was done Kapere was un cooperative and his blood group would not be discovered, but both his parents were of blood group A. Work out to find whether kapere would be the likely father of the baby.
A woman of blood group A claims that a man of blood group AB is the father of her child. A blood test reveals that the child’s blood group is O. is it possible that the woman’s claim is correct? Could the father have been of blood group B? Explain your reasoning.
Multiple allele.
Multiple allele is a situation where by more than two alleles are controlling a certain characteristic. For example alleles A, B and O control the ABO blood group system in man.
Other conditions in Man transmitted in mendellian fashion. (Monohybrid inheritance in man)
1. Albinism
Is a condition which results when the pigment for normal skin colour fails to form and this due to a recessive gene a.
Characteristics of albinism
White skin, Pink eyes and Golden hair.
To obtain an albino the child must receive recessive genes from both parents. This implies that an albino is homozygous recessive.
Gene for normal skin pigment: A and gene for Albino: a
Homozygous dominant: (AA) normal skin colour
Heterozygous: (Aa) Normal skin colour
Homozygous recessive: (aa) Failure of formation of normal skin pigment (albino)
To get a child who is an albino:
I) Both parents must be carriers
Parents Mother (carrier) X father (carrier)
Genotype A a A a
Gametes
Random fertilization
AA aa Aa Aa
AA: normal skin colour
Aa: Normal skin colour but carrier
aa: Albino
II) One parent is a carrier and the other is an albino
Parents Mother (albino) X father (carrier)
Genotype a a A a
Gametes
Random fertilization
Aa aa Aa aa
Aa: normal skin colour but carrier
aa: albino
From the above two marriages, the mode of transmission of genes is similar to the mendellian fashion.
2. Sickle cell anaemia
In this condition the person doesn’t possess bi concave shaped red blood cells but the shape is like that of a new moon. A person with sickle cells doesn’t have a large surface area so that sufficient oxygen can be transported through haemoglobin found in a normal person. People with sickle cell anaemia have short breath, tend to sleep when tired and have retarded growth.
Gene S is responsible for abnormal Haemoglobin.
Dominant gene H is responsible for normal haemoglobin.
NB: this is not an example of incomplete dominance.
Homozygous dominant HH: Normal haemoglobin
Heterozygous HS: sickle cell carrier (shows mild signs but never gets attacks)
Homozygous recessive SS: sickler
SEX DETERMINATION
Sex is determined by a special type of chromosome found in the sperms and the ova and they are termed as sex chromosomes. In man, since one chromosome is X and the second is Y, they may be referred to as heterozomes and those that are similar are autosomes. Ova can only carry the X chromosome; Sperms may either carry the X chromosome or Y chromosome. The sex of the child depends on which sperm fertilizes the egg. If its an X sperm, the off spring is XX (girl) and if it’s the Y sperm, the off spring is XY (boy). Each off spring has characteristics limited to it. These are termed as sex limited characteristics
Man Female
Have a penis Have a clitoris
Have beards No beards
Have narrow tips and nipples Have wide hips and breasts
Parents Male X female
Genotype X Y X X
Gametes
Random fertilization
XX XX XY XY
Females Males
Sex linkage: sex linked genes
Is a condition where the genes controlling a trait/characteristic have to be transmitted on a sex chromosome. Such traits are referred to as sex linked characters controlled by sex linked genes. Most of the sex linked genes are recessive and commonly found on the X chromosome and in rear cases on the Y chromosome
When the X chromosome has a recessive gene in males, normally the Y chromosome is empty. Since the chance for the Y chromosome to be empty is common, there fore males can inherit a recessive gene from a carrier mother and inherits an empty Y from the father and becomes a sufferer.
There fore sex linked characters are common in males than females. (in most cases females end up as carriers if they have a sex linked gene)
Examples of sex linked genes:
Haemophilia: Simply means failure of blood to clot such that a person bleeds for a long time.
XHXH-Normal female homozygous dominant:
XHXh-Carrier female (heterozygous)
XhXh – Female Haemophilia sufferer
XHY –normal male
XhY-Male Haemophilia sufferer
Colour blindness: is the inability to distinguish between primary colours ie red, green and blue.
XCXC-Normal female homozygous dominant:
XCXc-Carrier female (heterozygous)
XcXc – Colour blind female
XCY –normal male
XcY-Colour male
Premature balding
Browning of teeth
Porcupine man: the growth of thick hair at the entrance of the auditory canal. Its suspected to be associated with the Y chromosome because its found only in male.
GENETICS
Is the study of inheritance of characteristics or the study of transmission of characteristics/traits from the parents to the off springs.
Simplified illustrations:
sexual union
parents Male X female
↓ ↓
Gametes sperms eggs
↘ ↙
fertilization (Zygote)
↓ Growth and development
Off springs (sexually mature individual
Transmission of characters from the parents to off springs is by gametes. The male organism if animal contributes sperms and in plants pollen grains
The Female animal contributes ova and in plants it will contribute ovules. Animals have to mate to bring the two gametes together.
In human beings, they have sexual intercourse, in plants the two gametes come together by pollination (self/cross pollination). When the female and male gametes fuse, fertilization is said to have occurred. Fertilization is the fusion of the male and female nuclei to form a zygote.
In animals the zygote is formed in the fallopian tube and it begins to undergo growth (growth is an irreversible increase in the size of an organism.) Growth occurs by cell division.
The type of cell division which leads to growth is mitosis. The zygote also undergoes development. Development is the change in shape and form. Growth and development eventually lead to a sexually mature organism.
Sexual maturity in flowering plants is evidenced by the on set of flowering. In female animals its evidenced by ovulation and in male animals by sperm development.
Gametes are formed by meiosis (meiosis is the type of cell division resulting in formation of gametes and takes place in the reproductive cells while mitosis is the cell division that leads to growth of an organism and occurs in the non reproductive cells/somatic cells/body cells
Examples of somatic cells;
Liver cells, check cells, ovary cells, testis cells etc
Examples of reproductive cell;
Sortollic cells in the testis which form sperms
Follicles in the ovary that give rise to ova
The cell
With in the cell nucleus is the observable genetic material known as the chromosomes. In body cells chromosomes are found in pairs (Half from the female parent and half from the male parent.) In reproductive cells/gametes, they occur in a single set called haploid and represented by n but in body cells they occur in a double set called diploid and represented by 2n.
Chromosomes
These are threadlike structures found in the nucleus of the cell and they contain the genetic material responsible for inheritance. They form the physical basis for inheritance since their structure can be observed under a high power microscope.
Simplified structure
Each chromosome is made up of two longitudinal strands called the chromatids.
Each chromatid has a double helical DNA molecule. The two chromatids are held together by a structure called the centromere. During cell division, the spindle fibres are attached to the centromeres.
The chromosomes are present in pairs. The pairs are called the homologous pairs (they must be similar in structure and also have the same chemical composition). A species will always have the same number of chromosomes. This is called the chromosome number and it will always be an even number. This number is called the diploid number. During gamete formation, the homologous chromosomes separate and the gametes will have only half the number of chromosomes. This number is called the haploid number. Thus the somatic or the vegetative cells of all organisms are diploid and the gametes are haploid.
Number of chromosomes per cell nucleus varies from species to species. In man there are 46 chromosomes per nucleus (23 pairs) of somatic cells and 23 chromosomes in the gametes.
DNA
Is the chemical compound responsible for inheritance of characters.
DNA is one of the nucleic acids and the other is RNA.
IN FULL
DNA: Deoxyribo nucleic acid (less oxygen)
RNA: Ribo nucleic acid (more oxygen)
Both are similar in composition but different in structure.
Chemical composition of DNA
Contains a 5 carbon sugar (ribose sugar) in its structure and there fore has five corners.
It has a nucleic acid. An example is the phosphoric acid
Nitrogen/organic base is also present. There are four types namely
i) Adenine ii) Thymine iii) Cytosine iv) Guanine.
In both DNA and RNA adenine, Cytosine and Guanine are found.
Thymine is found in DNA while Uracil is found in RNA.
The following combine;
Adenine (A) + Thymine (T) for DNA or Adenine (A) + Uracil (U) in case of RNA.
Cytosine (C) + Guanine (G)
Always the pairing of bases as indicated above is due to the matching of their structure (i.e complimentary base pairing rule)
Formation of the DNA molecule
Formed from nucleotide units to form long chains
DNA replication
It’s the ability of DNA to produce a copy of its self.
DNA replication occurs in three stages and its catalyzed by a series of enzymes.
i) Twisted strands un wind giving two strands. The strands are still joined.
ii) Weak bonds between the nitrogen bases will be broken down to give two separate strands.
iii) One strand will induce the formation of another strand which is complimentary to it and the same thing will happen to the other strand.
After replicating, two new DNA molecules similar to the original DNA molecule are formed.
Why is DNA suitable for inheritance?
i) Because of its ability to replicate
ii) DNA is capable of carrying large a mount of genetic information
iii) DNA is a very stable chemical and therefore can not easily be changed.
Cell division
Cell division is a process which leads to cell multiplication.
It occurs in both plants and animals. Original cells which undergo division are known as parent cells and the new on ones resulting from division are known as daughter cells.
There are two types of cell division i.e Mitosis (mitotic cell division) which occurs in somatic cells and Meiosis (meiotic cell division) which occurs in reproductive cells.
MITOSIS
Stages of mitosis
1) Interphase (resting stage of the parent cell) During this stage the following happens to prepare a cell for nuclear division)
In this stage the cell builds up energy reserve in form of ATP
It also builds up food/nutrient reserve
Replication of DNA also takes place in the chromosomes. i.e the amount of DNA is doubled
There is synthesis/replication of new cell organelles/structures eg mitochondria, endoplasmic reticulum, centrioles, chloroplasts etc
prophase
Chromosomes become visible as long thin entangled threads.
The nucleolus begins to shrink and centrioles move to the opposite ends of the cell
Chromosomes shorten and they can be seen to comprise of 2 chromatid joined at the centromere
Nucleolus disappears
Nuclear membrane breaks up
Mendel’s contribution in genetics:
He was an Austrian and by practice he was a monk. He carried out experiments about inheritance in plants over 120 years ago.
The 1st experiment he carried out was referred to as monohybrid inheritance. The experiment considered one type of contrasting characters at a time. Hybrid is as a result of crossing between two different characteristics. In the first experiment mendel used pure breeding seeds
E.g tall plants crossed with tall plants Tall off springs only (no short plants)
He planted garden pea (Pisum sativum). The garden pea showed a variety of characteristics e.g colour of flowers, colour of pods, height of stems, nature and texture of pods, and shaped of pods.
The pattern of transmission of different characteristics was interesting eg when a plant showing one set of characteristic is cross pollinated with that showing opposite characteristic, the first generation off spring will be showing one parent’s characteristic.
When the first generation plants are self pollinated, a mixture of both parental characteristics is shown.
For example:
Parents: Tall cross pollinated with short
1st generation off springs: All tall
1st generation off springs self pollinated
2nd Generation off springs: ¾ tall and ¼short.
For colour of pods
Parent plants Green pods X Yellow pods
Gametes pollen grains ovules
Fertilization
1st Generation off springs green coloured pods
The seeds from the first generation are planted again and after flowering, self pollination was carried out.
1st Generation off springs Green pods X (self pollinated) green pods
Gametes pollen grains ovules
Fertilization
2nd Generation off springs ¾ green pod ¼ yellow pod plants
A mixture of green poded and yellow poded plants was got.
Mendel referred to what is responsible for the characteristic as genes carried by chromosomes.
A gene is a unit of inheritance:
There fore, A gene responsible for green pods is dominant (green pod is a dominant character) and is represented by letter G and yellow pod is a recessive character and the gene is represented by letter g.
Green pods X yellow pods
Parents GG gg
Gametes
Random fertilization
1st gen Gg Gg Gg Gg All off springs green poded
1st generation off springs self pollinated.
Parents Green pods X Green pods
Genotype Gg Gg
Gametes
Random fertilization
2nd gen GG gg Gg Gg
(GG, Gg, Gg) = ¾ 2nd generations plants with greens pods and (gg) = ¼ 2nd generation plants with yellow pods.
For height:
Tallness is dominant character and shortness is recessive character.
There fore;
Let the gene for tallness be T
Let the gene for shortness be t
There fore the genotype for the tall plant is TT and for the short plant is tt
Parents Tall plant X Short plant
Genotype T T t t
Gametes
Random fertilization
1st generation Tt Tt Tt Tt First generation plants, all tall
First generation off springs self pollinated
1st generation Tall plant X Tall plant
Genotype Tt Tt
Gametes
Random fertilization
2nd gen TT tt Tt Tt
(TT, Tt, Tt) = ¾ 2nd generation off springs tall and tt = ¼ 2nd generation off springs short.
Working out fertilization using the punnet/chi square
Pollen
ovules
T
t
T TT Tt
t Tt tt
Genetic terms
1. Genotype: is the genetic make up of an organism. From the illustrations above (Tallness), we see 3 genes TT, Tt and tt which gives 1:2:1 as the genotypic ratio.
TT and tt are known as homozygous genes
They are called so because they were formed from fusion of the same gene.
TT is homozygous dominant (tall) and tt is homozygous recessive (short)
TT and tt are pure breeds.
Tt is known as heterozygous (tall) created from different genes fusing together. Its not a pure breed.
2. Phenotype: is the external expression of a gene present in an organism. When expressing its self its known as an allele which is a short of allelomorph.
When not expressing its self, its simply termed as agene.
A dominant gene is one that over shadows a weaker gene known as a recessive gene.
A recessive gene is one that is over shadowed by a dominant gene.
This happens when both the recessive and dominant genes for a particular trait/ characteristic are present in an organism i.e heterozygous (Tt )
3. Filial generation: The off springs that result from fusion of gametes in various generations eg
F1 Generation 1st generation.
F2 Generation 2nd generation.
F3 Generation 3rd generation.
Test/back cross
Its used to determine the genotype of either homozygous dominant (TT, GG, HH) or Heterozygous (Tt, Gg, Hh). Since genotypes TT and Tt both produce tall plants, its not possible to know from the phenotype whether the tall plants are homozygous dominant or heterozygous.
The test or back cross is done by crossing the tall plants from the F1 generation with a true recessive plant (tt).
The proportion of tall and short off springs in F2 will determine the genotype in the tall F1 plants.
In case of homozygous dominant (TT), when crossed with homozygous recessive, the off springs are 100%tall
Parents (F1) Tall plant X Short plant
Genotype T T t t (Homozygous recessive)
Gametes
Random fertilization
2nd generation Tt Tt Tt Tt 2nd generation plants, all tall
An in case of Heterozygous (Tt)
Parents (F1) Tall plant X Short plant
Genotype T t t t (homozygous recessive)
Gametes
Random fertilization
2nd generation Tt tt tt Tt F2 generation plants, 50% tall and 50% short
Incomplete dominance/partial/co-dominance
This is a condition where genes controlling contrasting characteristics have equal influence when in heterozygous genotype. Such gene are said to be co-dominant genes.
E.g in hibiscus plants genes responsible for the red and white flower colours are co-dominant.
If a plant with red flowers is cross pollinated with that of white flowers, what are the possible genotype and phenotype of the F1 off springs?
Let the gene responsible for red flower colour be R and the gene for white flower colour be W. There fore the Genotype for plant with red flowers is RR and for the plant with white flowers is WW
Parents Red flower X White flower
Genotype R R W W
Gametes
Random fertilization
1st generation RW RW RW RW First generation: all pink flowered plants
F1 off springs are self pollinated, state the possible genotype, phenotype, genotypic ratio and phenotypic ratio
F1 off springs Pink flowered plant X Pink flowered plants
Genotype R W RW
Gametes
Random fertilization
2nd generation RR WW RW RW
Genotype = RR, RW and WW
Genotypic ratio= 1:2:1
Phenotype = Red flower plant (RR), Pink Flower Plants (RW and RW) and white Flower plant (WW)
Phenotypic ratio 1:2:1
Blood groups in human beings
A and B are co-dominant genes but dominant over O
Genes Possible genotype Phenotype
A AA or AO Blood group A
B BB or BO Blood group B
O O Blood O
A and B AB only Blood group AB
What is the possible genotype of off springs from a marriage between a man of blood group A and a woman of blood group B?
Possible genotype of the father: AA and AO and that of the mother: BB and BO
Parents Mother X father
Genotype B B A A
Gametes
Random fertilization
F1generation AB AB AB AB
Blood group B Blood group A
Parents Mother X Father Off springs
BB AA → all AB
BO AA → AB, AB, AO,AO
BB AO → AB, AB, BO, BO
BO AO → AB, BO, AO, O
There fore the possible blood groups of the F1 children are: A, B, AB and O
In a mixed day school, Angela got pregnant and she is of blood group B, Kapere a fellow student was accused to be responsible for her condition, which he denied. Angela gave birth to bouncing baby boy of blood group O. As an investigation was done Kapere was un cooperative and his blood group would not be discovered, but both his parents were of blood group A. Work out to find whether kapere would be the likely father of the baby.
A woman of blood group A claims that a man of blood group AB is the father of her child. A blood test reveals that the child’s blood group is O. is it possible that the woman’s claim is correct? Could the father have been of blood group B? Explain your reasoning.
Multiple allele.
Multiple allele is a situation where by more than two alleles are controlling a certain characteristic. For example alleles A, B and O control the ABO blood group system in man.
Other conditions in Man transmitted in mendellian fashion. (Monohybrid inheritance in man)
1. Albinism
Is a condition which results when the pigment for normal skin colour fails to form and this due to a recessive gene a.
Characteristics of albinism
White skin, Pink eyes and Golden hair.
To obtain an albino the child must receive recessive genes from both parents. This implies that an albino is homozygous recessive.
Gene for normal skin pigment: A and gene for Albino: a
Homozygous dominant: (AA) normal skin colour
Heterozygous: (Aa) Normal skin colour
Homozygous recessive: (aa) Failure of formation of normal skin pigment (albino)
To get a child who is an albino:
I) Both parents must be carriers
Parents Mother (carrier) X father (carrier)
Genotype A a A a
Gametes
Random fertilization
AA aa Aa Aa
AA: normal skin colour
Aa: Normal skin colour but carrier
aa: Albino
II) One parent is a carrier and the other is an albino
Parents Mother (albino) X father (carrier)
Genotype a a A a
Gametes
Random fertilization
Aa aa Aa aa
Aa: normal skin colour but carrier
aa: albino
From the above two marriages, the mode of transmission of genes is similar to the mendellian fashion.
2. Sickle cell anaemia
In this condition the person doesn’t possess bi concave shaped red blood cells but the shape is like that of a new moon. A person with sickle cells doesn’t have a large surface area so that sufficient oxygen can be transported through haemoglobin found in a normal person. People with sickle cell anaemia have short breath, tend to sleep when tired and have retarded growth.
Gene S is responsible for abnormal Haemoglobin.
Dominant gene H is responsible for normal haemoglobin.
NB: this is not an example of incomplete dominance.
Homozygous dominant HH: Normal haemoglobin
Heterozygous HS: sickle cell carrier (shows mild signs but never gets attacks)
Homozygous recessive SS: sickler
SEX DETERMINATION
Sex is determined by a special type of chromosome found in the sperms and the ova and they are termed as sex chromosomes. In man, since one chromosome is X and the second is Y, they may be referred to as heterozomes and those that are similar are autosomes. Ova can only carry the X chromosome; Sperms may either carry the X chromosome or Y chromosome. The sex of the child depends on which sperm fertilizes the egg. If its an X sperm, the off spring is XX (girl) and if it’s the Y sperm, the off spring is XY (boy). Each off spring has characteristics limited to it. These are termed as sex limited characteristics
Man Female
Have a penis Have a clitoris
Have beards No beards
Have narrow tips and nipples Have wide hips and breasts
Parents Male X female
Genotype X Y X X
Gametes
Random fertilization
XX XX XY XY
Females Males
Sex linkage: sex linked genes
Is a condition where the genes controlling a trait/characteristic have to be transmitted on a sex chromosome. Such traits are referred to as sex linked characters controlled by sex linked genes. Most of the sex linked genes are recessive and commonly found on the X chromosome and in rear cases on the Y chromosome
When the X chromosome has a recessive gene in males, normally the Y chromosome is empty. Since the chance for the Y chromosome to be empty is common, there fore males can inherit a recessive gene from a carrier mother and inherits an empty Y from the father and becomes a sufferer.
There fore sex linked characters are common in males than females. (in most cases females end up as carriers if they have a sex linked gene)
Examples of sex linked genes:
Haemophilia: Simply means failure of blood to clot such that a person bleeds for a long time.
XHXH-Normal female homozygous dominant:
XHXh-Carrier female (heterozygous)
XhXh – Female Haemophilia sufferer
XHY –normal male
XhY-Male Haemophilia sufferer
Colour blindness: is the inability to distinguish between primary colours ie red, green and blue.
XCXC-Normal female homozygous dominant:
XCXc-Carrier female (heterozygous)
XcXc – Colour blind female
XCY –normal male
XcY-Colour male
Premature balding
Browning of teeth
Porcupine man: the growth of thick hair at the entrance of the auditory canal. Its suspected to be associated with the Y chromosome because its found only in male.
Variation
Variation among organisms
This refers to differences among organisms of the same species due to the differences in the genes they inherit and the environment they survive in.
Type of Variation:
There are two main types of variation namely, Environmental variation and genetic variation.
Environmental variation
This refers to differences amongst organisms of the same species due to the different factors of the environment they are exposed to. Eg , exposure of organism to different temperatures, light, humidity, nutrients, loss of body parts via accidents, dehorning of cattle by man, lightening of the skin using cosmetics.
Such variations, because they are not genetically acquired but enviromentary acquired or influenced characters, can not be inherited from parents to off their springs.
Genetic variation:
This refers to differences amongst organisms of the same species due to the differences in the genes they inherit from their parents. Eg some individuals are tall and others are short. This is because they inherited different genes from their parents. Such variations can be inherited because they are genetically determined.
Types of genetic variation:
There are two type of genetic variation and these are,
continuous variation
Discontinuous variation.
Continuous variation:
This is the type of variation of a given character/trait where by differences among organisms of the same species are slight and grade into each other.
These characters can be measured and mean, mode and median can be obtained. eg Height, weight, intelligence, waist line, length and width of structures, skin colour, yield of milk, fertility, number of grains on a maize cob.
When the above are measured for any group of organisms, the biggest percentage of the measurement are intermediates a few are of low grade and a few are of long grades
It give a normal distribution curve/bell shaped curve,/Gaussian curve when we compare many organisms referring to one continuous character.
NB: No remarkable differences in value but continuous transmission from low to intermediate to high as shown by the normal distribution graph below.
Though genetically determined can be influenced by the environment. Such features can be used in the dichotomous key.
Discontinuous variation:
This the type of variation which shows clear-cut and sharp differences amongst organisms over a given trait.
In discontinuous variation differences do not merge into each other and there fore there are no intermediate grades. Features can not be measured but can be observed and there fore we can not obtain a normal distribution curve.
Features persist through out the life time of an organism. They show distinct differences. Eg sex, finger print, tongue rollers and non tongue roller, colour blindness, taster and non tasters to PTC (phenyl thio carbamide) blood groups, sickle cell anaemia, haemophilia, skin pigmentation (normal skin colour/albinism) eye colour etc. They are not affected by environmental condition.
These traits can be used when constructing a dichotomous key.
Causes of variation include;
1. Environmental factors such as a) diet, b) altitude, c) light intensity, d) temperature, e) pathogens and diseases, f) social function and g) age.
2. Genetic factors such as a) crossing over between homologous chromosomes during prophase I of meiosis, b) mutations (which bring about mainly discontinuous variation in a population)
Variation among organisms
This refers to differences among organisms of the same species due to the differences in the genes they inherit and the environment they survive in.
Type of Variation:
There are two main types of variation namely, Environmental variation and genetic variation.
Environmental variation
This refers to differences amongst organisms of the same species due to the different factors of the environment they are exposed to. Eg , exposure of organism to different temperatures, light, humidity, nutrients, loss of body parts via accidents, dehorning of cattle by man, lightening of the skin using cosmetics.
Such variations, because they are not genetically acquired but enviromentary acquired or influenced characters, can not be inherited from parents to off their springs.
Genetic variation:
This refers to differences amongst organisms of the same species due to the differences in the genes they inherit from their parents. Eg some individuals are tall and others are short. This is because they inherited different genes from their parents. Such variations can be inherited because they are genetically determined.
Types of genetic variation:
There are two type of genetic variation and these are,
continuous variation
Discontinuous variation.
Continuous variation:
This is the type of variation of a given character/trait where by differences among organisms of the same species are slight and grade into each other.
These characters can be measured and mean, mode and median can be obtained. eg Height, weight, intelligence, waist line, length and width of structures, skin colour, yield of milk, fertility, number of grains on a maize cob.
When the above are measured for any group of organisms, the biggest percentage of the measurement are intermediates a few are of low grade and a few are of long grades
It give a normal distribution curve/bell shaped curve,/Gaussian curve when we compare many organisms referring to one continuous character.
NB: No remarkable differences in value but continuous transmission from low to intermediate to high as shown by the normal distribution graph below.
Though genetically determined can be influenced by the environment. Such features can be used in the dichotomous key.
Discontinuous variation:
This the type of variation which shows clear-cut and sharp differences amongst organisms over a given trait.
In discontinuous variation differences do not merge into each other and there fore there are no intermediate grades. Features can not be measured but can be observed and there fore we can not obtain a normal distribution curve.
Features persist through out the life time of an organism. They show distinct differences. Eg sex, finger print, tongue rollers and non tongue roller, colour blindness, taster and non tasters to PTC (phenyl thio carbamide) blood groups, sickle cell anaemia, haemophilia, skin pigmentation (normal skin colour/albinism) eye colour etc. They are not affected by environmental condition.
These traits can be used when constructing a dichotomous key.
Causes of variation include;
1. Environmental factors such as a) diet, b) altitude, c) light intensity, d) temperature, e) pathogens and diseases, f) social function and g) age.
2. Genetic factors such as a) crossing over between homologous chromosomes during prophase I of meiosis, b) mutations (which bring about mainly discontinuous variation in a population)
EVOLUTION
This refers to the gradual development of complex organisms from simpler ancestral types over a long period of time. This is caused by changes in the populations resulting from inherited variations in individuals in successive generation.
Evolution begins with the production of new species which gradually differ more and more from each other until new genera, families, classes, have evolved.
Origin of life:
The exact origin of life is not known. How ever some theories have been put forward to show the origin of life which include;
Steady state theory: this suggests that life has no origin and it has been existence.
Spontaneous generation: This indicates that life arose from non living matter on numerous occasions.
Special creation: this indicates that life was created by a supernatural being at a particular time.
Cosmozaon theory: this suggests that life arrived on this planet from else where.
Biochemical evolution: Most accepted theory by scientists. It suggests that life arose from according to biochemical and physical laws which lead to formation of certain macromolecules which make up DNA and body cells.
Evolution theory explains that the different species of organisms existing today arose from common ancestors which were originally primitive but gradually under went changes along different evolutionary lines in different environments in order to survive in those environments. The trend of evolution there fore, is gradual change from primitive form of life to advance d form of life.
This refers to the gradual development of complex organisms from simpler ancestral types over a long period of time. This is caused by changes in the populations resulting from inherited variations in individuals in successive generation.
Evolution begins with the production of new species which gradually differ more and more from each other until new genera, families, classes, have evolved.
Origin of life:
The exact origin of life is not known. How ever some theories have been put forward to show the origin of life which include;
Steady state theory: this suggests that life has no origin and it has been existence.
Spontaneous generation: This indicates that life arose from non living matter on numerous occasions.
Special creation: this indicates that life was created by a supernatural being at a particular time.
Cosmozaon theory: this suggests that life arrived on this planet from else where.
Biochemical evolution: Most accepted theory by scientists. It suggests that life arose from according to biochemical and physical laws which lead to formation of certain macromolecules which make up DNA and body cells.
Evolution theory explains that the different species of organisms existing today arose from common ancestors which were originally primitive but gradually under went changes along different evolutionary lines in different environments in order to survive in those environments. The trend of evolution there fore, is gradual change from primitive form of life to advance d form of life.
Theories of evolution/mechanism of evolution
Lamarck’ theory of evolution/Lamarckism: based on acquired characters through use and disuse.
This theory was put forward by a French biologist Jean baptiste Larmarck in 1809. his theory resolves itself into 3 factors namely;
a) influence of the environment
b) Use and disuse
c) Inheritance of acquired characters
Based on the above factors, he suggested that; when an organism develops a need for a particular structure in a given environment, this will induce its appearance and there fore the structure will develop to carry out the need in that environment. This idea was based on the observation that the structures which are subjected to constant use become well developed and those which are not used tend to degenerate hence the theory of Use and disuse
For example;
i) Ancient giraffes were those living today. Lamarck urged that as the number of giraffes increased, there was shortage of food in form of grass, herbs and leaves from very short shrubs. This compelled them to stretch their necks so as to reach for leaves on higher branches of tall trees. The result was elongation of the necks.
The off springs of these giraffes inherited the longer necks, stretched further and the process was repeated until the present long necks were developed.
ii) exercise and training can lead to the development of muscles of a heavy weight lifter, since he suggested that these beneficial traits acquired in an individual’s life can be passed onto the off springs, hence evolutionary change can be achieved via transmission of acquired characteristics, This implies that a heavy weight lifter who has acquired big arm muscles produces children with big arm muscles.
However this was proved totally wrong by genetic evidence that acquired characters can be inherited. This theory there fore is not scientifically accurate.
Lamarck’ theory of evolution/Lamarckism: based on acquired characters through use and disuse.
This theory was put forward by a French biologist Jean baptiste Larmarck in 1809. his theory resolves itself into 3 factors namely;
a) influence of the environment
b) Use and disuse
c) Inheritance of acquired characters
Based on the above factors, he suggested that; when an organism develops a need for a particular structure in a given environment, this will induce its appearance and there fore the structure will develop to carry out the need in that environment. This idea was based on the observation that the structures which are subjected to constant use become well developed and those which are not used tend to degenerate hence the theory of Use and disuse
For example;
i) Ancient giraffes were those living today. Lamarck urged that as the number of giraffes increased, there was shortage of food in form of grass, herbs and leaves from very short shrubs. This compelled them to stretch their necks so as to reach for leaves on higher branches of tall trees. The result was elongation of the necks.
The off springs of these giraffes inherited the longer necks, stretched further and the process was repeated until the present long necks were developed.
ii) exercise and training can lead to the development of muscles of a heavy weight lifter, since he suggested that these beneficial traits acquired in an individual’s life can be passed onto the off springs, hence evolutionary change can be achieved via transmission of acquired characteristics, This implies that a heavy weight lifter who has acquired big arm muscles produces children with big arm muscles.
However this was proved totally wrong by genetic evidence that acquired characters can be inherited. This theory there fore is not scientifically accurate.
Darwin’s theory of evolution/ the base on natural selection or the theory of natural selection (Darwinism)
The first satisfactory explanation to the mechanism by which evolution takes place was proposed by Charles Darwin (1809-1882) and that was the theory of natural selection.
Natural selection is where by the well adapted organisms to changes in the environment are naturally favoured or selected for and survive while the poorly adapted organisms to changes in the environment are naturally selected against and die before reaching sexual maturity or before reproducing.
The well adapted and naturally favoured organisms which survive the changes in the environment pass on their beneficial traits/genes which made them to survive to their off springs (survival for the fittest)
And those which are less adapted will be naturally selected against and they will die off before reaching sexual maturity there fore leading to the elimination of un beneficial genes/traits from the population.
The first satisfactory explanation to the mechanism by which evolution takes place was proposed by Charles Darwin (1809-1882) and that was the theory of natural selection.
Natural selection is where by the well adapted organisms to changes in the environment are naturally favoured or selected for and survive while the poorly adapted organisms to changes in the environment are naturally selected against and die before reaching sexual maturity or before reproducing.
The well adapted and naturally favoured organisms which survive the changes in the environment pass on their beneficial traits/genes which made them to survive to their off springs (survival for the fittest)
And those which are less adapted will be naturally selected against and they will die off before reaching sexual maturity there fore leading to the elimination of un beneficial genes/traits from the population.
Ezymes
ENZYMES
Enzymes are biological catalysts, protein in nature which speed up and control the rate of chemical reaction in the body.
Classification of enzymes
There are two forms of enzymes,
1. Intracellular enzymes.
2. Extracellular enzymes.
Intracellular enzymes are those which work within the protoplasm of the cell in which they are made.eg respiratory enzymes (decarboxylase)
Extracellular enzymes are the enzymes which are secreted outside the cells in which they work. The majority of the digestive enzymes are extracellular.
ENZYME NOMENCLATURE
The Conventional Way of naming enzymes is,
1. By adding the suffix “ase” at the end of the food acted upon.
E.g.
Maltose is acted upon by maltase.
Sucrose is acted upon by…………sucrase
A lipid is acted upon by…………lipase
Cellulose is acted upon by……….cellulase
2. They may also be named according to the type of the reaction they catalyze
E.g.,
Dehydrogenase enzyme removes hydrogen from a compound
Transferase catalyses transfer of a group from one compound to another.
Hydrolases- splitting of large molecules into smaller molecules.
PROPERTIES OF ENZYMES
1. Enzymes are specific in the reactions they catalyze. A given enzyme catalyses and
Controls a particular reaction e.g. sucrose acts on controls not maltose.
2. They are produced in the cells of living organisms.
3. They are proteins in nature.
4. Only a small amount of enzyme is needed to produce a large amount of chemical change.
5. Enzymes are not used up in the reactions they catalyse. They remain the same after the reaction.
6. Enzymes can cause reactions to go in both directions. The direction to which the direction proceeds normally depends on concentration of reactants and products. An example Starch broken to maltose, maltose can form starch as well
7. Enzymes work but at specific (PH) degree of activity or alkalinity. Those working best in acidic conditions may not work in alkaline condition.
8. They are inactivated by chemical reactions eg cyanide (poison) such chemicals are called inhibitors.
9. They are denatured by heat.
ENZYMES
Enzymes are biological catalysts, protein in nature which speed up and control the rate of chemical reaction in the body.
Classification of enzymes
There are two forms of enzymes,
1. Intracellular enzymes.
2. Extracellular enzymes.
Intracellular enzymes are those which work within the protoplasm of the cell in which they are made.eg respiratory enzymes (decarboxylase)
Extracellular enzymes are the enzymes which are secreted outside the cells in which they work. The majority of the digestive enzymes are extracellular.
ENZYME NOMENCLATURE
The Conventional Way of naming enzymes is,
1. By adding the suffix “ase” at the end of the food acted upon.
E.g.
Maltose is acted upon by maltase.
Sucrose is acted upon by…………sucrase
A lipid is acted upon by…………lipase
Cellulose is acted upon by……….cellulase
2. They may also be named according to the type of the reaction they catalyze
E.g.,
Dehydrogenase enzyme removes hydrogen from a compound
Transferase catalyses transfer of a group from one compound to another.
Hydrolases- splitting of large molecules into smaller molecules.
PROPERTIES OF ENZYMES
1. Enzymes are specific in the reactions they catalyze. A given enzyme catalyses and
Controls a particular reaction e.g. sucrose acts on controls not maltose.
2. They are produced in the cells of living organisms.
3. They are proteins in nature.
4. Only a small amount of enzyme is needed to produce a large amount of chemical change.
5. Enzymes are not used up in the reactions they catalyse. They remain the same after the reaction.
6. Enzymes can cause reactions to go in both directions. The direction to which the direction proceeds normally depends on concentration of reactants and products. An example Starch broken to maltose, maltose can form starch as well
7. Enzymes work but at specific (PH) degree of activity or alkalinity. Those working best in acidic conditions may not work in alkaline condition.
8. They are inactivated by chemical reactions eg cyanide (poison) such chemicals are called inhibitors.
9. They are denatured by heat.
FACTORS AFFECTING ENZYME ACTIVITY
1. Substrate concentration.
If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for some time and then becomes constant. Any further increase in substrate concentration will result in a corresponding increase in the rate of the reaction.
2. Enzyme concentration.
The rate of an enzyme controlled reactions increases as the enzyme concentration increases as long as no other factors are limiting as shown above,
3. Temperature of the medium.
The rate of an enzyme- catalyzed reaction increases with temperature up to a maximum, called the optimum temperature.
Most enzymes work best (optimum temperature) between 30c-40c. Like all proteins enzymes are denatured when heated over 60c. They are in activated by low temperatures (0c and below).
4. PH.
Every enzyme has a particular PH range over which it works best. Some enzymes work best in acidic medium while others function best in alkaline medium.
Example.
Pepsin has its optimum PH at 2.2 while trypsin has its optimum PH of around 7-8 as shown below.
5. The presence of inhibitors. (These are small molecules).
They reduce the enzyme activity. They make the enzyme deformed rendering it useless hence lowering the rate of enzyme action.
6. Presence of activators.
These are mainly;
• Cofactors
• Coenzymes.
Cofactors are non protein compound, which promote efficiency activity e.g. Zn, Fe, Cu, etc.
Coenzymes are organic non- protein molecules which promote efficiency action of enzymes.
1. Substrate concentration.
If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for some time and then becomes constant. Any further increase in substrate concentration will result in a corresponding increase in the rate of the reaction.
2. Enzyme concentration.
The rate of an enzyme controlled reactions increases as the enzyme concentration increases as long as no other factors are limiting as shown above,
3. Temperature of the medium.
The rate of an enzyme- catalyzed reaction increases with temperature up to a maximum, called the optimum temperature.
Most enzymes work best (optimum temperature) between 30c-40c. Like all proteins enzymes are denatured when heated over 60c. They are in activated by low temperatures (0c and below).
4. PH.
Every enzyme has a particular PH range over which it works best. Some enzymes work best in acidic medium while others function best in alkaline medium.
Example.
Pepsin has its optimum PH at 2.2 while trypsin has its optimum PH of around 7-8 as shown below.
5. The presence of inhibitors. (These are small molecules).
They reduce the enzyme activity. They make the enzyme deformed rendering it useless hence lowering the rate of enzyme action.
6. Presence of activators.
These are mainly;
• Cofactors
• Coenzymes.
Cofactors are non protein compound, which promote efficiency activity e.g. Zn, Fe, Cu, etc.
Coenzymes are organic non- protein molecules which promote efficiency action of enzymes.
PROCESS OF URINE FORMATION
Each kidney has very minute tubular and convoluted structures known as urniferous tubules. Nephron has a double walled cup shaped structure called bowman’s capsule at its upper end.
The bowman’s capsule has numerous capillaries called glomerulus. The short region after the Bowman’s capsule is called the neck. After this the tubule is narrow and coiled. It consists of a proximal convoluted region, a Henle’s loop and a distal convoluted tubule. The post end of nephron is called collecting tubule.
Collecting tubule opens into the renal pelvis, which opens into the ureter
The waste material along with blood is brought to kidneys by the renal arteries. Blood is filtered out from blood capillaries into Bowman’s capsule under pressure which is known as Ultrafiltration. This filtrate passes through the lumen of tubular parts of nephron. During this useful products such as water, glucose, amino acid, materials, ions etc. are reabsorbedby blood capillaries surrounding the nephron. The remaining fluid contains excretory substance and is called urine. From the ureter urine passes into urinary bladder where is is stored. When the bladder is filled with urine, it contracts and urine passes out of the body.
Nephron
THE SKIN
2 Layers of the Skin
Epidermis – outer protective layer without blood vessels
Dermis – inner layer containing blood vessels, sensory nerve endings, sweat and
Functions of the Skin
Excretion – Wastes such as excess water, salt, urea and uric acid are removed from the body in sweat.
Waterproofing – The skin with its oil glands prevents the entry of water into, and loss of water out of the body.
Protection from Disease – The intact skin prevents invasion of micro-organisms and dust into the body.
Protection from Ultraviolet Rays – Pigments reduce the intake of UV rays.
Regulation of Body Temperature – The thin layer of fat cells in the dermis insulates the body. Contraction of small muscles attached to hairs forms ‘goosebumps’ and creates an insulating blanket of warm air. Also, sweat produced by sweat glands uses excess body heat to evaporate, providing a cooling effect.
Sensory Detection – The nerve endings or receptors in the dermis detect heat, cold, touch, pressure and pain.
Each kidney has very minute tubular and convoluted structures known as urniferous tubules. Nephron has a double walled cup shaped structure called bowman’s capsule at its upper end.
The bowman’s capsule has numerous capillaries called glomerulus. The short region after the Bowman’s capsule is called the neck. After this the tubule is narrow and coiled. It consists of a proximal convoluted region, a Henle’s loop and a distal convoluted tubule. The post end of nephron is called collecting tubule.
Collecting tubule opens into the renal pelvis, which opens into the ureter
The waste material along with blood is brought to kidneys by the renal arteries. Blood is filtered out from blood capillaries into Bowman’s capsule under pressure which is known as Ultrafiltration. This filtrate passes through the lumen of tubular parts of nephron. During this useful products such as water, glucose, amino acid, materials, ions etc. are reabsorbedby blood capillaries surrounding the nephron. The remaining fluid contains excretory substance and is called urine. From the ureter urine passes into urinary bladder where is is stored. When the bladder is filled with urine, it contracts and urine passes out of the body.
Nephron
THE SKIN
2 Layers of the Skin
Epidermis – outer protective layer without blood vessels
Dermis – inner layer containing blood vessels, sensory nerve endings, sweat and
Functions of the Skin
Excretion – Wastes such as excess water, salt, urea and uric acid are removed from the body in sweat.
Waterproofing – The skin with its oil glands prevents the entry of water into, and loss of water out of the body.
Protection from Disease – The intact skin prevents invasion of micro-organisms and dust into the body.
Protection from Ultraviolet Rays – Pigments reduce the intake of UV rays.
Regulation of Body Temperature – The thin layer of fat cells in the dermis insulates the body. Contraction of small muscles attached to hairs forms ‘goosebumps’ and creates an insulating blanket of warm air. Also, sweat produced by sweat glands uses excess body heat to evaporate, providing a cooling effect.
Sensory Detection – The nerve endings or receptors in the dermis detect heat, cold, touch, pressure and pain.
Excretion
Excretion
The process, by which waste product of metabolism from the system of an organism are eliminated from the body.
Organs of the Excretory System
Lungs – removal of excess carbon dioxide
Liver – produces urea and uric acid as a by-product of the breakdown of proteins
Skin – removal of excess water, salt, urea and uric acid
Urinary System – kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid
Kidneys perform several homeostatic functions:
Maintain volume of extracellular fluid
Maintain ionic balance in extracellular fluid
Maintain pH and osmotic concentration of the extracellular fluid.
Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.
Functioning of the kidney
The kidney removes metabolic and liquid toxic wastes as well as excess water from the organism.
Parts of the kidney
Renal Arteries – 2 renal arteries constantly transport blood to the kidneys.
Kidneys – 2 kidneys composed of millions of nephrons constantly filter about 170 to 200 litres of blood to produce about 1.5 to 2 litres of urine daily.
Renal Veins – 2 renal veins return useful nutrients back into the bloodstream.
Ureters – 2 ureters carry urine from the kidneys to the urinary bladder.
Urinary Bladder – The urinary bladder temporarily stores urine until it is released from the body.
Urethra – The urethra is the tube that carries urine from the urinary bladder to the outside of the body. The outer end of the urethra is controlled by a circular muscle called a sphincter.
Within each kidney there are an estimated one million microscopic nephrons, where blood filtration takes place. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a bowmans capsule surrounds each glomerulus. The blood that flows through the glomerulus is under great pressure. This causes water, glucose and urea to enter the bowmans capsule. White blood cells, red blood cells and proteins remain in the blood. As the blood continues in the excretory system, it passes through the renal tubule. During this time, reabsorption occurs: glucose and chemicals such as potassium, sodium, hydrogen, magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filtration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.
Excretion
The process, by which waste product of metabolism from the system of an organism are eliminated from the body.
Organs of the Excretory System
Lungs – removal of excess carbon dioxide
Liver – produces urea and uric acid as a by-product of the breakdown of proteins
Skin – removal of excess water, salt, urea and uric acid
Urinary System – kidneys filter the blood to form urine, which is excess water, salt, urea and uric acid
Kidneys perform several homeostatic functions:
Maintain volume of extracellular fluid
Maintain ionic balance in extracellular fluid
Maintain pH and osmotic concentration of the extracellular fluid.
Excrete toxic metabolic by-products such as urea, ammonia, and uric acid.
Functioning of the kidney
The kidney removes metabolic and liquid toxic wastes as well as excess water from the organism.
Parts of the kidney
Renal Arteries – 2 renal arteries constantly transport blood to the kidneys.
Kidneys – 2 kidneys composed of millions of nephrons constantly filter about 170 to 200 litres of blood to produce about 1.5 to 2 litres of urine daily.
Renal Veins – 2 renal veins return useful nutrients back into the bloodstream.
Ureters – 2 ureters carry urine from the kidneys to the urinary bladder.
Urinary Bladder – The urinary bladder temporarily stores urine until it is released from the body.
Urethra – The urethra is the tube that carries urine from the urinary bladder to the outside of the body. The outer end of the urethra is controlled by a circular muscle called a sphincter.
Within each kidney there are an estimated one million microscopic nephrons, where blood filtration takes place. Each nephron contains a cluster of capillaries called a glomerulus. A cup-shaped sac called a bowmans capsule surrounds each glomerulus. The blood that flows through the glomerulus is under great pressure. This causes water, glucose and urea to enter the bowmans capsule. White blood cells, red blood cells and proteins remain in the blood. As the blood continues in the excretory system, it passes through the renal tubule. During this time, reabsorption occurs: glucose and chemicals such as potassium, sodium, hydrogen, magnesium and calcium are reabsorbed into the blood. Almost all the water removed during filtration returns to the blood during the reabsorption phase. The kidneys control the amount of liquid in our bodies. Now only wastes are in the nephron. These wastes are called urine and include urea, water and inorganic salts. The cleansed blood goes into veins that carry the blood from the kidneys and back to the heart.
Excretion in amoeba
The amoeba lives in fresh water bodies like lakes, slow moving streams and ponds. Amoeba excretes excess carbon dioxide, water and ammonia. Ammonia is excreted across the cell membrane although it can also be excreted by the contractile vacuole when it dissolves in water.
Carbon dioxide is excreted by diffusing across the cell membrane. Osmoregulation is achieved by the contractile vacuole. The excess water collects in the contractile vacuole and then it migrates and fuses with the cell membrane hence releasing the water to the outside.
Excretion in insects
Insects excrete carbon dioxide and uric acid crystals. Uric acid being a nitrogenous waste product is excreted by the malpighian tubules which are found between the junctions of the mid gut projecting into the blood filled cavity.
Excretion in annelids
Excretion in the annelids such as the earthworms is carried out by the niphridia which are found in each segment. They release the waste products through the opening s found on the body surface
Excretion in birds
Birds excrete carbon dioxide and uric acid. They use the lungs to excrete carbon dioxide and the kidney to excrete uric acid.
The amoeba lives in fresh water bodies like lakes, slow moving streams and ponds. Amoeba excretes excess carbon dioxide, water and ammonia. Ammonia is excreted across the cell membrane although it can also be excreted by the contractile vacuole when it dissolves in water.
Carbon dioxide is excreted by diffusing across the cell membrane. Osmoregulation is achieved by the contractile vacuole. The excess water collects in the contractile vacuole and then it migrates and fuses with the cell membrane hence releasing the water to the outside.
Excretion in insects
Insects excrete carbon dioxide and uric acid crystals. Uric acid being a nitrogenous waste product is excreted by the malpighian tubules which are found between the junctions of the mid gut projecting into the blood filled cavity.
Excretion in annelids
Excretion in the annelids such as the earthworms is carried out by the niphridia which are found in each segment. They release the waste products through the opening s found on the body surface
Excretion in birds
Birds excrete carbon dioxide and uric acid. They use the lungs to excrete carbon dioxide and the kidney to excrete uric acid.
adaptations of xerophytes to their function
Xerophytes
These are plants which live in arid conditions such as deserts, and have a problem of dehydration.
They have the following adaptations for their survival
Some xerophytes have thick waxy cuticle impermeable to water e.g. cactus
Some have leaves modified into thorns or spines to reduce the surface area which minimizes on the rate of transpiration
Some shed off their leaves (deciduous) to reduce on the transpiration through the leaves
Some roll their leaves to trap still and damp air that reduces transpiration.
Some have sunken stomata which are guarded by hairs, the hair traps moisture which reduces on the rate of transpiration
Some have succulent tissues like stems which store water
They have a well developed tap root system for absorbing water from deep areas
These are plants which live in arid conditions such as deserts, and have a problem of dehydration.
They have the following adaptations for their survival
Some xerophytes have thick waxy cuticle impermeable to water e.g. cactus
Some have leaves modified into thorns or spines to reduce the surface area which minimizes on the rate of transpiration
Some shed off their leaves (deciduous) to reduce on the transpiration through the leaves
Some roll their leaves to trap still and damp air that reduces transpiration.
Some have sunken stomata which are guarded by hairs, the hair traps moisture which reduces on the rate of transpiration
Some have succulent tissues like stems which store water
They have a well developed tap root system for absorbing water from deep areas
Osmoregulation in plants
Plants are divided into four main groups depending on the amount of water available to them. They are; halophytes, mesophytes and hydrophytes, xerophytes.
Hydrophytes
These are plants which live partially or completely submerged in water. They have thin or no cuticle at all, no vascular tissue and reduced root systems because water is readily available to them, they also have many stomata on the upper surface.
Halophytes
These are plants that live in salty waters; they have special cells which have a higher concentration of solute than those of the ordinary plants. As a result they are able to take up water in the normal way
Mesophytes
These are plants which grow in normal water well watered soils and water lost by transpiration is replaced by absorption. They have no special means of conserving water although most of them have a well developed root system.
Xerophytes
These are plants which live in arid conditions such as deserts, and have a problem of dehydration.
Plants are divided into four main groups depending on the amount of water available to them. They are; halophytes, mesophytes and hydrophytes, xerophytes.
Hydrophytes
These are plants which live partially or completely submerged in water. They have thin or no cuticle at all, no vascular tissue and reduced root systems because water is readily available to them, they also have many stomata on the upper surface.
Halophytes
These are plants that live in salty waters; they have special cells which have a higher concentration of solute than those of the ordinary plants. As a result they are able to take up water in the normal way
Mesophytes
These are plants which grow in normal water well watered soils and water lost by transpiration is replaced by absorption. They have no special means of conserving water although most of them have a well developed root system.
Xerophytes
These are plants which live in arid conditions such as deserts, and have a problem of dehydration.
Excretion in plants
The main excretory products include water and oxygen. These wastes diffuse out of the plant through the stomata and lenticels of stems as they are formed.
Other plant wastes include; tannins, alkaloids, anthocyanins which are converted into insoluble compounds like granules and oil droplets which remain in the cells and are got rid of when certain parts of the plants e.g fruits, leaves and flowers fall off from the plants.
Excretion in plants differs from that in animals because of the following reasons
Plants have got a lower metabolic rate compared to animals therefore the rate of accumulation of metabolic waste is very low
Plants are autotrophs and therefore synthesize their own organic requirements according to the demand for them. There are never excess proteins in plants therefore very little excretion of nitrogenous wastes
Plants have a capacity to store excretory products in some structures where they can be lost at a later stage e.g. fruits, flowers, leaves, barks etc.
Much of the plant structure is based on carbohydrate and not protein. The products of carbohydrates carbon dioxide and oxygen can be used in photosynthesis as raw materials. The oxygen given out as a byproduct of photosynthesis can be used in respiration
The main excretory products include water and oxygen. These wastes diffuse out of the plant through the stomata and lenticels of stems as they are formed.
Other plant wastes include; tannins, alkaloids, anthocyanins which are converted into insoluble compounds like granules and oil droplets which remain in the cells and are got rid of when certain parts of the plants e.g fruits, leaves and flowers fall off from the plants.
Excretion in plants differs from that in animals because of the following reasons
Plants have got a lower metabolic rate compared to animals therefore the rate of accumulation of metabolic waste is very low
Plants are autotrophs and therefore synthesize their own organic requirements according to the demand for them. There are never excess proteins in plants therefore very little excretion of nitrogenous wastes
Plants have a capacity to store excretory products in some structures where they can be lost at a later stage e.g. fruits, flowers, leaves, barks etc.
Much of the plant structure is based on carbohydrate and not protein. The products of carbohydrates carbon dioxide and oxygen can be used in photosynthesis as raw materials. The oxygen given out as a byproduct of photosynthesis can be used in respiration
Gaseous exchange in mammals e.g. man
The breathing system of a mammal consists of a pair of lungs which are thin walled elastic sacs lying in the thoracic cavity. The walls of the thorax consists of the ribs and the intercostal muscles while the floor consists of the diaphragm, a muscular flap of tissue between the thorax and the abdomen
Diag. main parts of the breathing system in man
Air enters the lungs through the trachea which is devided into two brochi, one to each lung. The trachea and bronchi have walls made up of rings of cartilage. Inside the lungs , each bronchus is divided into smaller tubes called bronchioles. The bronchioles terminate in saclike atria giving rise to numerous air sacs or alveoli. Each alveolus is a thin walled sac covered by numerous blood capillaries
Ventilation
Exchange of air between the lungs and the outside is made possible by changes in the volume of the thoracic cavity. This volume is altered by the movements of the intercostal muscles and the diaphragm.
Inspiration
The following events happen during inspiration
• The diaphragm contracts and moves downwards
• The ribs are raised upwards and outxwards by the contraction of the external intercostals muscles
• The volume of the thoracic cavity increases, thus reducing the pressure. Air then rushes into the lungs from outside through the nostrils.
Expiration
• The diaphragm relaxes and is pushed upwards by the abdominal organs. It thus assumes a dome shape
• The internal intercostals muscles contract and the ribs move downwards and inwards
• The volume of the thoracic cavity decreases, thus increasing the pressure. Air is then forced to out of the lungs
Gaseous exchange between the alveoli and the capillaries
The walls of the alveoli and the capillaries are very thin and closely attached to each other. This makes diffusion of gases very efficient because the distance between the inside of the capillary and the inside of the alveolus is very small.
Furthermore, the lungs have over 700 million alveoli offering a large surface area for gaseous exchange
The walls of the alveoli are also moist, this makes oxygen dissolve easily
Blood from the tissues has a high concentration of carbondioxide and very little oxygen compared to alveolar air. The concentration gradient favours diffusion of carbondioxide into the alveolus and oxygen into the blood plasma in the capillaries. The oxygen is then picked by the haemoglobin of red blood cells and transported in combination with it as oxyhaemoglobin.
Carbondioxide which is at a higher concentration in the blood is normally carried as bicarbonate ions in the plasma. This breaks down and releases carbondioxide which then diffuses into the alveolus.
The breathing system of a mammal consists of a pair of lungs which are thin walled elastic sacs lying in the thoracic cavity. The walls of the thorax consists of the ribs and the intercostal muscles while the floor consists of the diaphragm, a muscular flap of tissue between the thorax and the abdomen
Diag. main parts of the breathing system in man
Air enters the lungs through the trachea which is devided into two brochi, one to each lung. The trachea and bronchi have walls made up of rings of cartilage. Inside the lungs , each bronchus is divided into smaller tubes called bronchioles. The bronchioles terminate in saclike atria giving rise to numerous air sacs or alveoli. Each alveolus is a thin walled sac covered by numerous blood capillaries
Ventilation
Exchange of air between the lungs and the outside is made possible by changes in the volume of the thoracic cavity. This volume is altered by the movements of the intercostal muscles and the diaphragm.
Inspiration
The following events happen during inspiration
• The diaphragm contracts and moves downwards
• The ribs are raised upwards and outxwards by the contraction of the external intercostals muscles
• The volume of the thoracic cavity increases, thus reducing the pressure. Air then rushes into the lungs from outside through the nostrils.
Expiration
• The diaphragm relaxes and is pushed upwards by the abdominal organs. It thus assumes a dome shape
• The internal intercostals muscles contract and the ribs move downwards and inwards
• The volume of the thoracic cavity decreases, thus increasing the pressure. Air is then forced to out of the lungs
Gaseous exchange between the alveoli and the capillaries
The walls of the alveoli and the capillaries are very thin and closely attached to each other. This makes diffusion of gases very efficient because the distance between the inside of the capillary and the inside of the alveolus is very small.
Furthermore, the lungs have over 700 million alveoli offering a large surface area for gaseous exchange
The walls of the alveoli are also moist, this makes oxygen dissolve easily
Blood from the tissues has a high concentration of carbondioxide and very little oxygen compared to alveolar air. The concentration gradient favours diffusion of carbondioxide into the alveolus and oxygen into the blood plasma in the capillaries. The oxygen is then picked by the haemoglobin of red blood cells and transported in combination with it as oxyhaemoglobin.
Carbondioxide which is at a higher concentration in the blood is normally carried as bicarbonate ions in the plasma. This breaks down and releases carbondioxide which then diffuses into the alveolus.
gaseous exchange in bony fish,frog and insects
Gaseous exchange in insects
The respiratory system consists of a network of tubes forming the tracheal system. The tubes open to the outside through pores called spiracles located on the sides of the thorax and the abdomen. The tubes called the trachea are lined with cuticle and have spiral rings which prevent the walls from collapsing inwards.
The trachea is divided into smaller tubes called tracheoles which are closely associated with the tissues. Some insects have air sacs connected to the trachea. These air sacs can be inflated or deflated in order to facilitate gaseous exchange
Ventilation is brought about by the contraction and relaxation of the abdominal muscles. In locusts, air is drawn into the body through the thoracic spiracles and expelled through the abdominal spiracles.
Diagram
Gaseous exchange in amphibians e.g. a frog
Amphibians live in two environments air and water and are therefore adapted to gaseous exchange in land and in water. They also show change of respiratory surfaces and organs as they develop from gills in tadpoles to lungs, skin and mouth in adults.
A tadpole lives in water all the time and carries out gaseous exchange with water by means of gills (external gills in young tadpoles and internal gills in older tadpoles). Gaseous exchange occurs at the gill filaments.
When the frog develops into an adult it begins to exchange gases with air and it uses three different respiratory surfaces. These are
1. Skin this is thin, making oxygen diffuse easily into the blood and carbondioxide out, moist by secretions from the mucous glands in it therefore oxygen can dissolve easily. It is also well supplied with blood
2. Lining of the mouth cavity- this is also moist and well supplied with blood
3. Lungs- these are thin walled, with internal folding
Diagram
The lining of the mouth cavity and the lungs are used for Gaseous exchange when the frog is out of the water. Lungs are not very efficient since some of the oxygen in the air reaching them has already been taken up by the lining of the mouth cavity. When a frog is in water , it relies almost entirely on the skin for Gaseous exchange
Ventilation
The floor of the mouth is lowered and air is drawn in through the nostrils. When the nostrilsare closed and the floor of the mouth is raised, air is forced into the lungs (inspiration). When the floor of the mouth is lowered again, the pressure of the abdominal contents forces air out of the lungs through the nostrils (expiration)
Gaseous exchange in bony fish (e.g. tilapia)
Gaseous exchange in fish takes place between the gills and the surrounding water. The gills are located in the opercular cavity covered by a flap of skin called the operculum. Each gill consists of a number of thin leaf like lamellae projecting from a skeletal base (brachial arch) situated in the wall of the pharynx.
Each gill is supported by a gill bar through which blood vessels send branches to the filaments.
Diagram of the gill
Functions of parts of the gill
1. Gill rakers. These filter large particles in the water before they reach and damage the gill filaments
2. Gill bar. These provide attachment and support for the gill filaments
3. Gill filaments. These are the sites of gas exchange
Ventilation
As the mouth opens, the floor of the mouth is lowered. Pressure inside the mouth is lowered and this causes water to be drawn into the bucal cavity. Meanwhile the operculum is closed, preventing water from entering or leaving through the opening.
As the mouth closes and the floor of the mouth is raised, pressure in the bucal cavity increases. Water is forced over the gills as the opercula are forced to open. As water passes over the gills, oxygen is absorbed and carbondioxide from the gills dissolves in the water.
The respiratory system consists of a network of tubes forming the tracheal system. The tubes open to the outside through pores called spiracles located on the sides of the thorax and the abdomen. The tubes called the trachea are lined with cuticle and have spiral rings which prevent the walls from collapsing inwards.
The trachea is divided into smaller tubes called tracheoles which are closely associated with the tissues. Some insects have air sacs connected to the trachea. These air sacs can be inflated or deflated in order to facilitate gaseous exchange
Ventilation is brought about by the contraction and relaxation of the abdominal muscles. In locusts, air is drawn into the body through the thoracic spiracles and expelled through the abdominal spiracles.
Diagram
Gaseous exchange in amphibians e.g. a frog
Amphibians live in two environments air and water and are therefore adapted to gaseous exchange in land and in water. They also show change of respiratory surfaces and organs as they develop from gills in tadpoles to lungs, skin and mouth in adults.
A tadpole lives in water all the time and carries out gaseous exchange with water by means of gills (external gills in young tadpoles and internal gills in older tadpoles). Gaseous exchange occurs at the gill filaments.
When the frog develops into an adult it begins to exchange gases with air and it uses three different respiratory surfaces. These are
1. Skin this is thin, making oxygen diffuse easily into the blood and carbondioxide out, moist by secretions from the mucous glands in it therefore oxygen can dissolve easily. It is also well supplied with blood
2. Lining of the mouth cavity- this is also moist and well supplied with blood
3. Lungs- these are thin walled, with internal folding
Diagram
The lining of the mouth cavity and the lungs are used for Gaseous exchange when the frog is out of the water. Lungs are not very efficient since some of the oxygen in the air reaching them has already been taken up by the lining of the mouth cavity. When a frog is in water , it relies almost entirely on the skin for Gaseous exchange
Ventilation
The floor of the mouth is lowered and air is drawn in through the nostrils. When the nostrilsare closed and the floor of the mouth is raised, air is forced into the lungs (inspiration). When the floor of the mouth is lowered again, the pressure of the abdominal contents forces air out of the lungs through the nostrils (expiration)
Gaseous exchange in bony fish (e.g. tilapia)
Gaseous exchange in fish takes place between the gills and the surrounding water. The gills are located in the opercular cavity covered by a flap of skin called the operculum. Each gill consists of a number of thin leaf like lamellae projecting from a skeletal base (brachial arch) situated in the wall of the pharynx.
Each gill is supported by a gill bar through which blood vessels send branches to the filaments.
Diagram of the gill
Functions of parts of the gill
1. Gill rakers. These filter large particles in the water before they reach and damage the gill filaments
2. Gill bar. These provide attachment and support for the gill filaments
3. Gill filaments. These are the sites of gas exchange
Ventilation
As the mouth opens, the floor of the mouth is lowered. Pressure inside the mouth is lowered and this causes water to be drawn into the bucal cavity. Meanwhile the operculum is closed, preventing water from entering or leaving through the opening.
As the mouth closes and the floor of the mouth is raised, pressure in the bucal cavity increases. Water is forced over the gills as the opercula are forced to open. As water passes over the gills, oxygen is absorbed and carbondioxide from the gills dissolves in the water.
characteristicd of respiration surfaces
. They have a large surface area in order to increase the rate of diffusion
2. They are usually thin and permeable in order to reduce the resistance to diffusion
3. They are moist to dissolve the gases
4. They are well supplied with blood.
Types of respiratory surfaces in animals
Small animals such as amoeba use their entire body surface for gaseous exchange. They have a high surface area /volume ratio. As organisms increase in size, the surface area/volume ratio decreases, hence there is need to have special respiratory system or organs
2. They are usually thin and permeable in order to reduce the resistance to diffusion
3. They are moist to dissolve the gases
4. They are well supplied with blood.
Types of respiratory surfaces in animals
Small animals such as amoeba use their entire body surface for gaseous exchange. They have a high surface area /volume ratio. As organisms increase in size, the surface area/volume ratio decreases, hence there is need to have special respiratory system or organs
Gaseous Exchange
Gaseous exchange in animals
The majority of animals need oxygen in order to oxidize the organic materials and produce energy for cellular activities.
The oxidation of the food not only yields energy but also carbon dioxide which must be constantly removed from the body.
The process of moving oxygen into the body and carbon dioxide out of the body is called breathing in or ventilation. Gaseous exchange involves the passage of carbon dioxide through a respiratory surface. Diffusion is the main transport process involved in gaseous exchange.
Gaseous exchange in animals
The majority of animals need oxygen in order to oxidize the organic materials and produce energy for cellular activities.
The oxidation of the food not only yields energy but also carbon dioxide which must be constantly removed from the body.
The process of moving oxygen into the body and carbon dioxide out of the body is called breathing in or ventilation. Gaseous exchange involves the passage of carbon dioxide through a respiratory surface. Diffusion is the main transport process involved in gaseous exchange.
Food web
In a natural community, several food chains are interlinked to form a food web. Several herbivores may feed on one plant. Similarly a given herbivore may be eaten by different carnivores
Examples
Pyramid of numbers
When the numbers of organisms at each trophic level are considered and the results represented in a graphic form, a pyramid shape is obtained. This is because one herbivore feeds on many green plants. One carnivore also feeds on many herbivores
Carnivores (tertiary consumers)
Carnivores (secondary consumers)
Herbivores (primary consumers)
Green plants (producers)
In a natural community, several food chains are interlinked to form a food web. Several herbivores may feed on one plant. Similarly a given herbivore may be eaten by different carnivores
Examples
Pyramid of numbers
When the numbers of organisms at each trophic level are considered and the results represented in a graphic form, a pyramid shape is obtained. This is because one herbivore feeds on many green plants. One carnivore also feeds on many herbivores
Carnivores (tertiary consumers)
Carnivores (secondary consumers)
Herbivores (primary consumers)
Green plants (producers)
explain using example the meaning of a food chain
FOOD CHAINS
A food chain is a linear feeding relationship between producers and consumers in an ecosystem. It represents the transfer of food energy from green plants through repeated stages of eating and being eaten.
There are two types of food chains
1. Grazing food chain. Starts with green plants
2. Detritus food chain. Starts with dead organic material (debris or detritus)
In construction of food chain, an arrow is used to link the different levels of organisms and the direction in which the arrow point is from the organism that is being consumed to the next consumer.
Examples
1. Water weeds tilapia nile parch crocodiles bacteria.
2. Plant debris bacteria protozoa mosquito larva
From one level to the next food energy is being transferred.
These different levels are referred to as energy levels/trophic levels. At various consumer levels, some of the food energy is utilized for respiration, while some of the energy is lost in form of heat through various processes such as;
1. urination
2. sweat
3. Panting.
4. Exhalation.
Therefore the amount of energy gained by the higher trophic levels keeps on decreasing such that at the final level (decomposers) the amount of energy is negligible.
A food chain is a linear feeding relationship between producers and consumers in an ecosystem. It represents the transfer of food energy from green plants through repeated stages of eating and being eaten.
There are two types of food chains
1. Grazing food chain. Starts with green plants
2. Detritus food chain. Starts with dead organic material (debris or detritus)
In construction of food chain, an arrow is used to link the different levels of organisms and the direction in which the arrow point is from the organism that is being consumed to the next consumer.
Examples
1. Water weeds tilapia nile parch crocodiles bacteria.
2. Plant debris bacteria protozoa mosquito larva
From one level to the next food energy is being transferred.
These different levels are referred to as energy levels/trophic levels. At various consumer levels, some of the food energy is utilized for respiration, while some of the energy is lost in form of heat through various processes such as;
1. urination
2. sweat
3. Panting.
4. Exhalation.
Therefore the amount of energy gained by the higher trophic levels keeps on decreasing such that at the final level (decomposers) the amount of energy is negligible.
describe the relationships within an ecosystem
RELATIONSHIPS WITHIN AN ECOSYSTEM
Food relations in an ecosystem
Food is a source of energy i.e. energy in chemical form. Food in an ecosystem exists as organic matter (biomass).
Biomass is the measure of the amount of living or organic material in an organism. It considers the dry weight (minus water and other fluids in the body).
Food relations is a common form of interaction which consists of eating (consuming) and being eaten (being consumed).
Within the relation there are different modes of feeding.
The modes of feeding depend on;
The nature of food and the feeding level. Green plants (Autotrophs) make their own food using sun light energy. They incorporate water and carbon dioxide into organic material (starch). This process is known as photosynthesis.
Some of the food energy is used by the plant for its own metabolic activities e.g. respiration. Some of the energy is lost during respiration in form of heat. The lost heat energy becomes part of the abiotic environment once it enters the atmosphere.
The balance of energy in the plant is therefore available to the next trophic level made up of the herbivores (primary consumers); omnivores- lower carnivores (secondary consumers) – top carnivores (tertiary consumers) – scavengers and decomposers.
Scavengers feed on carcasses of the animal killed by the carnivores. Primary consumers, carnivores, scavengers and decomposers are heterotrphs because they cannot manufacture their own food.
Trophic levels refer to energy levels (usually in terms of food). Within an eco system, green plants are therefore referred to as producers since energy enters the system through these plants from the sun.
NB, since the consumer does not eat all parts of the plant, it means that the available energy in plants is not all utilized.
Food relations in an ecosystem
Food is a source of energy i.e. energy in chemical form. Food in an ecosystem exists as organic matter (biomass).
Biomass is the measure of the amount of living or organic material in an organism. It considers the dry weight (minus water and other fluids in the body).
Food relations is a common form of interaction which consists of eating (consuming) and being eaten (being consumed).
Within the relation there are different modes of feeding.
The modes of feeding depend on;
The nature of food and the feeding level. Green plants (Autotrophs) make their own food using sun light energy. They incorporate water and carbon dioxide into organic material (starch). This process is known as photosynthesis.
Some of the food energy is used by the plant for its own metabolic activities e.g. respiration. Some of the energy is lost during respiration in form of heat. The lost heat energy becomes part of the abiotic environment once it enters the atmosphere.
The balance of energy in the plant is therefore available to the next trophic level made up of the herbivores (primary consumers); omnivores- lower carnivores (secondary consumers) – top carnivores (tertiary consumers) – scavengers and decomposers.
Scavengers feed on carcasses of the animal killed by the carnivores. Primary consumers, carnivores, scavengers and decomposers are heterotrphs because they cannot manufacture their own food.
Trophic levels refer to energy levels (usually in terms of food). Within an eco system, green plants are therefore referred to as producers since energy enters the system through these plants from the sun.
NB, since the consumer does not eat all parts of the plant, it means that the available energy in plants is not all utilized.
componets of an ecosystem
An ecosystem consists of two components/environments;
a) The biotic environment. (living component)
Consist of the animal and plant communities. Therefore biotic is considered to be the living organisms, whether micro or macro in size. These form a vital environment of an organism and are in a constant interaction with each other. The plant community is known as flora and the animal community is known as fauna.
b) The abiotic environment.
These are the non living components of an eco system.
They include;
i. Climatic elements of the atmosphere such as rainfall, light, temperature, humidity, air currents (wind), atmospheric pressure, cloud cover etc.
ii. Water bodies of all sizes and characteristics.
Some are fresh water bodies; others are marine (high salt concentration).
iii. Edaphic (soil) factors; include soil structure, profile, texture, pH, temperature etc.
iv. Lithosphere (rock types) factors or land forms e.g. metamorphic rocks, sedimentary rocks and igneous rocks.
a) The biotic environment. (living component)
Consist of the animal and plant communities. Therefore biotic is considered to be the living organisms, whether micro or macro in size. These form a vital environment of an organism and are in a constant interaction with each other. The plant community is known as flora and the animal community is known as fauna.
b) The abiotic environment.
These are the non living components of an eco system.
They include;
i. Climatic elements of the atmosphere such as rainfall, light, temperature, humidity, air currents (wind), atmospheric pressure, cloud cover etc.
ii. Water bodies of all sizes and characteristics.
Some are fresh water bodies; others are marine (high salt concentration).
iii. Edaphic (soil) factors; include soil structure, profile, texture, pH, temperature etc.
iv. Lithosphere (rock types) factors or land forms e.g. metamorphic rocks, sedimentary rocks and igneous rocks.
terms used in ecology,ecololgy notes
ECOLOGY
This is the study of inter-relations (interactions) between an organ ism or a group 0of organisms and their environment.
TERMS USED IN ECOLOGY
1. Habitat: is a place where an organism lives e.g. land habitat is known as terrestrial (mainly forest, deserts and savannahs), water habitat is aquatic (includes fresh water bodies and marine water bodies)
2. Biosphere: is the part of the earth and atmosphere where life can exist. This ranges from deep water bodies, land and a few metres in the atmosphere.
3. Species: this is a group of organisms which can interbreed to give rise to a viable or fertile offspring.
4. Population: a group of organisms of the same species occupying the same area at a given time e.g. a population of elephants in Queen Elizabeth national park, population of hippos in kasinga channel, population of parrot birds in Gayaza High School etc.
5. Community. This is a collection of populations of different organisms occupying the same area or a group of different species of organisms in the same area. E.g. a community of antelopes, elephants, lions, in Queen Elizabeth National park
6. Ecological niche: This is a term used in relation to a particular organism. It refers to the role/ profession of an organism in a given habitat eg the niche of a spirogyra in a pond is to photosynthesis or to produce food.
7. Biome: These are very large ecological divisions found all over the world. They have characteristic plant and animal communities, e.g. equatorial rain forests biome, Amazon, savannah grasslands and wood lands, temperate forests etc.
8. Environment: surrounding of an organism e.g. in Gayaza environment we have organisms like birds, leopards, foxes, rats etc.
9. An ecosystem. This is any unit of environment consisting of both living and non living components existing together as a harmony e.g. a pond where living components like fish, insect larvae, amphibians, and plants like spirogyra interact with the non living components such as water, rocks, sand etc.
This is the study of inter-relations (interactions) between an organ ism or a group 0of organisms and their environment.
TERMS USED IN ECOLOGY
1. Habitat: is a place where an organism lives e.g. land habitat is known as terrestrial (mainly forest, deserts and savannahs), water habitat is aquatic (includes fresh water bodies and marine water bodies)
2. Biosphere: is the part of the earth and atmosphere where life can exist. This ranges from deep water bodies, land and a few metres in the atmosphere.
3. Species: this is a group of organisms which can interbreed to give rise to a viable or fertile offspring.
4. Population: a group of organisms of the same species occupying the same area at a given time e.g. a population of elephants in Queen Elizabeth national park, population of hippos in kasinga channel, population of parrot birds in Gayaza High School etc.
5. Community. This is a collection of populations of different organisms occupying the same area or a group of different species of organisms in the same area. E.g. a community of antelopes, elephants, lions, in Queen Elizabeth National park
6. Ecological niche: This is a term used in relation to a particular organism. It refers to the role/ profession of an organism in a given habitat eg the niche of a spirogyra in a pond is to photosynthesis or to produce food.
7. Biome: These are very large ecological divisions found all over the world. They have characteristic plant and animal communities, e.g. equatorial rain forests biome, Amazon, savannah grasslands and wood lands, temperate forests etc.
8. Environment: surrounding of an organism e.g. in Gayaza environment we have organisms like birds, leopards, foxes, rats etc.
9. An ecosystem. This is any unit of environment consisting of both living and non living components existing together as a harmony e.g. a pond where living components like fish, insect larvae, amphibians, and plants like spirogyra interact with the non living components such as water, rocks, sand etc.
what are the functions of the liver.what is the differenc between anabolism and catabolism
Assimilation is the process by which food materials after being absorbed are built up into complex constituents of the organism.
Metabolism refers to all the chemical processes taking place within an organism. It involves two processes
i) Catabolism. Breaking down of organic compounds from complex to simpler with liberation of energy
ii) Anabolism. Building up of organic compounds from simple to complex using energy.
The body’s metabolic center is the liver.
FUNCTION OF THE LIVER
Assimilation and metabolism of carbohydrates (glucose). Glucose once absorbed is transported in the hepatic portal vein to the liver and is either broken down in respiration to provide energy or stored as glycogen. Stored glycogen is released as glucose under the influence of the hormones insulin produced in the pancrease which also controls it’s utilization in the body.
Assimilation and metabolism of proteins. The body is unable to store proteins or amino acids and any surplus is destroyed in the liver. Excess amino acids brought to the liver by the hepatic portal vein are deaminated by the liver cells. In this process the amino (NH2) group is removed from the amino acid the formation of ammonia. Another product Keto acids are oxidized in respiration to produce energy.
Assimilation and metabolism of lipids. The end products of digestion ie fatty acids and glycerol’s are absorbed and taken into the lacteal and later the lymphatic system they are transferred to the liver. Both can be used for respiration to provide energy or they may be to form fats which are stored in the body’s fat depots e.g. under the skin in the adipose tissue.
Storage of iron and other minerals. This is mainly from the won out red blood cells destroyed in the liver. The iron is stored for future use in the formation of heamoglobin in new red blood cell.
Production of bile. The bile is synthesized form broken down worn out red blood cells and is stored in the gall bladder before being transferred to the duodenum where they act on fats and lipids.
Manufacture of plasma proteins. This includes fibrinogen important for the clotting of blood. Other plasma proteins include albumen and globulin.
Storage of vitamins mainly A, D, and B12.
Production of heat. This is because of the many metabolic reactions taking place in the liver. The heat is distributed around the body and is usefull in temperature regulation.
Formation of red blood cells. This is only done in the foetus. In adults this cells are produced in the bone marrow.
Storage of blood. The blood vessels (veins) in the liver can expand and contract to a great extent such that it stores blood ranging from 300-1500cm3.
Elimination of sex hormones. These include testosterone and oestrogen. After they have done their work, they are either modified by the liver or sent to the kidney for excreation or eliminated in the bile.
Detoxification. The liver makes harmful/poisons substances harmless by altering their chemical; structure.
Metabolism refers to all the chemical processes taking place within an organism. It involves two processes
i) Catabolism. Breaking down of organic compounds from complex to simpler with liberation of energy
ii) Anabolism. Building up of organic compounds from simple to complex using energy.
The body’s metabolic center is the liver.
FUNCTION OF THE LIVER
Assimilation and metabolism of carbohydrates (glucose). Glucose once absorbed is transported in the hepatic portal vein to the liver and is either broken down in respiration to provide energy or stored as glycogen. Stored glycogen is released as glucose under the influence of the hormones insulin produced in the pancrease which also controls it’s utilization in the body.
Assimilation and metabolism of proteins. The body is unable to store proteins or amino acids and any surplus is destroyed in the liver. Excess amino acids brought to the liver by the hepatic portal vein are deaminated by the liver cells. In this process the amino (NH2) group is removed from the amino acid the formation of ammonia. Another product Keto acids are oxidized in respiration to produce energy.
Assimilation and metabolism of lipids. The end products of digestion ie fatty acids and glycerol’s are absorbed and taken into the lacteal and later the lymphatic system they are transferred to the liver. Both can be used for respiration to provide energy or they may be to form fats which are stored in the body’s fat depots e.g. under the skin in the adipose tissue.
Storage of iron and other minerals. This is mainly from the won out red blood cells destroyed in the liver. The iron is stored for future use in the formation of heamoglobin in new red blood cell.
Production of bile. The bile is synthesized form broken down worn out red blood cells and is stored in the gall bladder before being transferred to the duodenum where they act on fats and lipids.
Manufacture of plasma proteins. This includes fibrinogen important for the clotting of blood. Other plasma proteins include albumen and globulin.
Storage of vitamins mainly A, D, and B12.
Production of heat. This is because of the many metabolic reactions taking place in the liver. The heat is distributed around the body and is usefull in temperature regulation.
Formation of red blood cells. This is only done in the foetus. In adults this cells are produced in the bone marrow.
Storage of blood. The blood vessels (veins) in the liver can expand and contract to a great extent such that it stores blood ranging from 300-1500cm3.
Elimination of sex hormones. These include testosterone and oestrogen. After they have done their work, they are either modified by the liver or sent to the kidney for excreation or eliminated in the bile.
Detoxification. The liver makes harmful/poisons substances harmless by altering their chemical; structure.
CELLULOSE DIGESTION
Cellulose make up the plant cell wall.
Animals which depend on material e.g. leaves, wood have to digest cellulose in order to release the cell contents required for the nutrition of the animals. The enzyme which digest cellulose is called cellulase and it is not produced by most animals. Some micro organisms take bacteria and protozoans can produce cellulase. However animals which digest cellulose contain micro organisms in their gut which produce cellulose enzyme. This is a symbiotic relationship.
CELLULOSE DIGESTION IN RUMINANTS
Ruminants are animals which chew the cud. Cud is un chewed grass taken into the rumen which is returned to the mouth for chewing (regurgitation). Examples include Goats, Sheep, Cattle, Antelopes and Buffalos. They have a complicated stomach consisting of four chambers.
Diagram showing the stomach and movement of food
Mouth. There is no enzyme secretion in the mouth so only mastication and
Softening of food occurs. Movement of food in the oesophagus is by Peristalsis.
Rumen. This is the largest component of the stomach where food is stored temporarily before returning to the mouth for chewing. The food is return to the mouth by anti peristalsis. The ruminant then lies down quietly and chews the cud. When the food is sufficiently chewed it is swallowed and passed into the reticulum.
Reticulum. Bacteria action continues.
It also separates finely ground material from course ones and then retains and hard pieces of wood.
Omasum. Consists of parallel leaf like compartments with rough surfaces. The food is ground finely.
Absorption of water takes place at this region
Abomasum. Also called the true stomach.
Enzymatic action of proteins takes place here.
Beyond this point digestion takes place like in man.
DIFFERENCE BETWEEN RUMINANTS AND NON RUMINANTS.
RUMINANTS NONRUMINANTS
1) Have a four chambered stomach
2) Chew cud
3) Ptyalin is absent in the saliva
4) Most digestion and absorption takes place in the stomach
5) Can digest cellulose with the help of cellulose from bacteria
1) Have a single stomach
2) Do not chew cud
3) Ptyalin is present in saliva
4) Most digestion and absorption takes place in the ileum
5) Cannot digest cellulose
Other animals like termites eat wood, dry leaves etc which also contain cellulose. The digestion of cellulose in termites is also done by cellulase enzyme produced by protozoans which live symbiotically with the termites. The products of cellulose digestion may be glucose or acetic acid in other animals.
Cellulose make up the plant cell wall.
Animals which depend on material e.g. leaves, wood have to digest cellulose in order to release the cell contents required for the nutrition of the animals. The enzyme which digest cellulose is called cellulase and it is not produced by most animals. Some micro organisms take bacteria and protozoans can produce cellulase. However animals which digest cellulose contain micro organisms in their gut which produce cellulose enzyme. This is a symbiotic relationship.
CELLULOSE DIGESTION IN RUMINANTS
Ruminants are animals which chew the cud. Cud is un chewed grass taken into the rumen which is returned to the mouth for chewing (regurgitation). Examples include Goats, Sheep, Cattle, Antelopes and Buffalos. They have a complicated stomach consisting of four chambers.
Diagram showing the stomach and movement of food
Mouth. There is no enzyme secretion in the mouth so only mastication and
Softening of food occurs. Movement of food in the oesophagus is by Peristalsis.
Rumen. This is the largest component of the stomach where food is stored temporarily before returning to the mouth for chewing. The food is return to the mouth by anti peristalsis. The ruminant then lies down quietly and chews the cud. When the food is sufficiently chewed it is swallowed and passed into the reticulum.
Reticulum. Bacteria action continues.
It also separates finely ground material from course ones and then retains and hard pieces of wood.
Omasum. Consists of parallel leaf like compartments with rough surfaces. The food is ground finely.
Absorption of water takes place at this region
Abomasum. Also called the true stomach.
Enzymatic action of proteins takes place here.
Beyond this point digestion takes place like in man.
DIFFERENCE BETWEEN RUMINANTS AND NON RUMINANTS.
RUMINANTS NONRUMINANTS
1) Have a four chambered stomach
2) Chew cud
3) Ptyalin is absent in the saliva
4) Most digestion and absorption takes place in the stomach
5) Can digest cellulose with the help of cellulose from bacteria
1) Have a single stomach
2) Do not chew cud
3) Ptyalin is present in saliva
4) Most digestion and absorption takes place in the ileum
5) Cannot digest cellulose
Other animals like termites eat wood, dry leaves etc which also contain cellulose. The digestion of cellulose in termites is also done by cellulase enzyme produced by protozoans which live symbiotically with the termites. The products of cellulose digestion may be glucose or acetic acid in other animals.
Biology Syllabus
553 BIOLOGY
O-LEVEL 2006-2010
Uganda
Introduction:
An experimental approach particularly to physiological work is expected. An understanding of controls is essential, together with the realization that when there are several variables they must be investigated one at a time. Where appropriate, quantitative experiments should be carried out. Practical work, both in and outside the laboratory is of great importance and one of its main educational values is the stimulation of interest in Biology. The importance of accuracy and detail in biological drawing and keeping other records should be emphasised.
Aims and Objectives:
(i) To initiate an interest in Biology.
(ii) To promote a wider knowledge and understanding of Biology than at the primary level.
(iii) To develop practical skills further.
(iv) To promote a scientific approach to biological problems, attempt to formulate hypothesis, carry out investigations, analyse results and draw conclusions.
(v) To initiate ability to present and interpret biological materials precisely e.g graphs, charts, photographs, labelled diagrams, lists, tables, maps etc.
(vi) To learn how to communicate biological information clearly.
(vii) To promote an understanding of the importance of Biology in every day life and the ways in which man influences his environment.
(viii) To promote the ability to apply the knowledge and understanding gained during the course to their everyday life situations.
(ix) To stimulate the pupil’s ability to find out biological information for himself from text and reference books, investigations and life experiences.
(x) To make use of local materials and information whenever possible.
Notes on Examination.
Any section of the syllabus may be examined in any of the sections of the papers.
The practical examination is designed to test candidates for the following abilities:
(a) To follow carefully a sequence of instructions within a set time allowance.
(b) To use familiar and unfamiliar techniques in practicals. To record their observations and make deductions from them.
(c) To observe and recognise features of familiar and unfamiliar biological specimens, record observations and make deductions about functions of whole specimens or their parts.
(d) To make clear line drawing of the specimens provided, indicate magnification and to label familiar structures.
(e) To interpret unfamiliar data and draw conclusions from their interpretations.
(f) To employ manual skills in assembling apparatus, in using chemical reagents and in using such instruments as mounting needles, scalpels and razor blades, forceps and scissors, etc.
(g) To observe reactions, read simple measuring instruments and perform simple arithmetic calculations.
2 The food tests expected are as follows: -
(a) Reducing sugars: Fehling’s or Benedict’s solutions.
(b) Non-reducing sugars: Fehling’s or Benedict’s solution after hydrolysis with dilute hydrochloric acid.
(c) Starch: Iodine solution.
(d) Fats: Ethanol emulsion test/grease spot.
(e) Protein: Millon’s Reagent/Biuret test.
(f) Vitamin C: DCPIP (Dichloro- phenol-indo-phenol)
Examination Format:
There will be two papers.
Paper 1 (2 ½ hours)
This will consist of three sections: A, B and C.
Section A will consist of 30 compulsory multiple-choice questions. (30 marks)
Section B will consist of three compulsory, structured questions. (40 marks)
Section C will consist of four essay questions. Candidates will be required to answer two questions. (30 marks ).
Paper 2 (2 hours)
This will consist of three compulsory questions. Questions may be set on interpretation of new/unfamiliar biological data, which may include photographs. One question will require carrying out laboratory practical procedures.
Any section of the syllabus may be examined in any of the sections of the papers.
Detailed syllabus:
1. Diversity of Living Things:
1.1 Classification: distinction between living and non-living things; classification of plants and animals into groups; use of simple identification keys; quantitative sampling and methods of collection.
1.2 External features and internal structures of the flowering plant: roots and root modifications, leaves and leaf modification; flowers, fruits and seeds.
1.3 External features, life cycles and economic importance of insects: house fly; cockroach; mosquitoes; bees; butterflies.
1.4 Hand lens and microscopes; magnification; examination of pond water, plant and animal cells, eg. leaf epidermal cells, check cells, spirogyra filaments, etc.; structure and functions of plants and animal cells.
2. Soil:.
2.1 Soil formation, composition and soil profiles.
2.2 Physical and chemical properties of soils: importance of air and water; capillarity, porosity and drainage ;water-retaining properties of clay and humus, flocculation of clay and soil pH; inorganic plant nutrients and water culture experiments, (See Section 3.4 note (b) )
2.3 Soil erosion and its causes, effects and prevention; farming practices: shifting cultivation, mixed farming, crop rotation and mulching; fertilizers.
2.4 Soil micro-organisms; the role of bacteria in soil fertility; nitrogen cycle, carbon cycle.
3. Nutrition in Plants and Animals:
3.1 Nutrient compounds: Carbohydrates, proteins, fats, vitamins, and minerals;
importance of water; tests for reducing and non reducing sugars, starch, fats and proteins; deficiency diseases of proteins ( Kwashiorkor), vitamins and minerals in man; digestive and other enzymes and their properties as organic catalysts; e.g. their specificity, sensitivity to temperature, and pH. .
3.2 Nutrition in animals: feeding methods in Amoeba, insects, toad or frog, birds and
mammalian herbivores, carnivores and omnivores; structure and shape of mammalian
teeth related to feeding; dental formulae of man, dog and cow or sheep; care of teeth
in man, the alimentary tract in a mammal, including man; the function of a caecum
and rumen in herbivores; ingestion, digestion, absorption and assimilation; egestion.
3.3 Structure and nutrition of a common mould (Mucor or Rhizopus)
3.4 Nutrition in green plants, the process and rate of photosynthesis; the form and internal
structure of leaves in relation to photosynthesis; mineral nutrition.
Note:
(a) Experiments should be performed to show the necessity of light, carbon dioxide and chlorophyll and the formation of starch and oxygen.
(b) Experiments to show the importance of major plant nutrient elements, using water or sand cultures, should be performed (See also section 2.2).
4. Transport of Materials in Plants and Animals:
4.1 Transport of materials in animals: the necessity of a transport system in multi-cellular animals; the circulatory system of a mammal; the structure and function of the mammalian heart, arteries, veins and capillaries including diffusion through capillary walls; composition and functions of blood; structure and function of blood cells; phagocytosis, anti-bodies and clotting of blood; immunisation; lymphatic drainage and elephantiasis.
4.2 Transport of materials in higher plants: diffusion, osmosis and selective permeability; uptake of water and mineral salts; water loss, transpiration steam, turgor and rigidity in plants; environmental conditions and rate of transpiration; transport of products of photosynthesis.
4.3 Food storage: the liver; food storage organs in plants including vegetative
structures and seeds.
5. Respiration in Plants and Animals:
5.1 Gaseous exchange: breathing mechanisms in insects (e.g. locust or grasshopper),
bony fish, amphibians (tadpole and toad or frog) and mammals, including artificial respiration in man; gaseous exchange in the lungs of a mammal and gas analysis experiments; gaseous exchange in plants; diurnal variation of carbon dioxide in plant environment, including effect of light and darkness on this variation; gaseous relationship between aquatic plants and animals.
5.2 Tissue respiration: chemical oxidation of food and resulting release of energy in
cells; anaerobic respiration in muscles; yeast fermentation.
Note: Experiments should be carried out to demonstrate gaseous exchange and production of heat
6. Excretion:
Structure and function of the mammalian skin and kidney; water and heat loss and temperature control in the mammal: water and salt balance, including osmo-regulation in the mammal; urea formation and elimination; role of the mammalian lungs and liver in the regulation of the internal environment; gaseous exchange in flowering plants (See also section 5.1).
7. Co-ordination:
7.1 Tropisms in plants; experiments on phototropism and geotropism in shoots and geotropism in roots should be performed.
7.2 Control of response in plants: the hormone (auxin) explanation; the effects of
decapitating the coleoptiles of germinating cereals and applying indole-acetic acid (IAA) should be demonstrated.
7.3 Tactic responses to light, water and contact exhibited by invertebrates; simple
experiments on responses should be performed, e.g. with earth worms, woodlice,
blowfly larvae, ants and termites
7.4 The control of response in animals: endocrine organs and hormones; location of
the organs in the human body and the function of their secretions; reference should be made to insulin, adrenaline, thyroxin, sex hormones and pituitrine.
7.5 The nervous system: the mammalian nervous system; structure of a nerve cell
(neuron); synapses; reflex arcs; simple and conditioned reflexes; gross structure of the brain and spinal cord of a mammal related simply to function.
7.6 Receptor organs: in the skin; the eye; structure and function, accommodation
correction of long sight and short sight; the ear: structure and function, hearing and balance.
8. Growth and Development in Plants and Animals:
8.1 Increase in size: apical regions of growth in stems and roots; cell division
(mitosis).
8.2 Change of form: structure and germination of a named cereal grain and at
least one other named type of seed; metamorphosis in insects (See also section1.3)
9. Locomotion in Animals
9.1 Locomotion in an insect. e.g. locust or grasshopper; action of muscles on
the exoskeleton.
9.2 Locomotion in a bony fish; action of muscle blocks on either side of the body.
9.3 Flight in birds: adaptations to flight; structure and functions of feathers.
9.4 Locomotion in a mammal: the axial and appendicular skeleton; the way muscles act on the bones to cause movement.
Note: (a) A vertebra should be regarded as being composed of a body (centrum) carrying arches, neural spine and transverse processes with facets for articulation.
(b) A functional treatment of the skeleton: different types of joints illustrated by
shoulder or hip, elbow or knee.
10 Reproduction in Plants and Animals
10.1 Asexual reproduction: in Ameoba, in Mucor or Rhizopus; in spirogyra;
vegetative reproduction in flowering plants.
10.2 Sexual reproduction in plants: spirogyra, Mucor or Rhizopus structure and
function of flowers; pollination; fertilisation; ovarian development of fruit and seeds; dispersal of fruits and seed.
10.3 Sexual reproduction in animals: an insect e.g. locusts or grasshopper, an oviparous bony fish; an amphibian, e.g. toad or frog; a bird; mammal, including man.
Note: Breeding habits of these animals should be considered together with the parental care of the young organisms. A simple study of the structure and function of the male and female reproductive organs in a mammal, together with general outline of the development, nutrition, respiration and birth of the embryo is expected.
11. Genetics and evolution
11.1 Variation with in plant and animal species.
Note: Candidates should be aware of genetic and environmental causal factors, and reference should be made to some human characters such as skin colour, sickle cell, tongue rolling and height.
11.2 Monohybrid inheritance
Monohybrid crosses to illustrate complete and incomplete dominance should
be studied.
Note: Several examples to illustrate complete and incomplete dominance should include some involving human characters such as Albinism and the A, B, O blood groups.
Reference should be made to the pioneer work of Mendel, Darwin and Morgan.
11.3 Chromosomes and genes
Note: A mention of Chromosomes, genes and DNA without details of structure
: Mitosis (see also section 8.1) and Meiosis without details of stages.
Chromosomes and sex determination in man. A simple treatment of mutation as a change in chromosome or a gene and Natural Selection should be carried out. The role of variations as the raw material upon which Natural Selection operates to produce evolutionary change should be emphasised. Candidates should be familiar with practical work on variation in relation to plant and animal breeding.
12. Interrelationships
12.1 Food chains: food chains and webs; producers consumers and decomposers; biomass and pyramid of numbers.
12.2 Changes in population: factors affecting population size; control of microbial growth, e.g. temperature, sterilisation, ant-septics; oral hygiene and food spoilage; predator-prey relationships, competition, adaptation and survival; colonisation of habitats and succession by plants and animals; carrying capacity in a habitat; human population growth; birth rate, death rate and projections for future growth and change.
12.3 Parasitism and symbiosis: feeding habits and host-parasite balance in stomach worms; control of parasite life cycle in relation to tape worm, ticks, tomato blight fungus, malarial parasite and Tryponosoma, Nitrogen-fixing bacteria in root nodules and cellulose-digesting bacteria in the gut of ruminants.
12.4 Man and natural environment: Man’s interference with the environment;
the importance and conservation water, air, land, forests and wild life; pollution
of the environment and control of atmosphere pollutants.
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