Monday 6 October 2014
o level notes on effect of human activity on ecosystem
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Human Impact on an Ecosystem
Conservation
Conservation is positive care management of the environment to maintain biodiversity.
Involved Activities:
preservation of ecosystems
restoration of spoilt habitats
balanced use of resources
the safeguarding endangered species
Example of Conservation Practice (only one example required)
Set-aside in Agriculture
Farmland - a commercially managed habitat
Reduced species diversity, low population of native species
Set-aside - agricultural activity suspended in part of the farm
‘Return to nature’ and/or reintroduction of ‘lost’ species
Natural community re-established
Pollution
Pollution is any human activity that contaminates any part of the biosphere with substances that degrade or harm the natural community.
Pollution also threatens
human health
food production
supply of natural raw materials
restricts recreational activities
future generations are denied their right to a wholesome planet
Pollutant: a substance made during human activity in a quantity that harms the natural environment.
Sulphur Dioxide - an example of a pollutant (only one required)
Main Source: fossil fuel burning.
Converted to sulphuric acid in the atmosphere.
Pollution of land and water habitats by ‘acid rain’.
Increased acidity of soil and water - plant and animal life directly inhibited.
Soil Problems - less fertile.
Toxic metal levels increased.
Reduced mineral recycling due to decline in the populations of bacteria and fungi.
Aquatic Habitat Problems
Acidification kills algae and bacteria.
Insect and fish life decline.
Ultimately - lifeless lakes.
Terrestrial Plant Problems
Damages cell membranes and destroys chlorophyll.
Weakens plant’s immune system - greater disease damage.
Human Health Problems
Lung and breathing trouble.
Metal contaminated drinking water can cause nervous system difficulties.
Building Damage
Stonework, mortar and metalwork attacked.
Sulphur Dioxide Control
Burn natural gas instead of coal, oil or peat.
Remove sulphur dioxide before the waste gases are released.
Greater use of renewable energy sources and nuclear power.
Less use of the car - greater use of public transport.
Spread lime - reduces soil and water acidity.
Fossil Fuel Burning - an example of one human polluting activity. <SSH> (only one required)
Acid Rain
sulphur dioxide causes two thirds of the problem
nitrogen oxides causes the remainder of the problem
Carbon Dioxide - suspect in ‘Global Warming’ (enhanced Greenhouse Effect)
Carbon dioxide levels have risen by almost 30% since Industrial Revolution.
Carbon dioxide is a ‘greenhouse gas’.
Atmospheric temperature has been increasing.
Is carbon dioxide a major factor in ‘global warming’.
Suspected effects of ‘global warming’: sea level rise, climate change, increased
desertification, less agricultural land, plant and animal distribution changes.
Smoke: huge mass of tiny carbon particles.
Reduce photosynthesis - less light and blocked stomata.
Human health - lung damage.
Role of Micro-organisms in Pollution Control
Organic Waste (i.e. human sewage and farm slurry.)
Organic waste is food and nutrient source for bacteria and fungi.
Increased use of special ‘fermenters’ for household, district and city waste.
The natural gas produced can be used as an energy source.
Waste reduced to by 98% i.e. 2% of original mass.
Oil Spillage: bacterial decomposition of oil, speed up by inoculating the oil.
Bioremediation: bacteria and fungi can be used to decontaminate soil and groundwater of pesticides, metals and even radioactive materials.
Waste Management
Major Problems
Large volume: domestic (2 mt), agricultural (22 mt), industrial (6 mt) in Ireland. {mt = million tonnes}
Disposal: landfill, recycle, destroy or convert to other uses.
Landfill Difficulties
Local groundwater polluted.
Current sites almost full – strong local protest against new sites.
Incineration Difficulties
Atmospheric pollution - local and regional.
Strong local protest against placing an incinerator in their area.
Possible pollution of ground water.
Waste Minimisation
Much better than waste disposal.
Packaging makes up 50% of domestic waste and is easy to reduce.
New uses for materials previously dealt with as waste e.g. much slurry now use as organic fertiliser; fish waste used as poultry or pig feed; forestry waste now converted to sawdust for processed wood.
Recycle: multiple uses - glass bottles, metal cans, and paper.
Role of Micro-organisms in Waste Management
Breakdown of domestic and agricultural organic waste by bacteria and fungi.
Purposely designed treatment tanks are used for aerobic and anaerobic decay.
Kitchen organic waste can be broken down in a ‘compost bin’ for garden fertiliser.
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o level biology notes on ecology
Principles of Ecology
Definitions
Ecology: the study of how living organisms interact with each other and with their abiotic environment.
Abiotic Factors: non-living components of the environment.
Habitat: the organism place of residence to which it is adapted.
Population: a group of individuals of the same species living in the same area that interact and interbreed with each other.
Community: interacting populations of different species living in the same area.
Ecosystem: a community of organisms and the habitat’s non-living components.
Biosphere: the global ecosystem - the Earth’s ‘layer of life’.
Environmental Factors Affecting Living Organisms
Biotic Factors: the effect of other living organism of the same or other species.
Abiotic Factors: the effect of non-living items of the organism’s habitat.
Climatic Factors: the effect of the average weather conditions over time, e.g., temperature, rainfall, day length, humidity, wind, atmospheric pressure.
Edaphic Factors: the effect of soil conditions e.g. pH, aeration, porosity, water content, mineral nutrients, humus, soil type.
Aquatic Factors: e.g. wave action, tides, submergence time, exposure time, salinity, oxygen concentration, currents, sedimentation and light quality.
Nutritional Types of Organisms
Producer (Autotroph): makes its own food from inorganic materials.
Photosynthesis: light is the energy source.
Chemosynthesis: energy released by chemical reactions is the energy source.
Consumer (Heterotroph): cannot make food - uses ‘ready-made’ food.
Herbivore: plant eating animal e.g. rabbit, honey bee, green fly.
Carnivore: flesh eating animal e.g. fox, hawk, ladybird.
Omnivore: plant and flesh eating animal e.g. hedge hog, field mouse.
Decomposer: detritus feeder e.g. earthworm, most bacteria and fungi.
Saprophyte: bacterium or fungus that feeds on detritus.
Feeding Relationships
Food Chain: a list of species, each being food for the next species in the list, i.e.
Grass > Rabbit > Fox
Bramble > Aphid > Ladybird > Sparrow > Hawk
Trophic Level: the position of a species in a food chain.
Bramble: first trophic level or primary producer.
Aphid: second trophic level or primary consumer.
Ladybird: third trophic level or secondary consumer.
Sparrow: fourth trophic level or tertiary consumer.
Hawk: fifth trophic lever or quaternary consumer.
Short Food Chains
Inefficiency of energy transfer to the next trophic level.
The energy needs of each organism is about 90% of its food intake.
Almost 90% of an organism’s food is used in respiration.
Food Web
A food web is a flow chart showing the feeding connections in a community.
Textbook Diagram: food web diagram.
A food web is made by linking food chains.
The links are food sources used by two or more species.
All species in a community are connected through the food web.
A change in any one species causes changes in all populations.
Pyramid of Numbers
A Pyramid of Numbers is a bar chart showing the number of individuals at each trophic level of a food chain.
Textbook Diagram: normal and inverted pyramids of numbers.
The number at each trophic level is influence by:
Energy needs of an individual - the lower the need the great the population.
Mass of an individual - the greater the mass the greater its energy needs.
Energy transfer - only about 10% is transferred to the next level.
Other food sources - the species may be a member of other food chains.
Energy Flow
Textbook Diagram: flow char for energy flow.
About 1% of sunlight energy used for photosynthesis by primary producers.
Each trophic level 90% of the food is used for respiration and lost as heat.
Only about 10% of the food energy is transferred to the next trophic level.
Detritus (dead organic matter) is a very important energy source.
Ecological Cycles
Nutrient Cycling
Textbook Diagram: mineral cycling flow chart.
Carbon dioxide is the source of carbon and oxygen for organic molecules.
Water is the source of hydrogen for biomolecules.
Plants get the other elements as soluble salts from the abiotic environment.
Plants are the direct or indirect source of nutrients for consumers.
Consumers ‘steal’ the materials they need, as food, from other organisms.
Decomposers return the inorganic nutrients to the abiotic environment.
Carbon Cycle
Textbook Diagram: carbon cycle flow chart.
Carbon is the most important element in biomolecules as it forms their skeletal framework.
Nitrogen Cycle
Textbook Diagram: nitrogen cycle flow chart.
Bacteria in the Nitrogen Cycle - how they benefit from their roles in the nitrogen cycle:
Nitrogen Fixing Bacteria: usuable form of nitrogen for biomolecule formation.
Saprophytic Bacteria: receive a supply of materials for energy, growth and reproduction.
Nitrifying Bacteria: produce ATP by the nitrification process.
Denitrifying Bacteria: nitrites and nitrates are their oxygen source for ATP formation.
Biotic Factors
Competition
Competition is the rivalry between individuals of the same or different species for the same resources.
Plant Example: grass and daisies compete for light, space, water.
Animal Example: fox and hedgehog compete for food e.g. earthworms.
Competitive Adaptations
Yellow petals of buttercup flower: to win the battle for insect pollinators.
Antibiotics secreted by soil bacterial to inhibit their competitors for nutrients.
Ecological Benefit of Competition
Controls and limits the size of the competitive species.
Maintains a species at a sustainable level.
Competition is a major factor in the evolution.
Important factor in maintaining the ‘balance of nature’ in the community.
Predation
Predation is the hunting and killing of one animal by another for food.
Examples: fox killing rabbits; ladybird killing aphids.
Ecological Benefit of Predation
Maintains the prey species at a sustainable level.
Predation is a major factor in the evolution of the prey species.
Predator Adaptations, e.g., fox.
Reddish fur: camouflage to avoid detection by rabbits.
Long canine teeth: to kill the prey and tear flesh from it when feeding.
Great speed: to outrun the prey to capture it.
Prey Adaptations, e.g., rabbit.
Rests underground: predator avoidance.
Long ears: good hearing to detect the predator.
White tail: conspicuous warning signal to other rabbits.
Textbook Diagram: Predator-Prey Graph - Know how to interpret this graph.
Symbiosis
Symbiosis is the relationship between individuals of two or mores species living together.
Commensalism: symbiosis where one species gains benefit and the other species does not gain but is not at any serious disadvantage. Example: lichens and trees - the lichens gain a place to grow.
Parasitism: symbiosis where one species feeds off and harms the other. Example: lice on hawks.
Mutualism: symbiosis where all species gain. Example: lichens - the fungus gains food from the algae and the algae gain shelter, water plus mineral nutrients from the fungus.
Niche
A species niche is everything about how it lives and fits into the community.
Each species in a community has a unique niche.
Human Population
Food supply and disease are the major factors affecting human population.
Great prosperity is a major factor influencing the population of developed countries.
Textbook Diagram: Human Population Graph
The greater the food supply the greater the potential for population growth.
Famine reduces the population - death and/or migration.
Famine is often linked to war - war zones have reduced agricultural activity.
Prosperity leads to population reduction due to a decline in the birth rate.
Convenient, effective and easily available contraception reduces the birth rate.
Disease, especially among infants, often results in a high death rate.
Modern medical practice has massively reduced the death rate from disease.
Modern medicine and absence of contraception has led to hugh population increase in many developing nations.
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Nutrition – The Chemistry of Food
Food is material that is a good source of one or more of the following: protein, carbohydrate or lipid.
Living organisms need food for energy, growth, repair, defence and reproduction.
Food often contains vitamins and minerals.
Metabolism
Metabolism is the full set of chemical processes carried out by a living organism (anabolism + catabolism).
Anabolism: the formation of large complex organic molecules by linking smaller simpler organic molecules.
Catabolism: the breakdown of large complex molecules into smaller simpler biomolecules.
Anabolic reactions require energy input and catabolic reactions release energy.
Protein
Elements: C, H, O and N in all proteins. Some proteins also contain P and/or S.
Subunits: Amino acids are the subunits that are linked by peptide bonds in chains, folds and branches.
Twenty different amino acids — each different sequence of amino acids produces a different protein.
Each protein has a specific functional shape.
Proteins synthesis takes place at the ribosomes.
Meat, fish, eggs, milk, beans, peas and nuts are good sources of dietary protein.
Structural Role of Protein
Keratin: in hair and outer layer of the skin.
Myosin: major protein in skeletal and cardiac muscle.
Metabolic Role of Protein
Many proteins function as enzymes (specific biological catalysts).
Some proteins function as hormones.
Carbohydrate
Elements: CHO. General Formula: (CH2O)n or CX(H2O)Y
Monosaccharides: single sugar unit
Pentoses: C5H10O5 Deoxyribose of DNA and Ribose of RNA
Hexoses: C6H12O6 Glucose, Fructose, Galactose — use for respiration
Disaccharides: double sugars — two sugar units linked together
Maltose: glucose + glucose — intermediate between glucose and starch
Sucrose: glucose + fructose — food transported in the phloem of plants is a sucrose solution
Lactose: glucose + galactose — the sugar present in milk
Polysaccharides: multisugars — the three examples are multiglucoses
Starch: plant glucose reserve
Glycogen: glucose reserve of animals and fungi. Glycogen stored in skeletal muscle and liver
Cellulose: plant cells walls and fibre in our diet
Dietary Sources of Carbohydrates
Monosaccharides: fruit, honey and jam.
Disaccharides: Sucrose - fruit, table sugar. Lactose - milk. Maltose - germinating seeds.
Polysaccharides: Starch: bread, rice, pasta, potatoes, seeds.
Cellulose: fruit, vegetables, wholegrain cereals, nuts.
Structural Role of Carbohydrate
Cellulose walls of plant cells.
Chitin in the cell walls of fungi.
Metabolic Role of Carbohydrate
Energy Source: energy released by the respiration of glucose is used to make ATP.
Energy Storage: starch in plants, glycogen in animals and fungi.
Lipid
Elements: CHO – with more H but less O than carbohydrates.
Composed of glycerol with three fatty acids linked to the glycerol.
Fat – solid lipid at room temperature. Oil – lipid that is liquid at room temperature.
Phospholipid: two fatty acids and a phosphate group linked to the glycerol.
Good Dietary Sources: meat, milk, butter, cheese, plant oils, margarine.
Structural Role of Lipid
Lipids and Phospholipids are very important in cell membrane structure.
The protective wax cuticle on the outside of leaves.
Metabolic Role of Lipids
Energy storage: more than twice the energy of carbohydrate or protein.
Energy source: released during respiration.
Storage of fat-soluble vitamins.
Some lipids function as hormones.
Hormones as Regulators of Metabolic Activity
Hormones are chemical messengers that cause their target cells or tissues to adjust or alter their activity.
Hormones stimulate or inhibit specific metabolic reactions.
The level of stimulation or inhibition depends on the concentration of hormone in the blood.
Hormones play an important role in homeostasis.
Vitamins
A vitamin is an organic compound needed in small quantities in the diet for health.
Water-soluble Vitamin: Vitamin C (ascorbic acid)
Obtained in fresh fruit and vegetables.
Needed to make and maintain connective tissue and the absorption of iron by the gut.
Long term deficiency of vitamin C causes a disease called scurvy.
Scurvy symptoms: internal bleeding, bruising, bleeding gums, poor healing.
Fat-soluble Vitamin: Vitamin D (calciferol)
Obtained from milk, eggs, liver, fish liver oils and produced in skin exposed to UV light.
It is needed for bone and tooth formation, bone maintenance and the absorption of calcium from the gut.
Long term deficiency cause diseases known as rickets and osteomalacia.
Major deficiency symptoms: late teething and walking, deformed legs and arms, weak bones.
Minerals
Minerals or mineral nutrients are soluble inorganic salts that contain elements essential for metabolism.
Minerals are only needed in small quantities in comparison to protein, carbohydrate and lipid.
Plants obtain their minerals by absorbing them from external ‘water’ — soil water, freshwater and seawater.
Animals receive most of their minerals in the food they eat; some from the ‘water’ they drink.
Plant Mineral Requirement (any two)
Calcium: for the middle lamella that ‘glues’ neighbouring plant cell walls.
Magnesium: for the production of chlorophyll so vital for photosynthesis.
Animal Mineral Requirement (any two)
Calcium: formation of teeth and bones.
Iron: formation of haemoglobin so vital for oxygen transport in our blood.
General Role of Minerals in Living Organisms
Construction of Hard Parts: calcium for teeth and bone; nitrogen for chitin in the cell walls of fungi.
Formation of Soft Tissue: nitrogen and sulphur in the protein of muscle tissue.
Maintain Correct Fluid Concentration: sodium chloride role in blood plasma concentration.
Water: H2O
Importance of Water for Organisms
Fluid Component: 90% of cell cytoplasm, 92% of blood plasma, 97% of tissue fluid and lymph.
Multipurpose Solvent: medium for metabolism and transport.
Take Part in Metabolic Reactions
Photosynthesis: water is a raw material in the light stage.
Respiration: aerobic respiration produces water.
Anabolism: water in produced when the subunits of macromolecules link together.
Catabolism: water is used to break the bonds that hold together the subunits of macromolecules.
Movement of Materials through Cell Membranes: diffusion, osmosis and active transport.
Control Cell Shape
Immature plant cell enlarge to mature size and shape as a result of their absorption of water by osmosis.
Opening and closing of the stoma by change in shape of the guard cells by change in their turgor.
Turgor plays an important role in the support of soft plant tissue.
Good Absorber of Heat Energy
A lot of heat energy has to be absorbed to bring about an increase in temperature or vaporisation.
Water as a medium is a temperature-stable which is so important for homeostasis.
Vaporisation of water is an excellent cooling mechanism.
Mandatory Food Tests
Starch
Yellow-brown iodine solution is placed on the food sample.
A blue-black colour indicates that starch is present.
A yellow-brown colour indicates that starch is not present.
Reducing Sugar
E.g., glucose, fructose, maltose, lactose. (Sucrose is a non-reducing sugar).
Add an equal volume of blue Benedict’s Reagent to the food solution.
Heat but do not boil.
A brick-red colour indicates that reducing sugar is present.
A blue colour indicates that reducing sugar is not present.
Control: water – blue colour result.
Lipid
Rub the food onto brown paper.
A translucent stain that does not ‘dry out’ indicates fat is present.
Control: water – stain dries out and the brown paper remains opaque.
Protein
Biuret Test: Add sodium hydroxide solution to the food solution.
Then add a few drops of blue copper sulphate solution.
Shake the contents vigorously.
A purple-violet colour indicates protein is present.
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o level boilogy notes on nutrition in animals
Nutrition – The Chemistry of Food
Food is material that is a good source of one or more of the following: protein, carbohydrate or lipid.
Living organisms need food for energy, growth, repair, defence and reproduction.
Food often contains vitamins and minerals.
Metabolism
Metabolism is the full set of chemical processes carried out by a living organism (anabolism + catabolism).
Anabolism: the formation of large complex organic molecules by linking smaller simpler organic molecules.
Catabolism: the breakdown of large complex molecules into smaller simpler biomolecules.
Anabolic reactions require energy input and catabolic reactions release energy.
Protein
Elements: C, H, O and N in all proteins. Some proteins also contain P and/or S.
Subunits: Amino acids are the subunits that are linked by peptide bonds in chains, folds and branches.
Twenty different amino acids — each different sequence of amino acids produces a different protein.
Each protein has a specific functional shape.
Proteins synthesis takes place at the ribosomes.
Meat, fish, eggs, milk, beans, peas and nuts are good sources of dietary protein.
Structural Role of Protein
Keratin: in hair and outer layer of the skin.
Myosin: major protein in skeletal and cardiac muscle.
Metabolic Role of Protein
Many proteins function as enzymes (specific biological catalysts).
Some proteins function as hormones.
Carbohydrate
Elements: CHO. General Formula: (CH2O)n or CX(H2O)Y
Monosaccharides: single sugar unit
Pentoses: C5H10O5 Deoxyribose of DNA and Ribose of RNA
Hexoses: C6H12O6 Glucose, Fructose, Galactose — use for respiration
Disaccharides: double sugars — two sugar units linked together
Maltose: glucose + glucose — intermediate between glucose and starch
Sucrose: glucose + fructose — food transported in the phloem of plants is a sucrose solution
Lactose: glucose + galactose — the sugar present in milk
Polysaccharides: multisugars — the three examples are multiglucoses
Starch: plant glucose reserve
Glycogen: glucose reserve of animals and fungi. Glycogen stored in skeletal muscle and liver
Cellulose: plant cells walls and fibre in our diet
Dietary Sources of Carbohydrates
Monosaccharides: fruit, honey and jam.
Disaccharides: Sucrose - fruit, table sugar. Lactose - milk. Maltose - germinating seeds.
Polysaccharides: Starch: bread, rice, pasta, potatoes, seeds.
Cellulose: fruit, vegetables, wholegrain cereals, nuts.
Structural Role of Carbohydrate
Cellulose walls of plant cells.
Chitin in the cell walls of fungi.
Metabolic Role of Carbohydrate
Energy Source: energy released by the respiration of glucose is used to make ATP.
Energy Storage: starch in plants, glycogen in animals and fungi.
Lipid
Elements: CHO – with more H but less O than carbohydrates.
Composed of glycerol with three fatty acids linked to the glycerol.
Fat – solid lipid at room temperature. Oil – lipid that is liquid at room temperature.
Phospholipid: two fatty acids and a phosphate group linked to the glycerol.
Good Dietary Sources: meat, milk, butter, cheese, plant oils, margarine.
Structural Role of Lipid
Lipids and Phospholipids are very important in cell membrane structure.
The protective wax cuticle on the outside of leaves.
Metabolic Role of Lipids
Energy storage: more than twice the energy of carbohydrate or protein.
Energy source: released during respiration.
Storage of fat-soluble vitamins.
Some lipids function as hormones.
Hormones as Regulators of Metabolic Activity
Hormones are chemical messengers that cause their target cells or tissues to adjust or alter their activity.
Hormones stimulate or inhibit specific metabolic reactions.
The level of stimulation or inhibition depends on the concentration of hormone in the blood.
Hormones play an important role in homeostasis.
Vitamins
A vitamin is an organic compound needed in small quantities in the diet for health.
Water-soluble Vitamin: Vitamin C (ascorbic acid)
Obtained in fresh fruit and vegetables.
Needed to make and maintain connective tissue and the absorption of iron by the gut.
Long term deficiency of vitamin C causes a disease called scurvy.
Scurvy symptoms: internal bleeding, bruising, bleeding gums, poor healing.
Fat-soluble Vitamin: Vitamin D (calciferol)
Obtained from milk, eggs, liver, fish liver oils and produced in skin exposed to UV light.
It is needed for bone and tooth formation, bone maintenance and the absorption of calcium from the gut.
Long term deficiency cause diseases known as rickets and osteomalacia.
Major deficiency symptoms: late teething and walking, deformed legs and arms, weak bones.
Minerals
Minerals or mineral nutrients are soluble inorganic salts that contain elements essential for metabolism.
Minerals are only needed in small quantities in comparison to protein, carbohydrate and lipid.
Plants obtain their minerals by absorbing them from external ‘water’ — soil water, freshwater and seawater.
Animals receive most of their minerals in the food they eat; some from the ‘water’ they drink.
Plant Mineral Requirement (any two)
Calcium: for the middle lamella that ‘glues’ neighbouring plant cell walls.
Magnesium: for the production of chlorophyll so vital for photosynthesis.
Animal Mineral Requirement (any two)
Calcium: formation of teeth and bones.
Iron: formation of haemoglobin so vital for oxygen transport in our blood.
General Role of Minerals in Living Organisms
Construction of Hard Parts: calcium for teeth and bone; nitrogen for chitin in the cell walls of fungi.
Formation of Soft Tissue: nitrogen and sulphur in the protein of muscle tissue.
Maintain Correct Fluid Concentration: sodium chloride role in blood plasma concentration.
Water: H2O
Importance of Water for Organisms
Fluid Component: 90% of cell cytoplasm, 92% of blood plasma, 97% of tissue fluid and lymph.
Multipurpose Solvent: medium for metabolism and transport.
Take Part in Metabolic Reactions
Photosynthesis: water is a raw material in the light stage.
Respiration: aerobic respiration produces water.
Anabolism: water in produced when the subunits of macromolecules link together.
Catabolism: water is used to break the bonds that hold together the subunits of macromolecules.
Movement of Materials through Cell Membranes: diffusion, osmosis and active transport.
Control Cell Shape
Immature plant cell enlarge to mature size and shape as a result of their absorption of water by osmosis.
Opening and closing of the stoma by change in shape of the guard cells by change in their turgor.
Turgor plays an important role in the support of soft plant tissue.
Good Absorber of Heat Energy
A lot of heat energy has to be absorbed to bring about an increase in temperature or vaporisation.
Water as a medium is a temperature-stable which is so important for homeostasis.
Vaporisation of water is an excellent cooling mechanism.
Mandatory Food Tests
Starch
Yellow-brown iodine solution is placed on the food sample.
A blue-black colour indicates that starch is present.
A yellow-brown colour indicates that starch is not present.
Reducing Sugar
E.g., glucose, fructose, maltose, lactose. (Sucrose is a non-reducing sugar).
Add an equal volume of blue Benedict’s Reagent to the food solution.
Heat but do not boil.
A brick-red colour indicates that reducing sugar is present.
A blue colour indicates that reducing sugar is not present.
Control: water – blue colour result.
Lipid
Rub the food onto brown paper.
A translucent stain that does not ‘dry out’ indicates fat is present.
Control: water – stain dries out and the brown paper remains opaque.
Protein
Biuret Test: Add sodium hydroxide solution to the food solution.
Then add a few drops of blue copper sulphate solution.
Shake the contents vigorously.
A purple-violet colour indicates protein is present.
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o level notes on excretion,osmoregulation and homeostasis
Excretion, Osmoregulation and Homeostasis
Kidneys
Functions
Excretion: nitrogenous wastes (urea, uric acid), excess salts, excess water.
Osmoregulation: maintaining the blood at a suitable constant concentration.
Homeostasis: maintaining a suitable constant internal environment to sustain efficient metabolism.
Urinary System
The kidneys are a pair of fist-sized red-brown bean-shaped structures.
The kidneys are attached to the back wall of the abdominal cavity.
They lie on either side of the backbone just above the pelvis.
Each kidney receives a good supply of oxygenated blood from the renal artery, a branch of the dorsal aorta.
The renal vein takes the deoxygenated blood from the kidneys to the inferior vena cava.
The blood in the renal vein has less oxygen, salt, urea and uric acid than the renal artery.
Urine is carried to the bladder along the ureter by peristalsis for temporary in the bladder.
A sphincter muscle at the junction of the bladder and urethra regulates the retention and release of urine.
Urine is channelled to the exterior along the urethra.
Kidney Structure
Textbook Diagram: longitudinal section of a kidney showing its internal structure.
A smooth thin protective cover called the capsule surrounds each kidney.
Below the capsule is a thick reddish granular layer, the cortex.
The central part of the series of triangular structures is reddish-brown, the renal pyramids, the tips of which project into the upper expanded end of the ureter known as the pelvis.
Nephron
Textbook diagram: structure and blood supply of the nephron.
The nephron or renal tubule is the functional unit of the kidney.
The nephron has a number of functionally distinct parts.
Each human kidney has about one million nephrons.
Urine is manufactured by the nephrons.
Production of Urine: Filtration and Selective Reabsorption
Details of Urine Formation
Filtration
The glomerulus functions as a filter.
The glomerular capillary walls are porous.
The red blood cells, white cells, platelets and plasma proteins are too big to pass through the pores.
Therefore the glomerulus filters the blood.
The filtrate passing into Bowman’s Capsule.
Glomerular filtrate composition is water, glucose, amino acids, vitamins, salts, urea, and uric acid.
About 20% of the plasma volume passes out of the glomerulus.
The filtration is much higher than expected.
The blood pressure is unusually high in the glomerulus.
The blood pressure is generated by the pumping action of the heart.
The high blood pressure in the glomerulus is due to:
The arrangement of blood vessels: arteriole —> capillaries —> arteriole
This arrangement is unusual - normally low-pressure venules follow capillaries.
The efferent arteriole is narrower than the afferent arteriole.
The higher than normal filtration at the glomerular capillaries is known as ultrafiltration.
Selective Reabsorption
Much useful material was lost from the blood into Bowman’s Capsule.
The ‘useful’ materials are taken back into the blood from the nephron.
By de-selection, urea and uric acid remain in the nephron and are excreted in the urine.
Urine is the unabsorbed glomerular filtrate.
Proximal Convoluted Tubule (PCT)
Total reabsorption of glucose and amino acids.
Four fifths of the salts and water are reabsorbed.
Glucose, amino acids and salts are reabsorbed by active transport.
Water is reabsorbed by osmosis.
The cells lining the PCT are rich in mitochondria, which supply the ATP for active transport.
The Loop of Henle
This structure allows the kidney to reabsorb extra water in times of water stress. As a result it is possible for the kidney to produce hypertonic urine, i.e., more concentrated than blood plasma. A Loop of Henle is only present in mammals and birds — the only animals able to produce hypertonic urine.
About 5% of the water from the glomerular filtrate is reabsorbed from the Loop of Henle by osmosis.
The main function of the Loop is to develop an increasingly concentrated medulla. It accomplishes this by acting as a ‘hairpin counter current multiplier’. This allows extra water, if needed, to be absorbed from the collecting duct under the influence of ADH hormone.
Distal Convoluted Tubule (DCT)
Reabsorption of water is by osmosis.
The amount varies depending on the need of the body.
Water reabsorption by the DCT is under the influence of ADH (antidiuretic hormone).
Reabsorption of salt is by active transport.
The amount of salt reabsorbed depends on the needs of the body.
The role of the DCT is crucial in osmoregulation.
Osmoregulation is a major process in homeostasis.
Osmoregulation
Blood concentration is kept in check by varying the amount of water and salt reabsorbed by the kidneys nephrons.
Blood Concentration Rising
Cause: salty food, water loss due to sweating, inadequate water intake.
Response: increases water reabsorption, decreases salt reabsorption.
Blood Concentration Falling
Cause: excessive water intake, cold weather (sweating less than usual), diet very low on salt.
Response: decreases water reabsorption, increases salt reabsorption.
Note: the greater the excess protein in the diet the greater is the urea content of the urine.
Regulation of Body Fluids by the Kidney
The kidney maintains the blood at the correct composition and concentration by excretion and osmoregulation.
As a result all the other body fluids are kept at optimum condition i.e. tissue fluid and cell cytoplasm.
Role of ADH (antidiuretic hormone)
ADH is secreted to increase water reabsorption by the DCT and collecting duct when blood concentration rises.
Osmoreceptors in the brain’s hypothalamus detect the increase in osmotic pressure of the blood.
This stimulates the pituitary to increase the secretion of ADH into the blood.
ADH is transported everywhere throughout the body in the blood.
The DCT and collecting duct are the target tissues of this hormone.
ADH causes these parts of the nephron to become more permeable to water.
Extra water is now reabsorbed into the blood reducing its concentration back to normal.
The loss of extra water from the filtrate reduces the volume but increases the concentration of the urine.
Major Homeostatic Organs: kidneys, liver, lungs, skin and brain.
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Amoeba Amoeba proteus is a microscopic living organism which consists of a single cell. Like most plant and animal cells, it has cytoplasm, nucleus, cell membrane and a variety of inclusions in the cytoplasm. It is about 0.3 mm across and inhabits the mud at the bottom of fresh water ponds. Although it is just a single cell, it exhibits all the essential functions of any living organism.
Amoeba
Amoeba proteus is a microscopic living organism which consists of a single cell. Like most plant and animal cells, it has cytoplasm, nucleus, cell membrane and a variety of inclusions in the cytoplasm. It is about 0.3 mm across and inhabits the mud at the bottom of fresh water ponds. Although it is just a single cell, it exhibits all the essential functions of any living organism.
Amoeba proteus is a microscopic living organism which consists of a single cell. Like most plant and animal cells, it has cytoplasm, nucleus, cell membrane and a variety of inclusions in the cytoplasm. It is about 0.3 mm across and inhabits the mud at the bottom of fresh water ponds. Although it is just a single cell, it exhibits all the essential functions of any living organism.
agriculture tests for candidates of o level
S.4 AGRICULTURE TEST ON FARM STRUCTURES, 2013.
1. Farm structures can best be described as;
A: structures that separate neighbouring farms
B: structures that hold water and feeds for farm animals
C: physical constructions erected on the farm
D: irrigation and drainage structures.
2. The choice of farm structure the farmer will put up will largely depend on;
A: farmers’ financial position
B: government regulations
C: climate
D: soil structure.
3. One importance of internal fences to
A: minimize disputes over land
B: act as wind breaks
C: confine particular types of animals in an area
D: protect animals against predators.
4. Fences facilitate mixed farming by;
A: separating diseased animals from healthy ones
B: allowing animal keeping without animals being herded
C: allowing animals and crops to be on the same farm without any damage
D: allowing night paddocking.
5.Many peasant farmers in Uganda do not fence their land because
A: fences require a lot of money and labour to establish
B: they have large pieces of land that are clearly marked from the neighbours
C: fences reduce the value of land
D: fences increase the risk of fire on the farm
6. Wood used for fencing may be obtained from the following source , except one, which one is it?
A: isolated trees on the farm
B: local bushes
C: by- products from timber industries
D: protected forests.
7. Wood is commonly used in construction work on the farm because it is
A: resistant to shock and fire
B: structures made are firm and cannot be dismantled easily.
C: it is relatively cheap and easily obtainable
D: it is not damaged by weather or fungus.
8. The method of wood treatment where the chemical is forced into the wood under very high pressure is;
A: End diffusion treatment
B: sap displacement treatment
C: vacuum treatment
D: hot and cold treatment
9. The use of barbed wires in fencing is common in Uganda although;
A: barbs prevent animals from getting out of the enclosure
B: they need more skill to put up
C: they are the best for small and quiet animals
D: they must be used with woven wire
10. Fencing pliers have a heavy head that is used to
A: cut fencing staples
B: remove staples that have been put in badly
C: stretch wires to the right tension
D: hammer staples into fencing posts to hold the wires.
11. When constructing fences it is important to stretch wires tightly to;
A: prevent sagging and reduce chances of animals escaping or entering through the fences.
B: allow cutting of the wires between the posts to the required size
C: attach them on posts permanently.
D: prevent small animals like rabbits and goats from going through the fence.
12. Metal caps may be put on top of fencing posts;
A: to act as rat guards
B: to reduce termite attack
C: to protect them from rain water
D: to ensure that the treatment chemical does not flow out.
13. King posts are bigger than others and are placed deeper into the ground because they;
A: have to hold the strands of wire between corner posts
B: have to resist the strain of wire pulling in a certain direction
C: are put where there is a wide spacing between standards
D: provide additional support to the strainers against the pull of the wires.
14. One of the disadvantages of live fences is that;
A: materials required are not easily available.
B: the wind break they provide is inadequate.
C: when established, they need a lot of maintenance.
D: their establishment is limited by environmental factors.
15. A good cattle dip should have a large colleting yard
A: to allow acaricide to flow back into the dip tank
B: to avoid dilution of acaricide by rain water
C: to hold all animals at the same time so that they do not mix with the ones that have already been dipped.
D: to avoid loss of acaricide through seepage.
16. One importance of farm buildings is that;
A: animal parasites and diseases become easier to control
B: crop loss through spillage is eliminated
C: crop produce is protected from over drying
D: water is used carefully during their cleaning
17. Farm buildings are well maintained by;
A; not driving machinery into them
B: fencing around them
C: allowing minimum ventilation
D: washing and cleaning all dust, dirt, animal waste.
18. The type of roof on farm buildings is influenced by three of the following except one, which one is it?
A: the size of buildings
B: the use to which the building is to be put
C: resistance of the building to soil moisture
D: availability of skill to work with the material
19. One purpose of doors on farm buildings is to;
A: keep out rain and wind
B: provide security
C: allow proper ventilation
D: keep out bad odours
20. A farrowing unit must be constructed with;
A: short walls so that piglets see each other and do not get anxious
B: large space to avoid bulling
C: farrowing pen and creep area
D: adequate water bowls and feed troughs.
21. The strength of concrete is largely attributed to;
A: amount of cement used
B: time it is allowed to set
C: amount of water used
D: amount of earth added.
22. Gravel used in concrete making should be of various sizes so that
A: less money is used as small gravel costs less
B: mixing of ingredients becomes easier
C: curing is uniform on all sides
D: smaller gravel can fill in the spaces between large gravel
23. In making structures like beams and pillars it may be necessary to strengthen the concrete by;
A: using large stone aggregates
B: re wetting the concrete every now and again
C: adding steel bars to take the compression strength
D: adding chopped straw.
24. Many farmers are still using burnt murram bricks for farm buildings because
A: they are very durable.
B: they are relatively cheap and easily obtainable
C: they have uniform consistence
D: they are easier to join together with mortar.
25. During the drying of sand blocks they are covered with damp sacks
A: to prevent premature drying that leads to cracking
B: to increase on the moisture content that increases strength
C: to make the blocks fit in the moulds well
D: so that blocks are easier to lay out in construction
26. The use of thatch as a roofing material for farm structures is no longer common because;
A: it habours vermin and insects
B: it has poor insulation properties to heat and cold
C: it is not water tight even when properly constructed
D: thatching material is expensive.
27. In construction, plastics are used for internal structures since they ;
A: areexpensive and not easily available
B: are harmful to many animals and their products
C: farmers do not have the skills to work with them
D: deteriorate rapidly in bright sunshine.
28. Foundations of buildings are established on subsoil after all top soil has been removed
A: to discourage multiplication of animal parasites
B: to allow building of a wide plinth wall.
C: since subsoil is firm and will not cause buildings to sink
D: top soil will then be taken elsewhere to be used for growing crops.
29. A PVC sheet is laid on top of the plinth wall;
A: to ensure that vertical wall is straight
B: to prevent water infiltration in the vertical wall as well as termite attack
C: to improve on concrete strength
D: to ensure all round horizontal strength.
30. Concrete floors are recommended for farm buildings since,
A: they are easier to construct
B: they require less building material
C: they can be used for any purpose; crops, animals and machinery
D; they are easier to clean so discourage multiplication of pathogens and parasites
31. The height of the wall for farm buildings depends on three of the following, except one, which one is it?
A: The smoothness of the ground space
B: the size of the ground space
C: the purpose for which the house is intended
D: the roofing material to be used.
32. Trusses in farm buildings are
A: the apex of the roof
B: the base of roofs made of the tie beam and rafters
C: horizontally positioned bar on top of the rafters
D: the extended part of the bars that are beyond the vertical wall.
33. The first tool used on timber to shear the wood so that it becomes flat, level and straight is the
A: cross-cut saw
B: Jack plane
C: Rip saw
D: Tenon saw
34. The saw used to cut metal is known as;
A: Tenon saw
B: Rip saw
C: Hack saw
D: cross-cut saw.
35. One way of ensuring that saws remain in good working condition is by
A: Sharpening them on an oil stone
B: keeping teeth at the same size and shape using a 3 sided saw file
C: using any available saw for cutting wood.
D: keeping head tightly fixed on
36. The part of the hammer that is used to remove bent nails is known as;
A: head
B: striking face
C: claw
D: alloy handle
37. Pincers are used to
A: hammering chisels and wooden pegs
B: riveting metal
C: fitting frames together
D: cutting wires to a desirable size.
38. It is important to store small tools in atool box;
A: to keep them from rusting
B: to fit in a small space
C: to ensure they are stored flat
D: to keep them from getting damaged or lost
39. The try square of the following can be used for 3 eight except one, which one is it?
A: setting out right angles during planning of wood
B: measuring very short length of timber
C: holding mortar before it is placed in position
D: setting out and testing frames
40. Clamps are useful in
A: holding pieces of wood during cutting, planning and nailing
B: making holes in wood
C: avoid damaging the wood.
D: gripping the top of nuts.
Answers
1. C11. A21. A31. A2. A12. C22. D32. B3. C13. B23. C33. B4. C14. D24. B34. C5. A15. C25. A35. B6. D16. A26. A36. C7. C17. D27. D37. D8. C18. C28. C38. D9. A19. B29. B39. C10. D20. C30. D40. A
1. Farm structures can best be described as;
A: structures that separate neighbouring farms
B: structures that hold water and feeds for farm animals
C: physical constructions erected on the farm
D: irrigation and drainage structures.
2. The choice of farm structure the farmer will put up will largely depend on;
A: farmers’ financial position
B: government regulations
C: climate
D: soil structure.
3. One importance of internal fences to
A: minimize disputes over land
B: act as wind breaks
C: confine particular types of animals in an area
D: protect animals against predators.
4. Fences facilitate mixed farming by;
A: separating diseased animals from healthy ones
B: allowing animal keeping without animals being herded
C: allowing animals and crops to be on the same farm without any damage
D: allowing night paddocking.
5.Many peasant farmers in Uganda do not fence their land because
A: fences require a lot of money and labour to establish
B: they have large pieces of land that are clearly marked from the neighbours
C: fences reduce the value of land
D: fences increase the risk of fire on the farm
6. Wood used for fencing may be obtained from the following source , except one, which one is it?
A: isolated trees on the farm
B: local bushes
C: by- products from timber industries
D: protected forests.
7. Wood is commonly used in construction work on the farm because it is
A: resistant to shock and fire
B: structures made are firm and cannot be dismantled easily.
C: it is relatively cheap and easily obtainable
D: it is not damaged by weather or fungus.
8. The method of wood treatment where the chemical is forced into the wood under very high pressure is;
A: End diffusion treatment
B: sap displacement treatment
C: vacuum treatment
D: hot and cold treatment
9. The use of barbed wires in fencing is common in Uganda although;
A: barbs prevent animals from getting out of the enclosure
B: they need more skill to put up
C: they are the best for small and quiet animals
D: they must be used with woven wire
10. Fencing pliers have a heavy head that is used to
A: cut fencing staples
B: remove staples that have been put in badly
C: stretch wires to the right tension
D: hammer staples into fencing posts to hold the wires.
11. When constructing fences it is important to stretch wires tightly to;
A: prevent sagging and reduce chances of animals escaping or entering through the fences.
B: allow cutting of the wires between the posts to the required size
C: attach them on posts permanently.
D: prevent small animals like rabbits and goats from going through the fence.
12. Metal caps may be put on top of fencing posts;
A: to act as rat guards
B: to reduce termite attack
C: to protect them from rain water
D: to ensure that the treatment chemical does not flow out.
13. King posts are bigger than others and are placed deeper into the ground because they;
A: have to hold the strands of wire between corner posts
B: have to resist the strain of wire pulling in a certain direction
C: are put where there is a wide spacing between standards
D: provide additional support to the strainers against the pull of the wires.
14. One of the disadvantages of live fences is that;
A: materials required are not easily available.
B: the wind break they provide is inadequate.
C: when established, they need a lot of maintenance.
D: their establishment is limited by environmental factors.
15. A good cattle dip should have a large colleting yard
A: to allow acaricide to flow back into the dip tank
B: to avoid dilution of acaricide by rain water
C: to hold all animals at the same time so that they do not mix with the ones that have already been dipped.
D: to avoid loss of acaricide through seepage.
16. One importance of farm buildings is that;
A: animal parasites and diseases become easier to control
B: crop loss through spillage is eliminated
C: crop produce is protected from over drying
D: water is used carefully during their cleaning
17. Farm buildings are well maintained by;
A; not driving machinery into them
B: fencing around them
C: allowing minimum ventilation
D: washing and cleaning all dust, dirt, animal waste.
18. The type of roof on farm buildings is influenced by three of the following except one, which one is it?
A: the size of buildings
B: the use to which the building is to be put
C: resistance of the building to soil moisture
D: availability of skill to work with the material
19. One purpose of doors on farm buildings is to;
A: keep out rain and wind
B: provide security
C: allow proper ventilation
D: keep out bad odours
20. A farrowing unit must be constructed with;
A: short walls so that piglets see each other and do not get anxious
B: large space to avoid bulling
C: farrowing pen and creep area
D: adequate water bowls and feed troughs.
21. The strength of concrete is largely attributed to;
A: amount of cement used
B: time it is allowed to set
C: amount of water used
D: amount of earth added.
22. Gravel used in concrete making should be of various sizes so that
A: less money is used as small gravel costs less
B: mixing of ingredients becomes easier
C: curing is uniform on all sides
D: smaller gravel can fill in the spaces between large gravel
23. In making structures like beams and pillars it may be necessary to strengthen the concrete by;
A: using large stone aggregates
B: re wetting the concrete every now and again
C: adding steel bars to take the compression strength
D: adding chopped straw.
24. Many farmers are still using burnt murram bricks for farm buildings because
A: they are very durable.
B: they are relatively cheap and easily obtainable
C: they have uniform consistence
D: they are easier to join together with mortar.
25. During the drying of sand blocks they are covered with damp sacks
A: to prevent premature drying that leads to cracking
B: to increase on the moisture content that increases strength
C: to make the blocks fit in the moulds well
D: so that blocks are easier to lay out in construction
26. The use of thatch as a roofing material for farm structures is no longer common because;
A: it habours vermin and insects
B: it has poor insulation properties to heat and cold
C: it is not water tight even when properly constructed
D: thatching material is expensive.
27. In construction, plastics are used for internal structures since they ;
A: areexpensive and not easily available
B: are harmful to many animals and their products
C: farmers do not have the skills to work with them
D: deteriorate rapidly in bright sunshine.
28. Foundations of buildings are established on subsoil after all top soil has been removed
A: to discourage multiplication of animal parasites
B: to allow building of a wide plinth wall.
C: since subsoil is firm and will not cause buildings to sink
D: top soil will then be taken elsewhere to be used for growing crops.
29. A PVC sheet is laid on top of the plinth wall;
A: to ensure that vertical wall is straight
B: to prevent water infiltration in the vertical wall as well as termite attack
C: to improve on concrete strength
D: to ensure all round horizontal strength.
30. Concrete floors are recommended for farm buildings since,
A: they are easier to construct
B: they require less building material
C: they can be used for any purpose; crops, animals and machinery
D; they are easier to clean so discourage multiplication of pathogens and parasites
31. The height of the wall for farm buildings depends on three of the following, except one, which one is it?
A: The smoothness of the ground space
B: the size of the ground space
C: the purpose for which the house is intended
D: the roofing material to be used.
32. Trusses in farm buildings are
A: the apex of the roof
B: the base of roofs made of the tie beam and rafters
C: horizontally positioned bar on top of the rafters
D: the extended part of the bars that are beyond the vertical wall.
33. The first tool used on timber to shear the wood so that it becomes flat, level and straight is the
A: cross-cut saw
B: Jack plane
C: Rip saw
D: Tenon saw
34. The saw used to cut metal is known as;
A: Tenon saw
B: Rip saw
C: Hack saw
D: cross-cut saw.
35. One way of ensuring that saws remain in good working condition is by
A: Sharpening them on an oil stone
B: keeping teeth at the same size and shape using a 3 sided saw file
C: using any available saw for cutting wood.
D: keeping head tightly fixed on
36. The part of the hammer that is used to remove bent nails is known as;
A: head
B: striking face
C: claw
D: alloy handle
37. Pincers are used to
A: hammering chisels and wooden pegs
B: riveting metal
C: fitting frames together
D: cutting wires to a desirable size.
38. It is important to store small tools in atool box;
A: to keep them from rusting
B: to fit in a small space
C: to ensure they are stored flat
D: to keep them from getting damaged or lost
39. The try square of the following can be used for 3 eight except one, which one is it?
A: setting out right angles during planning of wood
B: measuring very short length of timber
C: holding mortar before it is placed in position
D: setting out and testing frames
40. Clamps are useful in
A: holding pieces of wood during cutting, planning and nailing
B: making holes in wood
C: avoid damaging the wood.
D: gripping the top of nuts.
Answers
1. C11. A21. A31. A2. A12. C22. D32. B3. C13. B23. C33. B4. C14. D24. B34. C5. A15. C25. A35. B6. D16. A26. A36. C7. C17. D27. D37. D8. C18. C28. C38. D9. A19. B29. B39. C10. D20. C30. D40. A
Thursday 18 September 2014
o level biology notes
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
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
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.
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