1] Characteristics and classification of living organisms

• movement as an action by an organism or part of an organism causing a change of position or place.
• respiration as the chemical reactions in cells that break down nutrient molecules and release energy for metabolism
• sensitivity as the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses.
• growth as a permanent increase in size and dry mass by an increase in cell number or cell size or both.
• reproduction as the processes that make more of the same kind of organism.
• excretion as removal of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements.
• nutrition as taking in of materials for energy, growth and development].
• species as a group of organisms that can reproduce to produce fertile offspring.
• binomial system of naming species as an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species.
• tissue as a group of cells with similar structures, working together to perform a shared function.
• organ as a structure made up of a group of tissues, working together to perform specific functions.
• organ system as a group of organs with related functions, working together to perform body functions.
• Cell organelles:
• nucleus: contains genetic formation on genes/chromosomes/DNA.
• cell wall: supports the cell and prevents it from bursting.
• cell membrane: controls what goes in and out of the cell.
• cytoplasm: contains nutrients such as sugars and proteins and contains all the cell organelles; site for metabolic reactions.
• vacuole: contains enough water to maintain turgor pressure and may contain sugar, ions and proteins.
• ribosome: on the membrane of rough endoplasmic reticulum; site for protein synthesis.
• mitochondria: site for aerobic respiration, to release energy.

2] Movement in and out of cells

• diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement.

• factors that influence diffusion: surface area, temperature, concentration gradients and distance.

• osmosis as the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), along the water potential gradient, through a partially permeable membrane.
• active transport as the movement of particles through a cell membrane from a region oflower concentration to a region of higher concentration using energy from respiration.
  • protein molecules move particles across a membrane during active transport
  • by changing shape and allowing them to be transported.
  • The ions move through the proteins.
  • They are located on the cell membrane.

3] Biomolecules

• Carbohydrates:
  • C, H, O.
  • Uses:
    • used for energy: 1 molecule releases 17 kJ of energy.
    • transported in the form of
    • stored in the form of starch or
  • Fats:
    • C, H, O.
    • 3 fatty acids and 1 glycerol.
    • Uses:
      • used for energy: one molecule releases twice as much energy as glucose [39kJ].
      • insulation in the form of adipose tissue.
      • store of energy.
      • protection from mechanical damage.
    • Proteins:
      • C, H, O, N.
      • Made up of long chains of amino acids.
      • Uses:
        • cell repair and mitosis.
      • Water:
        • Required for metabolic reactions in cells.
        • Required for transport as it is needed in blood plasma.
        • Required to dissolve nutrients in order for enzymes to act on them in the alimentary canal.
      • Describe the structure of DNA as:
        • two strands coiled together to form a double helix.
        • each strand contains chemicals called bases.
        • cross-links between the strands are formed by pairs of bases.
        • the bases always pair up in the same way: A with T, and C with G (full names are not required).

• Test for carbohydrates:
• Test for reducing sugars:
• Crush and grind to make extract.
• Add benedict’s solution.
• Gently heat the mixture.
• If present: mixture turns from blue to green to yellow to orange to brick red.
• If absent: remains blue.

• Test for starch:
  • Crush and grind to make extract.
  • Add iodine solution.
    • If present: mixture will turn blue-black.
    • If absent: remains
  • Test for fats:
    • Emulsion test:
      • Crush and grind to make extract.
      • Add ethanol to extract.
      • Add water to extract.
        • If present: solution turns milky white.
        • If absent: remains

• Test for proteins:
  • Biuret test.
    • Crush and grind to make extract.
    • Add copper sulphate and potassium hydroxide to the extract.
      • If present: turns purple/mauve/lilac.
      • If absent: remains
    • Test for Vitamin C:
      • DCPIP test:
        • crush and grind to make extract.
        • add DCPIP drop by drop using a pipette/burette.
        • shake after every drop.
        • if vitamin C is present:
          • turns from blue to colourless.
        • measure numberof drops/volume of DCPIP used.

4] Enzymes

• catalyst as a substance that increases the rate of a chemical reaction and is not changed by the reaction.
• enzymes as proteins that function as biological catalysts that increase the rate of a chemical reaction and are not changed by the reaction.
• Importance of enzymes:

• Without enzymes, processes occur too slowly.
• Enzymes are
• Enzymes reduce the activation energy.
• Reactions can take place at lower temperatures.

• Lock and key:

• Enzyme is the lock and substrate is the key.
• Enzyme has a ‘dent’ known as the active site.
• The shape of the active site is complimentary to the shape of the substrate.
• Enzyme and substrate bind at the active site to form a temporary structure known as enzyme-substrate complex.
• Product is formed.
• This product is no longer complimentary to shape of the active site, and so it is released.
• Enzyme can be used again.

• Factors affecting enzyme activity:
  • Temperature:
    • At 0 degrees, enzyme activity is zero because molecules have very less kinetic energy.
    • As temperature increases:
      • Kinetic energy of molecules increases.
      • Velocity of molecules increases.
      • Number of collisions increase per unit time.
      • Frequency of successful collisions
      • More enzyme-substrate complexes formed.
      • Enzyme activity increases.
    • At optimum temperature, enzyme activity is at the highest and enzyme functions fastest.
    • If temperature rises above the optimum temperature:
      • The enzyme denatures.
      • Shape of active site nolonger complimentary to shape of substrate.
      • Enzyme activity becomes zero.
    • pH:
      • Every enzyme has an optimum pH.
      • Any pH less or more than that pH causes the enzyme to denature.
    • Enzyme and substrate concentrations.

5] Plant Nutrition

• photosynthesis as the process by which plants manufacture carbohydrates from raw materials using energy from light.

• 6CO2 + 6H2O → C6H12O6 + 6O2
• Hydrogencarbonate indicator: used to measure carbon dioxide concentration in water.
• Importance of nitrates and magnesium ions.

Nitrate ions	Magnesium ions
Required for amino acid synthesis. · Reduced/stunted growth · Upper leaves turn pale green. · Lower leaves turn yellow · Thin stems and smaller roots	Required for chlorophyll synthesis. · Yellowing between veins of leaves. · Lower leaves turn green · Upper leaves turn yellow. -

• Starch test:
  • Boil the leaf [denatures enzymes temporarily and makes cell membrane fully permeable]
  • Boil the leaf in ethanol [removes chlorophyll, in order to see colour change later]
  • Wash the leaf [remove any excess ethanol]
  • Place leaf on a white tile and add a drop of iodine solution.
    • If present: turns blue-black.
    • If absent: remains brown
  • Proving chlorophyll is required for photosynthesis:
    • Use a variegated leaf.
    • Perform starch test.
    • Green parts will turn blue-black whereas other parts remain brown.
  • Proving light is needed for photosynthesis:
    • Destarch the plant [leave in a dark cupboard for 24-48 hours; ensuring that all starch produced is only during the investigation]
    • Cover one leaf [to prevent light from entering]
    • Keep the plant in an environment where all factors of photosynthesis are present, for 6 hours.
    • Perform starch test.
  • Control: an experimental setup that is given all the variables, including the independent variable, for comparison of results.
  • limiting factor as something present in the environment in such short supply that it restricts life processes.
    • Carbon Dioxide
    • Light Intensity
    • Temperature

6] Human Nutrition

• Balanced diet as a diet containing all seven nutrients in correct amounts and proportions.
• The seven nutrients are:
  • Minerals: inorganic substances required in small amounts. If enough is not supplied, it can cause a deficiency disease.

Mineral	Contained in:	Required for:	Deficiency effects
Calcium	Milk and other dairy products; bread	For bones and teeth; blood clotting	Rickets: brittle and deformed bones.
Iron	Red meat; egg yolk; dark green vegetables.	For making haemoglobin	Anaemia: not enough RBCs so less oxygen delivered to organs.

• Vitamins:organic substances required in small amounts. If enough is not supplied, it can cause a deficiency disease.

Vitamin	Contained in:	Required for:	Deficiency effects
Vitamin C	Citrus fruits	Making stretchy protein- collagen.	Scurvy: pain in joints and bleeding in gums.
Vitamin D	Butter; egg yolk	Helps calcium get absorbed; for making bones and teeth	· Rickets: bones become soft and deformed; · Muscle cramps · Stunted growth · Fatigue · Reduced ability to absorb calcium ions.

• Fibre [found in any cereal, bread or green vegetable]:
  • stimulates muscles along the alimentary canal to contract and relax in order to perform peristalsis.
  • cannot be digested.
  • adds volume to material in the alimentary canal.
  • prevents (colon) cancer.
  • absorbs fats / cholesterol in die.
  • removal of bacteria,
  •  Prevents muscles from becoming weak and prevents constipation.
• Fats: saturated fat contains cholesterol. Cholesterol can get deposited on the walls of coronary arteries and can lead to Found in red meat and dairy products.
• Proteins:
  • deficiency can lead to Kwashiorkor. Symptoms:
    • underweight
    • bloated stomach.
  • A protein and energy deficient diet can lead to marasmus. Symptoms:
    • lack of growth
    • diarrhoea / vomiting
    • fatigue
    • (more) prone to, infections / disease
• ingestion as the taking of substances, e.g. food and drink, into the body through the mouth.
• mechanical digestion as the breakdown of food into smaller pieces without chemical change to the food molecules. This increases the surface area and increases enzyme activity.
• chemicaldigestionas the breakdown of large, insoluble molecules into small, soluble molecules.
• absorption as the movement of small food molecules and ions through the wall of the intestine into the blood. Uses protein carriers that transport molecules using energy from respiration against a concentration gradient in a process known as active transport.
• assimilation as the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells.
• egestion as the passing out of food that has not been digested or absorbed, as faeces, through the anus.
• diarrhoea as the loss of watery faeces.
  • Process:
    • cholera bacterium releases a toxin, which attaches to the walls of the small intestine.
    • stimulates the cells in the wall of the small intestine to release chloride ions.
    • chlorideionsaccumulate in lumen of small intestine, reducing the water potential.
    • osmoticmovementofwater into the gut, causing diarrhoea and dehydration.
  • Treated by:
    • oral rehydration therapy: mixture of salts and sugar.
    • water must be sterilised.
  • Process of digestion:
    • throughout the alimentary canal, circular and longitudinal muscles work antagonistically to move food forward in a process known as peristalsis.

1. Mouth
   • food is ingested using the teeth.
   • teeth crush and grind to increase surface area[mechanical digestion].
     • Tooth Decay:
       • Process:
         • bacteria use sugar / AW (on teeth as a food source) ;
         • bacteria anaerobically respire ;
         • lactic acid is produced ;
         • corrodes through enamel and dentine
         • reaches nerves in pulp cavity causing pain
         • tooth falls out or needs removal.
       • Prevention:
         • regular, brushing / mouthwash / flossing / wash / clean, teeth
         • avoid sugary foods / diet described
         • dental check-ups
       • saliva contains salivary amylase which breaks down starch to maltose[chemical digestion]

2. Oesophagus
   • mechanical digestion: peristalsis [using outer longitudinal and inner circular muscles]
3. Stomach:
   • sphincter muscles are present at both the entrance and the exit to prevent acid reflux and keep the food in the stomach.
   • muscles contract and relax to churn food in order to increase surface area[mechanical digestion]
   • pepsin secreted that breaks down proteins to polypeptides[chemical digestion]
   • HCL secreted, to make the pH acidic as:
     • the optimum pH for pepsin is acidic
     • it kills any bacteria.

4. Small intestine:
   • pancreatic juice is secreted from the pancreas through the pancreatic duct [chemical digestion], containing:
     • pancreatic amylase
     • trypsin
     • lipase
   • bile is secreted by the gall bladder. Functions:
     • neutralises the acidic chyme from the stomach to give suitable pH for enzyme action.
     • emulsification: breaks up large fat globules into smaller ones to increase surface area for enzyme action of lipase.[mechanical digestion]
     • Also contains bile pigments made of old RBCs. It is egested along with faeces.
     • Also denatures enzymes from the stomach such as
   • villi: secrete enzymes for digestion of food.
     • The cells of the villi secrete the following enzymes:
       • maltase
       • sucrase
       • lactase
       • peptidase
       • lipase
     • Adaptations of the villus:
       • capillaries in close proximity: to allow faster diffusion and active transport; good blood supply.
       • lacteals in close proximity: to allow for faster diffusion and active transport, to absorb and carry fats and cholesterol.
       • lots of mitochondria: to provide energy for active transport by respiration.
       • villi wall is one cell thick: faster diffusion.
       • microvilli:to increase surface area for absorption, faster diffusion and active transport.
       • goblet cells present: secrete mucus to protect the villus from:
         • enzymes such as proteases and lipases.
         • physical damage.
         • acid from the stomach.
       • Most of water is absorbed in the colon.

5. Large intestine:
   • absorbs any leftover nutrients and water.

• Role of the liver:
  1. all nutrients are transported to the liver via the hepatic portal vein.
  2. excess glucose converted to glycogen and stored.
  3. excess amino acids are
  4. amino group is converted to urea and sent to kidney.
  5. rest of amino acids converted to glycogen and stored.
  6. haemoglobin removed from dead RBCs, and the remaining part is converted to glycogen and stored.
  7. Drugs are broken down
  8. Toxins are neutralised

7] Transport in plants

Xylem	Phloem
Made up of many dead cells joined end to end, where the end walls are dissolved.	Made up of many cells joined end to end, however they are not completely dissolved. They have perforations.
Transport water and mineral ions.	Translocate sucrose and amino acids.
No cytoplasm or nucleus.	No nucleus [cytoplasm is present]
Lignin present.	Lignin absent.
Unidirectional movement.	Bidirectional movement.

• Adaptations of Xylem:
  1. Lignin present: lignin is waterproof and prevents any loss of water from the xylem.
  2. No nucleus or cytoplasm: to allow a smooth flow of water.
  3. End walls dissolved: to allow a free, smooth passage of water.
  4. Low pressure at the top of the xylem and high pressure at the bottom of the xylem causes suction pressure and transpirational pull.
• Transpiration stream:
  1. water moves from root cells to xylem by cell-to-cell osmosis.
  2. this increases the pressure in the roots.
  3. evaporation/transpiration of water in the leaves at the top of the xylem, followed by diffusion of water vapour though stomatareduces the pressure at the top.
  4. pressure gradient causes water to move up, by transpirational pull.
  5. water moves up in a continuous column.
  6. cohesionbetween water molecules helps water move as a continuous column.
  7. adhesion causes water molecules to stick to lignin, allowing a continuous column of water.
• transpiration as loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata.

• Process of transpiration:
  1. The palisade and spongy mesophyll cells have a very large surface area, so osmosis takes place and water moves from a region of high water potential inside these cells to a region of low water potential in the air gaps outside the cells, through a partially permeable membrane and along the water potential gradient.
  2. The water is now on the surface of the mesophyll cells.
  3. Since they have a very large surface area, evaporation takes place and water is converted to water vapour.
  4. This water vapour diffuses from a region of high concentration in the air gaps to a region of low concentration outside the leaf, through the stomata and along a concentration gradient. This is known as
• Factors affecting transpiration:
  1. Temperature
  2. Humidity
  3. Wind velocity
• Advantages of transpiration:
  1. Keeps water moving up the xylem vessel due to transpirational pull that is created.
  2. Evaporation helps cool the leaves.
• Wilting:
  • when the absorption rate of water is less than the rate of transpiration. This causes loss of water through cell-to-cell osmosis, causing plant cells to become flaccid, and the plant starts to wilt.
  • Due to transpiration, the guard cells in the leaves also become flaccid, and close, to prevent any further loss of water.
• Adaptations of plants to take up water:
  • root hair cells have very large surface area for active transport and diffusion.
  • root hair cells also have many mitochondria to provide energy for active transport.
  • xylem vessels are hollow and narrow to provide an easy pathway for water.
  • many air spaces inside the leaves means large surface area for evaporation.
  • stomata being open allows vapour to diffuse easily out of the leaf.

• translocation in terms of the movement of sucrose and amino acids in phloem:
• – from regions of production (source)
• – to regions of storage or to regions where they are used in respiration or growth (sink)

Season	Source	Sink	Explanation
Summer	Leaf	All organs	Plant leaves photosynthesise to produce glucose which gets converted to sucrose and translocated to all parts of the plant.
End of winter/spring	Storage organs[vegetable]	New shoots	Storage organs contain starch which is used for respiration and energy for the shoot. It is converted to sucrose and translocated to the shoots for energy and development.
-	Germinating seeds	Plumule/radicle	Leaves have not yet developed to photosynthesise so energy is needed for the growth of the plumule and radicle. Glucose is stored in the form of starch, converted to sucrose and translocated to the plumule and radicle for growth.

8] Transport in animals

• consists of blood vessels, with a pump known as the
• Single circulation:
  • blood passes through the heart once in one complete circuit around the body.
• Double circulation:
  • blood passes through the heart twice during one complete circuit around the body.
  • one loop through the lungs and one loop through the rest of the body.
  • Advantages:
    • higher blood pressure/flow rate.
    • prevents mixing of oxygenated and deoxygenated blood.
    • allows animals to have high metabolic rates.
    • allows different blood pressure in each loop.
    • allows animals to be large/tall.
  • Consists of:
    • pulmonary circulation
    • systemic circulation

Pulmonary circulation	Systemic circulation
Between heart and lungs	Between heart and rest of the body
Involves pulmonary artery[de-oxygenated blood] and pulmonary vein[oxygenated blood]	Involves vena cava[de-oxygenated blood] and aorta[oxygenated blood]
Faster, because it involves a smaller circuit.	Slower, because it involves a bigger circuit.
Low pressure circulation: because of thinner walls of right ventricle	High pressure circulation: due to thicker walls of left ventricle.

• Left ventricle is thicker because:
  1. the left ventricle wall contains more muscle.
  2. left ventricle pumps blood further.
  3. left ventricle has to overcome more resistance.
  4. left ventricle pumps blood at higher pressure.
• Cardiac cycle:
  1. blood enters the left atrium[pulmonary vein] and right atrium[vena cava].
  2. atrial systole: atriums
  3. atrioventricular valvesopen and blood is pushed down to ventricles.
  4. right/left ventricles contract from bottom up to push blood
  5. atrioventricular valves close and semilunar valves open.
  6. blood flows to the aorta and pulmonary artery.
  7. semi-lunar valves close to prevent blood from flowing back.
• Function of valves:
  1. prevent backflow of blood.
  2. ensure that blood flows in one direction only.
• Function of septum:
  1. to prevent mixing of oxygenated and de-oxygenated blood.
• Heart rate can be monitored by:
  1. ECG[Electro Cardiogram].
  2. pulse rate.
  3. one ‘lub-dup’; the sound of valves opening and closing.

• Coronary Heart Disease[CHD]
  • caused by deposition of fat and cholesterol on coronary arteries.
  • Process:
    • deposition of fat on walls of coronary arteries.
    • narrows lumen, restricting blood flow[oxygen and glucose] to cardiac muscles.
    • thrombosis may occur[complete blockage].
    • less/no nutrients supplied to muscles.
    • increases blood pressure.
    • muscles respire anaerobically.
    • less/no aerobic
    • muscle cells in heart die as no nutrients supplied.
    • muscles cannot contract as sufficient energy is not provided.
    • cardiac arrest/heart attack.
  • Factors causing CHD:
    • lack of exercise.
    • high cholesterol diet.
    • genetic factors.
  • Prevention:
    • exercise (regularly).
    • reduce / stop smoking.
    • reduce (animal / saturated) fat / cholesterol in diet.
    • lose weight / avoid obesity.
    • reduce salt intake.
    • reduce alcohol intake.
    • avoid stress situations.
    • correct ref to medication.
    • control diabetes.
    • reduce blood pressure.
  • How does exercise help?
    • prevents blocked arteries / prevents thrombus formation.
    • lowers blood pressure.
    • lowers cholesterol / lowers fats / reduces risk of atheroma.
    • weight loss / using fats / avoids obesity.
    • lowersstress.
    • (heart) muscle stronger / lower (resting) pulse.

• CHD treatment:
  • drug treatment.
  • surgery / operation.
  • aspirin:
    • to, reduce risk of / prevent, blood clotting.
  • coronary by-pass:
    • a piece of another/ shunt blood vessel.
    • attached to carry blood around the blocked artery.
  • angioplasty:
    • tube or balloon inserted into artery .
    • balloon inflated to widen artery.
  • stent:
    • small mesh tube inserted in artery.
    • opens / supports, (narrow / weak) artery.
    • to restore blood supply (to heart muscle).
  • Effect of physical activity on heart rate:
    1. muscles need energy, thus requiring oxygen and glucose.
    2. heart pumps blood faster to send blood carrying oxygen and glucose to all parts of the body.
    3. heart also needs to remove carbon dioxide and lactic acid as they affect enzyme action, and so to remove them it needs pump blood faster.
    4. therefore, heart rate increases.
  • Blood vessels:

1. Arteries:

• carry oxygenated blood from heart to tissue/muscle[except for pulmonary artery]
• transport blood under high pressure and maintain it.
• Adaptations:
• thick muscular wall: withstands high pressure of blood.
• elastic fibre:stretches and recoils to maintain blood pressure and smoothen blood flow.
• fibrous tissue: maintains the shape of the artery and prevents it from bursting.
• small lumen: maintains blood pressure.
• folded/crinkly endothelium: allows artery to stretch, allowing a larger volume of blood to flow.

2. Veins:
   • carry de-oxygenated blood from the tissue/muscle to the heart[except for the pulmonary artery].
   • transport blood at low pressure.
   • Adaptations:
     • valves: prevent backflow of blood.
     • wide lumen: allows blood to flow with minimum resistance.
     • thin wall: allows contraction of muscles outside the veinto be felt inside the lumen, which allows blood to flow.

3. Capillaries:
   • exchange of substances between the blood and tissue/cells by diffusion occurs in capillaries.
   • Adaptations:
     • pores in capillary walls:
       1. allows filtration/movement of small molecules and nutrients between blood to tissue.
       2. allows WBCs to squeeze
     • one-cell thick:faster
     • very narrow:
       1. blood moves slowly in order to facilitate exchange of substances.
       2. ensures RBCs are closer to wall to facilitate diffusion of oxygen.
     • large number of capillaries/capillary bed: to increase surface area for faster

 

• Components of blood:

Component	Function
Red blood cells	Transporting oxygen. Haemoglobin absorbs oxygen and transports it.
White blood cells	Phagocytosis and antibody production.
Platelets	Clotting.
Plasma	Transport of blood cells, ions, soluble nutrients, hormones, proteins and carbon dioxide.

• Process of clotting:
  1. platelets stimulate clotting.
  2. platelets bump into rough edges of the wound and react, releasing clotting factors[thrombin].
  3. these clotting factors cause fibrinogen in blood to convert to fibrin.
  4. this creates a mesh around the wound.
  5. red blood cells get trapped in this mesh and it forms a scab.
• Advantages of blood clotting:
  1. prevents loss of blood.
  2. prevents entry of pathogen.
• Lymphatic system:
  1. Consist of lymphatic capillaries. They are present near the villi to transport any fats and cholesterol, and also collect tissue fluid.
  2. These capillaries join together to form lymph vessels.
  3. The vessels have lymph nodes which have many WBCs, to kill any pathogens and destroy toxins.
  4. They eventually join up to the blood vessels, because they need to empty out all the tissue fluid.
• Tissue fluid:
  • Capillaries empty nutrients into the tissue fluid, from which the nutrients diffuse into each cell. The function of tissue fluid is:
    • supplying cells with required nutrients.
    • keep environment constant: for optimum temperature for enzymes in cells.

9] Diseases and Immunity

• pathogen as a disease-causing organism.
• transmissible disease as a disease in which the pathogen can be passed from one host to another.
• Each pathogen has its own antigens, which are specific to that pathogen. Therefore, only specific antibodies can fit the specific shapes, and those antibodies are needed.
• Process of immunity:
  1. recognize a specific, pathogen / antigen.
  2. antibodies lock on to antigens.
  3. These antigens are on the membranes of the pathogen.
  4. antibodies / antigens, are specific.
  5. antibodies (have shape) complementary to antigen.
  6. antibodies destroy pathogens (directly).
  7. antibodies can cause bacteria to agglutinate/ clump.
  8. antibodies mark pathogens for destruction by phagocytes by phagocytosis.
  9. they neutralise / inhibit toxins.
• Pathogens can enter the body by:
  1. Direct Contact:
     • through blood.
     • other bodilyfluids.
  2. Indirect transmission:
     • contaminated food or surfaces.
     • from animals.
     • from
  3. Vectors
• The body has the following defences:
  1. mechanical barriers:
     • nostrils contain hair to trap bacteria.
     • skin has a layer of dead cells that prevent it from getting penetrated.
     • when skin is cut, a blood clot prevents further entry of pathogens.

2. chemical barriers:
   • mucus is present, produced by goblet cells, to trap dust and bacteria.
   • HCL produced by the stomach kills any bacteria present in the food.
   • pathogens are also killed by:
     • phagocytes:
     • lymphocytes:antibody production.
   • WBCs can be enhanced by vaccines.

• active immunity as defence against a pathogen by antibody production in the body.
• How vaccination works/how vaccination helps control spread of diseases:
  1. active immunity.
  2. harmless / dead / weakened pathogen / microorganisms.
  3. injected / ingested.
  4. the pathogen has a specific / unique antigen.
  5. stimulates an immune response.
  6. antigens triggers lymphocytes to produce antibodies.
  7. memory cells are produced.
  8. rapid immune response to if re-infected by (exposed to) the same pathogen / antigen.
  9. gives long-term immunity.
  10. herd immunity.
• Hygiene:
  1. Food hygiene:
     • keep bacteria away from food.
     • keep animals away from food.
     • do not keep food at room temperature for too long.
     • keep raw meat away from other food.
  2. Personal hygiene:
     • keep your body clean.
     • brush twice a day.
  3. Waste disposal:
     • methane produced when garbage decays, which is
     • placing pipes in rubbish can allow methane to escape without causing any damage.
  4. Sewage treatment:
     • raw sewage contains lots of bacteria needs to be treated. Otherwise, it could affect aquatic life.
     • water is a precious commodity and needs to be recycled.

• passive immunity is short-term defence against a pathogen by antibodies acquired from another individual, e.g. mother to infant.

Active immunity	Passive immunity
Antibodies produced by organism’s body.	Antibodies produced and acquired from another individual.
Memory cells produced.	Memory cells not produced.
Long-lived immunity.	Short-lived immunity.
Response in subsequent infection is faster.	Response in subsequent infection is slower.

• Auto-immune diseases:
  • some diseases are caused by the immune system targeting and destroying body cells.
  • Type 1 Diabetes:
    • WBCs attack and destroy beta cells in the pancreas, that produce the hormone insulin.
    • Pancreas produces less insulin, so blood glucose levels remain high.
    • Leads to:
      • weight loss.

10] Respiration and Gas Exchange

• aerobic respiration as the chemical reactions in cells that use oxygento break down nutrient molecules to release energy.
• C6H12O6 + 6O2 → 6CO2 + 6H2O
• anaerobic respiration as the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
• Anaerobic respiration in yeast:
  • glucose → ethanol + carbon dioxide.
  • C6H12O6 → 2C2H5OH + 2CO2
• In humans, anaerobic respiration produces lactic acid only.

Aerobic respiration	Anaerobic respiration
Presence of oxygen.	Absence of oxygen.
More energy released.	Less energy released.
Complete breakdown of glucose.	Incomplete breakdown of glucose.
Carbon dioxide and water produced.	In human muscle cells:lactic acid produced. In yeast:carbon dioxide and ethanol produced.
All living cells.	Only specific cells[muscle, yeast, etc.]

Breathing	Respiration
Mechanical process.	Chemical process.
Inhaling and exhaling.	Involves the breakdown of glucose to release energy.
Involves lungs, diaphragm, and ribcage muscles.	Takes place in every cell of the body.

• Uses of energy in the body:

• muscle contraction.
• protein synthesis.
• cell division.
• active transport.
• growth.
• the passage of nerve impulses.
• maintenance of a constant body temperature.

• Trachea:
  • Contains cartilage:
    1. keeps, airways / trachea / bronchi, open.
    2. allows (free flow of) air into (the lungs).
    3. allows flexibility / can breathe even when, bent / swallowing.
  • Adaptations of gas exchange surfaces:
    • Large surface area:
      1. alveoli are bunched like grapes.
      2. capillaries: form large network.
         • diffusion is faster, increasing absorption.

• Thin walls:
  1. walls are one-cell thick.
     • reduces diffusion distancefor oxygen and carbon dioxide.

• Concentration gradient:
  1. alveoli: high concentration of oxygen flowing in from bronchi.
  2. capillaries:high concentration of carbon dioxide by continuous flow of blood.
     • steeper concentration gradient, faster diffusion.

• Moist surface:
  1. inner surface of alveoli has a thin film of moisture,
  2. dissolves oxygen before diffusion.
     • diffusion is faster.

• Process of breathing:
  • Inhalation:
    1. external intercostal muscles
    2. internal intercostal muscles
    3. lifts ribs upwards and
    4. diaphragm contracts and flattens and drops.
    5. volume of thorax / lungs / chest
    6. pressure in thorax / lungs / chest
    7. air flows in.
    8. down the pressure gradient.
    9. lungs inflate.
  • Exhalation:
    1. internal intercostal muscles contract.
    2. external intercostal muscles relax.
    3. lifts ribs downwards and inwards.
    4. diaphragm relaxes to raise it to a dome shape.
    5. volume of thorax/lungs/chest
    6. pressure in thorax/lungs/chest
    7. air flows out.
    8. down the pressure gradient.
    9. lungs
  • Effect of exercise on breathing rate:
    • increase in muscle contraction.
    • increase in demand for energy.
    • increase in aerobic respiration.
    • increase in demand for oxygen.
    • increase in carbon dioxide concentration.
    • decrease in pH/increase in acid, in the blood.
    • detected by the, brain/chemoreceptors.
    • brain stimulates an increase in breathing rate/faster breathing.
    • brain stimulates an increase in depth of breathing.
  • Oxygen debt:
    • During exercise, enough oxygen cannot be supplied fast enough to meet the energy requirement of muscles.
    • Muscles switch to anaerobic respiration.
    • lactic acid
    • lowers pH and causes pain and fatigue.
    • extra oxygen required by the muscles after exercise to break down the lactic acid.
    • oxygen debt.
  • Breathing rate remains high after exercise:
    • to supply muscles with oxygen to break down lactic acid.
    • to remove carbon dioxide from the body.
    • to remove lactic acid from muscle cells and move it to the liver.

11] Excretion

Excretion	Egestion
The removal of toxic materials, waste products of metabolism and excess materials.	Removal of undigested or unabsorbed food, and fibre.
Excreted through the lungs, skin, kidneys and liver.	Egested through the anus.

• Excretory organs:
  • Lungs:
    • carbon dioxide.
  • Skin:
    • excess salts and water.
  • Kidney:
    • excess salts and water.
  • Liver:
    • bile pigments.
    • spent hormones.
  • deamination as the removal of the nitrogen-containing part of amino acids to form urea.
  • Process of deamination:
    1. nitrogen-containing part of excess amino acids is converted to ammonia, in the liver.
    2. ammonia is toxic and it kills cells.
    3. it is converted to urea and taken to the heart via the hepatic vein.
    4. it is then taken from the heart to the kidneys via the renal artery.
    5. remaining part of amino acids is converted to glycogen and stored in the liver.
  • Role of the liver:
    1. converts excess amino acids into urea and carbohydrates in a process known as deamination.
    2. synthesises plasma proteins such as fibrinogen from amino acids.
    3. stored carbohydrates as
    4. makes bile.
    5. neutralises toxins.
    6. breaks down harmful substances such as drugs.
    7. breaks down old RBCs, storing iron and excreting remaining part as bile pigments.
    8. stores vitamins A, B, D, E and K.
    9. stores potassium.
    10. makes cholesterol, for cell membrane repair.
  • Kidney has three main parts:
  • Leading from the pelvis is a tube to the urinary bladder, known as the ureter.
  • The kidneys are made of thousands of tiny tubules known as kidney tubules.
  • The role of kidney tubules:
    1. Filtration:
       • blood is brought into the renal capsule via the renal artery.
       • the blood goes through the afferent arteriole[which is wide], into the glomerulus. It leaves the glomerulus in the efferent arteriole[which is narrow].
       • the difference in pressure between the afferent and efferent arteriole causes high pressure in the capillaries in the glomerulus and causes nutrients to move out of the glomerulus.
       • therefore, glucose, urea, water and salts move into the renal capsule.
       • plasma proteinsdo not come out as they are too big.

2. Reabsorption:
   • takes place in all parts of the kidney tubule except for the renal capsule.
   • all glucose, almost all water and salts get reabsorbed by diffusion and osmosis.
   • they move into the capillaries which join up to form the renal vein.
   • the solution left in the kidney tubule after reabsorption:
     • excess salts.
     • excess water.
   • this solution is called urine.
   • this flows into the collecting duct and goes to the ureter.

Renal artery	Renal vein
Oxygenated blood.	De-oxygenated blood.
Urea.	No urea.
More water.	Less water.
More salts.	Less salts.
Toxins.	No toxins.

• Dialysis machine:
  • Functioning of the dialysis machine:
    • blood is taken from a vein in the hand, because:
      • hands are close and convenient.
      • veins are easy to find.
      • veins have low pressure blood flow.
    • blood flows from body into the dialysis machine.
    • through a tube that is made of a partially permeable membrane.
    • the tube is surrounded by dialysis fluid, containing:
      • glucose, salts and water[according to blood concentrations and osmotic potential]
      • no
    • the tube separates the person’s blood from the dialysis fluid.
    • all ureadiffuses across the partially permeable membrane out of the tube down the concentration gradient.
    • excess water and saltsmove out by diffusion and osmosis and enter the dialysis fluid.
    • glucose in the dialysis fluid is the same concentration as in blood so there is no diffusion/loss of glucose.
    • dialysis fluid is constantly refreshed to maintain the concentration gradient.
    • the dialysis fluid and blood flow in opposite directions, known as counter-current flow, which makes diffusion faster.
    • blood returns back to the vein.
  • Disadvantages:
    • inconvenient: need to visit the hospital multiple times a week; time consuming.
    • restricted
    • quality of life affected.
  • Kidney transplant:
    • Advantages:
      • noneed for dialysis.
      • noneed to go for hospital.
      • norestricted diet.
      • nolong term pain/discomfort.
      • improved quality of life.
    • Disadvantages:
      • rejection of kidney.
      • difficulty with finding donor.
      • riskassociated with operation.
      • need to take immunosuppressants.

12] Coordination & Response

• nerve impulse: an electrical signal that travels along nerve cells known as neurones.
• human nervous system consists of:
  1. central nervous system:
     • spinal cord.
  2. peripheral nervous system:

• Reflex arc:
  1. Stimulus: triggers a nerve impulse.
  2. Impulse is picked up by a
  3. This impulse travels along sensory neurones.
  4. Impulse is carried to the CNS. It processes the impulse.
  5. Response is sent via a motor neurone.
  6. To the appropriate
  7. Response to stimulus occurs.

• reflex action as a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands).

Voluntary action	Involuntary action
Not a rapid response.	Rapid response.
Requires conscious thought.	Does not require conscious thought.
Requires learning/not present from birth.	Does not require learning/present from birth.
Not protective in nature.	Protective in nature.

• Myelin sheath:
  • layer of fat and protein that wraps around a neurone.
  • Purpose:
    • insulates the neurone so impulses are carried faster.
    • prevents leakage of impulses.

• synapse as a junction between two neurones, consisting of a minute gap through which impulses travel by diffusion of a neurotransmitter.
• A synapse consists of:

1. vesicles containing chemicals called neurotransmitters.
2. synaptic cleft [minute gap].
3. receptor molecules.

Process:

1. in the pre-synaptic neurone, an impulse triggers the vesicles containing neurotransmitters to move towards the cell membrane.
2. vesicles fuse with the cell membrane.
3. neurotransmitters are released.
4. neurotransmitters diffuseacross the synaptic cleft.
5. neurotransmitters bind with receptor molecules on the cell surface of the post-synaptic neurone.
6. neurotransmitter and receptor molecules are complementary to each other.
7. binding results in an electrical impulse in the post-synaptic neurone.

Advantage of a synapse: ensures that impulses travel in one direction only.

Disadvantage of a synapse:drugs can act upon synapses.

sense organs as groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals.

• Functions of parts of the eye:

1. cornea:refracts light.
2. iris:controls how much light enters the pupil.
3. lens:focuses light onto the retina.
4. retina: contains light receptors, some sensitive to light of different colours.
5. optic nerve:carries impulses from the eye to the brain.

Pupil reflex:

1. In bright light:

• circular muscles contract.
• radial muscles relax.
• pupil constricts.
• less light enters the eye through the contracted pupil.
• to prevent damage to photoreceptors.

In dim light:

• circular muscles relax.
• radial muscles contract.
• pupil dilates.
• allows more light to enter in order to activate more receptors for clearer vision.

Accommodation:

1. When the object is near:

• ciliary muscles contract.
• suspensory ligaments slacken/loosen.
• muscle tension low.
• lens shape:fat/squat.
• increased refraction of light.

When the object is far:

• ciliary muscle relax.
• suspensory ligaments stretched/tense.
• muscle tension high.
• lens shape:thin/narrow.
• less refraction of light.

Rods	Cones
Sensitive to dim light.	Sensitive to bright light. [R, G, B]
Distributed throughout the retina.[except for the fovea and the blind spot.]	Concentrated mainly in the fovea.
Responsible for black and white vision.	Responsible for colouredvision and sharpimages.

• hormone as a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.
• Adrenaline:
• secreted by the adrenal gland.
• prepares for fight or flight response.

Effect	Reason	Target organs
Increases breathing and pulse rate.	Oxygen and glucose supplied to muscle cells for energy.	Lungs and heart.
Widens pupils.	More light enters the eye, leading to clearer vision.	Iris muscles [radial and circular muscles]
Increases blood concentration	More glucose supplied to muscles for energy.	Liver.
Blood vessels in skin and digestive system constrict. Blood vessels in leg muscles dilate.	Diverting blood[which contains oxygen and glucose] to leg muscles.	Artery and arteriole muscles.

• Insulin:
  • secreted by the pancreas.
  • controls the glucose concentration in blood.
• Oestrogen:
  • secreted by the ovaries.
  • cause development of secondary sexual characteristics in females, and helps in the control of the menstrual cycle.
• Testosterone:
  • secreted by testes.
  • cause development of secondary sexual characteristics in males.

Nervous system	Endocrine system
Made of neurones.	Made of secretory cells and hormones.
Impulses transmitted along nerve fibres.	Chemicals carried dissolved in plasma.
Information transmitted in the form of electrical impulses.	Information carried in chemicals called hormones.
Impulses travel quickly.	Hormones travel more slowly.
Effect of a nerve impulse is short-lived.	Effect of a hormone lasts long.

Plant growth substances

• gravitropism as a response in which parts of a plant grow towards or away from gravity.
• phototropism as a response in which parts of a plant grow towards or away from the direction of light.

• Auxins and positive phototropism in shoots:
  • auxins are produced in the shoot tip.
  • they are broken down by light, so they move away from light by diffusion.
  • therefore, they accumulate on the shaded side.
  • this results in a difference in concentrations in the shaded side and the side facing light.
  • cells with higher concentration of auxins absorb more water, stimulating more cell elongation.
  • this causes unequal growth in the shaded region and non-shaded region, leading to the shoot tip bending toward light.
  • Purpose:
    • grow towards light to expose more parts of the leaf to sunlight.
    • leading to more light absorbed.
    • more growth.
    • flowers are morelikely to attract pollinators.
    • more likely to disperse seeds.
  • Auxins and positive gravitropism in roots.
    • auxins are produced in the root tip.
    • they diffuse towards gravity.
    • they accumulate on the lower side.
    • this causes unequal concentrations in the lower side and the upper side.
    • auxins inhibit cell elongation on the lower side.
    • this causes unequal growth in the lower side and the upper side, leading to the root tip bending towards gravity.
    • Purpose:
      • better anchorage.
      • absorb more minerals ions and water.
    • Etiolation:
      • plant receives very little light.
      • auxins are distributed evenly around the shoot tip and shoot grows rapidly upwards[in search of light]
      • chlorophyll synthesisreduced.
      • stem and leaves become yellow[because of lack of chlorophyll] and spindly[lack of photosynthesis].
      • condition is reversed when grown in light.
    • Use of synthetic plant hormone 2,4-D as a weedkiller:
      • large concentrations of 2, 4-D are sprayed onto weeds.
      • shoot[leaves and stem] are stimulated to grow rapidly.
      • root growth is inhibited by high concentration of auxins.
      • roots cannot absorb enough water and minerals to support the rapid growth of the shoot.
      • plant weed eventually
      • only broad leaved plants affected as they absorb herbicide through the leaves[translocated through the phloem].

13] Homeostasis

• homeostasis as the maintenance of a constant internal environment.
• Skin:
  • consists of:
    • epidermis: a cornified waterproof layer made of dead cells. Contains melanin.
    • dermis: contains sweat glands, hair erector muscles, sensory neurones, blood vessels, and receptors.
    • layer of fatty tissue[adipose tissue].
  • Regulation of body temperature:
    • Response to increase in temperature above 37 degrees Celsius:
      • sweat: secreted by sweat glands. It evaporates from the surface of the skin and produces a cooling effect.
      • hair lies flat: hair erector muscles relax. Less air is trapped, so less insulation.
      • vasodilation: arterioles near the surface of the skin dilate and shunt vessels constrict, to allow more blood to flow to capillaries near the surface of the skin. This leads to more heat loss due to radiation/conduction/convection.
    • Response to decrease in temperature above 37 degrees Celsius:
      • muscles contract and relax rapidly: to produce
      • metabolism increases: releases heat.
      • erector muscles contract: hair stands up, traps more air, leading to more insulation.
      • vasoconstriction:constriction of arterioles near the skin’s surface. Shunt vessels dilate to allow more blood to flow through them, and less amount of blood flows through capillaries near the skin’s surface. Thus, decreasing the amount of heat lost due to conduction/convection/radiation.
    • Coordination of temperature regulation:
      • temperature receptors pick up change in temperature/stimulus.
      • impulses is passed along a sensory neurone.
      • to the hypothalamus in the brain.
      • response sent via a motorneurone to effector:
        • jaw muscles.
        • hair erector muscles.
        • sweat glands.
        • arteriole muscles.
        • liver[for increase in metabolism].

• Negative feedback:
  • body temperature needs to remain constant.
  • any increase or decrease in body temperature is detected as stimulus.
  • by the hypothalamus.
  • response is sent to appropriate effectors:
    • jaw muscles.
    • hair erector muscles.
    • sweat glands.
    • arteriole muscles.
    • liver[for increase in metabolism].
  • response occurs.
  • brings body temperature back to normal.
  • response is switched off.
  • integral part of homeostasis.
• Glucose metabolism:
  • Response to concentration of glucose higher than normal:
    • beta cells in pancreas secrete insulin.
    • stimulates the cells in the liver to absorb glucose and convert it to glycogen and/or respire it.
    • reduces concentration of glucose in blood.
  • Response to concentration of glucose lower than normal:
    • beta cells in pancreas secrete glucagon.
    • stimulates the liver cells to break down glycogen to give glucose.
    • glucose enters blood and blood glucose concentration becomes normal.
  • Negative feedback:
    • blood glucose concentration needs to be kept constant.
    • any increase or decrease is detected as a stimulus.
    • by hypothalamus in the brain.
    • responses are send to appropriate effector:
      • beta cells in
    • response occurs and glucose is absorbed/glycogen is broken down.
    • this increases/decreases blood glucose concentration.
    • concentration returns back to normal.
    • response is switched off.
    • integral part of homeostasis.
  • Diabetes:
    • Blood glucose concentration goes up and remains up as no insulin produced.
    • Leads to a condition known as
    • Symptoms of diabetes:
      • increased, more frequent urination.
      • weight loss.
      • itchy skin.
      • wounds heal slowly.
      • poor circulation.
      • blurred vision.
      • deeper breathing.
      • more glucose concentration in urine.
      • behavioural changes / confused.
      • high blood, glucose/sugar.

• Treatment:
  • insulin by injection.
  • regular blood sugar tests.
  • controlled diet with regular meals.
  • exercise.
  • restrictcarbohydrate content of diet.

14] Drugs

• drug as any substance taken into the body that modifies or affects chemical reactions in the body.
• Antibiotics:
  • drugs used to kill bacteria and treat a bacterial infection.
  • They kill bacteria by:
    • targeting bacterial enzymes: responsible for mitosis and cell division.
    • destroying their cell walls: by creating holes in them.
  • However they are ineffective against viruses, because:
    • viruses do not have cell walls.
    • they do not have any enzymes of their own, they use the host’s enzymes.
  • Antibiotic resistance Is increasing due to:
    • over usage of drugs, even when not needed.
    • indiscriminate use of antibiotics.
    • frequent prescriptions of antibiotics, leading to more antibiotic resistant bacteria.
  • Alcohol:
    • broken down in liver.
    • highly
    • depressant:slows down transmission of nerve impulses, increasing reaction time. Therefore, can lead to car accidents.
    • increases
    • people lose control and become violent.
    • large intakes can kill.
    • effects of alcohol addiction:
      • cirrhosis of the liver/liver failure.
      • liver cancer.
      • brain damage.
      • stomach ulcers.
      • oral cancer/throat cancer.
      • reduced fertility.
      • heart failure/stroke/heart attack.
    • Heroin:
      • produced by opiates found in opium poppies.
      • depressant: slows down functions of the brain, lengthens reaction time.
      • effects of heroin addiction:
        • muscle cramps.
        • vomiting,

• withdrawal symptoms:
  • intense carving for heroin.
  • extreme sweating.
  • nausea and vomiting.
  • severe muscle aches and pains.
  • extreme pain in joints.
• effect on neurotransmitters:
  • heroin is metabolised to morphine in the brain.
  • heroin diffuses into synapse.
  • heroin binds to receptors (for neurotransmitter) as endorphin.
  • heroin is complementary to receptor.
  • blocks neurotransmitter entering receptor site.
  • stimulates
  • reducespain.
  • it can also reduce the production of endorphin and other neurotransmitters.
  • also desensitizes the receptors, so after some time more is required to feel the same sensation.
• social implications of heroin:
  • heroin addicts are unable to hold down jobs.
  • often resort to crime to get money for drugs.
  • unable to support family.
  • use of non-sterile needles to inject heroin can lead to HIV.
• Cigarette:
• components of the cigarette smoke:

1. carbon monoxide:
   • poisonous/toxic gas.
   • combines with haemoglobin permanently and decreases the volume of oxygen it can carry.
   • puts strain on the heart, leading to exhaustion and tiredness.
2. nicotine:
   • stimulant: leads to hypertension and makes the user feel more alert by narrowing arterioles and increasing heart rate.
   • increases stickiness of blood platelets.
   • decreases appetite.
3. tar:
   • contains chemicals called carcinogens.
   • these can cause cells in the respiratory passage to divide, leading to a tumour and lung cancer.
   • it can cause irritation in the airways, leading to more mucus being produced by goblet cells.
   • carcinogens can also stick to alveoli and damage them. Leading to reduced surface for gas exchange.
4. smoke particles:
   • get trapped in the lungs.
   • WBCs try to remove them but end up damaging the alveoli.
   • leads to COPD and emphysema.

• respiratory diseases due to smoking:
  • emphysema:
    • breakdown of alveoli: alveolar surfaces weaken.
    • smoker’s cough: may burst weakened alveoli.
    • reduction of absorption surfaces, so less surface area for gas exchange.
    • oxygenation of blood decreases.
    • breathlessness and exhaustion.
  • lung cancer:
    • caused by carcinogens.
  • chronic bronchitis:
    • cilia damaged[cannot move].
    • excess production of mucus.
    • cilia unable to remove it: mucus and smoke collect in the bronchial lining.
    • inflammation of bronchial lining: bronchitis.
    • smoker’s cough.
  • smoking and heart disease:
    • nicotine and CO increase the tendency of blood to clot.
    • CO increases the rate of fat deposition on artery walls.
    • blockage of coronary arteries due to clots/fat deposits.
    • reduces the supply of oxygenated blood to heart muscles.
    • heart failure.
  • Anabolic steroids:
    • steroid hormones include reproductive hormones: testosterone, oestrogen and progesterone.
    • these hormones stimulate anabolic reactions that build up large molecules from small ones.
    • they lead to:
      • increase in bone density.
      • increase in protein synthesis that can lead to increased recovery from muscle damage.
      • increase in muscle size and strength.
      • growthof limb bones and increasein lung capacity.
      • increased
      • increasedaggression.
    • they are banned due to:
      • an unfair advantage.
      • increased aggression leading to more competitiveness.
      • they can damage immune system and

15] Reproduction in plants:

• asexual reproduction as a process resulting in the production of genetically identical offspring from one parent.

• in plants, it is known as vegetative propagation:
  • occurs in stem tubers.
• in bacteria, it is known as binary fission.
• Advantages of asexual reproduction to plants:
  • only one parent required:morechances of offspring being propagated.
  • faster adaptation: if parent plant is well adapted offspring will be well adapted also.
  • less energy:no need to have flowers and nectaries as there is no need for pollinators.
• Disadvantages of asexual reproduction to plants:
  • absence of genetic variation: offspring more susceptible to same disease.
  • lesschancesofevolution.
  • overcrowding leads to competition for resources.

• sexual reproduction as a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production of offspring that are genetically different from each other.
• fertilisation as the fusion of gamete nuclei.

• Advantages of sexual reproduction to plants:

• genetic variation: offspring have disease resistance.
• more chances of evolution.

• Disadvantages of sexual reproduction to plants:
• two parents required:less chance of offspring being propagated.
• more energy required:flowers need to attractive and nectaries need to be present to attract pollinators.
• Functions of parts of a flower:
• sepal:protects the flower when it is a bud.
• petal:brightly coloured/conspicuous, used to attract insects.
• anther:produces pollen grains containing male gamete[pollen nucleus].
• stigma:receives pollen grain, which germinates in it.
• ovary: contains female gamete[egg cell nucleus].

Part	Insect pollinated flower	Wind pollinated flower
Petal.	Large/conspicuous and brightly to attract insects.	Inconspicuous and dull.
Scent.	Have strong, attractive scent.	No scent.
Nectaries.	Present.	Absent.
Pollen.	Sticky, have ridges and grooves.	Smooth/aerodynamic.
Quantity of pollen.	Large amounts	Larger amounts.
Anther.	Inside the flower.	Hanging out/pendulous.
Stigma.	Inside flower; sticky.	Sticking out/pendulous; feathery.

• pollination as the transfer of pollen grains from the anther to the stigma.

• self-pollination as the transfer of pollen grains from the anther of a flower to the stigma of the same flower or different flower on the same plant.
• cross-pollination as transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.

Feature	Self-pollination	Cross-pollination
Variation.	No.	Yes.
Capacity to respond to changes to environment.	Less compared to cross-pollinated because there is no variation. However, if parent plant is well adapted, offspring will adapt well also.	Variation leads to adaptability, disease resistance, more chances of evolution.
Reliance of pollinators.	Pollinators are not always required.	Requires pollinators. Energy needs to be invested in petals and nectaries.

• Fertilisation:
  1. after landing on the stigma of a flower, pollen grains form a pollen tube.
  2. pollen tube grows and secretes enzymes to digest a pathway through the style.
  3. goes till ovary, and the pollen tube opens.
  4. pollen nucleus travels down the pollen tube and enters at the micropyle.
  5. pollen nucleus and egg cell nucleus
  6. formation of a diploid zygote.

• After fertilisation:
  1. diploid zygote à embryo plant[through mitosis].
  2. ovule à
  3. ovule wall à Testa [tough, protective covering].
  4. ovary à
  5. ovary wall à fruit skin.
  6. sepal, petals, stamen, style, stigma àfalls off and withers away.
• Embryo:
  1. plumule: forms shoot.
  2. radicle: forms root.
• Testa: prevents embryo from damage and prevents bacteria and fungi from entering the seed.
• Conditions for seed germination:
  1. Suitable temperature.

16] Reproduction in humans

• Parts of the male reproductive system:
  1. testes:
     • produce
     • make the hormone testosterone[stimulates changes during puberty].
  2. scrotum:
     • sac that covers testes which hangs outside the body to keep it cool as sperm cannot be matured or stored at temperatures above 37 degrees Celsius.
  3. epididymis:
     • small tubules outside testes that store sperm for maturation.
  4. urethra:
     • carries urine and sperm[not simultaneously].
     • have a sphincter muscle to prevent urine loss during sex.
  5. prostate gland[and other fluids]:
     • secrete fluid for sperm to swim in.
     • prostate gland secretes mucus and others secrete sugarsfor respiration for sperm cells.
  6. penis:
     • urethra runs down the centre of the penis.
     • main function is to deliver sperm to vagina for fertilisation.

• Parts of the female reproductive system:
  1. ovaries:
     • produce one egg cell every month.
     • produce female sex hormones[oestrogen & progesterone].
  2. fallopian tubes/oviducts:
     • egg passes out during ovulation into the oviducts.
     • cilia are present for peristalsis for movement of egg cell.
     • cilia also move to and fro to produce a current to waft the egg cell down the oviduct.
     • site for fertilisation.
  3. uterus:
     • foetus develops in uterus.
     • develops a spongy wall for implantation of embryo.
  4. cervix:
     • ring of muscles at the lower end of the uterus leading to the vagina.
     • separates vagina from uterus.
  5. vagina:
     • muscular tube.
     • an opening outside the body.
     • receives male penis during sexual intercourse.
     • sperm is deposited in vagina.

Sperm	Egg cell
Smaller.	Larger.
Motile, uses tale for movement.	Not motile, moved by cilia.
500,000 produced.	One produced once a month.
Less amount of food store.	Lots of food store.

• Sperm are produced in high numbers because:
  • to increase chances of fertilisation, as they are:
    1. viable for only 48-72 hours.
    2. needed to travel long distances.
  • Adaptations of sperm:
    • lots of mitochondria: required for energy for movement to egg cell.
    • flagellum: propels the sperm using a whiplash movement.
    • haploid
    • acrosome: contains hydrolytic enzymes that dissolve the membrane of the egg cell and allow sperm to penetrate.
  • Adaptations of egg cell:
    • jelly coating:hardens after fertilisation to prevent other sperm cells from entering.
    • cytoplasm: contains lots of food store and nutrients to provide nourishment to zygote, for energy for mitosis and development.
    • haploid
  • Fertilisation:
    • fertilisation is the fusion of the male gamete[sperm] and female gamete[egg cell] to form a diploid zygote.
    • takes place in oviducts.
  • Development of zygote and foetus:
    • cell division
    • zygote divides by mitosis.
    • forms a ball of cells/blastula.
    • wafted down the oviduct by peristalsis by cilia.
    • reaches the uterus and implantation occurs,.
    • blastula embeds/implants itself into the wall of the uterus and it is now called an
    • embryo continues to grow and develop and increase in complexity.
    • some of the cells form the placenta.
    • organs such as the heart develop at about 8 weeks. It is now called a
  • Placenta:
    • disk like structure formed from cells of the embryo.
    • attached to endometrium and embryo/foetus by a tube known as the umbilical cord.
    • at the junction between the placenta and the endometrium, blood vessels of both sides are close to each other, allowing for diffusion of nutrients and waste between the blood of the mother and the blood of the foetus.
    • Functions of the placenta:
      1. acts as a barrier between blood systems and prevents mixing of blood.
      2. provides protection against pathogens that may have affected the mother.
      3. allows oxygen and other nutrients to diffusefrom the mother’s blood to the foetal blood vessels in the umbilical cord.
      4. allows excretory products to diffuse out of the foetus’s blood and into the mother’s blood.
      5. allows transfer of antibodies[passive immunity].
      6. prevents harmful substances from entering foetal blood.
      7. as exchange takes place by diffusion, through the walls of the blood vessels, the mother’s high blood pressurecannot damage the thin blood vessels in the umbilical cord.
      8. also secretes oestrogen and progesteroneduring pregnancy.
    • however, some substances such as nicotine and rubella virus can pass through the placenta and affect the foetus.
  • Structure and function of the umbilical cord:
    • contains 2 arteries and 1 vein. Arteries carry oxygen and nutrients from mother’s blood to foetal blood whereas veins carry excretory products from foetal blood to mother’s blood.
  • Amniotic sac and fluid:
    • as foetus grows, it becomes enclosed in a sac known as the amniotic sac, containing amniotic fluid.
    • Functions of amniotic fluid:
      1. prevents entry of pathogens.
      2. protects against sudden movement.
      3. protects against sudden change in temperature.
      4. allows foetus to move.
      5. needed for bone/muscle growth.
      6. helps in development of lungs.
      7. collectsfoetal urine.
      8. provides sterile environment.
    • Antenatal care of pregnant women:
      • Diet:
        1. vitamin D: for absorption of calcium, growthof foetal bones.
        2. calcium: for growth of foetal bones.
        3. iron: for blood to be formed.
        4. protein and carbohydrates: for mitosis and development.
      • gentle exercise is also required as it plays an active part when giving birth.
      • pregnant women should not consume:
        1. alcohol: can cause birth defects and mental retardation.
        2. drugs: like heroin can give baby
        3. cigarettes: nicotine and CO result in premature and underweight
      • Breastfeeding:
        • Advantages of breastfeeding:
          1. antibodies provided[passive immunity].
          2. composition of breast milk changes with time so the correct nutrients are given at the right stages of development.
          3. protects the mother against breast cancer.
          4. help in weight loss/returning weight back to normal.
          5. contraceptive effect.
          6. always available.
          7. at body temperature.
          8. allows bonding with the mother.
        • Disadvantages of breastfeeding:
          1. viruses such as HIV can be transmitted to baby.
          2. cannot determine how much the baby has consumed.
          3. drugs/alcohol can be passed on to the baby.
          4. mastitis[sore nipple].
        • Labour and birth:
          • a few weeks before birth, the head of the baby turns towards the cervix.
          • hormones released by the foetus and the increase in pressure in the uterus stimulate hormonal changes in the mother.
          • the hormone oxytocin is released from the mother’s pituitarygland and it stimulates the uterine muscles to contract, and this is the beginning of labour.
          • the contraction become stronger and more frequent and the opening of the cervix stretches/dilates and the amnion breaks to release the amniotic fluid.
          • the amniotic fluid flows out and sterilises the vagina in the process.
          • the contractions are even stronger now, pushing the baby towards the cervix. The cervix dilates, pushing the baby through the vagina.
          • the umbilical is cut and tied just above where it attaches to the baby.
          • after a few minutes the placenta comes out, which is

• Role of hormones during puberty:
  • they stimulate the development and regulation of secondary sexual characteristics.
  • Males[testosterone]:
    1. enlargement of testes and penis.
    2. deepening of
    3. growth of hair in pubic region, armpits, face, and chest.
    4. rapid increase in growth.
  • Females[oestrogen]:
    1. increase in size of uterus and vagina.
    2. growth of
    3. widening of
    4. growthofhairin pubic region and armpits.
    5. rapid increase in growth.
  • Hormones in the menstrual cycle:

Hormone	Function
Follicle stimulating hormone[FSH]	Stimulates the maturing of eggs in the ovary and the production of oestrogen by ovaries.
Luteinising hormone[LH]	Stimulates the release of a mature egg cell from one of the ovaries in a process known as ovulation.
Oestrogen	Stimulates the thickening of the walls of the uterus and inhibits the production of FSH. Stimulates pituitary gland to produce LH.
Progesterone	Increases the thickening of the uterus wall. Prevents menstruation. Inhibits the production of LH.

• Menstrual cycle:
  1. FSH produced by pituitary gland stimulates an ovary to produce and mature an egg cell [0-5 days]:
     • the ovary also makes a follicle. It surrounds the egg cell and protects it, and gives it nutrition.
     • follicles also produces oestrogen, and allows the egg cell to grow,
     • oestrogen stimulates the thickening of the uterus wall.
  2. by 12 days, the egg cell is fully matured and ready to leave, and by this time the oestrogen produced by the follicular cells inhibits the production of FSH and stimulates the pituitary gland to produce LH.
  3. LH stimulates the release of the egg from one of the ovaries, which is ovulation [Day 14]:
     • the follicle ruptures and the egg cell is released.
     • the follicle becomes the corpus luteum.
     • the egg cell travels through the oviduct.
     • the corpus luteum produces oestrogen, and even progesterone now.
  4. the progesterone released stimulates and maintains the thickening of the uterus wall [14-28 days].
  5. if fertilisation does not occur, the corpus luteum becomes the corpus albicans.
     • this does not produce any hormones.
     • production of oestrogen and progesterone stops.
     • uterus wall sheds, along with the unfertilised egg cell and the corpus albicans.

• Changes in the uterus:
  1. extra-thickened uterus wall sheds, along with the unfertilised egg and blood.[0-5 days]
  2. endometrium wall thickening is rebuilt by oestrogen from ovary[5-14 days]
  3. lining continues to thicken and thickness is maintained by progesterone and oestrogen produced by corpus luteum in the ovary. [14-28 days]

• Birth control:
  • Natural Methods:
    • Abstinence:
      • couple avoids sexual intercourse.
    • Rhythm method:
      • monitoring:
        • body temperature.[increases during ovulation]
        • state of cervical mucus.[becomes more fluid during ovulation]
      • and determining when ovulation is about to occur, and avoiding sex at that time.
    • Artificial methods:
      • Barrier/mechanical methods:
        • Condom:
          • a rubbersheath placed on an erectpenis before sexual intercourse, which prevents sperm from reaching the uterus by trapping it.
          • reduces risk of STI transmission.
        • Femidom:
          • sheath or a pouch, made of rubber and inserted in the vagina. During intercourse, trapsthesperm.
          • reduces risk of STI transmission.
        • Diaphragm:
          • thin rubber disc which covers the cervix and prevents the sperm from entering.
          • used with spermicides.
          • does not prevent risk of STIs.
        • Chemical methods:
          • IUD:
            • T-shaped plastic and copper
            • inserted by a doctor or nurse.
            • prevents implantation of a fertilised ovum.
            • does not protect against STIs.
          • IUS:
            • releases progesterone which prevents
          • Contraceptive pill:
            • contains chemicals, that have the same effect as oestrogen and progesterone.
            • when mixed in suitable proportions, these hormones prevent ovulation and prevent conception/fertilisation.
            • menstrual cycle still occurs, but no egg cell is produced.
            • needs to be taken for 21 days daily during menstrual periods.
            • does not protect against STIs.
          • Spermicides:
            • chemicals that immobilise or killsperm.
            • present in the form of a gel.
            • prevents sperm from reaching the egg cell, therefore preventing fertilisation.
          • Surgical methods:
            • Vasectomy:
              • man’s sperm ducts are cut and sealed.
              • semen does not contain any sperm.
            • Female sterilisation:
              • oviducts are cut and tied, however ovaries are still functional.

• Fertility and conception treatments:
  • Artificial insemination:
    • sperm is harvested from a donor and stored in low temperatures.
    • injected through a tube into the uterus.
    • around the time of ovulation.
  • Fertility drugs:
    • drugs injectedearly in the menstrual cycle.
    • stimulates the production of FSH & LH.
    • inhibit action of oestrogen.
    • makes sure that FSH concentration is high enough.
    • stimulates ovaries to produce and mature several egg cells.
    • more eggs are released.
    • LH stimulates the release of egg cells.
    • many egg cells increase the chances of fertilisation.
  • Social implications of fertility treatments and contraception:
    • idea that stress is associated with difficulty having children.
    • stated problem with multiple births.
    • problems with unused embryos (when used with IVF).
    • issues with elderly parent(s).
    • religious objections to use of fertility drugs.
    • any reference to cost of the treatment.
    • increases populations / any negative effect of population increase.
    • can be used to increase populations / any positive effect of population increase.
  • Infertility in men:
    • Causes:
      • cannot produce sperm.
      • sperm duct damaged.
      • sperm cannot swim.
      • low sperm count.
      • result of an STI.
    • Treatment:
      • artificial insemination.
      • in vitro fertilisation: used when surgery cannot repair blocked oviducts. Woman is given fertilitydrugs that stimulate her ovaries to produce multiple eggs. It is taken and mixed with the husband’s semen. Initial zygote is developed in the lab and later injected into the uterus.
    • Infertility in women:
      • Causes:
        • low concentration of FSH and LH produced.
        • follicles do not
        • damages
        • uterus wall does not
        • low concentration of progesterone.
      • Treatment:
        • fertilitydrugs.
        • tablets that make pituitary gland insensitive to oestrogen.
      • sexually transmitted infection as an infection that is transmitted via body fluids through sexual contact.
      • an example is HIV, which causes AIDS.
      • HIV:
        • Methods of transmission:
          • in blood[by contaminated needles].
          • in semen.
          • unprotected sex.
          • blood transfusion.
          • across placenta.
          • at birth, when the two blood streams come in close contact.
          • breast milk.

• Methods of prevention:
  • free needle exchange schemes.
  • antiviral drugs.
  • condoms and femidoms.
  • careful screening of donated blood.
• Process:
  • HIV attacks T-lymphocytes, which stimulate other lymphocytes to produce antibodies.
  • Due to HIV, number of T-lymphocytes decreases.
  • so, there are fewerantibodies every time an infection occurs.
  • cancer/other diseases can be formed which cannot be destroyed.
  • symptoms:
    • swollen glands.
    • high body temperature.
    • weight loss.
    • brain functioning decreases.

17] Inheritance

• inheritance as the transmission of genetic information from generation to generation.
• chromosome as a thread-like structure of DNA, carrying genetic information in the form of genes.
• gene as a length of DNA that codes for a protein.
• allele as an alternate version of a gene.
• haploid nucleus as a nucleus containing a single set of unpaired chromosomes, e.g. in gametes.
• diploid nucleus as a nucleus containing two sets of chromosomes, e.g. in body cells.
• mitosis as nuclear division giving rise to genetically identical cells.
• Mitosis:
  • there is exact duplication of chromosomes before
  • during mitosis, the copies of chromosomes separate, maintaining the chromosome number.
  • it is when a diploid cell divides to form two daughter cells.
  • importance of mitosis:
    • it is required for:
      • repair of tissue.
      • replacement of tissue/cells.
      • asexual reproduction.
    • stem cells:
      • unspecialisedcells that divide by mitosis to produce daughtercells that become specialised for specificfunctions.
      • found in:
        • umbilical cord.
        • bone marrow, skin, liver.

• meiosis as reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells.

• Meiosis:
  • exactduplication of maternal and paternal chromosomes occurs before meiosis.
  • maternal and paternal chromosomes cross over, resulting in new combinations of maternal and paternal chromosomes, producing variation.
  • during meiosis, chromosomes are separated and chromosome number is halved from diploid to haploid.
  • meiosis results in 4 daughter cells.

• importance of meiosis:
  • production of gametes.
  • produces variation in genes due to crossing over.
• Genes and protein synthesis:
  • each gene codes for a specific protein, and the sequence of bases in a gene is the genetic code for putting together amino acids in the correct order to make the specific protein.
  • this genetic code for the protein remains in the nucleus.
  • mRNA molecules carry a copy of the gene from the nucleus to the cytoplasm.
  • the mRNA passes through the ribosomes.
  • ribosomes assemble the amino acids in the correctorder and convert it into protein molecules.
  • the specific order of amino acids is determined by the sequenceofbases in the mRNA.
  • all body cells in an organism contain the same genes, but many genes in a particular cell are not expressed because the cell only makes the specific proteins it needs.
• genotype as the genetic make-up of an organism in terms of the alleles present.
• phenotype as the observable features of an organism.
• homozygous as having two identical alleles of a particular gene.
• heterozygous as having two different alleles of a particular gene.

• dominant as an allele that is expressed if it is present.
• recessive as an allele that is only expressed when there is no dominant allele of the gene present.
• sex-linked characteristic as a characteristic in which the gene responsible is located on a sex chromosome and that this makes it more common in one sex than in the other.
• examples: red-green colour blindness, haemophilia.
• Co-dominance:
• both alleles of a particular gene express themselves in the heterozygous combination, resulting in a third distinct phenotype.
• this phenotype is an intermediate of the two phenotypes.
• neither allele is dominant or recessive, they are co-dominant.
• example: ABO blood groups in humans.

18] Variation and Selection

• variation as differences between individuals of the same species.

Continuous variation	Discontinuous variation
Results in a range of phenotypes between two extremes.	Results in a limited number of distinct phenotypes and no intermediates.
Caused by genes and environment. [phenotypic variation]	Caused by genes only.[genotypic variation]

• Causes of variation:
  • Meiosis:
    • during meiosis, maternal and paternal chromosomes crossover and exchange genes before separating. This results in new combinations, that makes the gametes genetically different.
    • maternal and paternal chromosomes separate during meiosis, which also causes variation.
  • Fertilisation:
    • any two gametes of opposite sexes can fuse together. This leads to many combinations of genes in the zygote, leading to variation.
  • Mutation:

• mutation as genetic change.

• genemutationas a change in the base sequence of DNA.
• new alleles are formed by mutation.
• they are the only source of new characteristics in a gene pool. Genetic variations are caused solely by mutation.
• mutations are caused by:
  • ionising radiation.
• Sickle cell anaemia:
  • Caused by:
    • change in DNA base sequence from CTT à CAT [single base substitution].
    • mRNA code changes from GAA à
    • amino acid sequence changes from GLUTAMATE à
    • people can inherit the allele for sickle cell anaemia, which is either in homozygous recessive combination [HbS HbS] or heterozygous combination.[HbS HbA]
    • this change in base sequence of the gene for haemoglobin results in an abnormal haemoglobin.
    • red blood cells have sickle shape.
  • the alleles for this disease are co-dominant.
  • symptoms:
    • red blood cells become sickle shaped.
    • less haemoglobin in blood.
    • fewer normal RBCs.
    • less efficiency in transporting oxygen.
    • fatigue, pain, exhaustion, due to:
      • capillaries being blocked.
      • sickle shaped RBCs not being able to carry enough oxygen.
    • can lead to sickle cell crisis, which leads to:
      • damage to certain organs.
      • failure of certain organs.
    • slow
    • reduced life span.
    • susceptible to infection.
    • shortness of breath.
    • chest
    • fast
    • headache.
    • brittle
    • poor
  • Malaria and sickle cell anaemia:
    • malaria acts as an agent for natural selection for individuals who have the heterozygous genotype[codominant] of sickle cell anaemia.

Genotype	Result
HbA HbA [homozygous: normal RBCs]	Individuals are highly susceptible to malaria, which is fatal. The malarial parasite passes a few stages of its life cycle in RBCs, so it is a breeding ground.
HbS HbS [homozygous: all RBCs sickle shaped]	Individuals are not susceptible to malaria[because the parasite cannot survive], but seriously affected by sickle-cell anaemia, leading to death.
HbA HbA [heterozygous: 50% RBCs are sickle shaped]	These individuals are less likely to suffer from a fatal attack of malaria and are resistant, and are not seriously affected by sickle cell anaemia. They therefore have a selective advantage. They are able to survive and pass on this allele to the next generation.

• adaptive feature as the inherited functional features of an organism that increase its fitness.

• fitness as the probability of an organism surviving and reproducing in the environment in which it is found.

• Adaptations of xerophytes:
  • thick
  • smaller surface area of leaves.
  • shedding of leaves, fewer leaves.
  • fleshy / succulent leaves to store more water.
  • hairs to absorb more water.
  • sunken
  • wide spreading roots.
• Adaptations of hydrophytes.
  • air spaces/gaps/pockets in stem and leaves: to allow plant to float in order to absorb sunlight.
  • floating leaves: in order to absorbsunlight and allowdiffusion of oxygen/carbon dioxide.
  • no cuticle:not required as there is no need to conserve water.
  • little/no roots:no need for roots to absorb mineral ions/water.
  • stomata on upper surface only: as only upper surface is exposed to air.
  • aerial roots: to allow roots to absorboxygen.
  • leaves have large surface area: to allowflotation.
  • little xylem/lignin: as the waterprovidessupport.
  • submerged leaves are divided: to provide largesurfacearea for photosynthesis.
• Natural selection:
  • Process:
    • variation within population.
    • production of many offspring.
    • competition for resources.
    • struggle for survival.
    • reproduction by individuals that are better adapted to their environment than others.
    • passing on of their alleles to the next generation.
  • Evolution of anti-biotic resistant bacteria:
    • arisen due to mutation.
    • these mutations have resulted in variants that are stronger, have less permeable cell walls, and are therefore not destroyed by antibiotics such as penicillin.
    • some variants produce an enzyme that breaks down the antibiotic.
    • the antibiotic kills all variants that are not resistant, which is struggle for survival.
    • therefore, the antibiotic acts an agent for natural selection.
    • the resistant bacteria reproduceand pass on the mutated allele to the next generation, resulting in the development of an antibiotic resistant variety.
      • increased use of antibiotics results in the creation of selective pressure, which favours the development of resistant forms of bacteria.
    • evolution is the change in adaptive features of a population over time as the result of natural selection.
    • process of adaptation as the process, resulting from natural selection, by which populations become more suited to their environment over many generations.
    • Artificial selection:
      • Process:
        • selection by humans.
        • of individuals with desiredfeatures.
        • these individuals are bredtogether.
        • by:
          • manual pollination.
          • artificial insemination.
          • embryo implantation.
        • offspring that express the desiredfeatures are bredagain.
        • done over many generations.
      • it leads to the production of variations of plants and animals with increased economic importance.

• animals:
  • cows: milk [quantity and quality], mass/muscle [quantity and quality].
  • sheep: wool, different colors of wool, types of wool.
  • techniques:
    • artificial insemination.
    • embryo implantation.
  • plants:
    • size of crop.
    • amount of crop.
    • disease/frost/drought resistance.
    • height of plants.
    • technique:
      • manual pollination.

Natural selection	Artificial selection
Organisms are selected by nature.	Organisms are selected by humans.
Results are unpredicted.	Results are predicted and planned.
Species are more adapted to the environment.	Species are more useful to humans.

• Disadvantages of selective breeding:
  • selective breeding between closely related organisms results in inbreeding and harmful recessive genes being passed on to future generations. This can reduce the fitness of the variety.
  • loss of variability: by eliminating all offspring that do not express the desired features, many genes are lost from the gene pool/population.
  • at a future date, when the new combinations of genes are needed, some potentially useful genes may no longer be available.

19] Organisms and their environment

• The sun is the principal source of energy.
• food chain as showing the transfer of energy from one organism to the next, beginning with a producer.
• trophic level as the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass.
• food web as a network of interconnected food chains.
• producer as an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis.
• consumer as an organism that gets its energy by feeding on other organisms.
• herbivore as an animal that gets its energy by eating plants.
• carnivore as an animal that gets its energy by eating other animals.
• decomposer as an organism that gets its energy from dead or waste organic material.
• Energy transfer:
  • energy is transferred between organisms by ingestion.
  • only 10% of energy is passed on to the next trophic level as 90% is lost between trophic levels due to:
    • parts that are not edible/reachable.

• Why are only a few top predators present in a food chain:
  • only 10% of energy is passed on to the next organism.
  • as 90% is lost due to movement, heat, excretion and parts that are not eaten.
  • top consumers have bigger body/volume.
  • they need to consume more organisms to fulfil their energy requirements.
  • therefore, large numbers cannot be sustained by the environment.
• Why soya is a better food compared to animals for humans:
  • more energy is available in soya.
  • energy loss between food chains due to movement, heat, respiration and excretion.
  • little energy loss in growth.
  • leads to 90% being lost and only 10% passed on to humans.
• Why some feeding relationships better represented by food webs than food chains:
  • many consumers can be at each trophic level.
  • one organism can feed at multiple trophic levels.
• Why pyramid of biomass is a better representation compared to pyramid of numbers:
  • biomass shows the dry mass.
  • gives a better idea of the actual quantity of the plant/animal material that is being consumed at each trophic level.
• Nitrogen cycle:
  • Decomposition: dead organisms are decomposed by bacteria, that convert them in ammonium compounds.
  • Nitrification: ammonium compounds are converted to nitrates by nitrifying bacteria.
  • Nitrogen fixation:
    • lightning: makes nitrogen in air combine with oxygen to form nitrogen oxides. These oxides dissolve in rain and are washed into the soil, where they form
    • nitrogen-fixing bacteria taken nitrogen from the air and convert it into nitrates and store them in root nodules of legumes. After the legumes die, the nitrates are released into the soil and can be reabsorbed by plants.
  • nitrogen is absorbed by plants for amino acid synthesis in the form of nitrates by active transport.
  • plants are eaten by animals, where the amino acids are deaminated and converted to urea, which is then
  • de-nitrification:de-nitrifying bacteria convert nitrate ions to nitrogen in air.
• population as a group of organisms of one species, living in the same area, at the same time.
• community as all of the populations of different species in an ecosystem.
• ecosystem as a unit containing the community of organisms and their environment,interacting together.
• Sigmoid growth curve:
  • lag phase:
    • not too many organisms which can reproduce to increase the population quickly.
    • time need to adjust to new habitat or attain reproductive maturity.
  • exponential/log phase:
    • rapid reproduction.
    • birth rate > death rate.
    • population growth not being limited by competition.
  • stationary phase:
    • birth rate = death rate.
    • competition for resources increases.
    • increase in limiting factors:
      • less
      • less
      • less

• death phase:
  • resources severely limited.
  • death rate > birth rate.
  • severe limiting factors:
    • no
    • no
    • no
  • build-up of waste that is toxic.
• Factors influencing the population of an organism:
  • food supply.
  • competition with other types of predators.
  • hunting/poaching.
  • habitat destruction.
  • rate of reproduction.
• Predator-prey populations:
  • population of a predator depends on the population of the prey.
  • increase in prey population is always morethan predator population.
  • increases and decreases in predator populations always lag behind corresponding increases/decreases in prey population.
• Human population:
  • humans have not reached the stationary phase yet, because people are living longer due to:
    • Reduction in disease:
      • water supply: greater access to clean water.
      • hygiene: better sanitation, sewage treatment, garbage removal, increase in awareness and information on importance of hygiene.
      • personal hygiene: increase in awareness about healthy lifestyle.
      • medicinal facilities: greater access to hospitals.
    • Increase in food supply:
      • increase in land under cultivation.
      • moreefficientfoodproduction due to fertilisers/pesticides.
      • improved food storage and distribution.

20] Biotechnology

• Bacteria are used in biotechnology because:
  • they are small and easy to grow in labs.
  • they have rapidreproductionrates.
  • they can form complex molecules.
  • they have no ethical concerns.
  • the genetic code is universal and can be shared with other organisms.
  • they have plasmids [loops of DNA], which makes DNA easily transferrable.
• Yeast and biofuels:
  • Process:
    • maize can be used as a crop in the process to make ethanol.
    • it is first treated with amylase to break down starch to glucose.
    • then, yeast is added, and allowed to respire the glucose in anaerobic respiration.
    • ethanol is produced, which is then extracted by fractional distillation.

• Advantages:
  • uses renewable and sustainableresources[plants] to make ethanol.
  • even though carbon dioxide is released in the process, it can be taken in for growth by the plants used in the process for photosynthesis, reducing the amount of carbon dioxide added to the atmosphere.
• Disadvantages:
  • does not contain as much energy per litre, so it is mixed with gasoline, to make fuel for vehicle engines.
  • crops that are used in the process take up space, which could have been used to growfood for people.
  • using large quantities of maize and other crops puts up their price, making them expensive to other people.
• Making bread using ethanol:
  • to make bread, flour is mixed with water and yeast, making dough.
  • amylase enzymes are also added to break down starch to glucose.
  • the yeast then uses this glucose in aerobic respiration, producing carbon dioxide.
  • the bubbles of carbon dioxide get trapped in the dough.
  • gluten is stretchy, so the carbon dioxide bubbles cause the dough to rise.
• Biological washing powders:
  • contain less chemicals, which is good for sensitive skin.
  • contain enzymes and detergents.
  • detergents help remove grease and dirt by mixing them with water, so they can be washed away.
  • enzymes known as proteases are also present, which catalyse the breakdown of proteins, such as blood stains [haemoglobin].
  • these smallermoleculesdissolveinwater and are washed away.
  • other enzymes such as lipases catalyse the breakdown of fats to fatty acids and glycerol, which are solubleinwater and are also washed away.
  • these enzymes are packed in microscopic capsules, that dissolve when water is added, which prevents them from harming the user’s skin.
  • proteases have been developed that work at much higher temperature, so the powder can be used in a variety of temperatures. This is also beneficial as other components of washing powders such as detergent, work well at high temperatures.
• Pectinase:
  • fruit juice is extracted by an enzyme known as pectinase.
  • pectin is a substance that helps plant cells stick together.
  • fruits such as apple and orange contain lots of pectin.
  • pectinase is used to break down pectin, so it is much easier to squeeze the juice from the fruit.
  • also helps make juices clear.
• Lactose-free milk:
  • Production:
    • lactase is obtained from yeast or bacteria.
    • lactase is bound to the surface of alginate beads.
    • milk is passed repeatedly over the beads.
    • lactose is broken down to glucose and galactose.
    • the immobilised enzyme[lactase] remains to be used again and does not affect the quality of lactose-free milk.
  • Uses:
    • to make milk drinkable for lactose-intolerant people.
    • increases the sweetness of milk, so no requirement of artificial sweeteners.
    • as a way of reducing crystallisation in ice creams.
    • as a way of reducing production time for yoghurts or cheese [as bacteria ferment glucose and galactose more readily than lactose].

• Fermentation of penicillin:
  • nutrient/culture medium in a fermenter contains:
    • sugar [carbohydrates].
    • nitrogen source [ammonia and ammonium compounds].
  • the water jacket surrounding the container:
    • maintains optimum/constant temperature.
    • when the fungus respires and releases heat, temperature inside the fermenter increases, which could kill the fungi, so no penicillin would be produced.
  • acids and alkalis are added to the mixture to:
    • maintain constant/optimum pH.
    • A change in pH will affect enzyme activity and reduce the rate of the reaction.
  • probes are used to:
    • monitor pH and temperature and ensure it is kept constant.
  • stirrers/paddles present to:
    • keep the bacteria/fungus supplied with nutrients.
    • roll the fungi into pellets which can be separated from the liquid medium during downstream processing.
  • downstream processing:
    • filtration:
      • solid [microbe] and liquid [culture medium] are separated.
    • the part that contains the product is processed to extract the product.
    • purification of product.
  • cleaning the fermenter:
    • UV light is used for
    • steam used because:
      • it reaches all the crevices.
      • does not contaminate.
      • high temperature kills bacteria.
    • genetic engineering as changing the genetic material of an organism by removing, changing or inserting individual genes.
    • Examples:
      • insertion of human insulin genes into bacteria to produce human insulin.
      • insertion of genes into crop plants to make them herbicide/pesticide resistant.
      • insertion of genes into crop plants to provide additional vitamins.
    • Using bacteria to produce human insulin:
      • human cell usually taken from the skin.
      • isolation of the DNA making up a human gene using restriction enzymes, forming sticky ends.
      • cutting of bacterial plasmid DNA with the same restriction enzymes, forming complementary sticky ends.
      • insertion of human DNA into bacterial plasmid DNA using DNA ligase to form a recombinant plasmid.
      • insertion of plasmid into bacteria.
      • replication of bacteria containing recombinant plasmids which make human protein as they express the gene.
    • Advantages of GM crops:
      • produces crop that is disease/drought/salt/frost/pest/herbicide resistant.
      • crops that are pesticide/herbicide resistant are beneficial to the environment.
      • crops have higher yield.
      • pest/insect resistant crops prevent use of pesticides that are broad spectrum and damage many closely related insects, which might not be pests. Helps
      • crops that are drought/salt/frost resistant allow food production in extreme environments, which helps reduce food shortages.
      • GM procedures allow rapid improvement to crop, using characteristics that are not present in natural population.
    • Disadvantages of GM crops:
      • GM seeds are
      • risk of creation of
      • crops containing toxins may affect human health.