on Tuesday, December 23, 2008

Exam Syllabus (Biology 5094)

1. Cell Structure and Organisation Content

(a) identify organelles of typical plant and animal cells from diagrams, photomicrographs and as seen under the light microscope using prepared slides and fresh material treated with an appropriate temporary staining technique:

• chloroplasts
• cell membrane
• cell wall
• cytoplasm
• cell vacuoles (large, sap-filled in plant cells, small,
temporary in animal cells)
• nucleus

(b) identify the following membrane systems and organelles from diagrams and electron micrographs:

• endoplasmic reticulum
• mitochondria
• Golgi body
• ribosomes

(c) state the functions of the membrane systems and organelles identified above
• endoplasmic reticulum –Rough endoplasmic reticulum transports proteins made by ribosomes to the Golgi apparatus for secretion out of the cell.
Smooth endoplasmic reticulum synthesise substances such as fat and steroids. Sex hormones in mammals are steroids.
Converts harmful substances into harmless materials.

• mitochondria –Aerobic respiration occurs in the mitochondria where food substances are oxidised to release energy.

• Golgi body-stores and modifies substances made by the ER and packages these substances in vesicles for secretion out of the cell.

• ribosomes They are sites for protein synthesis. The ribosomes attached to RER make proteins that are usually transported out of the cell. The ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of that cell.

(d) compare the structure of typical animal and plant cells

Plant cell Animal cell
Cell wall present Cell wall absent
Chloroplasts present Chloroplasts absent
Centrioles absent Centrioles present
A large central vacuole Vacuoles are small and many

(e) state, in simple terms, the relationship between cell function and cell structure for the following:

• absorption - root hair cells
To absorb water and mineral salts from the soil:-Long and narrow structure increases surface area to volume ratio so that water and mineral salts can be efficiently absorbed from the soil

• conduction and support - xylem vessels
To transport water and mineral salts- Xylem vessels are long, hollow tubes to enable water and mineral salts to be conducted from the roots up to the stem and leaves.
Do not have cross-walls or protoplasm to enable water to move easily through the lumen.

• transport of oxygen - red blood cells
To deliver oxygen to all parts of the body:- Contains a red pigment called haemoglobin which transports oxygen from the lungs to all parts of the body
Has no nucleus, enabling it to carry more haemoglobin and hence more oxygen
Has a circular biconcave shape which increases the surface area to volume ratio of the cell, so that oxygen can diffuse into and out of the entire cell at a faster rate.
It is elastic so it can squeeze through capillaries easily.

(f) differentiate cell, tissue, organ and organ system
A cell is unit of all living things e.g. amoeba, cheek cell,
A tissue is a group of similar cells which work together to perform a specific function.
An organ is made up of many different tissues working together to perform a specific function e.g. skin,
An organ system is made up of several organs working together for a common purpose.

2. Movement of Substances

(a) define diffusion and discuss its importance in nutrient uptake and gaseous exchange in plants and humans
Diffusion in the movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.
It is important as the cells of the lungs exchange oxygen and carbon dioxide through diffusion. Digested food substances such as amino acids and glucose diffuse through the villi into the blood capillaries.
Plant cells take in oxygen and remove carbon dioxide through diffusion.

(b) define osmosis and discuss the effects of osmosis on plant and animal tissues
Osmosis is the movement of water molecules from a solution of higher water potential to a solution of lower water potential, across a partially permeable membrane.
Animal cells will shrink and have little spikes appear on the cell surfacae membrane when placed in a solution of low water potential. The crenated cell will become dehydrated and eventually die.
When placed in a solution of high water potential, they will swell and burst.

Water enters the plant cell by osmosis. As water enters the cell, the vacuole increases in size and pushes the cell contents against the cellulose cell walls. The cell wall is strong and relatively inelastic. It prevents over-expansion of the cell by exerting an opposing pressure as water enters the cell. This prevents the entry of more water, The plant expands and becomes turgid. The turgor pressure keeps the cell turgid. Turgor helps to maintain the shape of soft tissues in plant and keep them firm and erect. The surrounding cells pushed against each other creating support for the plant.
• It also causes some flowers to open during the day and close at night.
• The changes in turgor of cells in the small swellings at the base of the leaflets of mimosa plant causes them to fold when they are touched.
• The closing and opening of the stomata is due to the changes in turgor of the guard cells.

Plasmolysis causes tissues to become limp or flaccid. Cells will be kille dif they remain plasmolysed for too long.

(c) define active transport and discuss its importance as an energy-consuming process by which substances are transported against a concentration gradient, as in ion uptake by root hairs and uptake of glucose by cells in the villi
Active transport is the movement of substances against a concentration gradient, from a region of lower concentration to a region of higher concentration. It is an energy-consuming process.

Dissolved mineral salts is absorbed by active transport through the root hair cells and glucose and amino acids by cells of the small intestine.

3. Biological Molecules
(a) state the roles of water in living organisms
Water is a solvent for many substances.
It is the medium or substance in which chemical reactions occur in an organism.
It helps to transport dissolved substances around the body e.g. digested products from the small intestine to other parts of the body; excretory products or waste products from the tissue cells to the excretory organs for removal form the body and hormones from the glands to parts of the body which require tehm
It is the key component of protoplasm, lubricants found in joints, the digestive juices, blood and tissue fluid

(b) list the chemical elements which make up
• carbohydrates
Carbon, hydrogen and oxygen

• fats
Carbon, hydrogen and oxygen

• proteins
Carbon, hydrogen and oxygen, nitrogen

(c) describe and carry out tests for

• starch (iodine in potassium iodide solution)

• reducing sugars (Benedict’s solution)

• protein (biuret test)

• fats (ethanol emulsion)

(d) state that large molecules are synthesised from smaller basic units

• glycogen from glucose
A condensation reaction is a chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one molecule of water.

• polypeptides and proteins from amino acids

• lipids such as fats from glycerol and fatty acids

(e) explain enzyme action in terms of the ‘lock and key’ hypothesis
Enzyme has active sites on the surface into which the substrate molecules can fit just like a lock and a key. The enzyme is the lock and the substrate is the key. The substrate binds to the enzyme, forming an enzyme-substrate complex. Reactions take place at the active sites to convert the substrate molecules into product molecules. The product molecules separates, leaving the enzyme molecule unchanged and free to combine again with more substrate molecules.

(f) explain the mode of action of enzymes in terms of an active site, enzyme-substrate complex, lowering of activation energy and enzyme specificity
An enzyme is a catalyst. It acts on a substrate and converts it into a product. The binding of a substrate to the active site of an enzyme is specific in nature. A substrate fits into an enzyme's active site, like how a key fits into a lock, forming an enzyme-substrate complex. An enzyme lowers the activation energy needed for a reaction. Activation energy is the energy needed to start a chemical reaction,

(g) investigate and explain the effects of temperature, pH on the rate of enzyme catalysed reactions
Enzymes work best under optimum temperature which is 370C for most enzymes found in our body. A high temperature increases the kinetic energy supplied to the reacting molecules, which then increases the rate of collision between substrates and enzymes. The rate of the reaction increases up to the optimum temperature. Beyond the optimum temperature, an enzyme, being protein in nature, will be denatured and will lose its active site configuration. The increase in vibrations in the atoms of the enzymes will cause the hydrogen bonds in the enzyme to break.The rate of the biological reaction will therefore decrease.

Enzymes are sensitive to acidity or alkalinity of a solution. Some work best in acidic conditions e.g. pepsin whereas other work best in alkaline conditions e.g. pancreatic amylase. Enzymes are proteins in nature. Extreme change in pH denature the enzyme. When an enzyme is denatured, it loses its active site configuration and its biological activity decreases.

4. Animal Nutrition

(a) describe the functions of main regions of the alimentary canal and the associated organs: mouth, salivary glands, oesophagus, stomach, duodenum, pancreas, gall bladder, liver, ileum, colon, rectum, anus, in relation to ingestion, digestion, absorption, assimilation and egestion of food, as appropriate

(b) describe peristalsis in terms of rhythmic wave-like contractions of the muscles to mix and propel the contents of the alimentary canal
Peristalsis is a rhythmic, wave-like contractions of the gut walls. When the circular muscles contract, the longitudinal muscles relax. As a result, the wall of the gut constricts, that is, the gut becomes narrower and longer. The food is squeezed or pushed forward. When the longitudinal muscles contracts, the circular muscles relax. The gut dilates and becomes wider and shorter, this widens the lumen for the food to enter.

(c) describe digestion in the alimentary canal, the functions of a typical amylase, protease and lipase, listing the substrate and end-products

(d) describe the structure of a villus and its role, including the role of capillaries and lacteals in absorption

Finger-like structure to increase surface area to volume ratio for absorption of digested food.
Richly supplied with blood capillaries to transport the absorbed food away, thus maintaining concentration gradient.
Presence of microvilli on the epithelia cells to increase surface area to volume ratio for absorption of digested food.
Glucose and amino acids are absorbed by diffusion into the blood capillaries of the villi.
Glycerol and fatty acids diffuse into the epithelium. They combine to form minute fat globules which enter the lacteals.
The continuous flow of blood through the capillaries transports the absorbed food substances away from the villi. This maintains the diffusion gradient.

(e) state the function of the hepatic portal vein as the route taken by most of the food absorbed from the small intestine
The hepatic portal vein transports the sugars, amino acids to the liver.

(f) state the role of the liver in

• carbohydrate metabolism
The liver controls the blood glucose level by converting excess glucose to glycogen for storage, with the help of insulin. When the body needs energy, the liver converts the stored glycogen back into glucose. The glucose is then transported by the blood to the cells.

• fat metabolism
The liver secretes bile which emulsifies fats and provides the alkaline pH necessary of the action of the enzymes in the duodenum.

• breakdown of red blood cells
Red blood cells are destroyed in the spleen and the haemoglobin is brought to the liver. The liver breaks down the haemoglobin and stores the iron that is released in the process. Bile pigments are also formed form the breakdown of the haemoglobin.

• metabolism of amino acids and the formation of urea
Amino acids enter the cells and are converted into new protoplasm that is used fo r growth and repair of worn-out parts of the body.
Amino acids are also used to form enzymes and hormones.
Excess amino acids are deaminated in the liver. The amino groups are removed and converted into urea. The remains of the deaminated amino acids are converted into glucose.

• breakdown of alcohol, including the effects of excessive alcohol consumption
An enzyme alcohol dehydrogenase in the liver cells break down alcohol to a compound called acetaldehyde. Acetaldehyde can be broken down further to compounds that can be used in respiration to provide energy for cell activities.

Excessive alcohol consumption stimulates acid secretion in the stomach. Excess stomach acid increase the risk of gastric ulcers.
Prolonged alcohol abuse may lead to cirrhosis of the liver in which the liver cells are destroyed and replaced with fibrous tissue, making the liver less able to function. Liver failure and death can arise.

5. Plant Nutrition
(a) identify and label the cellular and tissue structure of a dicotyledonous leaf, as seen in cross-section under the microscope and describe the significance of these features in terms of their functions, such as the

• distribution of chloroplasts in photosynthesis
More chloroplasts found on the palisade mesophyll which enable them to absorb maximum sunlight for photosynthesis.

• stomata and mesophyll cells in gaseous exchange
All the mesophyll cells are covered with a thin film of moisture so that carbon dioxide can dissolve in it. Interconnecting system of air spaces in the spongy mesophyll allow rapid diffusion of carbon dioxide into mesophyll cells.
Stomata are found more on the lower epidermis than on the upper epidermis. They open in sunlight, allowing carbon dioxide to diffuse in and oxygen to diffuse out of the leaf.
• vascular bundles in transport
Vascular bundles are present in the spongy mesophyll. Xylem transports water and mineral salts to mesophyll cells. Phloem transports sugars away from the leaf.

(b) state the equation, in words and symbols, for photosynthesis
light energy
carbon dioxide + water glucose + oxygen + water

light energy
6CO2 + 12 H2O C6H12O6 + 6O2 + 6H2O

(c) outline the intake of carbon dioxide and water by plants
Higher concentration of carbon dioxide in the atmospheric air than in the leaf. Carbon dioxide diffuses from the surrounding air through the stomata into the air spaces in the leaf. The surface of the mesophyll cells are always covered by a thin film of water so that carbon dioxide can dissolve in it. The dissolved carbon dioxide then diffuses into the cells as a solution.

The veins in the leaf form the branches which end among the mesophyll cells. The xylem transports water and dissolved mineral salts to the leaf from the roots. Once out of the veins, the water and mineral salts move from cell to cell right through the mesophyll of the leaf by osmosis.

(d) state that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage
Chlorophyll absorbs and transforms light energy to chemical energy used in the manufacture of sugars.

(e) investigate and discuss the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis (e.g. in submerged aquatic plant)
Increasing the light intensity increases the rate of photosynthesis, until a constant rate is reached.
Increasing the temperature increases the rate of photosynthesis, until a constant rate is reached.
Increasing the concentration of carbon dioxide rate of photosynthesis, until a constant rate is reached.

(f) discuss light intensity, carbon dioxide concentration and temperature as limiting factors on the rate of photosynthesis
Under natural conditions, carbon dioxide is usually the limiting factor since atmospheric carbon dioxide concentration remains constant at 0.03%.

6. Transport in Flowering Plants

(a) identify the positions and explain the functions of xylem vessels, phloem (sieve tube elements and companion cells) in sections of a herbaceous dicotyledonous leaf and stem, under the light microscope
Xylem tissue conducts water and dissolved mineral salts from the roots to the stems and leaves. The xylem vessel has an empty lumen without protoplasm or cross-walls, this reduces resistance of water flowing through the xylem.

Xylem tissue provides mechanical support for the plant. The walls of xylem are thickened with lignin, which is made of a hard and rigid substance that prevents collapse of the vessel.
(b) relate the structure and functions of root hairs to their surface area, and to water and ion uptake

(c) explain the movement of water between plant cells, and between them and the environment in terms of water potential (Calculations on water potential is not required)

(d) outline the pathway by which water is transported from the roots to the leaves through the xylem vessels
The root hairs grow between the soil particles and are in close contact with the water surrounding them. The sap in the root hair cell is a relatively concentrated solution of sugars and various salts. Thus, the sap has a lower water potential than the soil solution. These two solutions are separated by the partially permeable cell surface membrane of the root hair cells. Water enters the root hairs by osmosis. The entry of water dilutes the sap. The sap of the root hair cell becomes more diluted than that of the next cell. Therefore, water passes by osmosis from the root hair cells into the other inner cells of the cortex. This process continues until the xylem vessels and moves up the plant.
The living cells around the xylem vessels in the root use active transport to pump the mineral salts or ions into the vessel. This lowers the water potential in the xylem vessel. Water therefore passes from the living cells into the xylem by osmosis and flows upwards.
The absorbed water that is in excess (not used by the plant), together with the water produced by the cells during respiration, will be removed through transpiration. The evaporation of water from the leaves removes water from the xylem vessels, resulting in a suction force which pulls water up the xylem vessels. Water flows up the xylem vessels into the leaves, where it evaporates and escapes as vapour through the stomata in the leaves.

(e) define the term transpiration and explain that transpiration is a consequence of gaseous exchange in plants
Transpiration is the loss of water vapour from the aerial parts of a plant
Transpiration by the leaves creates a transpiration pull which sucks water up the xylem vessels in the leaves.
Transpiration helps to remove latent heat of vapourisation and cool the plant. It creates a transpirational pull which enables water to be transported to the leaves from the roots, through the xylem vessels. This helps water to reach the leaves even in very tall trees. In this way, water is carried to cells for the maintenance of turgor, to supply mineral ions for use in leaf cells for photosynthesis.

(f) describe
• the effects of variation of air movement, temperature, humidity and light intensity on transpiration rate
The higher the humidity of the air, the slower the rate of transpiration. Transpiration involves the evaporation of water vapour through the stomata of leaves. Decrease in humidity means that the air would contain less water vapour hence increase the diffusion gradient between the atmosphere and the air spaces in the leaf, increases the evaporation of water into the surrounding air. Therefore decrease in humidity increases the transpiration.
The stronger the wind or the faster the air movement, the faster the rate of transpiration.

The higher the temperature of the air, the higher the rate of transpiration because of increase rate of evaporation. . Higher temperature increase the rate of movement of water molecules .
In sunlight, stomata open and increase the rate of transpiration.

• how wilting occurs
When transpiration exceeds absorption, it will cause wilting. When a plant loses water from the leaves and the leaf stalk due to excessive transpiration, and this water cannot be replaced, the leaf cells lose their turgidity and become plasmolysed. As a result the tissue becomes flaccid and this will result in wilting.
Wilting will occur when the atmospheric temperature is high, windy, low humidity and the light intensity is high as well as low water content of the soil. All these factors will increase the rate of transpiration.

(g) define the term translocation as the transport of food in the phloem tissue and illustrate the process through translocation studies
Translocation is the transport of manufactured food substances such as sugars and amino acids in the phloem tissue. The sucrose molecule moves from the mesophyll cells in the leaf through the sieve tubes of the phloem in a vascular bundle of the leaf. Translocation studies using aphids- aphids feed on organic food substances manufactured by plants. Studies show that aphids extend their feeding stylets inot the phloem and the liquid they take in contains manufactured food.
Ringing experiment- removing the outer layer of phloem tissue from a plant will cause the plant to swell just above the cut area.
Using radioactive 14C to show that manufactured food substances are transported by the phloem.

7. Transport in Humans

(a) identify the main blood vessels to and from the heart, lungs, liver and kidney

(b) state the functions of blood

• red blood cells - haemoglobin and oxygen transport
Oxygen is transported by the red blood cells. Haemoglobin of the red blood cells combines readily with oxygen to form the unstable compound oxyhaemoglobin in the capillaries of the lungs.

• white blood cells - phagocytosis, antibody formation and tissue rejection
The phagocytes engulf and destroy bacteria and other pathogens. They gather at a wound and prevent the entry of microbes through the wound.
The lymphocytes produce antibodies which provide immunity against diseases. These antibodies not only act against foreign bodies and their toxins but also help to clump the bacteria so that the phagocytes can engulf and destroy them easily.

• platelets - fibrinogen to fibrin, causing clotting
When blood vessels are damaged, damaged tissues and blood platelets release an enzyme known as thrombokinase. Thrombokinase converts the protein prothrombin into thrombin. Calcium ions must be present before this can take place. Thrombin catalyses the conversion of the soluble protein fibrinogen to insoluble threads of fibrin. Fibrin threads entangle blood cells and the whole mass forms a clot.
• plasma - transport of blood cells, ions, soluble food substances, hormones, carbon dioxide, urea, vitamins, plasma proteins
Carbon dioxide is transported mainly by the blood plasma. Carbon dioxide from the tissues diffuses into the blood and enters the red blood cells. Carbon dioxide reacts with water to form carbonic acid. The reaction is catalysed by the enzyme carbonic anhydrase. The carbonic acid is then converted into hydrogen carbonate ions which diffuse out of the red blood cells into the blood plasma.
(c) list the different ABO blood groups and all possible combinations for the donor and recipient in blood transfusions

(d) relate the structure of arteries, veins and capillaries to their functions

(e) describe the transfer of materials between capillaries and tissue fluid

Dissolved food substances and oxygen diffuse from the blood through the walls of
the capillaries into the tissue fluid while waste products diffuse from the tissue fluid
through the capillary walls into the blood.

(f) describe the structure and function of the heart in terms of muscular contraction and the working of valves
The function of the left ventricle is to pump blood at high pressure around the body, while the right ventricle only pumps blood to the lungs which are a short distance from the heart, requiring a much lower pressure.

(g) outline the cardiac cycle in terms of what happens during systole and diastole (Histology of the heart muscle, names of nerves and transmitter substances are not required)

During atrial systole the atria contract and ventricles relaxed;
Atrio-ventricular valve (biscupid and tricuspid) open, blood from atria flow to ventricles;
After a sort pause, the ventricular systole occurs-the ventricles contract while the atria relax; The increase in blood pressure forces the AV valves to close to prevent backflow, blood flow to aorta and pulmonary artery forcing open the semilunar valves to open;
Ventricular diastole takes place when atria and ventricles relaxed, The drop in pressure causes the AV to open and the semilunar valves to close. Blood enters the atria from the venae cava and pulmonary vein.

(h) describe coronary heart disease in terms of the occlusion of coronary arteries and list the possible causes, such as diet, stress and smoking, stating the possible preventative measures
Coronary heart disease is caused by blockage of the coronary arteries which supply oxygenated blood to the heart muscle. Excessive intake of saturated fats will cause cholesterol to be deposited in the lining of the coronary arteries, thus constricting the lumen. This will block blood flow to the heart muscles. As a result the heart muscles do not get oxygen and glucose and this will cause coronary thrombosis (coronary heart failure)

8. Respiration

(a) identify on diagrams and name the larynx, trachea, bronchi, bronchioles, alveoli and associated capillaries

(b) state the characteristics of, and describe the role of, the exchange surface of the alveoli in gaseous exchange

The alveolus is highly folded and spherical in shape, hence it has large surface area to volume ratio. Wall in one-cell thick, so it is easy for gases to diffuse through. It is richly supplied with blood capillaries. The flow of blood establishes a concentration gradient of the gases. Its surface is lined with moisture for gases to dissolve in.

(c) describe the removal of carbon dioxide from the lungs, including the role of the carbonic anhydrase enzyme
In the lungs, hydrogen carbonate ions diffuse back into the red blood cells where they are converted into carbonic acid and then into water and carbon dioxide. The carbon dioxide then diffuses out of the blood capillaries into the alveoli and is expelled during exhalation.

(d) describe the role of cilia, diaphragm, ribs and intercostals muscles in breathing
The cilia help to remove mucus from the trachea to the pharynx by their sweeping action. This prevents the accumulation of mucus in the bronchi and alveoli.

The diaphragm is a dome-shaped structure between the thorax and abdomen.
Inhalation (inspiration) - Lowering or flattening of the diaphragm helps to increase the volume of the thorax and reduce the pressure in the lungs. This enables air to enter the lungs through the nose, trachea and the bronchi.

Exhalation (expiration)- The diaphragm becomes dome-shaped again, thus reducing the volume and increasing the pressure in the lungs.

The intercostals muscles help to raise or lower the ribs.
Inhalation- the external intercostals muscles contract. This raises the ribs and pushes the sternum outwards thus increasing the volume of the thorax and decreases the pressure in the lungs.
Exhalation- the external intercostals muscles relax and the ribs are lowered bringing the sternum also inwards thus reducing the volume of the thorax and increasing the pressure in the lungs.

(e) describe the effect of tobacco smoke and its major toxic components - nicotine, tar and carbon monoxide, on health
Nicotine is additive, causes the release of adrenaline and makes blood clot easily hence it increases heartbeat and blood pressure and increased risk of blood clots in blood vessels

Tar contains cancer causing chemicals which induced uncontrolled cell division of the epithelium and paralyses cilia lining the air passages and hence it blocks the air sacs and reduces efficiency of gaseous exchange. Dust particles trapped in the muus lining the airways cannot be removed.

Carbon monoxide- combines with haemoglobin to form carboxyhaemoglobin which reduces oxygen transport efficiency of red blood cells
Increases rate of fatty deposits on the inner arterial wall and damages the lining of blood vessels, death can take place and increased risk of atherosclerosis

(f) define and state the equation, in words and symbols, for aerobic respiration in human
Aerobic respiration is the oxidation of food substances in the presence of oxygen with the release of energy in living cells.
glucose + oxygen → carbon dioxide + water + more energy
C6H12O6 + 6 O2 → 6CO2 + 6H2O + Energy

(g) define and state the equation, in words only, for anaerobic respiration in human
Anaerobic respiration is the breakdown of food substances in the absence of oxygen.
glucose → lactic acid + less energy

(h) describe the effect of lactic acid in muscles during exercise
Lactic acid is produced during anaerobic respiration. Lactic acid concentrations build up slowly in the muscles and may cause fatigue and muscular pains.
During resting, the breathing rate continues to be fast for some time to provide sufficient oxygen to repay the oxygen debt. Lactic acid is removed from the muscles and transported to the liver.
In the liver, the lactic acid is oxidised to produce energy. The energy is used to convert the remaining lactic acid into glucose. When the lactic acid is used up, the oxygen debt is repaid.

9. Excretion

(a) define excretion and explain the importance of removing nitrogenous and other compounds from the body
Excretion is the process by which metabolic waste products and toxic materials are removed from the body.

(b) outline the function of kidney tubules with reference to ultra-filtration and selective reabsorption in the production of urine

Each tubule ( nephron) is made up of:
Bowman’s capsule-As blood passes from the renal artery into the glomerulus in the Bowman's capsule, water and small molecules e.g. glucose, amino acids, mineral salts and nitrogenous waste products are forced out of the glomerular blood capillaries into the Bowman's capsule by the high blood pressure in the glomerulus forming the filtrate.
Proximal convoluted tubule
Loop of Henle
Distal convoluted tube

(c) outline the role of anti-diuretic hormone (ADH) in the regulation of osmotic concentration
After drinking water, the water potential in the blood is increased and this stimulates the hypothalamus which causes the pituitary gland to secrete less antidiuretic hormone. Hence less water is reabsorbed back into the bloodstream and more water remains in the urine.
Kidneys are osmoregulators. They help to control the amount of water in the blood plasma. When the water content of the plasma increases, kidneys remove the excess water from the blood with the aid of the ADH. Similarly, the ADH will help the kidneys to reabsorb water from the filtrate into the blood when the water content of the blood plasma decreases. Thus the kidneys help to control the osmotic pressure of the blood.

(d) outline the mechanism of dialysis in the case of kidney failure

The dialysis machine consists of a long cellulose tube coiled up in a water bath. The patient’s blood is led from an artery in the arm and pumped through a cellulose tubing which is the dialysis tubing. The dialysis tubing is selectively permeable membrane and allows small molecules, such as those of salts, glucose and urea to move out into the water bath (dialysis fluid), blood cells and protein molecules are too large to get through the pores. This stage is similar to the filtration process in the glomerulus. This dialysis fluid in the water bath consists of a solution of sugar and salts of the correct composition as the blood so that only the substances above this concentration can diffuse out of the blood into the dialysis fluid or diffuse from the dialysis fluid into the blood in the tubing. Thus urea, uric acid and excess salts are removed as the dialysis fluid does not contain metabolic wastes products. the dialysis fluid is also kept at body temperature and is constantly changed as the unwanted blood solutes accumulate in it. The direction of blood flow is opposite to the flow of the dialysis fluid to maintain the concentration gradient for the removal of wasted products. The blood is then returned to the patient’s arm.

10. Homeostasis

(a) define homeostasis
Homeostasis is the maintenance of a constant internal environment such as pH and temperature of the blood and tissue fluid.

(b) explain the basic principles of homeostasis in terms of stimulus resulting from a change in the internal environment, a corrective mechanism and a negative feedback
When the blood glucose level rises, it is detected by the hypothalamus which sends impulses to the pancreas which responds by secreting insulin. Insulin increases the permeability of the cell surface membrane to glucose. It stimulates the liver cells to convert excess glucose to glycogen. The blood glucose level drops and then insulin production decreases. A negative feedback to the receptor is sent and the blood glucose concentration is back to normal.

(c) identify on a diagram of the skin: hairs, sweat glands, temperature receptors, blood vessels and fatty tissue

(d) describe the maintenance of a constant body temperature in humans in terms of insulation and the role of: temperature receptors in the skin, sweating, shivering, blood vessels near the skin surface and the co-ordinating role of the brain

The skin is responsible for temperature regulation. The skin has receptors which detect changes in the surrounding air.

Hot environment: Any change in the internal body temperature is detected by the hypothalamus which sends impulses to the skin,

Vasodilation of arterioles to control the amount of blood flow near skin surface, thereby allowing more heat loss by radiation, conduction and convection.
Secretion of sweat in which the evaporation of water in sweat removes latent heat of vaporisation.
The hairs are lowered.

Cold environment: Vasoconstriction of arterioles to reduce blood supply to the skin thus preventing heat loss by radiation. Sweat production ceases and therefore heat is not lost for evaporation of water in the sweat.
When there is a significant drop in body temperature, the body muscles contract spasmodically, causing shivering. This increases heat production.
Metabolism increase, more heat is produced,
Muscular contraction increases heat production
Hair erector muscle contract and cause the hair to stand on end. This will trap a layer of still air between the hairs. As air is a bad conductor of heat, it reduces the heat loss.

11. Co-ordination and Response

(a) state the relationship between receptors, the central nervous system and the effectors
The receptors (sense organs) receive stimuli and inform the central nervous system of any change in the surroundings by producing electrical messages called nerve impulses, transmitted by nerves. The CNS will then send nerve impulses to the effectors (muscles) to effect an action.

(b) describe the gross structure of the eye as seen in front view and in horizontal section

(c) state the principal functions of component parts of the eye in producing a focused image of near and distant objects on the retina
Distant object- the ciliary muscles relax, pulling on the suspensory ligaments. Suspensory ligaments become taut, which in turn will pull on the edge of the lens. This causes the lens to become thinner and less convex, which increases the focal length. Light rays from the distant object will then be sharply focused on the retina. Photoreceptors are stimulated. Nerve impulses produced are transmitted by the optic nerves to the CNS. The brain interprets the impulses and the person sees the distant object.

(d) describe the pupil reflex in response to bright and dim light
Dim light- impulses are produced that send signals to the central nervous system(CNS). The CNS in turn generates signals via the motor neurones, which will cause the radial muscles to contract and the circular muscles to relax. This allows each pupil to dilate, therefore increasing the amount of light entering the eyes.

Bright light- The circular muscle of the iris will contract while the radial muscles will relax. Each pupil constricts to reduce the amount of light entering the eyes.

(e) state that the nervous system - brain, spinal cord and nerves, serves to co-ordinate and regulate bodily functions

(f) outline the functions of sensory neurons, relay neurones and motor neurons
The sensory neurone transmits nerve impulses from the sense organs to the central nervous system.
The motor neurone transmits nerve impulses from the central nervous system to the effectors .
The relay neurone transmits nerve impulses from the sensory neurones to the motor neurones.

(g) discuss the function of the brain and spinal cord in producing a co-ordinated response as a result of a specific stimulus in a reflex action
When the hand touches a hot object, the heat on the object stimulates the nerve endings (receptors) in the skin. Nerve impulses are produced. The nerve impulses travel along the sensory neurone to the spinal cord. In the spinal cord, the nerve impulses are transmitted first across a synapse to the relay neurone, and then across another synapse to the motor neurone. At the same time, nerve impulses are transmitted to the brain. Nerve impulses leave the spinal cord along the motor neurone to the effector. The effector is the biceps muscle, which then contracts. This causes the hand to withdraw suddenly.

(h) define a hormone as a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver
A hormone is a chemical substance, produced by an endocrine gland, carried by the blood, which alters the activity of one or more specific target organs and is then destroyed by the liver

(i) explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas

Ductless glands that secrete hormones directly into the bloodstream.
Insulin is produced by the islets of Langerhans (pancreas) and is secreted into the bloodstream.

(j) state the role of the hormone adrenaline in boosting blood glucose levels and give examples of situations in which this may occur
Adrenaline is secreted when a person is afraid, angry, anxious or stressed.
Adrenaline has wide-ranging effects on the body. It increases blood glucose levels by stimulating the liver to convert glycogen to glucose, metabolic rate, heartbeat, blood pressure and the rate and depth of ventilation. Adrenaline also constricts arterioles in the skin, increases the rate of blood coagulation, causes pupils to dilate and contracts hair muscles. It prepares the body of the person concerned for ‘fight or flight’ situations or for states of emergency.

(k) explain how the blood glucose concentration is regulated by insulin and glucagons as a homeostatic mechanism
The islets of Langerhans in the pancreas produce insulin when the concentration of blood glucose increases above normal levels. The rise in blood glucose level is detected by the hypothalamus which sends impulses to the pancreas which responds by secreting insulin. Insulin decreases blood glucose concentration by increasing the permeability of cell membranes to glucose, thus increasing the rate of glucose uptake by cells; stimulating the conversion of glucose into glycogen for storage in the liver and muscles; and increasing the oxidation of glucose during tissue respiration.

The islets of Langerhans produce glucagon when the concentration blood glucose decreases below normal levels. Glucagon increases blood glucose concentration by stimulating the conversion of glycogen into glucose, the breakdown of fats and amino acids to glucose, and the conversion of lactic acid into glucose

(l) describe the signs, such as an increased blood glucose level and glucose in urine, and the treatment of diabetes mellitus using insulin
A persistently high blood glucose level, the presence of glucose in the urine after a meal, healing of wounds is slow or difficult.

People with type 1 diabetes can be treated by means of insulin injections into their bodies and a supply of sugary food to their diet. People with type 2 diabetes need to observe their diet and exercise regularly, metformin tablets and insulin injections are used only when lifestyle changes fail.

Nervous System Hormonal System
Involves nerve impulses (electrical signals) Involves hormones (chemical substances)
Impulses are transmitted by neurones Hormones are transported by the blood
Usually quick responses Usually slow responses
Responses are short-lived Responses may be short-lived or long-lived
May be voluntary or involuntary Always involuntary
Usually localised Tend to affect more than one target organ

12. Reproduction
(a) define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent
Asexual reproduction is the process resulting in the production of genetically identical offspring from one parent, without the fusion of gametes

(b) define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring
Sexual reproduction is the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring

(c) identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one, locally available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains under a microscope

(d) state the functions of the sepals, petals, anthers and carpels

Sepals: Enclose and protect the other parts of the flower in the bud stage.
Petals: Are brightly coloured to attract insects for pollination, and provide a platform for insects to land.
Stamens: Pollen sacs in anther produce pollen grains which contain the male gametes. Filament holds the anther in a suitable position to disperse the pollen.
Carpels: Ovary contains the ovule which produces the female gamete
(ovum). Stigma receives the pollen grains

(e) use a hand lens to identify and describe the stamens and stigmas of one, locally available, named, wind-pollinated flower, and examine the pollen grains under a microscope

(f) outline the process of pollination and distinguish between self-pollination and cross pollination
Pollination is the transfer of pollen grains from the anther to the stigma of the same flower (self-pollination) or to the stigma of another flower of the same species (cross-pollination)

(g) compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower
Insect-pollinated flower
• Are brightly coloured to attract insects for pollination.
• Provide a platform for insects to land.
• Nectar guides guide insects to the nectar deep inside the flower.
Wind-pollinated flower
Structure Adaptation
Stigma Large and feathery, provides large surface area to trap
Anther Large, produces an abundance of pollen to offset wastage;
pollen grains tiny and light so easily float in air.
Filament Long and protrude out of bracts to expose anther to wind;
slender and pendulous, sway readily in wind to dislodge
pollen from the anther.

(h) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (production of endosperm and details of development are not required)
Pollen grains germinate in response to the sugary fluid secreted by the mature stigma. A pollen tube grows out from each pollen grain. This cytoplasm and the two nuclei (pollen tube nucleus and generative nucleus) of each pollen grain pass into the pollen tube. The growth of the pollen tube is controlled by the pollen tube nucleus. As the pollen tube grows, it secretes enzymes to digest the surrounding tissue of the stigma and style. Thus the pollen tube penetrates right through the style as it grows. The pollen tube enters the ovule usually through an opening in the ovule wall called the micropyle. Along the way, the generative nucleus divides to form two male gametes, the pollen tube nucleus soon disintegrates. Within the ovule, the tip of the pollen tube absorbs saps and bursts, releasing the two male gametes.
Fertilisation- One of the male gamete fuses with the ovum to form a zygote. The other male gamete fuses with the definitive nucleus to form the endosperm nucleus.

(i) identify on diagrams of the male reproductive system and give the functions of: testes, scrotum, sperm ducts, prostate gland, urethra and penis

(j) identify on diagrams of the female reproductive system and give the functions of ovaries, oviducts, uterus, cervix and vagina

(k) briefly describe the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in its length, and the fertile and infertile phases of the cycle with reference to the effects of progesterone and estrogen only
Menstrual flow stage
- Menstruation begins
- Anterior pituitary gland secretes follicle-stimulating hormone (FSH- Follicle stage
- FSH stimulates follicles to develop into Graafian follicle
- FSH stimulates follicles to secrete oestrogen
- Oestrogen causes uterine lining to thicken
- High levels of oestrogen inhibit FSH production, no more follicles develop
- Ovulation
- Luteinising hormone (LH) causes ovulation
- LH causes corpus luteum formation; also stimulates corpus luteum to secrete progesterone and some oestrogen
- Corpus luteum stage
- Progesterone stimulates uterine lining to thicken and to become well-supplied with blood
- Progesterone inhibits ovulation and FSH production

(l) describe fertilisation and early development of the zygote simply in terms of the formation of a ball of cells which becomes implanted in the wall of the uterus

Sperms released into the vagina meet an egg in the oviduct. The acrosome of one sperm releases an enzyme to disperse the follicle cells that surround the egg and break down the egg membranes. Only one haploid sperm nucleus enters the egg and fuses with the haploid egg nucleus to give rise to a fertilised egg or diploid zygote.
After fertilisation, the zygote passes along the oviduct to the uterus. It divides by mitosis to form a hollow ball of cells called the embryo. The embryo eventually implants itself in the uterine lining. In the uterus, the embryo grows and develops into a fetus.

(m) state the functions of the amniotic sac and the amniotic fluid
Amniotic sac protects the embryo. It encloses the fetus in the amniotic cavity which contains amniotic fluid.
Amniotic fluid supports and cushions the fetus and allows it to move freely during growth
Supports and acts and a shock absorber for the fetus.
Protects the fetus from mechanical injury

(n) describe the function of the placenta and umbilical cord in relation to exchange of dissolved nutrients, gases and excretory products (Structural details are not required)
Placenta- is the tissue through which the fetus is connected to the uterus wall. It contains both fetal and maternal tissues as well as blood vessels of both fetus and the mother. The fetus is attached to the placenta through the umbilical artery and umbilical vein.
Two umbilical arteries are responsible for transporting carbon dioxide, urea and metabolic waste products from the fetus to the placenta. The umbilical vein is responsible for transporting oxygenated blood and food substances such as amino acids, glucose, and other nutrients, antibodies from the placenta to the fetus.

(o) discuss the spread of human immunodeficiency virus (HIV) and methods by which it may be controlled
HIV is spread when one has sexual intercourse with an infected person, shares hypodermic needles with an infected person, undergoes blood transfusion with blood from an infected person, or during pregnancy when the virus is passed from the infected mother to her fetus.

The spread of HIV can be controlled by keeping to one sex partner or do not have sex. Males should wear condoms especially if they are unsure whether their partners or themselves are infected with AIDS. Needles and instruments that are likely to break the skin and be contaminated with blood should not be shared. Instruments should always be sterilised or use disposable instruments.

13. Cell Division

(a) state the importance of mitosis in growth, repair and asexual reproduction
Mitosis- a cell divides into two genetically identical daughter cells. The nucleus of each daughter cell has the same number of chromosomes as the parent nucleus. DNA replication is precisely controlled in a dividing cell to ensure that all the information stored in the chromosomes is accurately copied. Daughter cells thus contain all sections of DNA needed for subsequent cell division and differentiation. The daughter cells are said to be genetically stable.

Mitosis is important for the growth of an organism, e.g. in the growth of a plant
• Mitosis is important for repair of worn-out parts of the body of an organism, e.g. when you brush your teeth and rinse your mouth, dead and worn-out cheek cells are shed into your saliva; and also for healing of wounds, e.g. if you get cut, your skin produces new cells to help seal the cut.
• In some organisms, mitosis is important for asexual reproduction, e.g. in flowering plants that reproduce vegetatively.

(b) explain the need for the production of genetically identical cells and fine control of replication
• DNA replication and mitosis must be precisely controlled in a dividing cell to ensure that daughter cells produced by mitosis contain all the sections of DNA (genes) needed for subsequent cell division and differentiation/ in other words the daughter cells are genetically stable. If error occurs during replication, it will be transmitted to the daughter cells and may lead to harmful changes to the genes and affect normal growth of the cells such as cancerous growth of cells.

(c) identify, with the aid of diagrams, the main stages of mitosis
interphase, metaphase, anaphase, telophase

(d) state what is meant by homologous pairs of chromosomes
Homologous chromosomes come in pairs. One chromosomes in the pair comes from the male parent and the other from the female parent. They are similar in shape and size. They have exactly the same sequence of genes, but may carry different alleles.

(e) identify, with the aid of diagrams, the main stages of meiosis (Names of the sub-divisions of prophase are not required)
meiosis I and meiosis II

(f) define the terms haploid and diploid, and explain the need for a reduction division process prior to fertilisation in sexual reproduction
A haploid cell contains half the number of chromosomes as parent cells.
A diploid cell contains same number of chromosomes as parent cells.

During sexual reproduction, two gametes fuse to form a zygote. Thus,
each gamete must be haploid (have only half the number of chromosomes as the zygote), in order to maintain the chromosome number of the species. A reduction division is necessary to produce such haploid cells

(g) state how meiosis and fertilisation can lead to variation
Daughter nuclei produced during meiosis contain half the number of chromosomes as the parent nucleus. Crossing over during prophase leads to variations in the daughter cells (gametes) . independent assortment of chromosomes also leads to genetic variation. The fusion of gametes is random so variation occurs when the zygote is formed.

Meiosis produces haploid gametes and results in variations in the
gametes produced. Variations increase the chances of survival of the species during changes in the environment.

14. Molecular Genetics

(a) outline the relationship between DNA, genes and chromosomes
A chromosome is a coiled and condensed structure found in the nucleus during cell division. It is made up of DNA and histone proteins. It carries genes.

(b) state the structure of DNA in terms of the bases, sugar and phosphate groups found in each of their nucleotides
Each DNA molecule consists of two parallel strands twisted around each other to form a double helix. The basic unit of DNA is a nucleotide. Each nucleotide is made up of a sugar called deoxyribose, a phosphate group and a nitrogen-containing base, adenine, cytosine, guanine and thymine.

(c) state the rule of complementary base pairing
Adenine always bond with thymine and Cytosine always bond with Guanine.

(d) state that DNA is used to carry the genetic code, which is used to synthesise specific polypeptides
DNA carried genetic information which is used to make specific proteins.

(e) state that each gene is a sequence of nucleotides, as part of a DNA molecule
A gene the basic unit of inheritance. It is a small segment of DNA in a chromosome where specific genetic information is stored. It controls the production of a specific protein. It can also be described as a sequence of nucleotides in a DNA molecule, which controls the development of a particular characteristic in an organism.

(f) explain that genes may be transferred between cells. Reference should be made to the transfer of genes between organisms of the same or different species – transgenic plants or animals

Step 1: Isolate the gene of interest by using a restriction enzyme to cut
the gene out from the chromosome.
Step 2: Use the same restriction enzyme used in step 1 to cut a plasmid.
Step 3: Mix the plasmid with the DNA fragment containing the gene of interest, using the enzyme DNA ligase to join the two.
Step 4: Mix the plasmid with bacteria. Treat the bacteria with temporary heat or electric shock to take up the DNA obtained in step 3.

(g) briefly explain how a gene that controls the production of human insulin can be inserted into bacterial DNA to produce human insulin in medical biotechnology
The insulin produced by genetically engineered bacteria is exactly the same as human insulin. Patients using this insulin will not develop antibodies against it. They are likely to respond to it as though it were being manufactured by their own bodies.
Older methods of treatment involved patients using animal insulin. Such patients often developed antibodies to animal insulin or, after some time, were unable to respond to the animal insulin.

(h) outline the process of large-scale production of insulin using fermenters
Insulin is manufactured in large quantities by inserting the human insulin gene into special non-disease producing special laboratory strain of Escherichia coli bacteria that has been genetically altered by the addition of a gene for human insulin production.
• Obtain the human chromosome containing the human insulin gene. Use a restriction enzyme to cut the gene to produce the ‘sticky ends’
• A plasmid from bacteria is cut across both strands by a restriction enzyme, leaving those ‘sticky ends’ to which DNA can be attached.
• DNA ligase is used to join insulin gene to plasmid
• Recombinant plasmid is inserted into a bacterial cell, E.Coli
• The recombinant plasmids and the bacterial cells are mixed together. Plasmids enter the bacteria.
• The recombinant plasmid multiply and replicate to produce million of cells containing the human gene
• Grown in a fermenter, nutrients and optimum conditions are maintained to favour production of insulin
• Insulin is packaged for commercial and medical use
(i) discuss the social and ethical implications of genetic engineering, with reference to a named example
Recombinant DNA technology has been used to modify corn and soya plants to produce healthier, more nutritious and disease-resistant grains or seeds.
e.g. Bt Corn is genetically modified species of corn which contains genetic material formthe bacterium Bacillus thuringeinsis(Bt) that confers insect resistance.

Concerns that transfer genes from GMOs to wild (naturally occurring) type crops may occur during pollination. This gene flow may “ pollute’ the genetic make up of the local wild species.

Bt corn pollen has adverse effect on the larvae of Monarch butterfly. Larvae that fed on milkweed leaves dusted with Bt Corn pollen had a higher death rate than those which did not.

Investors who fund the research many control their intellectual property and put profit above the welfare of consumers and small-scale farmers

15. Inheritance

(a) define a gene as a unit of inheritance and distinguish clearly between the terms gene and allele
A gene is a unit of inheritance. It is a small segment of DNA in a chromosome where specific genetic information is stored.
Different forms of the same gene are called alleles, which occupy the same locus in homologous chromosomes.

(b) explain the terms dominant, recessive, codominant, homozygous, heterozygous, phenotype and genotype
Genotype is the genetic make-up of an organism, that is, the combination of genes in an organism.

Phenotype is the expressed trait. It is the result of its genes and the effects of its environment.

A dominant allele expresses itself and gives the same phenotype in both the homozygous and heterozygous conditions.
A recessive allelle does not express itself in the heterozygous condition, but only in the homozygous conditions.
When a pair of alleles is similar for a trait, they are referred to as homozygous.
When a pair of alleles is different trait, they are referred to as heterozygous.
(c) predict the results of simple crosses with expected ratios of 3:1 and 1:1, using the terms homozygous, heterozygous, F1 generation and F2 generation

(d) explain why observed ratios often differ from expected ratios, especially when there are small numbers of progeny
Observed ratios may not be quite accurate because a smaller number of samples are used. Statistically, ratios are inaccurate when the sample numbers are small. Since the ratio figures are base on chance and probabilities, the actual number of progeny would be unlikely to match the expected number precisely,

(e) use genetic diagrams to solve problems involving monohybrid inheritance (Genetic diagrams involving autosomal linkage or epistasis are not required)

(f) explain co-dominance and multiple alleles with reference to the inheritance of the ABO blood group phenotypes – A, B, AB, O, gene alleles IA, IB and Io
Codominance results when two alleles controlling a trait express themselves, such that an intermediate phenotype results. A gene that has more than two forms of alleles is said to have multiple alleles. The human blood group is controlled by multiple alleles. Allels IA and IB are codominant. IO is recessive to both IA and IB.

(g) describe the determination of sex in humans – XX and XY chromosomes
In human, the female gametes or eggs contain an X chromosome each. The male sex cells from her mother and one X chromosome from her father. A baby boy receives carry either an X chromosome or a Y chromosome. When male and female gametes fuse during fertilisation during fertilisation, there is a 50% chance that the offspring could be male and a 50% chance that it could be female. A baby girl inherits one X chromosome and X chromosome from his mother and a Y chromosome from his father.

(h) describe mutation as a change in the structure of a gene such as in sickle cell anaemia, or in the chromosome number, such as the 47 chromosomes in a condition known as Down Syndrome

A mutation is a spontaneous (sudden) change in a gene or a chromosome, which may affect the appearance or physiology of an organism. Mutation occurs when there is an error during the replication of the gene e.g sickle cell anaemia or the chromosome e.g. Down’s syndrome.
The gene mutation that causes sickle-cell anaemia may be advantageous in places where malaria is common. Individuals who are heterozygous for the sickle-cell allele are more resistant to malaria because a small percentage off their red blood cells are sickle-cell allele are more resistant to malaria because a small percentage of their red-blood cells are sickle-shaped(mutated). As these individuals do not fully contract either disease, they have better chances of surviving and reproducing compared to homozygous or normal individuals.

(i) name radiation and chemicals as factors which may increase the rate of mutation
Mutation can also be caused by mutagens such as radiation and chemicals.

(j) describe the difference between continuous and discontinuous variation and give examples of each

Continuous variation is brought about by the combined or additive effect of many genes and has intermediate forms from one extreme to the other. The traits can be affected by environmental conditions. Examples of continuous variation (any one): skin colour, intelligence, weight, height.
Discontinuous variation is brought about by one or a few genes. This results in clear-cut phenotypes with no intermediate forms between traits . The traits are easily distinguishable and are not affected by environmental conditions.
Examples of discontinuous variation (any one): ability to roll the tongue, ABO blood groups in humans, single- and double-eyelids, normal and vestigial wings in Drosophila).

(k) state that competition which arises from variation leads to differential survival of, and reproduction by, those organisms best fitted to the environment
Variations in organisms may arise due to mutation. Crossing different varieties of plants and animals produces even more variations in the offspring. Competitions for food and space occur among these different varieties of organisms. Nature selects those varieties that are more competitive, more resistant to disease and better adapted to changes in the environment to survive and reproduce their kind. The other varieties that are susceptible to disease or environmental changes may die.-Natural selection.

(l) give examples of environmental factors that act as forces of natural selection
Diseases, competition for food,

(m) assess the importance of natural selection as a possible mechanism for evolution
The environment selects for varieties with characteristics that best fitted to the environment. These organisms that survive reproduce and pass down their genes over generations. Eg. Darwin’s finches
Natural selection occurs when natural environmental conditions change. Those organisms in a species that are able to survive the changes will pass on their genes to the next generation. Varieties of organisms may be produced as a result of mutation and natural selection.

(n) give examples of artificial selection such as in the production of economically important plants and animals
Artificial selection occurs when humans select the varieties of organisms that suit their needs, varieties of organisms are produced though selective breeding processes.
E,g. Improving plants- soya beans with high oil content- select plants with high oil content, and allow the seeds to grow and self-fertilised. Seeds with highest oil content are selected and used again as parents for the next generation. After many generations, the plants with the desired qualities can be obtained to ensure the desirable genes are inherited by future generation of plants.
- sugar cane rich in sugar is cross-breed with wild type that is resistant to diseases to obtain a new variety that has the desirable combination of genes from the two parental varieties.

Improving animals by selection- cows with produce plenty of milk and good meat are used to mate with a bull with known required traits.
Mating Jersey cow ( which produce plenty of good milk but does not thrive well in warm climates) with Brahman breed of cattle ( thrive well in warm climates but are not good milk producers) to produce a good breed. Inbreeding will take place to maintain the improved breed.

16. Organisms and their Environment

(a) briefly describe the non-cyclical nature of energy flow
The main source of energy in an ecosystem comes from the sun. Light energy absorbed by chlorophyll in producers is converted into chemical energy during photosynthesis. Energy in the producers is passed from one trophic level to another by feeding. As energy flows through the ecosystem, some of it is lost to the environment as heat. Living organisms cannot use heat energy to do work. They cannot use light and chemical energy. Energy that is lost as heat cannot be recycled. Hence, energy has to be constantly supplied to the ecosystem.

(b) explain the terms producer, consumer and trophic level in the context of food chains and food webs
Producers convert energy from the sun or light energy into chemical energy and store it as food during photosynthesis.
Consumers are animals that obtain their energy by feeding on other organisms.
Trophic level is each stage in a food chain.

(c) explain how energy losses occur along food chains, and discuss the efficiency of energy transfer between trophic levels

Energy is lost to the environment as food is transferred from one trophic level to the next. Energy is lost as
• heat during respiration at each trophic level
• in uneaten body parts
• through undigested matter egested by consumers and
• through waste products excreted by consumers e.g. urea

The total energy level is highest at the first trophic level and lowest at the last trophic level.

(d) describe and interpret pyramids of numbers and biomass
A pyramid of number compares the number of organisms present in each trophic level at a particular time. All the organisms at each trophic level are counted, regardless of their size and stage of development.

A pyramid of biomass compares the mass of organisms present in each trophic level at a particular time.
It is constructed based on the dry mass of organisms in each trophic level at any one time.

(e) describe how carbon is cycled within an ecosystem

Removal of carbon dioxide from the environment
During photosynthesis, green plants absorb carbon dioxide from the atmosphere and use it to manufacture carbohydrates e.g. glucose. Glucose may be changed to other organic compounds such as fats, amino acids and proteins. When animals feed on green plants, the carbon compounds become part of the bodies of these animals. The carbon compounds may also be preserved in fossil fuels such as coal, natural gas and oil.
Release of carbon dioxide into the environment
Carbon dioxide is released into the environment through
• respiration –when living organisms respire, carbon compounds like glucose are broken down in their bodies and carbon dioxide is release into the environment
• combustion- when fossil fuels like coal and natural gas are burnt or undergo combustion, carbon compounds preserved in the fossil fuels are broken donw and carbon dioxide is release into the environment.
• Decay- when organisms die, their bodies decay or are broken down into simple substances by decomposer. Carbon dioxide is released into the environment. When decomposers respire, carbon dioxide is release into the environment.

(f) evaluate the effects of

• water pollution by sewage and by inorganic waste
Sewage when discharged into rivers and seas will be decomposed by aerobic bacteria to nitrates. These bacteria will use up the oxygen in the rivers and it will result in the death of fish and other organisms in the water. The nitrates formed will also increase the number of algae which will result in eutrophication. The death of these algae will also increase the number of these aerobic bacteria.
Discharge of sewage can also spread diseases such as cholera, dysentery and typhoid. Sewage may contain these bacterial and if they get into the drinking water it can spread these disease.

• pollution due to insecticides including bioaccumulation up food chains and impact on top carnivores
Some insecticides are non-biodegradable, can remain in the oil or water for many years, may be carried by rainwater into streams, rivers and lakes, in high concentrations, they may poison fish or animals that take in the polluted water or feed on the contaminated fish.

Some insecticides, e.g. DDT is insoluble in water, and is not excreted or broken down, but stored in the fatty tissues of organisms, This results in the insecticides being passed along food chains, increasing in concentration in the bodies of organisms along the trophic levels. This process is called bioamplification. The chemicals are accumulated in the bodies and concentrate in the final consumers. This is called bioaccumulation.

(g) outline the roles of microbes in sewage disposal as an example of environmental biotechnology

The use of decomposers to treat sewage is an example of environmental biotechnology. Water pollution can be caused by releasing untreated sewage into the environment. Sewage is treated in sewage treatment plants by decomposers, and disease-causing microorganisms are removed from the treated sewage before it is released into the environment.
Sewage from households is drained into large containers called settling tanks and then into sedimentation tanks. In these tanks, the heavier sandy materials in the sewage settle to the bottom of the tank and are removed.
In the aeration tank, bacteria is mixed with the sewage. The bacteria secrete enzymes to digest the solid organic waste in the sewage into harmless soluble substances and carbon dioxide . Bacteria also feed on the digested products. The liquid that is generated from this bacterial digestion is filtered and disease-causing microorganisms are removed before the filtrate is discharged into rivers or seas. The digested solid that remains after filtration is called sludge.
Anaerobic bacteria break down organic matter in the sludge in anaerobic sludge digesters and the sludge is then removed form the tank, dried and used as fertilisers.

(h) discuss reasons for conservation of species with reference to the maintenance of biodiversity, management of fisheries and management of timber production

The effects of many organisms on the ecosystem are yet unknown. Loss of species could greatly upset the ecological balance. Biodiversity is also a valuable natural resource. Conservation is necessary for the maintenance of the Earth’s biodiversity.
Biodiversity- Many organisms that have not yet been studied may be potentially of great economic importance, e.g. by providing raw materials for industries, cures for diseases, new sources of food.
To prevent the extinction of plant and animal species.
To maintain a large gene pool. Many wild plants and animals possess favourable genes. By cross-breeding the different varieties of wild plants and animals, we can improve agricultural produce, e.g gaining a better yield of milk or producing plants with better resistance to diseases and drought.
To ensure the conservation of marine life as they are a major source of human food.

Uncontrolled fishing not only reduces the biodiversity (number of species) living in the coral reef community, it may also destroy the coral reef habitat.
Measures must be taken to eliminate the pollution of rivers and seas. Fishing grounds or fisheries must also be carefully managed to prevent over-fishing and discriminate fishing.

Timber production Prevent indiscriminate cutting down of forest trees or tree felling. Forests, a major source of oxygen, help to moderate the weather and provide shade and protection for the soil. The production of timber must be managed to conserve forests. Trees are cut down selectively and at a regulated rate. Young trees are not cut down. New seedlings are planted to replace those trees that were cut down for timber.


TASHFAIN said...


jheanel said...

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