Answers to sample examination Paper 1 1 a) The students should have de-starched the plant by putting it into a dark cupboard prior to the experiment. They should have also tested one of the leaves of the plant for starch prior to the experiment after they took it out of the dark cupboard to ensure that the plant was completely de-starched. This would ensure that any new starch found would be from the exper iment. [4] b) The area of the leaf covered by the silver paper would not turn black from the potassium iodide (iodine) solution but the other parts of the leaf would. [2] c) i) So that when the test for starch is done it is easy to determine if the test is positive or not. The green leaf colour interferes with the natural colour of the potassium iodide (iodine) solution and appears black. down the membranes in the leaf so the potassium iodide ii) This breaks down (iodine) solution can come into contact with the starch in the chloroplasts. [4] [1] d) To test for the presence of starch.
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2 a) Fo o d
Two examples of good sources of the food
One important function in the body
Protein
Fish
Used for growth
Chicken, beans Carbohydrates
Bread, yam Sugar
Fat
Butter Fatty meat
Calcium and phosphorus
Milk
Iron
Calaloo, spinach
Strengthens bones and teeth
Cheese
Liver Vitamin D
Provides the body with energy
Fish liver
Important component of haemoglobin in red blood cells Prevents rickets
Eggs Vitamin C
Cherries
Oranges
Prevents scurvy, bleeding gums
[15] b) Biuret test. [1] [1] c) A purple colour. d) In autotrophic nutrition an organism synthesises its own food from simple inorganic material. In heterotrophic nutrition an organism feeds on another organism or part of it. [2]
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2 minutes. [1] 60 beats/ beats/minute. minute. [1] They were were anxiou anxiouss before starting the race. [1] It supplies more blood thus there there is an increased oxygen oxygen supply to the muscles for respiration. [2] c) The body is trying to take in extra oxygen to pay the oxygen debt generated during the exercise. The lactic acid build up during the period of anaerobic respiration has to be broken down since it is toxic in high amounts. Oxygen Oxygen is needed for the breakdo breakdown wn of lactic acid. [3]
3 a) i) ii) b) i) ii)
4 a) Increasing the sample size increases the reliability of the experiment. [2] b) Solution A – this solution is hypertonic/more concentrated than the solution inside the t he potato cells. Solution B – this solution is hypotonic/ less concentrated/more dilute than the solution inside the potato cells. [2] [1] c) i) Osmosis. ii) Plants: entry of water into the roots. This is important as plants need water as a reactant in photosynthesis. Animals: absorption of water from the intestines. Water is important to animals as it is a solvent for all chemical reactions in the body. [4] iii) Minerals are taken up by the process of active transport, which is movement from an area of low concentration to one of high concentration, with the use of energy in the form of ATP. Osmosis is the movement of water from an area of high concentration to an area of low concentration. [2] iv) Oxygen leaves a green leaf by the process of diffusion through the stomata. This is the movement of a gas from an area of high concentration to an area of low concentration. [2] 5 a) From the droppings of the bird, or from seeds discarded into the soil from the birdseed that was in the cage. [2] b) Moist soil; warm days and nights. [2] c) Appropriate level of sunlight; soil quality. [2] d) Some plants had deeper root systems than others, thus by the process of natural selection, these plants survived as they were better adapted to the soil conditions. Some plants may have been naturally taller, thus were more effective at absorbing sunlight for photosynthesis than others. [4]
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Free-response questions 6 a)
aorta pulmonary artery
pulmonary artery left atrium
pulmonary valve (or semi-lunar valve) right atrium
pulmonary veins
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mitral valve or bicuspid valve
tricuspid valve left ventricle right ventricle
Blood enters the right side of the heart in diastole. The blood then leaves the atrium through the tricuspid valve in atrial systole and enters the right ventricle. The right r ight ventricle then contracts in ventricular systole, increasing the pressure in the ventricle and closing the mitral valve and opening the pulmonary valve. Blood is forced into the pulmonary trunk (or pulmonary arteries) passing through the pulmonary valves. The pulmonary arteries enter the lungs, splitting into arterioles and capillaries which surround the alveoli. The blood flows into the capillary beds where oxygen moves by diffusion into the blood and carbon dioxide diffuses out. The capillaries unite to form venules, then the pulmonary vein, which empties into the left atrium. Blood enters the left side of the heart via the left atrium in diastole. It passes from the left atrium to the left ventricle through the mitral or bicuspid valve, the atrium being emptied of blood in atrial systole. In ventricular systole the mitral valve closes and the blood is forced through the aortic valv valvee into the aorta. [7] b) Plasma is located within the blood vessels; tissue fluid is in the interstitial spaces; lymph is in the lymphatic vessels. Plasma contains a higher concentration of nutrients than tissue fluid and lymph. Lymph contains lymphocytes (white blood cells) and tissue fluid does not. Tissue fluid has a higher concentration of carbon dioxide than plasma and lymph. [6]
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c) Capillaries are the smallest blood vessels. They have walls that are one-cell thick and have no valves. They also have spaces in their walls which allow fluid to leak out. Veins have walls that consist of three layers. They have the largest lumen, but their walls have less smooth muscle and elastic tissue than arteries. They also have valves to ensure one-way flow of blood. Arteries, like veins, have three external layers but they have more muscle and elastic tissue ti ssue than veins. Thus the walls of arteri arteries es are more elastic than those of veins, and stretch and recoil as blood flows through them. Arteries carry oxygenated blood away from the heart, with the exception of the pulmonary artery ar tery which carries car ries deoxygenated blood.Veins carry deoxygenated blood towards the heart, with the exception of the pulmonary vein which carries oxygenated blood. Capillaries bring blood and its constituent nutrients into close contact with cells, thus enabling gaseous exchange and nourishment nour ishment of the cells. They also allow removal removal of wastes from the intercellular environment. [7] 7 a) air sucked in
external intercosta intercostall muscles contract pulling ribs forwards and up diaphragm contracts and lowers
The intercostal intercostal muscles contract raising the ribs up and out. out. The diaphragm also contracts, moving down. This increases the volume in the thorax and reduces the pressure inside the thorax. The thorax is i s thus at a lower pressure than the atmosphere. Air moves down the pressure gradient through the mouth and nostrils, through through the trachea, bronchi and bronchioles into the alveoli. [7] b) i) exchange. e. Large surface area: more space for exchang ventilated: ed: steep concentration concentrati on gra gradient dient across surf surface, ace, thus quicker Well ventilat gas exchange. of a transport system such as capillaries: capillaries: also also Near to components of maintains a steep concentration gradient across surface, surf ace, thus quicker gas exchange. travel, thus quicker gas exchange. Thin: less distance for gases to travel, exchangee to occur. [4] Moist: gases must be dissolved for effective exchang ii) gill arch rakers
filaments or
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lamellae
[4]
c) Aerobic respiration occurs with the use of oxygen; anaerobic respiration occurs without oxygen. Carbon dioxide and water are the products of aerobic respiration; anaerobic respiration produces lactic acid. A large amount of ATP ATP is produced in aerobic respiration; only a small amount is produced in anaerobic respiration. Anaerobic respiration only occurs in the muscles of humans; aerobic respiration occurs in all cells of humans. Anaerobic respiration only occurs dur ing strenuous exercise; aerobic respiration occurs all the time. [5]
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Answers to sample examination Paper 2 1 a) For a) For the test for starch the result was a colour change to brown. The inference the student made is incorrect because a positive starch test gives a dark blue/black colour. colour. The second test is used to test for the presence of a non-reducing sugar. However, the reducing sugar test has to be done first. In this case it was not done, so although the correct colour change occurred, it cannot be conclusively stated that non-reducing sugar was present in the solution. The last test was done incor incorrectly rectly.. The mixture should never be heated. never be Because the test was not done correctly it cannot be concluded that protein was absent from the solution. [6] To ensure a fair test, the tubes should be cleaned and labelled. For the b) To b) non-reducing sugar test, first the reducing sugar test should be carried out on a sample of the test solution and only if the result is negative should the non-reducing sugar test be carried out. For the test for protein, the mixture must never be heated. The colour change occurs in the absence of heat. [4] By the time food reaches the small intestine starch and protein have been c) By c) digested to glucose and amino acids. Starch is first digested to maltose in the mouth by the enzyme amylase. In the small intestine more of the enzyme amylase digests any remaining starch. Maltose is then further digested into glucose by the enzyme maltase, which is found in the small intestine. Protein is first digested to polypeptide chains in the stomach by the enzyme pepsin. In the small intestine the polypeptides are further digested by other enzymes such as trypsin into amino acids. Thus the food from the small intestine does not give a positive result for a protein or a starch test. [6] A small sample of the test solution is added to an equal volume of ethanol d) A d) in a tube. The contents of the tube are then shaken vigorously. The contents are then poured into a tube containing distilled water. A milky white suspension is seen if lipids are present in the sample. [4] e) i) The duodenum. [1] [1] ii) Bile. ii) The lipids are broken up into very small droplets. There is no chemical iii) The iii) change in the lipid structure. [2] Emulsification of lipids in the alimentary canal is very important iv) Emulsification iv) because it provides a larger surface area for the enzyme lipase to work on. This improves the efficiency of the enzyme. [4]
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2 a) Stage a) Stage 1 – active transport; stage 2 – nutrition (feeding); stage 3 – decay/ decomposing. [3] [1] b) Microorganisms/bacteria. Makes carbon available for living organisms. Makes carbon dioxide c) Makes c) available for photosynthesis. [2] Extensive deforestation and an increase in the burning of fossil fuels. [2] d) Extensive d) Reduce the burning of fossil fuels by reducing our dependence on the e) Reduce e) fuel for energy. Stop cutting down trees at such a rapid rate and increase the rate of reforestation. [4]
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3 a)
Graph showing the rate of reaction at different temperatures 4 3.5 3 s / g 2.5 m / 2 e t a 1.5 R 1 0.5 0 0
5
10
15
20
25
30
35
40
45
50
55
60
temperature / °C
[6]
b) As the temperature rises the rate of the reaction gradually rises. b) As This happens until about 40 °C when the rate of reaction is at its highest. This is the optimum temperature of the enzyme. At temperatures higher than 40 °C the rate of reaction starts to decrease sharply as the enzyme becomes denatured and is unable to catalyse the reaction any more. [4] [1] c) 40 °C. pH; concentrations of reactant and enzyme. [2] d) pH; d) e) i) The optimum temperature is near to human normal body temperature. [1] metabo lic reactions efficiently. effi ciently. ii) To enable enzymes to catalyse metabolic [2] catalys es the break down of starch into maltose. malt ose. f) For example, amylase – catalyses (Or any other example. You may check your textbook to determine if you are correct if you use other enzymes.) [1] atrium; E – – left 4 a) A – aorta; B – aorta; C – pulmonary vein; D – right atrium; E ventricle; F – right ventricle; G – mitral (or bicuspid) valve; H – left atrium; I – pulmonary artery; J artery; J – – septum. [5] Deoxygenated blood. b) Deoxygenated b) [1] ri ght ventricle pumps blood to the lungs that are nearby, nearby, whereas the c) The right left ventricle is responsible for pumping blood to all parts of the body, thus it requires more force to send the blood than the right ventricle and thus has a more muscular wall. If the force of the blood going to the lungs is too great it could damage the delicate structures in the lungs. [4] The pressure in the left ventricle is reduced. The blood does not have d) The d) enough force to be pumped to all parts par ts of the body. body. This happens because some of the blood goes back into the left atrium when the ventricle contracts. [5]
Free-response questions 5 a) i) The outer layer of the tooth is a very hard white substance called enamel. Just below the layer of enamel is a bony substance called dentine. Both these outer layers protect the inner layer of the tooth called the pulp cavity. The pulp cavity is made up of blood vessels and nerve endings. The section of the tooth that is embedded in the gum is covered cov ered with a substance called cementum. This anchors the tooth into the gum and jawbone. [3] 2
ii) crown enamel dentine
pulp cavity
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cementum gum
root
[5] She will not be able to mechanically digest her food in her mouth. Starch, b) She b) which is partly digested in the mouth, needs to be chewed to give a larger surface area for the enzyme amylase to work on. Therefore, without teeth the larger surface area will not be provided for the enzyme to work on. She may have to rely on foods that are soft so that her food will be able to be digested properly. [6] c) i) Fluoride toughens the enamel and protects it from the potential damage from acid that causes tooth decay decay.. ii) Acid secreted by bacteria damages teeth. Alkaline mouthwash neutralizes the acid preventing it from damaging the teeth. A toothbrush removes leftover food stuck to the teeth. By removing iii) A iii) leftover food the bacteria have less food to feed on and therefore produce less harmful har mful acid. [6]
6 a) Once a) Once the food is ingested (enters the mouth) mechanical digestion takes place by the action of chewing. The enzyme amylase in i n the saliva starts to break down starch in the potato. The food is then swallowed and travels down the oesophagus and into the stomach where it is churned and mixed with gastric gastr ic juice. The juice contains the enzyme pepsin which begins the digestion of protein. Pepsin only works in acidic conditions. This is pro provided vided by the presence of acid in the stomach. When the food f ood finally leaves the stomach it passes into the duodenum, which is the first part of the small intestine. The pancreas secretes pancreatic juice, a mixture of enzymes and sodium hydrogen carbonate, into the small intestine. The sodium hydrogen carbonate neutralizes the acid coming from the stomach. This provides the cor rect pH envir environment onment for the enzymes to work. Amylase completes the work on any undigested starch and then the enzyme maltase acts on the maltose. [10]
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supplement s could make the athletes faster, stronger and bigger. b) i) These supplements Because of the immense pressure to succeed they sometimes try these things to give them an ‘edge’ ov over er other athletes. ii) I disagree with the practice. The reasons for this are that sometimes these supplements can cause major side effects and they give an unfair advantage to these athletes over those who are not taking the supplements. [4] The two teenagers need to have a diet high in energy. This is because c) The c) the teenagers are probably more active than their grandmother. They will also need more protein than their grandmother. This is because they are growing and require protein for this growth and development. The grandmother is not gro g rowing wing and devel developing, oping, therefore therefore she does not need as much protein. The teenagers also need a diet rich r ich in iron, especially the girl. This is because iron is needed for red blood cells. The girl g irl may be menstruating and needs the extra iron in her diet. [6] 7 a)
afferent (arriving) arteriole Bowman’s capsule proximal convoluted tubule
glomerulus, network of blood capillaries
distal convoluted tubule
efferent (leaving) arteriole
renal cortex
direction of blood flow
renal medulla descending limb of Henle
collecting duct, leading to the ureter
ascending limb of Henle
loop of Henle
The nephron is almost like a Buchner’s Buchner’s funnel. The first part, the Bowman’s capsule, is responsible for the ultra-filtration of the blood. As the blood goes through the glomerulus it is forced against the walls of the tiny capillaries. capillar ies. The substances that are small enough pass through the holes in the capillaries. The substances that get through pass down to the proximal pro ximal convoluted convoluted tubule where some of the substances are reabsorbed into the blood. These include all of the glucose, some water and some amino acids. Further down the tube is the loop of Henle where more water is reabsorbed into the blood. The rest of the filtrate makes m akes its way to the distal convoluted tubule where some salts and other impurities enter the filtrate from the surrounding tissue fluid. The filtrate then passes to the collecting duct where the final reabsorption of water takes place to adjust the concentration according to the amount of water in the blood. The urine is then sent to the bladder via the ureter. [10]
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[1] b) Juxtamedullary; cortical nephron. b) Juxtamedullary; The hypothalamus detects a low blood water level and signals the pituitary c) The c) gland to start secreting anti-diuretic anti-di uretic hormone. This causes the collecting duct to change its permeability to water. More water is reabsorbed back into the blood. This makes the urine ur ine more concentrated, smaller in volume and quite pungent. [3] Urine is dark in colour and is produced in small amounts. d) Urine d) [2] A diuretic causes the members of the team to lose a lot of water in their e) A e) urine. Even if the blood water levels are normal or low, the diuretic causes more water to remain in the filtrate of the nephron than usual. Thus, there will be less reabsorption of water at the convoluted tube. This will cause the players to become easily dehydrated. This will lead to poor performance of the players. [4]
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