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O Level Biology Practice Paper 2
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TuitionGoWhere Practice Paper - Biology O-Level
TuitionGoWhere Practice Paper (AI)
Subject: Biology
Level: O-Level (6093)
Paper: Practice Paper — Version 2 of 5
Duration: 1 hour 45 minutes
Total Marks: 80
Name: _________________________
Class: _________________________
Date: _________________________
Instructions to Candidates
- This paper consists of three sections: Section A, Section B, and Section C.
- Answer all questions in Section A and Section B.
- In Section C, answer either Question 11 or Question 12.
- Write your answers in the spaces provided.
- The number of marks is given in brackets [ ] at the end of each question or part question.
- You are advised to spend no more than 40 minutes on Section A, 35 minutes on Section B, and 30 minutes on Section C.
Section A: Structured Questions (30 marks)
Answer all questions in this section.
1. Fig. 1.1 shows an electron micrograph of an animal cell.
(a) Identify the organelles labelled P and Q. [2]
P: _________________________
Q: _________________________
(b) Organelle P is involved in the synthesis and transport of proteins. Explain how its structure is adapted for this function. [2]
(c) Organelle Q is the site of aerobic respiration. State one structural feature of organelle Q that increases the efficiency of this process and explain your answer. [2]
[Total: 6 marks]
2. A student investigated the effect of different concentrations of sucrose solution on potato strips. Five potato strips of equal length were placed in sucrose solutions of different concentrations for 30 minutes. The results are shown in Table 2.1.
Table 2.1
| Concentration of sucrose solution (mol/dm³) | Final length of potato strip (mm) | Change in length (mm) |
|---|---|---|
| 0.0 (distilled water) | 56 | +6 |
| 0.2 | 53 | +3 |
| 0.4 | 50 | 0 |
| 0.6 | 47 | –3 |
| 0.8 | 44 | –6 |
(a) State the initial length of each potato strip. [1]
(b) Explain why the potato strip in distilled water increased in length. [3]
(c) The potato strip in 0.4 mol/dm³ sucrose solution showed no change in length. Explain what this indicates about the water potential of the sucrose solution relative to the cell sap of the potato cells. [2]
[Total: 6 marks]
3. Fig. 3.1 shows the human digestive system.
(a) Name the organs labelled A, B, and C. [3]
A: _________________________
B: _________________________
C: _________________________
(b) Describe the role of bile in the digestion of fats. [2]
(c) The enzyme lipase digests fats into fatty acids and glycerol. Explain why lipase cannot digest starch. [2]
[Total: 7 marks]
4. Fig. 4.1 shows a diagram of the human heart.
(a) Name the blood vessels labelled X and Y. [2]
X: _________________________
Y: _________________________
(b) Explain why the wall of the left ventricle is thicker than the wall of the right ventricle. [2]
(c) Describe the role of the valves in the heart. [2]
[Total: 6 marks]
5. A student set up an experiment to investigate the effect of temperature on the activity of the enzyme amylase. Amylase was added to a starch solution at different temperatures, and the time taken for the starch to be completely digested was recorded. The results are shown in Table 5.1.
Table 5.1
| Temperature (°C) | Time taken for starch digestion (minutes) |
|---|---|
| 10 | 12.0 |
| 20 | 6.5 |
| 30 | 3.0 |
| 40 | 1.5 |
| 50 | 4.0 |
| 60 | No digestion observed |
(a) Explain why the time taken for starch digestion decreases as temperature increases from 10 °C to 40 °C. [2]
(b) Explain why no digestion was observed at 60 °C. [2]
(c) State one variable that must be kept constant in this experiment to ensure a fair test. [1]
[Total: 5 marks]
Section B: Free-Response Questions (30 marks)
Answer all questions in this section.
6. Describe the double circulation of blood in the human circulatory system. In your answer, name the chambers of the heart and the main blood vessels involved. [6]
[Total: 6 marks]
7. Explain how the structure of a villus in the small intestine is adapted for the absorption of digested food. [6]
[Total: 6 marks]
8. Describe the process of aerobic respiration in humans. In your answer, state where it occurs, the raw materials required, the products formed, and the importance of this process to living organisms. [6]
[Total: 6 marks]
9. A person eats a meal rich in carbohydrates. Describe how the body regulates blood glucose concentration after this meal. In your answer, name the hormones and organs involved. [6]
[Total: 6 marks]
10. Describe the pathway taken by a molecule of oxygen from the atmosphere to a respiring muscle cell in the leg. In your answer, name the structures through which the oxygen passes and explain how it is transported. [6]
[Total: 6 marks]
Section C: Data-Based / Extended Response (20 marks)
Answer either Question 11 or Question 12.
11. Fig. 11.1 shows the rate of photosynthesis of a plant at different light intensities and at two different carbon dioxide concentrations.
Table 11.1
| Light intensity (arbitrary units) | Rate of photosynthesis at 0.04% CO₂ (cm³ O₂ produced per hour) | Rate of photosynthesis at 0.12% CO₂ (cm³ O₂ produced per hour) |
|---|---|---|
| 0 | 0 | 0 |
| 2 | 10 | 18 |
| 4 | 20 | 36 |
| 6 | 30 | 54 |
| 8 | 35 | 70 |
| 10 | 35 | 80 |
| 12 | 35 | 80 |
(a) Using the data in Table 11.1, describe the effect of light intensity on the rate of photosynthesis at 0.04% CO₂. [3]
(b) Explain why the rate of photosynthesis at 0.04% CO₂ does not increase beyond a light intensity of 8 arbitrary units. [3]
(c) Compare the rate of photosynthesis at the two carbon dioxide concentrations. Explain the difference. [4]
(d) Describe how you would test a leaf to show that starch has been produced by photosynthesis. [5]
(e) Explain why photosynthesis is important for life on Earth. [5]
[Total: 20 marks]
OR
12. Fig. 12.1 shows the changes in the thickness of the uterine lining during a 28-day menstrual cycle.
Table 12.1
| Day of cycle | Thickness of uterine lining (mm) |
|---|---|
| 1 | 2 |
| 5 | 2 |
| 9 | 4 |
| 14 | 6 |
| 19 | 8 |
| 23 | 8 |
| 28 | 2 |
(a) Describe the changes in the thickness of the uterine lining during the menstrual cycle shown in Table 12.1. [3]
(b) Explain the role of oestrogen in the changes that occur between day 5 and day 14. [3]
(c) Explain the role of progesterone in the changes that occur between day 14 and day 23. [3]
(d) Explain why the thickness of the uterine lining decreases between day 23 and day 28. [3]
(e) Describe the process of fertilisation in humans and explain how the developing embryo is supported during the early stages of pregnancy. [8]
[Total: 20 marks]
END OF PAPER
Answers
TuitionGoWhere Practice Paper - Biology O-Level — Answer Key and Marking Scheme
Version 2 of 5
Section A: Structured Questions (30 marks)
1. Fig. 1.1 shows an electron micrograph of an animal cell.
(a) Identify the organelles labelled P and Q. [2]
- P: Rough endoplasmic reticulum (RER) [1]
- Q: Mitochondrion [1]
(b) Organelle P is involved in the synthesis and transport of proteins. Explain how its structure is adapted for this function. [2]
- The RER has ribosomes attached to its surface [1]; ribosomes are the site of protein synthesis, so the RER provides a surface where proteins can be synthesised and then transported through its internal channels/cisternae to other parts of the cell [1].
(c) Organelle Q is the site of aerobic respiration. State one structural feature of organelle Q that increases the efficiency of this process and explain your answer. [2]
- The inner membrane is highly folded into cristae [1]; this increases the surface area for the attachment of respiratory enzymes and electron carriers, allowing more ATP to be produced per unit time [1].
Total: 6 marks
2. A student investigated the effect of different concentrations of sucrose solution on potato strips.
(a) State the initial length of each potato strip. [1]
- 50 mm [1]
(b) Explain why the potato strip in distilled water increased in length. [3]
- Distilled water has a higher water potential than the cell sap of the potato cells [1]; water enters the potato cells by osmosis, from a region of higher water potential to a region of lower water potential, across the partially permeable cell membrane [1]; the cells become turgid, causing the potato strip to increase in length [1].
(c) The potato strip in 0.4 mol/dm³ sucrose solution showed no change in length. Explain what this indicates about the water potential of the sucrose solution relative to the cell sap of the potato cells. [2]
- The water potential of the 0.4 mol/dm³ sucrose solution is equal to the water potential of the cell sap [1]; therefore, there is no net movement of water into or out of the potato cells by osmosis [1].
Total: 6 marks
3. Fig. 3.1 shows the human digestive system.
(a) Name the organs labelled A, B, and C. [3]
- A: Stomach [1]
- B: Pancreas [1]
- C: Liver [1]
(b) Describe the role of bile in the digestion of fats. [2]
- Bile emulsifies fats [1]; it breaks large fat globules into smaller fat droplets, increasing the surface area for lipase action, which speeds up the digestion of fats [1].
(c) The enzyme lipase digests fats into fatty acids and glycerol. Explain why lipase cannot digest starch. [2]
- Enzymes are specific in action [1]; the active site of lipase has a specific three-dimensional shape that is complementary only to the shape of fat/lipid molecules (substrate), not to starch molecules, so starch cannot fit into the active site to form an enzyme-substrate complex [1].
Total: 7 marks
4. Fig. 4.1 shows a diagram of the human heart.
(a) Name the blood vessels labelled X and Y. [2]
- X: Aorta [1]
- Y: Pulmonary artery [1]
(b) Explain why the wall of the left ventricle is thicker than the wall of the right ventricle. [2]
- The left ventricle pumps blood to the entire body (systemic circulation), requiring higher pressure to overcome the resistance of the extensive capillary networks [1]; the right ventricle only pumps blood to the nearby lungs (pulmonary circulation), which requires lower pressure [1].
(c) Describe the role of the valves in the heart. [2]
- Valves prevent the backflow of blood [1]; they ensure that blood flows in one direction only — from atria to ventricles, and from ventricles to arteries [1].
Total: 6 marks
5. A student set up an experiment to investigate the effect of temperature on the activity of the enzyme amylase.
(a) Explain why the time taken for starch digestion decreases as temperature increases from 10 °C to 40 °C. [2]
- As temperature increases, the kinetic energy of the enzyme and substrate molecules increases [1]; this increases the frequency of effective collisions between enzyme and substrate molecules, so more enzyme-substrate complexes are formed per unit time, increasing the rate of reaction [1].
(b) Explain why no digestion was observed at 60 °C. [2]
- At 60 °C, the high temperature has denatured the amylase enzyme [1]; the three-dimensional shape of the active site has been permanently altered, so the starch substrate can no longer fit into the active site, and no enzyme-substrate complexes can be formed [1].
(c) State one variable that must be kept constant in this experiment to ensure a fair test. [1]
- Any one of: pH / enzyme concentration / substrate (starch) concentration / volume of enzyme solution / volume of starch solution [1].
Total: 5 marks
Section B: Free-Response Questions (30 marks)
6. Describe the double circulation of blood in the human circulatory system. In your answer, name the chambers of the heart and the main blood vessels involved. [6]
Marking scheme:
- Deoxygenated blood from the body enters the right atrium via the vena cava [1].
- Blood passes from the right atrium to the right ventricle, which pumps deoxygenated blood to the lungs via the pulmonary artery (pulmonary circulation) [1].
- In the lungs, gaseous exchange occurs: carbon dioxide diffuses out and oxygen diffuses into the blood [1].
- Oxygenated blood returns from the lungs to the left atrium via the pulmonary vein [1].
- Blood passes from the left atrium to the left ventricle, which pumps oxygenated blood to the rest of the body via the aorta (systemic circulation) [1].
- The double circulation ensures that oxygenated and deoxygenated blood are kept separate, maintaining a steep concentration gradient for efficient oxygen delivery to respiring tissues [1].
Total: 6 marks
7. Explain how the structure of a villus in the small intestine is adapted for the absorption of digested food. [6]
Marking scheme:
- The villus has a large surface area due to its finger-like projections, increasing the rate of absorption of digested food [1].
- The epithelium of the villus is one cell thick, providing a short diffusion distance for absorbed nutrients [1].
- The epithelial cells have microvilli on their surface, further increasing the surface area for absorption [1].
- The villus contains a dense network of blood capillaries, which rapidly transport absorbed glucose and amino acids away, maintaining a steep concentration gradient for continued absorption [1].
- The villus contains a lacteal (lymphatic vessel), which absorbs fatty acids and glycerol (products of fat digestion) and transports them away [1].
- The villus contains many mitochondria in the epithelial cells, providing ATP energy for active transport of nutrients against their concentration gradient [1].
Total: 6 marks
8. Describe the process of aerobic respiration in humans. In your answer, state where it occurs, the raw materials required, the products formed, and the importance of this process to living organisms. [6]
Marking scheme:
- Aerobic respiration occurs in the mitochondria of cells [1].
- The raw materials required are glucose and oxygen [1].
- Glucose is completely oxidised/broken down to release energy [1].
- The products formed are carbon dioxide, water, and a large amount of energy (ATP) [1].
- The word equation: Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP) [1].
- Importance: The energy (ATP) released is used for cellular activities such as muscle contraction, active transport, cell division, growth, and maintaining body temperature [1].
Total: 6 marks
9. A person eats a meal rich in carbohydrates. Describe how the body regulates blood glucose concentration after this meal. In your answer, name the hormones and organs involved. [6]
Marking scheme:
- After a carbohydrate-rich meal, digestion breaks down carbohydrates into glucose, which is absorbed into the bloodstream, causing blood glucose concentration to rise above normal levels [1].
- The rise in blood glucose concentration is detected by the pancreas (specifically the islets of Langerhans) [1].
- The pancreas secretes the hormone insulin into the bloodstream [1].
- Insulin stimulates the liver and muscle cells to take up glucose from the blood and convert it into glycogen for storage [1].
- Insulin also increases the permeability of cell membranes to glucose, allowing more glucose to enter cells for respiration [1].
- As a result, blood glucose concentration decreases back to normal levels (negative feedback/homeostasis) [1].
Total: 6 marks
10. Describe the pathway taken by a molecule of oxygen from the atmosphere to a respiring muscle cell in the leg. In your answer, name the structures through which the oxygen passes and explain how it is transported. [6]
Marking scheme:
- Oxygen enters the body through the nose/mouth and passes down the trachea [1].
- The trachea branches into two bronchi, which further divide into bronchioles, leading to the alveoli in the lungs [1].
- In the alveoli, oxygen diffuses across the thin alveolar wall and the capillary wall into the blood, down a concentration gradient [1].
- In the blood, oxygen binds to haemoglobin in red blood cells to form oxyhaemoglobin, which is how oxygen is transported [1].
- The oxygenated blood travels via the pulmonary vein to the left atrium, then to the left ventricle, and is pumped out through the aorta [1].
- The aorta branches into arteries, arterioles, and eventually capillaries that supply the leg muscle, where oxygen diffuses from the blood into the muscle cells for aerobic respiration [1].
Total: 6 marks
Section C: Data-Based / Extended Response (20 marks)
11. Fig. 11.1 shows the rate of photosynthesis of a plant at different light intensities and at two different carbon dioxide concentrations.
(a) Using the data in Table 11.1, describe the effect of light intensity on the rate of photosynthesis at 0.04% CO₂. [3]
Marking scheme:
- As light intensity increases from 0 to 6 arbitrary units, the rate of photosynthesis increases proportionally/steadily from 0 to 30 cm³ O₂ per hour [1].
- From 6 to 8 arbitrary units, the rate of photosynthesis continues to increase but at a slower rate, from 30 to 35 cm³ O₂ per hour [1].
- Beyond 8 arbitrary units (from 8 to 12 arbitrary units), the rate of photosynthesis remains constant at 35 cm³ O₂ per hour (a plateau is reached) [1].
(b) Explain why the rate of photosynthesis at 0.04% CO₂ does not increase beyond a light intensity of 8 arbitrary units. [3]
Marking scheme:
- Beyond a light intensity of 8 arbitrary units, light is no longer the limiting factor [1].
- Carbon dioxide concentration (0.04%) has become the limiting factor [1].
- The rate of photosynthesis cannot increase further because there is insufficient carbon dioxide available for the light-independent (Calvin cycle) reactions, regardless of how much light energy is available [1].
(c) Compare the rate of photosynthesis at the two carbon dioxide concentrations. Explain the difference. [4]
Marking scheme:
- At every light intensity above 0, the rate of photosynthesis at 0.12% CO₂ is higher than at 0.04% CO₂ [1].
- At 0.12% CO₂, the rate continues to increase up to a light intensity of 10 arbitrary units, reaching a higher maximum rate of 80 cm³ O₂ per hour, compared to 35 cm³ O₂ per hour at 0.04% CO₂ [1].
- The higher carbon dioxide concentration provides more substrate (CO₂) for the light-independent reactions of photosynthesis [1].
- With more CO₂ available, the enzymes involved in carbon fixation (e.g., RuBisCO) can work at a faster rate, producing more glucose and releasing more oxygen, as long as light intensity is not limiting [1].
(d) Describe how you would test a leaf to show that starch has been produced by photosynthesis. [5]
Marking scheme:
- Boil the leaf in water for about 2 minutes to kill the cells and stop all chemical reactions [1].
- Transfer the leaf to a boiling tube containing ethanol and place the boiling tube in a hot water bath to remove chlorophyll (decolourise the leaf) [1].
- Remove the leaf from the ethanol and rinse it in warm water to soften it [1].
- Spread the leaf flat on a white tile and add a few drops of iodine solution [1].
- If starch is present, the leaf will turn blue-black; the blue-black colour indicates that starch has been produced by photosynthesis [1].
(e) Explain why photosynthesis is important for life on Earth. [5]
Marking scheme:
- Photosynthesis converts light energy from the sun into chemical energy stored in glucose, which is the primary source of energy for almost all living organisms [1].
- Photosynthesis produces oxygen as a by-product, which is essential for aerobic respiration in most organisms, including humans [1].
- Photosynthesis removes carbon dioxide from the atmosphere, helping to regulate the Earth's climate and reduce the greenhouse effect [1].
- Photosynthesis is the basis of most food chains and food webs; plants (producers) are eaten by herbivores, which are in turn eaten by carnivores [1].
- Photosynthesis by plants and algae in oceans and forests acts as a carbon sink, storing carbon in biomass and helping to maintain the balance of atmospheric gases [1].
Total: 20 marks
OR
12. Fig. 12.1 shows the changes in the thickness of the uterine lining during a 28-day menstrual cycle.
(a) Describe the changes in the thickness of the uterine lining during the menstrual cycle shown in Table 12.1. [3]
Marking scheme:
- From day 1 to day 5, the uterine lining remains thin at 2 mm (menstruation) [1].
- From day 5 to day 19, the uterine lining gradually thickens from 2 mm to 8 mm [1].
- From day 19 to day 23, the thickness remains constant at 8 mm; then from day 23 to day 28, the lining decreases/thins from 8 mm back to 2 mm [1].
(b) Explain the role of oestrogen in the changes that occur between day 5 and day 14. [3]
Marking scheme:
- After menstruation, the pituitary gland secretes FSH (follicle-stimulating hormone), which stimulates the development of a follicle in the ovary [1].
- The developing follicle secretes oestrogen [1].
- Oestrogen stimulates the repair and thickening of the uterine lining (endometrium), preparing it for possible implantation of a fertilised egg [1].
(c) Explain the role of progesterone in the changes that occur between day 14 and day 23. [3]
Marking scheme:
- After ovulation (around day 14), the ruptured follicle develops into the corpus luteum [1].
- The corpus luteum secretes progesterone [1].
- Progesterone maintains and further thickens the uterine lining, making it spongy and rich in blood vessels, to prepare for the implantation of an embryo [1].
(d) Explain why the thickness of the uterine lining decreases between day 23 and day 28. [3]
Marking scheme:
- If fertilisation does not occur, the corpus luteum degenerates/breaks down [1].
- The degeneration of the corpus luteum causes a decrease in progesterone (and oestrogen) levels [1].
- Without progesterone to maintain it, the thickened uterine lining breaks down and is shed, resulting in menstruation [1].
(e) Describe the process of fertilisation in humans and explain how the developing embryo is supported during the early stages of pregnancy. [8]
Marking scheme:
- Fertilisation occurs when the nucleus of a sperm cell fuses with the nucleus of an egg cell (ovum) in the fallopian tube/oviduct, forming a zygote [1].
- The zygote undergoes repeated mitotic cell divisions as it travels down the fallopian tube towards the uterus, forming an embryo [1].
- The embryo develops into a blastocyst, which implants into the thickened uterine lining (endometrium) [1].
- After implantation, the embryo develops structures for support:
- The placenta develops from embryonic and maternal tissues, allowing exchange of substances between mother and fetus without mixing of blood [1].
- The placenta allows oxygen and nutrients (e.g., glucose, amino acids) to diffuse from the mother's blood into the fetal blood [1].
- The placenta allows waste products (e.g., carbon dioxide, urea) to diffuse from the fetal blood into the mother's blood for excretion [1].
- The umbilical cord connects the fetus to the placenta, containing blood vessels that transport substances to and from the fetus [1].
- The amniotic sac and amniotic fluid surround and protect the developing fetus, acting as a shock absorber and allowing movement [1].
Total: 20 marks
END OF ANSWER KEY