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Secondary 4 Combined Science Biology Preliminary Examination Paper 5
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TuitionGoWhere Practice Paper - Combined Science Biology Secondary 4
TuitionGoWhere Secondary School (AI)
PRELIMINARY EXAMINATION - Version 5
Subject: Combined Science Biology (5087/5088) Level: Secondary 4 Paper: Biology Paper 2 (Structured & Free Response) Duration: 1 hour 15 minutes Total Marks: 65
Name: _________________________ Class: _________________________ Date: _________________________
Instructions to Candidates
- This paper consists of two sections: Section A and Section B.
- Answer all questions in Section A.
- Answer one question from Section B.
- 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 about 55 minutes on Section A and 20 minutes on Section B.
Section A: Structured Questions (50 marks)
Answer all questions in this section.
Question 1: Cell Structure and Function (8 marks)
(a) Figure 1.1 shows a diagram of a typical animal cell as seen under a light microscope.
(Assume a simple diagram of an animal cell with labels A, B, C, D pointing to: nucleus, cell membrane, cytoplasm, mitochondrion)
(i) Identify the structures labelled A and D. [2]
A: _________________________
D: _________________________
(ii) State one function of the structure labelled B. [1]
(iii) Explain why structure D is found in large numbers in muscle cells compared to skin cells. [2]
(b) Table 1.1 shows the number of mitochondria found in three different types of human cells.
Table 1.1
| Cell Type | Number of Mitochondria per Cell |
|---|---|
| Red blood cell | 0 |
| Skin cell | 200 |
| Heart muscle cell | 5000 |
(i) Explain why red blood cells have no mitochondria. [1]
(ii) Suggest a reason for the difference in the number of mitochondria between skin cells and heart muscle cells. [2]
Question 2: Movement of Substances (7 marks)
(a) Figure 2.1 shows a model cell made from dialysis tubing containing a starch solution, placed in a beaker of distilled water. The dialysis tubing is permeable to water and iodine but not to starch.
(Assume a diagram showing dialysis tubing in a beaker with iodine added to the water)
(i) After 30 minutes, the contents of the dialysis tubing turned blue-black. Explain this observation. [2]
(ii) Name the process by which iodine molecules entered the dialysis tubing. Explain your answer. [2]
Process: _________________________
Explanation: _________________________________________________________________________
(b) A student investigated the effect of temperature on the rate of diffusion of a dye through agar jelly. The results are shown in Table 2.1.
Table 2.1
| Temperature (°C) | Distance diffused by dye in 10 minutes (mm) |
|---|---|
| 10 | 3 |
| 20 | 5 |
| 30 | 8 |
| 40 | 12 |
| 50 | 15 |
(i) Describe the relationship between temperature and the distance diffused by the dye. [1]
(ii) Explain the effect of temperature on the rate of diffusion. [2]
Question 3: Enzymes and Biomolecules (8 marks)
(a) Figure 3.1 shows the effect of pH on the activity of two enzymes, P and Q, found in the human digestive system.
(Assume a graph showing two bell-shaped curves: Enzyme P with optimum at pH 2, Enzyme Q with optimum at pH 8)
(i) Identify the likely location in the digestive system where Enzyme P is most active. Explain your answer. [2]
(ii) Explain why Enzyme Q shows very low activity at pH 2. [2]
(b) A student carried out a food test on an unknown sample. The results are shown in Table 3.1.
Table 3.1
| Test | Observation |
|---|---|
| Benedict's test (heated) | Brick-red precipitate formed |
| Biuret test | Solution remained blue |
| Iodine test | Solution remained brown |
| Ethanol emulsion test | Cloudy white emulsion formed |
(i) Identify the biomolecules present in the unknown sample. [2]
(ii) Explain why the Biuret test gave a negative result. [1]
(iii) Name one function of the biomolecule detected by the ethanol emulsion test. [1]
Question 4: Photosynthesis and Plant Transport (9 marks)
(a) Write the word equation for photosynthesis. [1]
(b) A student investigated the effect of light intensity on the rate of photosynthesis in an aquatic plant. The results are shown in Table 4.1.
Table 4.1
| Distance of lamp from plant (cm) | Number of oxygen bubbles produced per minute |
|---|---|
| 10 | 45 |
| 20 | 32 |
| 30 | 20 |
| 40 | 10 |
| 50 | 2 |
(i) Describe the trend shown in Table 4.1. [1]
(ii) Explain why the number of oxygen bubbles decreases as the distance of the lamp increases. [2]
(iii) Suggest one other factor, apart from light intensity, that could limit the rate of photosynthesis in this investigation. [1]
(c) Figure 4.1 shows a cross-section of a leaf.
(Assume a diagram showing upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis, stomata)
(i) Describe and explain the distribution of chloroplasts in the palisade mesophyll and spongy mesophyll layers. [3]
(ii) State one function of the air spaces in the spongy mesophyll. [1]
Question 5: Human Transport System (9 marks)
(a) Figure 5.1 shows a diagram of the human heart.
(Assume a diagram of the heart with labels E, F, G, H pointing to: right atrium, left ventricle, aorta, vena cava)
(i) Identify the structures labelled F and G. [2]
F: _________________________
G: _________________________
(ii) Describe the function of the structure labelled F. [1]
(b) Table 5.1 shows the concentration of oxygen in blood at different locations in the circulatory system.
Table 5.1
| Location | Oxygen concentration (arbitrary units) |
|---|---|
| Pulmonary artery | 40 |
| Pulmonary vein | 95 |
| Aorta | 95 |
| Vena cava | 40 |
(i) Explain the difference in oxygen concentration between the pulmonary artery and the pulmonary vein. [2]
(ii) Explain why the oxygen concentration in the aorta is the same as in the pulmonary vein. [1]
(c) Describe in detail how a molecule of oxygen present in the air breathed into the lungs reaches a muscle cell in the leg. Name the structures involved. [3]
Question 6: Respiration and Gas Exchange (9 marks)
(a) State two differences between aerobic and anaerobic respiration in humans. [2]
(b) An athlete runs a 100-metre sprint. During the race, the athlete's muscles carry out anaerobic respiration.
(i) Name the product of anaerobic respiration that accumulates in the athlete's muscles. [1]
(ii) Explain why the athlete breathes heavily after completing the race. [2]
(c) Figure 6.1 shows the gaseous exchange at an alveolus.
(Assume a diagram showing an alveolus with a capillary, arrows showing oxygen moving into blood and carbon dioxide moving out)
(i) Name the process by which oxygen moves from the alveolus into the blood. [1]
(ii) Explain two features of the alveolus that make it efficient for gas exchange. [2]
(iii) State one reason why carbon dioxide moves from the blood into the alveolus. [1]
Section B: Free Response Question (15 marks)
Answer one question from this section. Write your answer on the lined pages provided.
Question 7: Cells, Transport, and Enzymes
(a) Describe the structure of the cell membrane and explain how it controls the movement of substances into and out of the cell. [6]
(b) Explain how enzymes speed up biochemical reactions, using the lock-and-key hypothesis. [4]
(c) A student investigated the effect of temperature on the activity of the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen. The student measured the volume of oxygen produced in 2 minutes at different temperatures. The results are shown in Table 7.1.
Table 7.1
| Temperature (°C) | Volume of oxygen produced (cm³) |
|---|---|
| 10 | 5 |
| 20 | 12 |
| 30 | 22 |
| 40 | 28 |
| 50 | 15 |
| 60 | 2 |
(i) Explain why the volume of oxygen produced increases from 10°C to 40°C. [2]
(ii) Explain why the volume of oxygen produced decreases from 40°C to 60°C. [2]
(iii) Suggest how the student could modify the investigation to obtain more reliable results. [1]
Question 8: Photosynthesis, Plant Transport, and Ecology
(a) Describe how the structure of a leaf is adapted for photosynthesis. [6]
(b) Explain how water and mineral salts are transported from the roots to the leaves of a plant. [4]
(c) Scientists are carrying out trials of 'carbon farming', where large masses of fast-growing plants are grown to absorb and store carbon dioxide from the atmosphere. The harvested plants are then used as biofuel.
(i) Using your knowledge of photosynthesis, explain how carbon farming could help reduce atmospheric carbon dioxide levels. [2]
(ii) Suggest two limitations of using carbon farming as a long-term solution to climate change. [2]
(iii) Explain why burning the harvested plants as biofuel may not reduce net carbon dioxide emissions. [1]
END OF PAPER
Answers
TuitionGoWhere Practice Paper - Combined Science Biology Secondary 4
PRELIMINARY EXAMINATION - Version 5: ANSWER KEY & MARKING SCHEME
Total Marks: 65
Section A: Structured Questions (50 marks)
Question 1: Cell Structure and Function (8 marks)
(a)(i) [2 marks]
- A: Nucleus [1]
- D: Mitochondrion [1]
(a)(ii) [1 mark]
- B (Cell membrane): Controls the movement of substances into and out of the cell / selectively permeable barrier / protects the cell contents. [1]
- Accept any one correct function.
(a)(iii) [2 marks]
- Muscle cells require more energy/ATP for contraction [1]
- Mitochondria are the site of aerobic respiration where ATP is produced [1]
- Award [1] for stating energy demand, [1] for linking to mitochondrial function.
(b)(i) [1 mark]
- Red blood cells lack a nucleus and other organelles / red blood cells are specialised for oxygen transport and do not carry out aerobic respiration / red blood cells obtain energy through anaerobic respiration only. [1]
(b)(ii) [2 marks]
- Heart muscle cells contract continuously and require more energy/ATP than skin cells [1]
- Therefore, heart muscle cells have more mitochondria to carry out more aerobic respiration to meet their higher energy demands [1]
- Award [1] for identifying difference in energy demand, [1] for linking to mitochondrial function.
Question 2: Movement of Substances (7 marks)
(a)(i) [2 marks]
- Iodine molecules diffused from the beaker into the dialysis tubing [1]
- Iodine reacted with starch inside the tubing to form a blue-black complex [1]
(a)(ii) [2 marks]
- Process: Diffusion [1]
- Explanation: Iodine molecules moved from a region of higher concentration (in the beaker) to a region of lower concentration (inside the dialysis tubing) down the concentration gradient / the dialysis tubing is permeable to iodine but not starch, so iodine can pass through [1]
(b)(i) [1 mark]
- As temperature increases, the distance diffused by the dye increases / there is a positive correlation between temperature and distance diffused. [1]
(b)(ii) [2 marks]
- At higher temperatures, molecules have more kinetic energy [1]
- Therefore, molecules move faster, increasing the rate of diffusion / dye molecules spread through the agar more quickly [1]
- Award [1] for kinetic energy, [1] for linking to rate of diffusion.
Question 3: Enzymes and Biomolecules (8 marks)
(a)(i) [2 marks]
- Location: Stomach [1]
- Explanation: Enzyme P has an optimum pH of 2, which matches the acidic environment of the stomach (due to hydrochloric acid) [1]
(a)(ii) [2 marks]
- Enzyme Q has an optimum pH of 8 (alkaline) [1]
- At pH 2, the acidic conditions cause the enzyme to denature / the shape of the active site changes, so the substrate can no longer bind / the enzyme loses its catalytic function [1]
- Award [1] for identifying pH mismatch, [1] for explaining denaturation.
(b)(i) [2 marks]
- Reducing sugar (glucose/fructose/maltose) — indicated by the brick-red precipitate with Benedict's test [1]
- Lipids (fats/oils) — indicated by the cloudy white emulsion with the ethanol emulsion test [1]
- Award [1] for each correct biomolecule identified with supporting evidence.
(b)(ii) [1 mark]
- The Biuret test detects proteins, and the sample did not contain proteins / the solution remained blue, indicating the absence of peptide bonds. [1]
(b)(iii) [1 mark]
- Any one correct function of lipids:
- Long-term energy storage
- Thermal insulation
- Protection of vital organs
- Component of cell membranes (phospholipids)
- Source of fat-soluble vitamins (A, D, E, K)
- Accept any one valid function.
Question 4: Photosynthesis and Plant Transport (9 marks)
(a) [1 mark]
- Carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll) [1]
- Accept the word equation with correct reactants and products. Conditions (light, chlorophyll) may be written above the arrow.
(b)(i) [1 mark]
- As the distance of the lamp from the plant increases, the number of oxygen bubbles produced per minute decreases / the rate of photosynthesis decreases with increasing distance. [1]
(b)(ii) [2 marks]
- As the distance increases, the light intensity reaching the plant decreases [1]
- Light is required for the light-dependent reactions of photosynthesis / light provides energy for photosynthesis / lower light intensity reduces the rate of photosynthesis, so less oxygen is produced [1]
(b)(iii) [1 mark]
- Any one correct limiting factor:
- Carbon dioxide concentration
- Temperature
- Availability of water
- Amount of chlorophyll
- Accept any one valid factor.
(c)(i) [3 marks]
- Palisade mesophyll: Contains many chloroplasts / chloroplasts are densely packed [1] because these cells are located near the upper epidermis and receive the most direct light for photosynthesis [1]
- Spongy mesophyll: Contains fewer chloroplasts [0.5] because these cells receive less light / are located deeper in the leaf / the primary function is gas exchange through large air spaces [0.5]
- Award [1] for palisade description, [1] for palisade explanation, [0.5] for spongy description, [0.5] for spongy explanation.
(c)(ii) [1 mark]
- Any one correct function:
- Allow diffusion of carbon dioxide and oxygen for photosynthesis and respiration
- Facilitate gas exchange between the leaf cells and the atmosphere
- Provide a large surface area for gas exchange
- Accept any one valid function.
Question 5: Human Transport System (9 marks)
(a)(i) [2 marks]
- F: Left ventricle [1]
- G: Aorta [1]
(a)(ii) [1 mark]
- The left ventricle pumps oxygenated blood to all parts of the body (except the lungs) via the aorta / the left ventricle has thick muscular walls to generate high pressure to pump blood throughout the systemic circulation. [1]
- Accept any one correct function.
(b)(i) [2 marks]
- The pulmonary artery carries deoxygenated blood from the heart to the lungs (low oxygen concentration) [1]
- In the lungs, gas exchange occurs at the alveoli: oxygen diffuses from the alveoli into the blood, so the pulmonary vein carries oxygenated blood back to the heart (high oxygen concentration) [1]
(b)(ii) [1 mark]
- The aorta receives oxygenated blood directly from the left ventricle, which has just received oxygenated blood from the pulmonary vein via the left atrium / there is no change in oxygen concentration as blood passes through the left side of the heart. [1]
(c) [3 marks]
- Pathway:
- Oxygen enters the lungs during inhalation and diffuses across the alveolar epithelium into the blood capillaries [1]
- Oxygen binds to haemoglobin in red blood cells and is transported via the pulmonary vein to the left atrium → left ventricle → aorta [1]
- Oxygenated blood travels through arteries and arterioles to capillaries in the leg muscle, where oxygen diffuses from the blood into the muscle cells [1]
- Award [1] for each major stage of the pathway. Must name at least three structures (e.g., alveoli, pulmonary vein, left atrium, left ventricle, aorta, capillaries).
Question 6: Respiration and Gas Exchange (9 marks)
(a) [2 marks]
- Any two correct differences:
- Aerobic respiration requires oxygen; anaerobic respiration does not require oxygen [1]
- Aerobic respiration produces carbon dioxide and water; anaerobic respiration produces lactic acid (in humans) [1]
- Aerobic respiration releases more energy/ATP (38 ATP per glucose); anaerobic respiration releases less energy/ATP (2 ATP per glucose) [1]
- Aerobic respiration occurs in the mitochondria; anaerobic respiration occurs in the cytoplasm [1]
- Award [1] for each correct difference. Accept any two.
(b)(i) [1 mark]
- Lactic acid [1]
(b)(ii) [2 marks]
- The athlete has built up an oxygen debt during the sprint [1]
- Heavy breathing provides extra oxygen to break down/oxidise the lactic acid accumulated in the muscles / to repay the oxygen debt / to convert lactic acid back to pyruvate or glucose in the liver [1]
(c)(i) [1 mark]
- Diffusion [1]
(c)(ii) [2 marks]
- Any two correct features with explanations:
- Thin walls (one cell thick): The alveolar epithelium and capillary endothelium are only one cell thick, providing a short diffusion distance for gases [1]
- Large surface area: The alveoli are numerous and highly folded, providing a large surface area for gas exchange [1]
- Moist surface: The alveolar surface is moist, allowing gases to dissolve before diffusing [1]
- Rich blood supply: The alveoli are surrounded by a dense network of capillaries, maintaining a steep concentration gradient for rapid diffusion [1]
- Award [1] for each correct feature with explanation. Accept any two.
(c)(iii) [1 mark]
- Carbon dioxide diffuses from the blood (higher concentration) into the alveolus (lower concentration) down its concentration gradient / carbon dioxide is a waste product of respiration and must be removed from the body. [1]
Section B: Free Response Question (15 marks)
Question 7: Cells, Transport, and Enzymes
(a) [6 marks]
- Structure of cell membrane (3 marks):
- The cell membrane is composed of a phospholipid bilayer [1]
- Phospholipids have hydrophilic (water-loving) heads facing outward and hydrophobic (water-fearing) tails facing inward [1]
- Proteins are embedded in the phospholipid bilayer (fluid mosaic model) / the membrane also contains cholesterol and glycoproteins [1]
- Control of movement (3 marks):
- The cell membrane is selectively permeable / partially permeable [1]
- Small, non-polar molecules (e.g., oxygen, carbon dioxide) can diffuse directly through the phospholipid bilayer [1]
- Larger or charged molecules (e.g., glucose, ions) require transport proteins (carrier proteins or channel proteins) to cross the membrane / active transport uses carrier proteins and ATP to move substances against the concentration gradient [1]
- Award marks for accurate description of structure and clear explanation of how structure relates to function.
(b) [4 marks]
- Lock-and-key hypothesis:
- The active site of an enzyme has a specific three-dimensional shape that is complementary to the shape of its specific substrate [1]
- The substrate fits into the active site like a key fits into a lock, forming an enzyme-substrate complex [1]
- This binding lowers the activation energy required for the reaction to occur [1]
- The reaction takes place, products are formed, and the products are released from the active site; the enzyme remains unchanged and can be reused [1]
- Award [1] for each key point. Accept diagrams if clearly labelled and explained.
(c)(i) [2 marks]
- As temperature increases from 10°C to 40°C, the kinetic energy of enzyme and substrate molecules increases [1]
- This increases the frequency of successful collisions between enzyme and substrate molecules / more enzyme-substrate complexes form per unit time, increasing the rate of reaction [1]
(c)(ii) [2 marks]
- Above 40°C (the optimum temperature), the enzyme begins to denature [1]
- The high temperature breaks the hydrogen bonds and other bonds maintaining the enzyme's tertiary structure / the active site changes shape, so the substrate can no longer bind / the enzyme loses its catalytic function [1]
(c)(iii) [1 mark]
- Any one correct suggestion:
- Repeat the investigation at each temperature and calculate the mean/average volume of oxygen produced
- Control other variables such as pH, enzyme concentration, or substrate concentration
- Use a water bath to maintain a constant temperature throughout each trial
- Accept any one valid suggestion for improving reliability.
Question 8: Photosynthesis, Plant Transport, and Ecology
(a) [6 marks]
- Leaf adaptations for photosynthesis:
- Large surface area: The leaf blade is broad and flat to capture maximum light energy [1]
- Thin structure: The leaf is thin, allowing carbon dioxide to diffuse quickly to photosynthetic cells and oxygen to diffuse out [1]
- Palisade mesophyll cells: These cells are elongated, tightly packed, and contain many chloroplasts; they are located near the upper epidermis to receive the most direct light [1]
- Chloroplasts: Contain chlorophyll, which absorbs light energy for photosynthesis [1]
- Stomata: Pores on the lower epidermis allow carbon dioxide to enter and oxygen to exit; guard cells regulate stomatal opening and closing [1]
- Network of veins (xylem and phloem): Xylem transports water to photosynthetic cells; phloem transports sugars away from the leaf [1]
- Award [1] for each correct adaptation with explanation. Accept any six valid points.
(b) [4 marks]
- Transport of water:
- Water enters root hair cells by osmosis from the soil [1]
- Water moves through the root cortex to the xylem vessels [1]
- Water is transported up the xylem through the stem to the leaves by transpiration pull (cohesion-tension theory) / transpiration creates a negative pressure that pulls water up the xylem [1]
- Transport of mineral salts:
- Mineral salts are absorbed by root hair cells by active transport (against the concentration gradient, requiring ATP) [0.5]
- Mineral salts are dissolved in water and transported up the xylem along with water to all parts of the plant [0.5]
- Award [1] for each key point. Must cover both water and mineral transport.
(c)(i) [2 marks]
- Plants absorb carbon dioxide from the atmosphere during photosynthesis [1]
- Carbon dioxide is converted into glucose and other organic compounds, which are stored in the plant biomass (carbon sequestration) / growing large masses of plants removes significant amounts of carbon dioxide from the atmosphere [1]
(c)(ii) [2 marks]
- Any two correct limitations:
- Land used for carbon farming may compete with land needed for food production / may lead to deforestation or loss of biodiversity [1]
- When plants die and decompose, or are burned, the stored carbon is released back into the atmosphere as carbon dioxide [1]
- Carbon farming requires large amounts of water, fertilisers, and other resources, which may have their own environmental impacts [1]
- The rate of carbon dioxide absorption may decrease as plants mature or if environmental conditions are unfavourable [1]
- Accept any two valid limitations.
(c)(iii) [1 mark]
- Burning the plants releases the same amount of carbon dioxide that the plants absorbed during photosynthesis / there is no net removal of carbon dioxide from the atmosphere if the plants are burned / the carbon cycle remains balanced (carbon neutral) rather than achieving net carbon sequestration. [1]
END OF ANSWER KEY