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Secondary 3 Biology Cells Biomolecules Quiz
Free Sec 3 Biology Cells Biomolecules quiz, DeepSeek Exam version, with questions, answers, and O Level-style practice for Singapore students.
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Secondary 3 Biology Quiz - Cells Biomolecules - ANSWER KEY
Total Marks: 40
Section A: Multiple Choice (5 marks)
1. D - Rough endoplasmic reticulum [1] Radioactive amino acids are incorporated into proteins at ribosomes on the RER. The RER is the first organelle in the protein synthesis pathway.
2. C - A tissue in an organ [1] A group of similar cells performing the same function (producing insulin) is a tissue. The pancreas is the organ.
3. C - Golgi body – modification and packaging of proteins [1] Golgi body modifies proteins and packages them into vesicles for secretion.
4. B - A plant leaf [1] Cell wall, chloroplasts, and large central vacuole are characteristic of plant cells.
5. C - Enzymes lower the activation energy of a reaction [1] Enzymes are biological catalysts that lower activation energy; they are not used up, are specific, and denature at high temperatures.
Section B: Short Answer (10 marks)
6. Any two differences: [2]
- Plant cell has a cell wall; animal cell does not.
- Plant cell has chloroplasts; animal cell does not.
- Plant cell has a large central vacuole; animal cell has small, temporary vacuoles (if present).
- Plant cell has a fixed/regular shape; animal cell has an irregular shape. (Award 1 mark each for any two correct differences.)
7. (a) Structure 4 (Golgi body) [1] (b) Structure 3 (mitochondrion) is the site of aerobic respiration / produces energy (ATP) for the cell. [1]
8. Red blood cells do not have a nucleus to provide more space for haemoglobin [1], which enables them to carry more oxygen for transport around the body [1].
9. Osmosis is the net movement of water molecules [1] from a region of higher water potential to a region of lower water potential through a partially permeable membrane [1].
10. Any two factors: [2]
- Temperature
- pH
- Substrate concentration
- Enzyme concentration (Award 1 mark each for any two correct factors.)
Section C: Structured Response (15 marks)
11. (a) Cell: P (nerve cell) [1] Explanation: The nerve cell has a long axon which allows rapid transmission of electrical impulses/signals over long distances [1].
(b) Cell: S (epithelial cell) [1] Explanation: The epithelial cell has microvilli which increase the surface area for absorption of nutrients [1].
12. (a) Reducing sugars / maltose / glucose [1] Explanation: Amylase breaks down starch into reducing sugars (maltose). These are small molecules that can pass through the Visking tubing into the surrounding water [1].
(b) Starch molecules are too large to pass through the pores of the Visking tubing [1]. The Visking tubing acts as a partially permeable membrane that only allows small molecules to pass through [1].
13. Root hair cell adaptations (award up to 4 marks):
- Long, narrow extension/projection – increases surface area for absorption of water and mineral ions [1]
- Thin cell wall – reduces the diffusion distance for water and mineral ions [1]
- Large number of mitochondria – provides energy (ATP) for active transport of mineral ions against the concentration gradient [1]
- Cell membrane contains carrier proteins – for active transport of mineral ions [1]
- No chloroplasts – as root hair cells are underground and do not photosynthesise [1] (Award 1 mark for each correct adaptation with explanation, up to 4 marks.)
14. At pH 8, the enzyme would have very low or no activity / would be denatured [1]. Explanation: The enzyme extracted from the stomach works best at pH 2 (acidic conditions). At pH 8 (alkaline conditions), the shape of the active site changes [1], so the substrate can no longer fit into the active site (lock-and-key model disrupted). The enzyme is denatured [1].
15. Mitochondria and chloroplasts comparison: [3]
- Mitochondria are the site of aerobic respiration; chloroplasts are the site of photosynthesis [1].
- Both have a double membrane [1].
- Mitochondria have cristae (folded inner membrane); chloroplasts have thylakoids/grana [1]. (Award 1 mark for each correct point of comparison, up to 3 marks.)
Section D: Data-Based Question (10 marks)
16. (a) Graph: [4]
- Correct axes labels: x-axis "Temperature (°C)", y-axis "Rate of reaction (arbitrary units)" [1]
- Appropriate scales on both axes [1]
- All 6 points plotted accurately [1]
- Points joined with a smooth curve (not straight lines) [1]
(b) As temperature increases from 10°C to 40°C, the rate of reaction increases [1]. This is because the enzyme and substrate molecules have more kinetic energy, so they move faster and collide more frequently, increasing the chance of successful enzyme-substrate complex formation [1].
(c) Between 50°C and 60°C, the rate of reaction decreases sharply because the enzyme is denatured [1]. The high temperature breaks the bonds that maintain the three-dimensional shape of the enzyme, changing the shape of the active site so the substrate can no longer bind [1].
(d) 40°C [1]
(e) The rate of reaction at 70°C would be 0 (or close to 0) [1] because the enzyme would be completely denatured and unable to catalyse the reaction.
17. (a) Phospholipid / phospholipid molecule [1] (b) The protein channel allows specific molecules/ions to pass through the membrane / facilitates diffusion of substances across the membrane [1].
18. The concentrated sugar solution has a lower water potential than the potato cells [1]. Water moves out of the potato cells by osmosis, causing the cells to become plasmolysed/flaccid, so the potato becomes soft [1].
19. A plant cell has a strong, rigid cell wall that prevents it from bursting [1]. An animal cell lacks a cell wall, so in a hypotonic solution, water enters by osmosis and the cell swells and may burst (lyse) [1].
20. The lock-and-key hypothesis states that the active site of an enzyme has a specific shape that is complementary to the shape of the substrate [1]. The substrate fits into the active site like a key fits into a lock, forming an enzyme-substrate complex, and the reaction takes place [1].
END OF ANSWER KEY