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Secondary 4 Pure Biology Cells Biomolecules Quiz
Free Sec 4 Pure Biology Cells Biomolecules quiz, Qwen3.6 AI version, with questions, answers, and O Level-style practice for Singapore students.
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Secondary 4 Pure Biology Quiz - Cells Biomolecules: Answer Key
1. (a) Rough Endoplasmic Reticulum (Rough ER) [1] (b) Protein synthesis [1] (c) Muscle cells require more energy for contraction [1]. Mitochondria are the site of aerobic respiration which releases energy [1].
2. (a) Plant cell [1] (b) Provides structural support / Maintains cell shape / Prevents bursting due to osmotic pressure [1] (c) Cell Y is an animal cell (or non-photosynthetic cell) [1]. Chloroplasts are required for photosynthesis, which animal cells do not perform [1].
3. (a) Haemoglobin [1] (b) Increases surface area to volume ratio [1], allowing for faster diffusion of oxygen into and out of the cell [1]. (c) Provides more space for haemoglobin [1], allowing the cell to carry more oxygen [1].
4. (a) Osmosis [1] (b) The long projection increases the surface area [1] for absorption, allowing water to enter the cell at a faster rate [1].
5.
- Nucleus: Absent (No true nucleus) / Present (True nucleus with membrane) [1]
- Ribosomes: Smaller (70S) / Larger (80S) [1] (Note: Accept "Present" for both if distinction not made, but distinction is preferred)
- Mitochondria: Absent / Present [1]
6. Diffusion is the net movement [1] of particles from a region of higher concentration to a region of lower concentration [1], down a concentration gradient.
7. (a) Volume increases / Tubing swells [1] (b) The sugar solution inside has a lower water potential than the distilled water outside [1]. Water moves by osmosis [1] from the region of higher water potential (outside) to lower water potential (inside) through the partially permeable membrane [1].
8. (a) The movement of substances from a region of lower concentration to a region of higher concentration [1], against a concentration gradient, using energy [1]. (b) 1. Energy (ATP) [1] 2. Carrier proteins [1] (c) Mitochondria produce energy (ATP) via respiration [1]. Active transport requires energy to pump ions against the gradient [1].
9. (a) Solution P [1] (b) Solution R has a lower water potential than the potato cell sap [1]. Water moves out of the potato cells by osmosis [1]. The cells lose turgor pressure and become flaccid/plasmolysed [1].
10. (a) Active transport [1] (b) Diffusion only moves substances down a concentration gradient (high to low) [1]. Here, ions are moving from low concentration (soil) to high concentration (cell), which is against the gradient [1].
11.
- Starch Building Block: Glucose [1]
- Starch Test: Iodine Solution [1]
- Protein Building Block: Amino Acids [1]
- Fat Test: Ethanol (Emulsion test) [1]
12. Add Benedict’s solution to the food sample [1]. Heat the mixture in a water bath (boil) [1]. A positive result is indicated by a colour change from blue to green/yellow/orange/brick-red precipitate [1]. The specific colour depends on the amount of sugar [1].
13. (a) A substance that speeds up the rate of a chemical reaction [1] without being used up or changed in the process [1]. (b) The substrate has a specific shape that fits into the enzyme’s active site [1], like a key fits into a lock [1]. This forms an enzyme-substrate complex [1]. The reaction occurs, and products are released, leaving the enzyme unchanged [1].
14. (a) As temperature increases, kinetic energy of enzyme and substrate molecules increases [1]. This leads to more frequent collisions [1] and more enzyme-substrate complexes forming per unit time [1]. (b) High temperature breaks the bonds holding the enzyme structure together [1]. The enzyme denatures [1]. The shape of the active site changes [1]. The substrate can no longer fit into the active site [1]. (Any 3)
15. (a) pH 2 (Acidic) [1] (b) Pepsin will denature [1]. The high pH (alkaline) changes the shape of the active site [1]. Pepsin can no longer bind to its substrate/protein [1].
16. (a) Digestion of waste materials / Breakdown of worn-out organelles / Digestion of pathogens [1] (b) Waste materials/organelles will accumulate in the cell [1]. This may lead to cell dysfunction or death [1].
17. (a) All active sites of the enzyme molecules are occupied/saturated [1]. Adding more substrate cannot increase the rate because there are no free active sites available [1]. The rate is limited by enzyme concentration [1]. (b) Increase the enzyme concentration [1].
18. Mitochondria are the site of aerobic respiration [1]. Cyanide stops ATP production [1]. Cells require ATP for essential life processes (e.g., active transport, synthesis) [1]. Without energy, cells cannot function and die [1]. (Any 3)
19. (a) Glucose [1] (b) Glucose molecules are small enough to pass through the pores of the partially permeable membrane [1]. Starch molecules are large polysaccharides [1] and are too big to pass through the membrane pores [1].
20. Enzymes have a specific 3D shape [1]. The active site has a unique shape complementary to only one specific substrate [1]. Only the correct substrate can fit into the active site to form an enzyme-substrate complex [1].