Secondary 1 Science Life Sciences Quiz

Secondary 1 Science Quiz - Life Sciences: Answer Key

Total Marks: 40

Section A: Multiple Choice (Questions 1–5)

Marks: 5 (1 mark each)

1. C) Photosynthesis [1]

Teaching note: The seven characteristics of living things are: movement, respiration, sensitivity, growth, reproduction, excretion, and nutrition (MRS GREN). Photosynthesis is a process used by plants to achieve nutrition—it is not itself a universal characteristic of all living things. Animals, for example, do not perform photosynthesis but are still living.

2. D) Storing cell sap and helping maintain cell shape [1]

Teaching note: The leader line points to the vacuole, the large central structure in a plant cell. The vacuole contains cell sap (a solution of salts, sugars, and pigments) and maintains turgor pressure against the cell wall, keeping the cell rigid. Option A describes the cell membrane; B describes mitochondria; C describes the nucleus.

3. B) Boil the leaf in ethanol to remove chlorophyll [1]

Teaching note: Chlorophyll is the green pigment that masks the colour change when iodine (yellow-brown) reacts with starch (blue-black). The correct sequence is: boil water → place leaf in boiling water (kills cell and breaks cell walls) → boil leaf in ethanol (removes chlorophyll) → rinse in water → add iodine solution.

4. C) Large intestine [1]

Teaching note: While the small intestine absorbs most digested nutrients (glucose, amino acids, fatty acids, vitamins, minerals), the large intestine primarily absorbs water and mineral salts, converting liquid chyme into solid faeces. The stomach mainly digests; the oesophagus only transports.

5. B) X = Reptiles, Y = Birds, Z = Amphibians [1]

Teaching note:

• Reptiles (X): cold-blooded, scales, lay eggs on land with leathery or hard shells
• Birds (Y): warm-blooded, feathers, lay hard-shelled eggs
• Amphibians (Z): cold-blooded, moist skin, lay eggs in water (no shells, would dry out)

Fish have fins/scales but are fully aquatic; mammals have hair/fur and typically give live birth.

Section B: Short Answer (Questions 6–15)

Marks: 22

6. Any two from: [2]

• Has a cell wall (animals do not)
• Has chloroplasts for photosynthesis (animals do not)
• Has a large central vacuole (animals have small or no vacuoles)
• Often has a more regular/rectangular shape due to cell wall

Marking: 1 mark per valid difference; must state presence in plant and absence in animal (or vice versa) for full credit.

7. Photosynthesis [1]

Teaching note: From Greek photo- (light) + synthesis (putting together). The word equation: carbon dioxide + water → glucose + oxygen (in the presence of light and chlorophyll).

8. (a) Y = Left ventricle [1]

(b) Chamber W is the right ventricle, which pumps blood to the lungs (pulmonary circulation) only. Chamber Z is the left atrium, which receives oxygenated blood from the lungs and passes it to the left ventricle. The right ventricle has a thicker wall than the left atrium because the atrium only needs to pump blood a short distance into the ventricle (low pressure), while the ventricle must pump blood out of the heart to the lungs or body (higher pressure needed). [2]

Alternative accepted answer: If student identifies W as left ventricle and Z as right atrium (depending on labeling variation), then: W pumps blood to the entire body (systemic circulation) so has the thickest wall of all; Z (right atrium) only receives blood from the vena cava.

Marking note: Accept either interpretation based on standard heart diagrams. The key is explaining wall thickness in relation to pumping distance/pressure required.

9.

Marking: 1 mark per correct row. For starch, accept "salivary amylase" or "pancreatic amylase"; end product can be maltose (intermediate) or glucose (final after maltase action).

10. Any two from: [2]

• Long length (approximately 6–7 m in adults) provides large surface area for absorption
• Villi and microvilli lining the inner surface greatly increase surface area
• Thin wall (one cell thick/epithelium) allows short diffusion distance for nutrients
• Rich blood supply (capillaries) maintains concentration gradient by removing absorbed nutrients quickly
• Lacteals present for fat absorption

Marking: 1 mark per valid adaptation with explanation; "large surface area" alone insufficient without mention of villi/microvilli or length.

11. (a) Carbon dioxide concentration [1] (or "temperature" if interpreted differently, but most likely CO₂ at this stage)

Revised more likely answer: At the point where curve first plateaus, light intensity is no longer limiting—another factor limits rate. Given only light and temperature are variables shown, the limiting factor is most likely carbon dioxide concentration (usually the next limiting factor in standard experiments). Accept "carbon dioxide" or "CO₂ concentration."

(b) Curve B is at 30°C, which is closer to the optimum temperature for enzyme activity in photosynthesis. At 20°C (Curve A), enzyme activity is lower, so the maximum rate of photosynthesis is reduced. Higher temperature increases kinetic energy of molecules and enzyme activity up to optimum. [2]

Marking: Must mention enzymes (or "chemical reactions") and optimum temperature concept for 2 marks.

12. Fish use gills for gas exchange; water flows over the gills and dissolved oxygen is extracted. Mammals use lungs; air is breathed in and oxygen diffuses across alveoli into blood. [2]

Alternative valid points: Fish have a two-way flow system (water enters and exits same path); mammals have a tidal breathing system (air in and out same route) or more efficiently described as airflow through dead-end sacs. Accept any clear structural-functional comparison.

13.

• Exposed leaf (in light): Tests positive for starch (blue-black with iodine) [1]
• Covered leaf (in darkness): Tests negative for starch (iodine remains brown/yellow) [1]
• Explanation: The de-starching period in darkness removes stored starch. Only the exposed leaf can perform photosynthesis using light energy to produce glucose, which is converted to starch for storage. The foil-covered leaf receives no light, so no photosynthesis occurs and no starch is produced. [1]

Marking: 1 mark for each result; 1 mark for explanation linking light to photosynthesis to starch production.

14. (a) Palisade mesophyll (or "palisade layer") [1]

(b) This layer is closest to the upper surface of the leaf where light intensity is greatest. The cells are column-shaped and tightly packed with many chloroplasts to maximise light absorption for photosynthesis. [2]

Marking: 1 mark for position/arrangement; 1 mark for function (maximise light absorption).

15. Any two from: [2]

• Increase carbon dioxide concentration (add CO₂ generators or ventilate)
• Increase light intensity (use artificial lighting, especially in winter)
• Maintain optimum temperature (use heating/cooling systems)
• Add mineral fertilisers (especially nitrogen, magnesium for chlorophyll; phosphorus, potassium)

Marking: Must relate to factor affecting photosynthesis rate. Generic "add fertiliser" insufficient without linking to photosynthesis (e.g., magnesium for chlorophyll).

Section C: Structured Response (Questions 16–20)

Marks: 13

16. (a) Tube A is in bright light, so the plant can perform photosynthesis. This process produces oxygen gas as a by-product, seen as bubbles. Tube B is in darkness, so no photosynthesis occurs and no oxygen is produced. [2]

Marking: 1 mark for linking light to photosynthesis; 1 mark for oxygen production (not just "bubbles"—must identify process).

(b) The gas is oxygen. [1] Test: Place a glowing splint into the collected gas; it will relights/rekindles in the presence of oxygen. [1]

17. (a) Food P [1] (reducing sugar present, starch absent—Benedict's positive, iodine negative)

(b) Food S [1] (protein → Biuret purple; fat → translucent stain)

(c) (i) Brick red / orange-red precipitate (when heated) [1] (ii) White emulsion forms (or "cloudy white layer"), OR translucent spot on brown paper [1]

18. (a) W = Small intestine (duodenum/ileum region); Y = Large intestine (colon/rectum region) [2]

Note: Based on standard diagram interpretation where W points to the narrow tube immediately after stomach (duodenum start), X is the main coiled small intestine, Y is large intestine, Z is anus.

(b) The small intestine (X) has: [2]

• Villi that increase surface area enormously
• Thin walls (one cell thick) for short diffusion distance
• Rich blood supply in villi to maintain concentration gradient
• Microvilli on epithelial cells for further surface area increase

Marking: 2 marks for two valid adaptations with explanations; 1 mark for two adaptations without explanation.

19. (a) At 37°C (body temperature), amylase is at or near its optimum temperature. The enzyme works efficiently to break down starch into maltose, so no starch remains and the iodine test stays brown (negative result). [2]

Marking: 1 mark for optimum temperature; 1 mark for starch broken down/no starch detected.

(b) At 0°C: Temperature is too low; enzyme molecules and substrate have insufficient kinetic energy—fewer successful collisions occur, reaction rate very slow/enzyme essentially inactive. Not denatured, just inactive. [1]

At 80°C: Temperature is too high; the enzyme is denatured—the active site changes shape permanently due to breaking of bonds in the protein structure. Substrate can no longer fit. [1]

Marking: Must distinguish between low temperature (slow/inactive, reversible) and high temperature (denatured, permanent damage).

20. (a) Phytoplankton [1]

(b) Energy is lost between trophic levels due to: [2]

• Respiration (metabolic processes release energy as heat)
• Movement and other life processes
• Heat loss to the environment
• Incomplete digestion (not all organism is eaten or absorbed)
• Excretion of waste materials

Marking: 1 mark for respiration/heat loss; 1 mark for any other valid reason.

(c) Short-term predictions: [2]

• Large fish population increases: Fewer sharks to prey on them, so mortality decreases
• Small fish population decreases: More large fish surviving means more predation pressure on small fish

OR alternative valid prediction with explanation.

Marking: 1 mark for each population trend with correct explanation linked to shark removal. Must show understanding of predator-prey dynamics.

END OF ANSWER KEY