Primary 6 PSLE Science Weighted Assessment 1 (Term 1) Paper 2

TuitionGoWhere Practice Paper - Science Primary 6 PSLE

Answer Key & Marking Scheme Paper: WA1 (Version 2 of 5) Topic Focus: Diversity

Section A (28 marks)

1. (2)

   • Reasoning: Yeast reproduces by budding (asexual) and Hydra reproduces by budding (asexual). Ferns and Mosses reproduce by spores (often considered asexual in primary context regarding seeds/flowers, but strictly spores are distinct; however, Bacteria/Amoeba are asexual, so 3 is wrong. Rose/Hibiscus are sexual, so 4 is wrong. Fern/Moss do not have flowers/seeds, so 1 is wrong in the context of "sexual" usually implying seeds/flowers in primary syllabus, but technically spores are asexual reproduction methods in terms of gamete fusion visibility. However, Option 2 is the most clearly correct pair for asexual methods taught at P6: Budding). Correction: In P6, Ferns/Mosses are often grouped separately. Yeast/Hydra are classic asexual examples.

2. (2)

   • Reasoning: R has a backbone and fur, which are characteristics of mammals. Mammals give birth to young ones. P is an insect (6 legs), Q is an arachnid (no 6 legs, no backbone in this key logic? Wait, key says "Has backbone? No -> Has 6 legs?"). If Q has no backbone and not 6 legs, it could be a spider. Spiders do not have backbones. So (4) is false. P is insect, Q is not necessarily insect (could be spider). So (1) is false. S has backbone, no fur. Could be bird or reptile. Not all lay hard shells (some reptiles have leathery). But (2) is definitely true for mammals.

3. (3)

   • Reasoning: Frogs are food for snakes. If frogs decrease, snakes have less food. Snakes might eat more rabbits, but the direct impact on the next trophic level up (Eagle) is that their food source (Snake) might struggle or decrease eventually. However, the most immediate and direct effect in these questions is often on the predator of the removed species. If Frogs decrease, Snakes have less food, so Snake population may decrease. If Snakes decrease, Eagles have less food, so Eagle population decreases. Option 3 is the most logical downstream effect. Option 1 is wrong (Grasshoppers would increase). Option 2 is wrong (Snakes would decrease). Option 4 is wrong (Rabbits might decrease if Snakes eat more of them, but Eagle decrease is a more standard "energy flow" answer). Refinement: If Frogs decrease, Snakes lose a food source. Snake population decreases. Eagles eat Snakes. Eagle population decreases.

4. (2)

   • Reasoning: Thick, waxy skin (cuticle) reduces water loss through transpiration, which is crucial in dry environments.

5. (2)

   • Reasoning: X has flowers and seeds (Flowering Plant, e.g., Rose). Y has no flowers/seeds but has spores (Non-flowering, e.g., Fern). Z has no flowers but has seeds (Non-flowering seed plant, e.g., Pine Tree/Conifer).

6. (2)

   • Reasoning: The nucleus contains genetic material and controls cell activities. (1) is wrong (animal cells don't have cell walls). (3) is wrong (root cells don't have chloroplasts). (4) is wrong (plant cells are often larger due to vacuole).

7. (2)

   • Reasoning: Destarching ensures that any starch detected after the experiment was produced during the experiment, not stored from before.

8. (1)

   • Reasoning: Energy flows from the Sun to Producers (plants), then to Consumers (animals), and finally to Decomposers.

9. (2)

   • Reasoning: The larva (caterpillar) stage is the main feeding stage where it grows rapidly and stores energy for the pupal and adult stages.

10. (3)

    • Reasoning: Melting of ice is a change of state (solid to liquid) without forming a new substance. The others are chemical changes.

11. (3)

    • Reasoning: Fat acts as an insulator to reduce heat loss to the cold environment.

12. (2)

    • Reasoning: Bees get nectar (food) and flowers get pollinated (reproduction). Both benefit. (1) is parasitic. (3) is predator-prey. (4) is parasitic.

13. (3)

    • Reasoning: In predator-prey graphs, an increase in predators (A) leads to a decrease in prey (B) due to predation. The graph shows A peaking after B, and B dropping as A rises.

14. (3)

    • Reasoning: Not all living things move from place to place (e.g., plants). They all respond to changes, grow, and reproduce.

Section B (28 marks)

15. (a) Algae [1]

    • Teaching Note: Producers are organisms that make their own food, usually through photosynthesis. Algae are plant-like producers.

    (b) The population of tadpoles will increase because there are fewer small fish to eat them. The population of herons will decrease because there are fewer small fish for them to eat. [2]

    • Marking: 1 mark for correct direction of tadpole change + reason. 1 mark for correct direction of heron change + reason.

    (c) Energy is lost at each trophic level (as heat/waste/movement). Therefore, less energy is available to support a large population of top consumers like herons. [1]

    • Teaching Note: Only about 10% of energy is transferred to the next level.

16. (a) Distance from the lamp (or Light intensity). [1]

    (b) As the distance from the lamp increases, the number of bubbles produced decreases. [1]

    (c) As distance increases, light intensity decreases. Photosynthesis requires light. With less light, the rate of photosynthesis slows down, producing less oxygen (bubbles). [2]

    • Marking: 1 mark for linking distance to light intensity. 1 mark for linking light intensity to rate of photosynthesis/oxygen production.

    (d) Repeat the experiment and take the average. [1]

    • Teaching Note: Repeating reduces the effect of random errors.

17. (a) Pistil (or Female reproductive part). [1]

    (b) To produce pollen (male gametes). [1]

    • Teaching Note: The anther produces pollen.

    (c) Ovary. [1]

    (d) To attract pollinators (such as insects or birds) for pollination. [1]

18. (a) It has fur and gives birth to young ones (does not lay eggs). [1]

    • Note: Either characteristic is acceptable, but "gives birth" is the definitive mammalian trait vs birds/reptiles. Fur is also key.

    (b) It has feathers and lays eggs. [1]

    (c) Dolphins breathe with lungs (fish use gills) and do not lay eggs (most fish lay eggs, though some don't, but the lung feature is definitive for mammals vs fish). Also, they have smooth skin, not scales. [2]

    • Marking: 1 mark for mentioning lungs. 1 mark for contrasting with fish (gills) or mentioning live birth/smooth skin.

19. (a) Bacteria / Fungi / Mushrooms. [1]

    (b) Decomposers break down dead organisms and waste materials. This releases carbon dioxide back into the atmosphere through respiration, which is then used by plants for photosynthesis. [2]

    • Marking: 1 mark for breaking down dead matter. 1 mark for releasing CO2/carbon cycle link.

    (c) Dead organisms and waste would accumulate, and nutrients would not be recycled back into the soil/atmosphere. [1]

20. (a) To ensure that any starch found in the leaf after the experiment was produced during the experiment and not stored from before. [1]

    (b) Setup X: Starch is present (Leaf turns blue-black). [1] Setup Y: No starch is present (Leaf remains brownish/yellow). [1]

    (c) Setup Y was kept in the dark. Light is necessary for photosynthesis. Without light, the plant cannot make food (starch). [2]

    • Marking: 1 mark for stating light is needed for photosynthesis. 1 mark for linking absence of light to no starch production.