Primary 6 PSLE Science Weighted Assessment 3 (Term 3) Paper 5

Answer Key - Science Primary 6 PSLE (WA3) - Version 5

Section A (28 marks)

1. (3)

   • Reasoning: Birds are characterized by having feathers and laying eggs. P has wings but no feathers (could be an insect or bat). Q has no feathers (could be reptile, amphibian, mammal). R has feathers and lays eggs, which definitively identifies it as a bird. S has no wings, so it cannot be an insect (insects have 6 legs and usually wings, though some don't, but the lack of wings alone doesn't define it as an insect vs other invertebrates). The most accurate classification based on standard primary science is R.

2. (2)

   • Reasoning:
     • W: Has Flowers -> Has Fruits. Roses are flowering plants that produce fruits (rose hips).
     • X: Has Flowers -> No Fruits. This branch is tricky in simplified keys, but usually, ferns/mosses are under "No Flowers". Let's re-read the key structure.
     • Correction based on standard biology:
       • Has Flowers: Angiosperms (e.g., Rose).
       • No Flowers: Gymnosperms (Pine - has cones), Ferns, Mosses.
       • The key says: No Flowers -> Has Cones (Y) -> Pine. No Flowers -> No Cones (Z) -> Fern/Moss.
       • Wait, the key in Q2 image description: 'Has Flowers' splits to 'Has Fruits' (W) and 'No Fruits' (X). 'No Flowers' splits to 'Has Cones' (Y) and 'No Cones' (Z).
       • Option 2: W=Rose (Flower/Fruit), X=Fern (Wait, Ferns have no flowers). This option is flawed if X is under "Has Flowers".
       • Let's look at Option 2 again: W: Rose, X: Fern. If X is under "Has Flowers", Fern is wrong.
       • Let's look at Option 1: W: Fern (No flower). Wrong.
       • Let's look at Option 3: W: Rose, X: Pine. Pine has no flowers. Wrong.
       • Let's look at Option 4: W: Moss. Wrong.
       • Self-Correction: In Primary 6, some keys simplify. However, Ferns do NOT have flowers. Pines do NOT have flowers.
       • Let's re-evaluate the key logic vs options.
       • If W=Rose (Flower/Fruit). Correct.
       • If Y=Pine (No Flower/Cone). Correct.
       • If Z=Moss (No Flower/No Cone). Correct.
       • What is X? "Has Flowers" but "No Fruits". This is biologically rare for primary examples unless it refers to a plant where the fruit isn't obvious or it's a trick. However, looking at Option 2: X=Fern. Ferns don't have flowers.
       • Let's look at the options again.
       • (2) W: Rose, X: Fern, Y: Pine, Z: Moss. This implies X is under "Has Flowers". This is incorrect biology.
       • Is there a better option?
       • Maybe the key implies "Seed Plants" vs "Non-Seed"? No, it says Flowers.
       • Let's assume the question implies X is a flowering plant that doesn't produce a visible fruit in the context, OR the key is "Has Seeds" vs "No Seeds". But the text says "Has Flowers".
       • Actually, let's look at (2) again. If the key was "Has Seeds" -> "Has Fruits" / "No Fruits (Cones)", then W=Rose, X=Pine. But Y is under "No Flowers".
       • Let's stick to the most distinct features.
       • R in Q1 was clear.
       • In Q2, Y=Pine (Cones) and Z=Moss (No cones/flowers) is the strongest anchor.
       • Options with Y=Pine and Z=Moss: (2) and (3).
       • Option (2): W=Rose, X=Fern.
       • Option (3): W=Rose, X=Pine.
       • If X is under "Has Flowers", neither Fern nor Pine fits.
       • However, if we assume a typo in the question generation or a specific curriculum simplification where "Flowering" is conflated with "Seed-bearing" in the student's mind? No, MOE is strict.
       • Let's look at the structure again. Maybe X is a plant like a Gymnosperm which is sometimes confused? No.
       • Let's assume the key meant: Top split: Vascular / Non-Vascular? No.
       • Let's select the "Best" fit. Rose (W) is definitely Flower/Fruit. Pine (Y) is No Flower/Cone. Moss (Z) is No Flower/No Cone.
       • This leaves X. In Option 2, X is Fern. In Option 3, X is Pine.
       • If X is Pine, then Y cannot be Pine.
       • Therefore, Option 2 is the intended answer despite the biological inaccuracy of placing Fern under "Has Flowers" in this specific hypothetical key, OR the key actually said "Has Seeds" and I transcribed "Has Flowers". Given the prompt constraints, I must provide the answer that fits the logic of the distractors.
       • Correction: Actually, many primary questions use "Flowering Plant" to mean Angiosperm. Ferns are non-flowering.
       • Let's look at Option 2 again. If the key is flawed, we pick the one where W, Y, Z are correct.
       • W=Rose (Correct). Y=Pine (Correct). Z=Moss (Correct).
       • X=Fern is the outlier.
       • Option 3: W=Rose, X=Pine, Y=Fern, Z=Moss. Y=Fern under "Has Cones"? No.
       • So Option 2 is the only one where Y and Z are correctly placed in the "No Flower" branch. We assume X is a distractor or error in the hypothetical key's label, but (2) is the intended answer by elimination of Y and Z.

3. (2)

   • Reasoning: Snakes eat frogs and rabbits. If snakes decrease, fewer frogs are eaten, so the frog population increases. Eagles eat snakes and birds; if snakes decrease, eagles might eat more birds, but the immediate direct effect is on the prey of the snake.

4. (1)

   • Reasoning: Ferns, Mosses, and Mushrooms (Fungi) all reproduce via spores. Pine uses seeds (cones). Rose uses seeds. Grass uses seeds.

5. (3)

   • Reasoning: The change from Pupa (C) to Adult (D) involves metamorphosis, where the body structure completely reorganizes from a resting stage to a winged adult.

6. (2)

   • Reasoning: Thick, waxy skin (cuticle) reduces water loss through evaporation, which is critical in dry environments. Broad leaves increase water loss.

7. (3)

   • Reasoning: A sudden, drastic drop in all trophic levels (Algae, Small Fish, Big Fish) suggests an environmental factor like pollution or toxicity rather than a biological predator-prey fluctuation.

8. (3)

   • Reasoning: Fungi are saprophytes; they secrete enzymes to break down dead organic matter externally and absorb the nutrients. They do not have chlorophyll (1), roots/stems/leaves (2), or seeds (4).

9. (1)

   • Reasoning: Polar bears live in the Arctic. Thick fur and fat (blubber) provide insulation against the cold. Camels live in deserts; humps store fat (not water directly, but energy/metabolic water), and eyelashes protect from sand.

10. (2)

    • Reasoning: Animals dependent on trees for food and shelter will lose their habitat. They must either migrate to find similar resources or die due to starvation/exposure. They cannot instantly adapt (1) or change diet (3) immediately.

11. (3)

    • Reasoning: Growing from tubers is vegetative propagation, a form of asexual reproduction. Hens, cats, and bees (sexual pollination leading to seeds) involve sexual reproduction.

12. (2)

    • Reasoning: Snakes eat rats. If the food source (rats) decreases, the predator (snake) population will decrease due to lack of food.

13. (2)

    • Reasoning: The primary classification for vertebrates vs invertebrates is the presence or absence of a backbone (vertebral column).

14. (1)

    • Reasoning: This is a classic predator-prey cycle. An increase in prey (deer) provides more food for predators (wolves), causing the predator population to rise. As predators rise, they eat more prey, causing the prey population to fall, which subsequently causes the predator population to fall.

Section B (28 marks)

(a) Fungus (or Mushroom/Mould) [1]

• Note: It has no chlorophyll, does not make own food, and reproduces by spores.

(b) Ferns reproduce by spores, but Organism A reproduces by seeds/flowers (implied by "No" to spores and "Yes" to chlorophyll/food making, typically a flowering plant). [2]

• Marking: 1 mark for stating ferns use spores. 1 mark for stating Organism A does not use spores (or uses seeds).

(c) They both reproduce by spores. (Or: They both do not have flowers/seeds). [1]

(a) Leaves [1]

(b) The population of ladybirds will increase. [1] Because spiders are the predators of ladybirds. With fewer spiders, fewer ladybirds are eaten. [1]

(c) Leaves $\rightarrow$ Aphid $\rightarrow$ Ladybird $\rightarrow$ Spider [2]

• Marking: 1 mark for correct order. 1 mark for 4 organisms. Arrows must point in direction of energy flow.

(a) Incomplete metamorphosis (or 3-stage life cycle). [1]

(b) The nymph does not have wings, while the adult has wings. (Or: The nymph is smaller). [1]

(c) The egg case protects the eggs from drying out (desiccation) and from predators. [2]

• Marking: 1 mark for protection from physical damage/predators. 1 mark for protection from drying out/environment.

(a) Amount of light (or Light intensity). [1]

(b) 1. Amount of water [1] 2. Type/Amount of soil (Or: Number of seeds, Type of pot, Temperature). [1]

(c) Plants need light to make chlorophyll. [1] Without light, they cannot produce chlorophyll, so they remain yellow (etiolated). [1]

• Note: Do not accept "plants need light to make food" as the direct reason for color. The color is due to chlorophyll absence.

(a) R [1]

• Reasoning: No backbone -> 8 legs. Spiders are arachnids with 8 legs.

(b) It has gills to breathe. (Or: It has fins to swim / It lays eggs in water). [1]

(c) Bats have fur/hair. [1] Bats give birth to live young (and produce milk). [1]

• Note: Flying is not a defining characteristic of class Aves in this context; mammals are defined by fur and mammary glands/live birth.

(a) 1. To hold the tree upright in the soft mud. [1] 2. To absorb oxygen from the air for respiration. [1]

(b) The roots provide shelter/hiding places from larger predators. [1]

(c) Coastal erosion will increase. (Or: Loss of habitat for fish / Water quality may decrease). [1]