Primary 6 PSLE Science Semestral Assessment 2 (End of Year) Paper 1

Answer Key - Science Primary 6 PSLE (SA2 Practice Paper Version 1)

Topic: Diversity
Total Marks: 56

Section A (28 marks)

1. (3)
Reasoning: Birds are characterized by having feathers, wings, and laying eggs. Organism R has all three. P has wings and lays eggs but no feathers (likely an insect or bat). Q lays eggs but no wings/feathers (likely a reptile or amphibian). S has none of these.

2. (3)
Reasoning: Group Y produces seeds and has chlorophyll. This describes flowering plants (angiosperms) or cone-bearing plants (gymnosperms). Rose plant is a flowering plant. Ferns (Group X) produce spores. Mushrooms (Group B) do not have chlorophyll. Grasshoppers (Group Z) are animals.

3. (3)
Reasoning: Stage C is the Pupa. During the pupal stage, the caterpillar is enclosed in a chrysalis, does not feed, and undergoes metamorphosis to become an adult.

4. (3)
Reasoning: Fungi are heterotrophs; they cannot make their own food (no chlorophyll). They obtain nutrients by absorbing them from dead or decaying organic matter. They reproduce via spores, not eggs.

5. (1)
Reasoning: J has 8 legs and 2 body parts, characteristic of arachnids (Spider). K has 6 legs and 3 body parts, characteristic of insects (Ant). L has many legs and segments, characteristic of myriapods (Earthworm is an annelid, but in primary science context, "many legs" often points to centipedes/millipedes, but Earthworm has no legs. Wait, let's re-evaluate Option 1 vs 2. Option 1: L is Earthworm. Earthworms have 0 legs. The table says "Many". This is a trick. Let's look at Option 2: L is Centipede. Centipedes have many legs. J is Scorpion (Arachnid, 8 legs). K is Bee (Insect, 6 legs). This fits better. Let's re-read the table. L: Many legs. Earthworm has 0. So Option 1 is incorrect for L. Option 2: L is Centipede (Many legs). Correct. Option 3: L is Millipede (Many legs). J is Crab (Crustacean, usually 10 legs, not 8). So Option 3 is incorrect for J. Option 4: L is Leech (0 legs). Incorrect. Therefore, Option 2 is the best fit. Correction: The question asks for the correct identification. Re-evaluating Option 1: J=Spider (8 legs, 2 parts). K=Ant (6 legs, 3 parts). L=Earthworm (0 legs). Table says "Many". Mismatch. Re-evaluating Option 2: J=Scorpion (8 legs, 2 parts). K=Bee (6 legs, 3 parts). L=Centipede (Many legs). Match. Answer: (2)

6. (4)
Reasoning: Frogs are eaten by snakes. If frogs decrease, snakes have less food, so their population decreases. Eagles eat snakes and rabbits. If snakes decrease, eagles might rely more on rabbits, but the direct impact on the snake population is a decrease. The question asks for the most likely immediate effect. A decrease in prey (frog) leads to a decrease in predator (snake). Consequently, eagles (which eat snakes) may also decrease if they cannot compensate with rabbits. However, looking at the options: (1) Grasshoppers would increase (less predation). (2) Snakes would decrease. (3) Earthworms are eaten by frogs, so they might increase. (4) Eagles might decrease. Between 2 and 4, the effect on snakes is more direct. Wait, option 2 says "increase". That is wrong. Option 4 says "decrease". This is plausible. Let's re-read carefully. Option 1: Grasshoppers decrease? No, they increase. Option 2: Snakes increase? No, they decrease. Option 3: Earthworms increase? Yes, because frogs eat them. Option 4: Eagles decrease? Possible, but they have alternative food (rabbits). So, (3) is a strong candidate. Let's check the food web again. Dead leaves -> Earthworm -> Frog. If Frogs decrease, Earthworms have fewer predators, so Earthworms increase. This is a direct effect. Answer: (3)

7. (2)
Reasoning: Cacti live in dry environments. A thick, waxy skin (cuticle) reduces water loss through evaporation. Broad leaves would increase water loss. Shallow roots are for absorbing rain, but the waxy skin is the primary adaptation for retention.

8. (4)
Reasoning: Pointed shape -> Go to B. Net-like veins (not parallel) -> Leaf S.

9. (1)
Reasoning: Whales, bats, and dolphins are all mammals (give birth to live young, feed milk, have hair/fur at some stage). Penguins are birds. Sharks are fish. Frogs are amphibians.

10. (2)
Reasoning: In a predator-prey graph, the predator population peak follows the prey population peak. Here, X peaks first, then Y peaks. This suggests X is the prey and Y is the predator. As X increases, Y has more food and increases. As Y increases, it eats more X, causing X to fall.

11. (2)
Reasoning: Flowering plants produce seeds. (1) is false (birds, reptiles, fish have backbones). (3) is false (insects have 6 legs). (4) is false (fungi are not green).

12. (2)
Reasoning: Part B is the Cotyledon, which stores food for the embryo. Part A is the seed coat (protection). Part C is the embryo.

13. (2)
Reasoning: White fur provides camouflage against the snow, helping polar bears hunt prey and avoid detection.

14. (3)
Reasoning: Not all living things move from place to place (e.g., plants). All living things grow, reproduce, and respond to stimuli.

Section B (28 marks)

15.
(a) [5 marks]

• Organism A: Plant (Has green parts, does not lay eggs/has seeds/spores implied by exclusion of animal traits). Note: Specifically, it has chlorophyll.
• Organism B: Fish (Has gills, lays eggs, no hair).
• Organism C: Reptile (Lays eggs, no hair, no gills, not green). *Note: Birds also lay eggs, but usually "no hair" distinguishes from mammals. Between Bird and Reptile, without "feathers" specified, Reptile is a safe bet, or Bird. However, looking at D (Mammal), C is likely Reptile or Bird. Let's assume standard classification questions: A=Plant, B=Fish, C=Reptile/Bird, D=Mammal, E=Plant. Wait, E has green parts but no seeds? No, E has green parts, no eggs, no hair, no gills. E is likely a Plant (non-flowering or flowering). A is also a Plant. Let's look closer. A: Green, No Eggs. E: Green, No Eggs. Both are plants. C: No Green, Eggs, No Hair, No Gills. This fits Reptile or Bird. D: No Green, No Eggs, Hair. Mammal.
  • Refined Answer:
    • A: Plant
    • B: Fish
    • C: Reptile (or Bird)
    • D: Mammal
    • E: Plant
  • Marking: 1 mark for each correct classification. Accept "Bird" for C if justified, but "Reptile" is standard for "scales/skin" implied by lack of feathers/hair. Given the options, C is likely a Reptile.

(b) [1 mark]

• Mammals (D) feed their young with milk, whereas Reptiles/Birds (C) do not. OR Mammals provide parental care, while many reptiles do not.

16.
(a) [1 mark]

• Leaf (or the Plant producing the leaf).

(b) [2 marks]

• Energy is lost at each trophic level as heat/respiration/movement. [1]
• Therefore, less energy is available to support a large population of snakes compared to caterpillars. [1]

(c) [2 marks]

• The population of the original Bird species will decrease. [1]
• Because the Mynah bird competes with the original Bird for the same food source (caterpillars), leading to less food available for the original Bird. [1]

17.
(a) [1 mark]

• Test tube B. (It has both water and air, the standard conditions for germination).

(b) [1 mark]

• Test tube B.

(c) [2 marks]

• Test tube A did not germinate because it lacked water. [1]
• Test tube C did not germinate because it lacked air (oxygen). [1]

18.
(a) [2 marks]

• Lion and Tiger (or Lion and House Cat, or Tiger and House Cat). Any pair from Felidae. [1]
• They belong to the same Family (Felidae), which is a more specific classification group than the different Families (Felidae vs Canidae). [1]

(b) [1 mark]

• They have fur/hair. OR They give birth to live young. OR They feed their young with milk. (Any mammalian/feline trait).

19.
(a) [1 mark]

• The soil is salty (high salinity) and muddy (low oxygen/waterlogged), which is harmful to most plants.

(b) [2 marks]

• The prop roots provide support to keep the tree upright in the soft, muddy soil. [1]
• They also allow the tree to absorb oxygen/air directly from the atmosphere, as the muddy soil lacks oxygen. [1]

20.
(a) [1 mark]

• Ladybird (eats Aphids/Larva, eaten by Spider) OR Spider (eats Ladybird, eaten by Bird).

(b) [2 marks]

• The population of spiders will decrease. [1]
• Aphids are food for Ladybirds. If Aphids die, Ladybird population decreases. Spiders eat Ladybirds, so with fewer Ladybirds, Spiders have less food. [1]

(c) [1 mark]

• Introduce natural predators (e.g., more Ladybirds or Birds). OR Use physical barriers (nets). OR Hand-pick the larvae.