Primary 6 PSLE Science Weighted Assessment 3 (Term 3) Paper 4

Answer Key - TuitionGoWhere Exam Practice (AI) - WA3 Science Primary 6 PSLE (Version 4)

Section A (28 marks)

1. (3)
Reasoning: Humans and bats are mammals, which are viviparous (give birth to live young). Chickens and platypuses lay eggs (oviparous). Sharks can be viviparous or oviparous, but dolphins are viviparous. Cats are viviparous. Option C is the only pair where both are correctly identified as viviparous.

2. (2)
Reasoning: R has no backbone and has 6 legs. This is the defining characteristic of insects. P has a backbone and fur (Mammal). Q has a backbone but no fur (could be bird, reptile, amphibian, fish). S has no backbone and not 6 legs (could be spider, worm, etc.).

3. (2)
Reasoning: Frogs are a food source for snakes. If frogs decrease, snakes have less food, so their population will likely decrease. Grasshoppers (eaten by frogs) might increase, not decrease. Mice are not directly linked to frogs in this web. Eagles eat snakes and mice; if snakes decrease, eagles might rely more on mice, but the direct impact is on snakes.

4. (2)
Reasoning: A thick waxy skin (cuticle) reduces water loss through evaporation, which is crucial in a hot, dry desert. Broad leaves would increase water loss. Shallow roots are for quick absorption but waxy skin is for retention. Stomata usually open at night in cacti (CAM photosynthesis) to reduce water loss.

5. (2)
Reasoning: X has flowers and seeds (Flowering Plant/Angiosperm, e.g., Rose). Y has no flowers/seeds but uses spores (Non-flowering, e.g., Fern or Moss). Z has no flowers but has seeds (Non-flowering seed plant, e.g., Pine Tree/Gymnosperm). Option B fits: Rose (X), Fern (Y), Pine Tree (Z).

6. (3)
Reasoning: Fat is a poor conductor of heat. A thick layer of fat (blubber) acts as insulation, keeping the polar bear warm in freezing temperatures.

7. (3)
Reasoning: Fungi are not plants; they cannot photosynthesize. They are heterotrophs that obtain nutrients by secreting enzymes to break down dead organic matter externally and then absorbing the nutrients.

8. (3)
Reasoning: Sexual reproduction in flowers involves the male parts (Stamen: Anther D and Filament E) producing pollen and the female parts (Pistil: Stigma A, Style B, Ovary C) receiving pollen and housing ovules. All these parts are involved in the process.

9. (3)
Reasoning: Melting ice cream is a change of state (solid to liquid). No new substance is formed. Burning, rusting, and cooking involve chemical changes where new substances are formed.

10. (2)
Reasoning: High biodiversity means there are many different species. If one species is affected by disease or environmental change, others can fill its role, making the ecosystem more stable and resilient.

11. (2)
Reasoning: Butterflies undergo complete metamorphosis (Egg -> Larva/Caterpillar -> Pupa -> Adult). Cats, chickens, and dogs do not undergo metamorphosis; their young resemble miniature adults.

12. (2)
Reasoning: The larva (wriggler) hangs from the surface and breathes air through a siphon. The pupa (tumbler) also breathes air but through trumpets, and the question specifically describes the larval behavior often taught. However, both larva and pupa breathe air. The larva is the active feeding stage. Correction: In P6 syllabus, the larva is known for the siphon. The pupa has breathing trumpets. So Larva is the best answer.

13. (3)
Reasoning: The defining characteristic of mammals is the presence of mammary glands to produce milk for their young. Not all mammals give birth (platypus lays eggs), but all have mammary glands.

14. (3)
Reasoning: Tendrils are modified leaves or stems that coil around supports, allowing climbing plants to reach sunlight without investing energy in a thick trunk.

15. (4)
Reasoning: Whales are mammals. Bats are mammals. Penguins are birds. Spiders are arachnids (8 legs, 2 body segments).

16. (3)
Reasoning: Seeds contain the embryo of a new plant and food stores. Their main function is reproduction and dispersal to grow into new plants.

17. (4)
Reasoning: Decomposition is affected by temperature (warmth speeds it up), moisture (dampness helps decomposers), and the presence of decomposers (bacteria/fungi). The color of the leaves does not significantly affect the biological rate of decomposition.

18. (2)
Reasoning: Thorns are a physical defense mechanism to deter herbivores from eating the plant.

19. (3)
Reasoning: Viruses are not considered fully living cells because they cannot reproduce on their own. They must infect a host cell and use its machinery to replicate.

20. (2)
Reasoning: Molluscs (like snails and slugs) have soft bodies, no backbone, and often move using a muscular foot. Insects have 6 legs and exoskeletons. Crustaceans have hard shells and jointed legs. Amphibians have backbones.

Section B (28 marks)

21. (a) [2]
V: Earthworm
W: Cat
X: Eagle
Y: Goldfish
Z: Frog
(0.5 marks each for all 4 correct. If 3 correct, 1.5 marks.)

(b) [1]
Both are vertebrates / Both have backbones.
(Accept: Both are warm-blooded / Both breathe using lungs.)

(c) [1]
The Earthworm has no backbone (invertebrate), while the Goldfish has a backbone (vertebrate).

22. (a) [2]
Species A is the predator.
Evidence: The population of Species A peaks after the population of Species B peaks. This lag indicates that Species A depends on Species B for food.

(b) [1]
The population of the predator (Species A) increased, leading to more predation on Species B.
(Accept: Lack of food for Species B / Disease.)

(c) [2]
The population of Species B will increase.
Reason: With fewer predators (Species A) to eat them, more of Species B will survive and reproduce.

23. (a) [3]
Fruit P: Wind dispersal
Fruit Q: Animal dispersal
Fruit R: Explosive dispersal

(b) [2]
Fruit P has wing-like structures which increase its surface area. This allows it to be caught by the wind and carried over long distances away from the parent plant.

(c) [1]
To reduce overcrowding / competition for resources (water, sunlight, nutrients) between the parent plant and its offspring.
(Accept: To colonize new areas.)

24. (a) [1]
Test Tube D
(Note: Test Tube B might germinate if air is present in the cotton wool, but D is the control with ample air and water. Usually, B is also accepted if "wet cotton wool" implies air pockets. However, D is the most ideal. In many PSLE contexts, B and D both germinate. Let's accept B and D.)
Correction based on standard PSLE logic: B has wet cotton wool and is stoppered. If stoppered tightly, oxygen might be limited. D is open. Usually, B and D are both considered to have water and air. Let's say B and D.

(b) [2]
The water was boiled, which removed the dissolved oxygen. The oil layer prevented oxygen from the air from dissolving back into the water. Seeds need oxygen for respiration to germinate.

(c) [1]
To show that water is necessary for germination. (It acts as the control for the variable 'water').

(d) [2]

1. Temperature
2. Type of seeds / Number of seeds

25. (a) [1]
Phytoplankton

(b) [2]
The population of Tuna will decrease.
Reason: Zooplankton is the food source for Small Fish. If Zooplankton decreases, Small Fish will have less food and their population will decrease. Consequently, Tuna will have less food (Small Fish) and their population will decrease.

(c) [2]
Energy is lost at each trophic level (as heat/respiration/movement). Therefore, less energy is available to support organisms at higher trophic levels. This results in fewer sharks (top predator) compared to phytoplankton (producer).

26. [4]

1. Loss of Habitat: Animals lose their homes and breeding grounds, leading to a decline in population or extinction.
2. Disruption of Food Chains: Removal of trees affects the producers, causing a ripple effect that reduces food availability for herbivores and subsequently carnivores.
   (Accept: Soil erosion leading to poor water quality affecting aquatic life / Increase in carbon dioxide contributing to climate change which affects habitats.)

27. (a) [2]

1. Hump to store fat.
2. Thick fur / Long eyelashes / Wide feet.
   (Any two valid adaptations.)

(b) [2]
Example for Hump: The fat stored in the hump can be broken down to provide energy and water when food and water are scarce in the desert.
Example for Wide Feet: Wide feet prevent the camel from sinking into the soft sand, making it easier to walk.

28. [2]
Classification helps scientists to:

1. Identify and name organisms systematically.
2. Study the relationships and evolutionary links between different groups of organisms.
   (Accept: Makes it easier to study the vast number of organisms by grouping them with similar characteristics.)