Primary 6 PSLE Science Life Cycles Quiz

Primary 6 PSLE Science Quiz – Life Cycles

Answer Key

Section A: Multiple Choice Questions (10 marks)

1. C [1]

• Explanation: Complete metamorphosis in a butterfly follows the sequence: Egg → Larva (caterpillar) → Pupa (chrysalis) → Adult.
• Common mistake: Students may confuse the order of larva and pupa (choosing A).

2. D [1]

• Explanation: The froglet (young frog) stage is when the tadpole undergoes significant changes, including the development of lungs and legs, allowing it to live on land. Tadpoles breathe through gills.
• Common mistake: Students may choose B (tadpole) because they associate change with the tadpole, but lungs develop during the froglet stage.

3. C [1]

• Explanation: Grasshoppers undergo incomplete metamorphosis (egg → nymph → adult). Butterflies, mosquitoes, and beetles undergo complete metamorphosis.
• Common mistake: Students may select mosquito (B) as it is also a common insect, but mosquitoes undergo complete metamorphosis with a pupal stage.

4. B [1]

• Explanation: Complete metamorphosis has four stages including a pupa stage, while incomplete metamorphosis has three stages with no pupa stage.
• Common mistake: Students may choose D, but it is the reverse — complete metamorphosis involves a larva, while incomplete involves a nymph.

5. A [1]

• Explanation: Seeds contain the embryo of a new plant and represent the beginning of a new generation in the plant life cycle.

6. C [1]

• Explanation: A nymph resembles a smaller version of the adult but lacks fully developed wings and reproductive organs. It does not look drastically different (unlike a larva).

7. B [1]

• Explanation: The mealworm beetle undergoes complete metamorphosis. The missing stage between larva and adult is the pupa.

8. B [1]

• Explanation: Germination occurs after the seed has been dispersed and lands in a suitable environment with water, air, and warmth.
• Common mistake: Students may choose D, but pollination must occur before fertilisation.

9. C [1]

• Explanation: The caterpillar's outer skin (exoskeleton) does not stretch, so it must shed (moult) its skin to grow bigger.

10. C [1]

• Explanation: Houseflies undergo complete metamorphosis (egg → larva/maggot → pupa → adult). Cockroaches, dragonflies, and grasshoppers undergo incomplete metamorphosis.

Section B: Short Answer Questions (20 marks)

11. (a) [1]

• A tadpole has a tail / breathes through gills / has no legs / lives in water, whereas an adult frog has legs / breathes through lungs / has no tail / can live on land.
• Accept any valid difference. Award 1 mark for a clear, correct difference.

(b) [2]

• A tadpole breathes through gills, which can only extract oxygen from water. [1]
• An adult frog has developed lungs (and can also breathe through its skin), which allow it to breathe air on land. [1]
• Award 1 mark for each valid point. Students must link the breathing structure to the habitat.

12. [4]

• Award ½ mark for each correct answer. Total: 4 marks.

13. (a) [1]

• Germination

(b) [2]

• Water / moisture [1]
• Warmth / suitable temperature [1]
• Accept also: oxygen / air. Any two valid conditions. Award 1 mark each.

(c) [2]

• Seed dispersal reduces competition between the parent plant and the offspring for resources such as water, sunlight, and nutrients. [1]
• It also allows the species to spread to new areas / colonise new habitats, increasing the chances of survival of the species. [1]
• Award 1 mark for each valid point. Students must explain the benefit, not just define dispersal.

14. (a) [1]

• Seeds contain stored food (in the cotyledons / endosperm) that provides energy for germination, so they do not need soil initially. [1]
• Accept: The wet cotton wool provided water, which is needed for germination.

(b) [2]

• The seedlings would grow into healthy green plants. [1]
• This is because, once planted in soil and placed near a window, the seedlings can obtain water and minerals from the soil and light from the window for photosynthesis, allowing them to make their own food and grow. [1]
• Award 1 mark for the prediction and 1 mark for the reason. Accept reasonable alternatives (e.g., seedlings grow taller/greener).

15. (a) [1]

• W → X → Y → Z [1]
• (Caterpillar → Chrysalis → Emerging butterfly → Butterfly laying eggs)

(b) [1]

• The caterpillar's body is broken down and reorganised into the body of an adult butterfly (wings, legs, antennae, etc.). [1]
• Accept any valid description of the transformation inside the chrysalis.

16. [2]

• Mosquito larvae live in stagnant water and can develop into adult mosquitoes. [1]
• Adult mosquitoes spread diseases such as dengue fever and malaria when they bite humans, causing illness. [1]
• Award 1 mark for linking larvae to the harmful adult stage and 1 mark for naming the harm (disease transmission). Accept other valid reasons (e.g., larvae compete with other aquatic organisms for food).

Section C: Structured / Application Questions (10 marks)

17. (a) [2]

• The butterflies lay eggs on the cabbage plants. [1]
• The eggs hatch into caterpillars (larvae), which feed on the cabbage leaves. [1]
• Award 1 mark for each logical step linking butterflies to caterpillars.

(b) [2]

• The number of butterflies on the farm would decrease. [1]
• This is because removing the caterpillars means they cannot develop into pupae and then into adult butterflies, so fewer butterflies will be produced. [1]
• Award 1 mark for the prediction and 1 mark for the explanation.

18. (a) [2]

• Insect P undergoes complete metamorphosis. [1]
• This is because its life cycle includes a pupal stage, which is characteristic of complete metamorphosis. [1]
• (Insect Q has a nymph stage and no pupal stage, indicating incomplete metamorphosis.)

(b) [1]

• Total = 4 + 14 + 10 + 30 = 58 days [1]
• Award 1 mark for the correct answer. Accept if working is shown.

(c) [1]

• At a lower temperature, the metabolic rate of the larva decreases, so it grows and develops more slowly, taking longer to complete the larval stage. [1]
• Accept any valid explanation linking temperature to the rate of development.

19. (a) [1]

• Light / amount of light / presence or absence of light [1]

(b) [2]

• Temperature [1]
• Amount of water / moisture / wet cotton wool [1]
• Accept also: type of seed, number of seeds, type of container. Award 1 mark each for any two valid controlled variables.

(c) [1]

• Light is not necessary for the germination of bean seeds. [1]
• Accept: Seeds can germinate in both light and dark conditions. Award 1 mark for a conclusion consistent with the results.

20. (a) [2]

• The mayfly undergoes incomplete metamorphosis. [1]
• This is because its life cycle has three stages (egg → nymph → adult) and does not include a pupal stage. [1]
• Award 1 mark for identifying the type and 1 mark for the reason.

(b) [1]

• The adult mayfly lives for only one to two days and its sole purpose is to reproduce (mate and lay eggs). It does not have enough time to feed and does not need energy for long-term survival. [1]
• Accept: It does not have functional mouthparts / it uses stored energy from the nymph stage.

(c) [1]

• The nymph stage lasts longer because the nymph needs time to feed and grow / store enough energy to develop into an adult and reproduce. [1]
• Accept any valid reason. Award 1 mark.

Total: 40 marks