Primary 6 PSLE Science Life Cycles Quiz

Primary 6 PSLE Science Quiz - Life Cycles (Answer Key)

Total Marks: 50

Section A: Multiple-Choice Questions (10 marks)

1. C – Butterfly undergoes a four-stage life cycle (egg, larva, pupa, adult). Grasshopper and chicken have three-stage life cycles; frog has a distinct metamorphosis but is not classified as four-stage in the same way.

2. B – The larva (wriggler) of a mosquito breathes through a siphon at the water surface. The pupa also breathes at the surface but through trumpets; the question specifies "siphon" which is characteristic of the larva.

3. B – In a four-stage life cycle (complete metamorphosis), the sequence is: Egg → Larva → Pupa → Adult.

4. C – In a three-stage life cycle (incomplete metamorphosis), the nymph resembles a smaller version of the adult without fully developed wings. It lives in the same habitat and feeds on the same food.

5. B – Fertilisation occurs after pollination (pollen reaches stigma) and before fruit formation. The fertilised ovule develops into a seed, and the ovary develops into the fruit.

6. B – The tadpole breathes through gills (external then internal). The froglet and adult frog breathe through lungs and skin.

7. D – Animals with three-stage life cycles undergo incomplete metamorphosis, not complete metamorphosis. Complete metamorphosis (four-stage) involves a pupal stage where the young look very different from the adult.

8. B – Hatching into a nymph that moults several times before becoming an adult is characteristic of a three-stage life cycle (incomplete metamorphosis).

9. C – The cotyledon (seed leaf) stores food (starch, proteins, oils) that provides energy and building materials for the growing seedling until it can photosynthesise.

10. C – Frog lays eggs in water (spawn), and the tadpole (larva) lives in water with gills. Butterflies lay eggs on leaves; grasshoppers lay eggs in soil; chickens lay eggs on land.

Section B: Structured Questions (16 marks)

11.
(a) Pupa (or Chrysalis) [1]
(b) The larva (caterpillar) has chewing mouthparts and eats leaves, while the adult butterfly has a proboscis (siphoning mouthpart) and feeds on nectar. [1]
Accept: Larva eats solid food (leaves); adult sucks liquid food (nectar).

12.
(a) 2 + 10 + 2 = 44 days [1]
(b) Adult stage (30 days) [1]

13.
(a) The nymph is smaller and has wing buds, while the adult is larger and has fully developed wings. [1]
Accept: Nymph lacks wings / has wing buds; adult has full wings. Or size difference.
(b) The grasshopper undergoes incomplete metamorphosis because the young (nymph) resembles the adult, lives in the same habitat, and there is no pupal stage. [1]
Key points: Resemblance, same habitat, no pupa.

14.
(a) Pupa [1]
(b) The larva stops moving and eating to undergo internal reorganisation (metamorphosis) into the adult form inside the pupal case. [1]
Accept: To transform into adult / for metamorphosis / to conserve energy for transformation.

15.
(a) Anther [1]
(b) Fertilisation [1]
Note: The growth of the pollen tube is "pollen tube growth"; the fusion of male and female gametes in the ovule is fertilisation. The question asks for the process of the tube growing down to reach the ovule – this is often called "pollen tube growth" but in PSLE context, "fertilisation" is the overall process after pollination. Accept "pollen tube growth" or "fertilisation".

16.
(a) The tadpole breathes through gills (in water), while the adult frog breathes through lungs and moist skin (on land and in water). [1]
(b) The tail is used for swimming in water. [1]
Accept: For locomotion / movement in water.

17. Set-up A only. [2]
Seeds need all three conditions: water (to activate enzymes, swell seed), air/oxygen (for respiration to release energy), and suitable temperature (for enzyme activity). Set-up B lacks water, C lacks air, D has unsuitable (too low) temperature.

18.
(a) Pappus (or parachute / feathery hairs) [1]
(b) The pappus increases the surface area of the fruit, allowing it to be caught by the wind and carried far from the parent plant. [1]
Key: Increases surface area / air resistance; caught by wind; dispersed far away.

Section C: Open-Ended Questions (24 marks)

19.
(a) Both life cycles begin with an egg stage and end with an adult stage. [1]
Accept: Both have egg and adult stages; both involve growth and development; both involve moulting.

(b) Any two of the following: [2]

• Butterfly has four stages (egg, larva, pupa, adult); grasshopper has three stages (egg, nymph, adult).
• Butterfly undergoes complete metamorphosis; grasshopper undergoes incomplete metamorphosis.
• Butterfly has a pupa stage; grasshopper has no pupa stage.
• Butterfly larva looks very different from adult; grasshopper nymph resembles the adult.
• Butterfly larva and adult have different feeding methods/ habitats; grasshopper nymph and adult have similar feeding methods/ habitats.

(c) The caterpillar's exoskeleton (cuticle) is hard and does not stretch, so it must shed it (moult) to allow its body to grow larger. [1]
Key: Exoskeleton is rigid / non-living / cannot expand; moulting allows growth.

(d) After moulting, the caterpillar remains a larva (still looks like a caterpillar), but the grasshopper nymph develops larger wing buds and looks more like the adult with each moult. [1]
Key difference: Caterpillar moults → still larva; Nymph moults → progressively more adult-like (wing development).

(e) If grasshoppers cannot moult, the nymphs cannot grow larger or develop into adults. They will die as nymphs, so the population will decrease over time as no new adults can reproduce. [1]
Key: Moulting essential for growth and development to reproductive adult; no adults → no reproduction → population decline.

20.
(a) To find out which conditions (water, air, temperature) are necessary for seed germination. [1]
Accept: To investigate the conditions needed for germination.

(b) Tube 1 is the control set-up. It has all three conditions (water, air, suitable temperature) present. [1]
Control has all variables present; experimental set-ups each lack one condition.

(c) Seeds will germinate in Tube 1 only. [1]
Tube 1 has water, air, and suitable (warm) temperature – all three conditions needed for germination. Tube 2 lacks water, Tube 3 has unsuitable (too low) temperature. [1]
Mark breakdown: Correct tube (1m), Correct explanation with all three conditions (1m).

(d) This tube tests whether air (oxygen) is needed for germination. [1]
Boiled water removes dissolved air; oil layer prevents atmospheric oxygen from dissolving. So no oxygen available.

(e) The radicle (embryonic root) grows downwards to anchor the seedling in the soil and absorb water and mineral salts from the soil. [1]
Accept: Anchor plant; absorb water and minerals.

Marking Notes for Teachers

• Section A: 1 mark each. No half marks.
• Section B: 2 marks each. Award 1 mark for each correct sub-part.
• Section C: 6 marks each. Follow the mark breakdown shown.
• Common mistakes to watch for:
  • Q4: Confusing nymph (incomplete) with larva (complete).
  • Q7: Thinking three-stage = complete metamorphosis.
  • Q11(b): Vague answers like "eat different food" – must specify chewing vs siphoning / solid vs liquid.
  • Q15(b): Confusing pollen tube growth with fertilisation.
  • Q19(c): Saying "to grow" without mentioning the rigid exoskeleton.
  • Q19(d): Not contrasting the outcome (larva stays larva vs nymph becomes more adult-like).
  • Q20(b): Identifying wrong tube as control.
  • Q20(d): Not linking boiled water + oil to removal of oxygen.

Total: 50 marks