Primary 6 PSLE Science Life Cycles Quiz

Primary 6 PSLE Science Quiz - Life Cycles: Answer Key

Total Marks: 40

Section A: Multiple Choice (Questions 1–8)

Section A Total: 8 marks

Section B: Structured Questions (Questions 9–16)

Question 9 [4 marks]

(a) Complete metamorphosis [1]

Key concept: Mosquitoes have four distinct life stages (egg, larva, pupa, adult) with very different body forms, unlike incomplete metamorphosis where the nymph resembles a small adult.

(b) The larva and pupa are aquatic stages [1] that have adapted to breathe dissolved oxygen in water (larva has a siphon, pupa has trumpets) [1]. The adult mosquito is terrestrial/aerial, so early stages require water for survival and development.

Marking note: Must mention water as essential habitat and some structural adaptation (siphon/trumpets/breathing) for full marks.

(c) Remove standing water / oil on water surface to suffocate larvae / clear drains / introduce larvae-eating fish [1]

Any reasonable method targeting egg, larva, or pupa stages accepted.

Q9 Total: 4

Question 10 [4 marks]

(a) Any two from: [2]

• Feathery/extended stigma to catch airborne pollen [1]
• Anthers hang outside flower to release pollen into wind [1]
• No colourful petals (not needed to attract insects) [1]
• Produces large amounts of light, smooth pollen [1]

(b) Insect-pollinated flowers have targeted delivery [1]: insects visit flowers specifically, carrying pollen directly to another flower of the same species. Wind-pollinated flowers rely on chance; most pollen is wasted [1], so they must produce much more to ensure some reaches the right target.

Concept: Pollination efficiency—biotic pollination is more precise than abiotic pollination.

Q10 Total: 4

Question 11 [3 marks]

(a) Animal B [1]

Reason: Gives birth to live young is characteristic of mammals [1] (or long development time suggests parental care typical of mammals).

Accept: Longest development time with most parental investment.

(b) Animal B [1]

Longest development time to adulthood (12 years) [1] indicates extended parental teaching, protection, and learning needed for complex survival skills / higher chance of reaching reproductive age [1].

Concept: K-selection: fewer offspring, more parental care, longer development.

Q11 Total: 3

Question 12 [4 marks]

(a) X = cotyledon(s) [1]; Y = endosperm (if present in diagram) OR accept two cotyledons as "food store structure" [1]

For bean (dicot): cotyledons are the food stores. If "endosperm" labelled, accept. Must name two distinct food-storing structures shown.

(b) Water is needed to activate enzymes [1] that digest stored food into soluble substances [1]. Also softens testa for radicle emergence.

Marking: enzyme activation essential; food mobilisation/digestion for second mark.

Q12 Total: 4

Question 13 [4 marks]

(a) No water means enzymes cannot function / metabolic processes cannot begin / food stores cannot be mobilised [1]

(b) Warm temperature is needed for germination [1]

(c) Seeds in Set 5 would still germinate [1] because light is not required for germination in most seeds (light needed only for some small seeds like lettuce); warmth, water and air are the essential three conditions [1].

Common error: Students think light is needed because plants need light for photosynthesis later, but germination itself is independent of light.

Q13 Total: 4

Question 14 [3 marks]

(a) Sporophyte is diploid (2n) [1]; spores are haploid (n) [1] — accept "sporophyte has double the number of chromosomes" for 1 mark.

Half mark if only state "2n" without explanation.

(b) Sperm (antherozoids) must swim in water [1] from antheridium to archegonium to fertilise the egg [1]. Dry conditions would prevent this; water allows flagellated sperm movement.

Concept: Ferns retain ancestral dependence on water for fertilisation, unlike seed plants with pollen tubes.

Q14 Total: 3

Question 15 [3 marks]

(a) Stamen / anther [1] (accept filament+anther; "stamen" alone acceptable)

(b) The pollen tube grows down the style [1] to deliver male gametes (nuclei) directly to the ovule / egg cell in the ovary [1], ensuring precise fertilisation without sperm needing to swim.

Q15 Total: 3

Question 16 [3 marks]

(a) As the number of offspring per reproduction increases, survival rate to adulthood decreases [1] (negative correlation / inverse relationship).

(b) Many offspring = r-selection strategy [1]: parents cannot care for all, so invest little energy per offspring; some will survive by chance in favourable conditions [1]. Few offspring = K-selection with heavy parental investment ensuring high survival.

Accept: Energy/resources are limited; cannot care for hundreds. Quantity traded against quality of care.

Q16 Total: 3

Section B Total: 20

Section C: Application and Reasoning (Questions 17–20)

Question 17 [4 marks]

(a) Bees are needed for cross-pollination [1]. Without bee visits, pollen may not reach other flowers / self-pollination may occur but seeds are not viable / fertilisation did not occur properly [1]. Tomato flowers are typically self-fertile but benefit from buzz pollination; total failure suggests pollination mechanism not triggered.

Alternative acceptable answer: Fruits can form through parthenocarpy or incomplete fertilisation (fruit without viable seeds); seeds need fertilisation (fusion of gametes) to develop.*

(b) Introduce bee-attracting plants nearby / hand-pollinate flowers using brush to transfer pollen between flowers [1]. This ensures cross-pollination leading to fertilisation and viable seed development [1].

Q17 Total: 4

Question 18 [4 marks]

(a) Frog eggs lack a protective shell [1]; they are covered only by jelly that allows water exchange but not pollution blocking. Land reptile eggs have leathery/ hard shells that reduce pollutant entry and gas exchange with cleaner air [1]. Tadpoles also breathe through permeable skin, absorbing pollutants directly from water [1] — any two points for 2 marks.

(b) Any two: [2]

• Frogs eat insects; decline allows insect population increase [1]
• Frogs are prey for snakes/birds; their decline reduces food for predators [1]
• Frogs occupy middle trophic level; removal disrupts energy flow through food web [1]
• Frogs control pest insect populations; agricultural pest damage may increase [1]

Q18 Total: 4

Question 19 [3 marks]

(a) Any one: [1]

• Faster growth / earlier harvest (no need to grow from seed)
• Genetically identical to parent with desired traits
• No need for pollination / can grow in greenhouse without insects

(b) All plants from seed potatoes are genetically identical (clones) [1]. If parent was susceptible to a disease, all offspring will lack resistance and entire crop could be destroyed simultaneously [1]. Genetic uniformity = no variation for natural selection to act upon.

Concept: Genetic diversity provides insurance against disease; monocultures are vulnerable.

Q19 Total: 3

Question 20 [5 marks]

(a) Any one: [1]

• Polyp can filter feed continuously in one productive location
• Corals of polyps can colonise and build reef structures
• Protected from predators and rough water conditions
• Asexual budding produces many new polyps in safe location

(b) Different forms exploit different niches/habitats [1]: polyp survives as sessile filter-feeder in stable locations; medusa disperses to find new habitats, mates, and escape local competition/predation [1]. This reduces intraspecific competition and spreads risk.

(c) They are same species because: [2]

• One life stage develops into the other in a continuous life cycle [1]
• They share identical DNA/genetic material (medusa buds off from polyp asexually; fertilised egg develops into both) [1]
• Can interbreed (medusa produces gametes that combine to form zygote developing into polyp) [1] — any two points.

Concept: Metamorphosis changes body form but not species identity; same genetic program expressed differently in each stage.

Q20 Total: 5

Section C Total: 12

Grand Total: 40 marks

Difficulty Distribution Summary

Timing estimate: 40 minutes appropriate; 2 min/Q1–8, 3–4 min/Q9–16, 5–6 min/Q17–20, with 4 min review buffer.