Primary 5 Science Semestral Assessment 2 (End of Year) Paper 4

TuitionGoWhere Exam Practice (AI) - SA2 Version 4

Answer Key and Marking Scheme

Subject: Science
Level: Primary 5
Total Marks: 60

Section A: Multiple Choice (2 marks each)

Section A Total: 20 marks

Section B: Structured Questions

Question 11 (4 marks)

(a) Answer: Leaf A [1 mark]

Reason: Leaf A has a thick waxy cuticle/layer that reduces water loss. [1 mark]

Teaching note: In dry environments, plants need to conserve water. The thick, waxy cuticle on Leaf A acts as a waterproof barrier, preventing water from evaporating from the leaf surface. The smaller size also reduces surface area for water loss.

(b) Answer: Leaf B is large and broad, which gives it a large surface area to capture more sunlight for photosynthesis. [2 marks]

Marking breakdown:

• Large surface area identified [1 mark]
• Link to photosynthesis/sunlight capture [1 mark]

Teaching note: Broad, thin leaves are typical of plants in shady or wet environments where water conservation is less critical. The large surface area maximises light absorption for photosynthesis, where plants convert light energy into food (glucose).

Question 12 (5 marks)

(a) Answer: Worm/Other group [1 mark]

Working: Earthworm → No backbone → No jointed legs → No shell → Worm/Other

(b) Answer: Both have jointed legs (and an exoskeleton). [1 mark] Following the key, this places them both in the Arthropod group. [1 mark]

Teaching note: A dichotomous key uses one characteristic at a time to split organisms into smaller groups. Despite looking different, grasshoppers and spiders share the key feature of jointed legs, which is the branch point used here. Other arthropod features include body segmentation and hard outer covering (exoskeleton).

(c) Answer: Reptile/Fish/Amphibian branch (or "the non-feather, non-fur group") [1 mark]

Explanation: It has a backbone but no feathers and no fur; scales suggest fish or reptile. Since it lives in water with scales, it is most likely a fish. [1 mark]

Teaching note: The key branches at "backbone → feathers → fur." Without feathers or fur, the animal falls into the remaining vertebrate category. Scales are found on fish and reptiles, but the aquatic habitat strongly indicates fish.

Question 13 (4 marks)

(a) Answer: Bacteria have no nucleus / protozoa have a nucleus (or bacteria are prokaryotes, protozoa are eukaryotes). [1 mark]

(b) Answer: Viruses are non-living / viruses cannot reproduce by themselves. [1 mark] They need to infect a host cell to reproduce. [1 mark]

Teaching note: Living things carry out life processes independently—nutrition, respiration, growth, reproduction, excretion, movement. Viruses lack cellular structure and cannot reproduce or carry out any life process without entering a living host cell. They are considered at the boundary of life.

(c) Answer: Yeast is used to make bread rise / mushrooms are eaten as food / fungi used to make antibiotics like penicillin / fungi decompose dead matter to recycle nutrients. [1 mark] (Any valid example accepted)

Question 14 (4 marks)

(a) Answer: Mangrove leaves / the mangrove plant. [1 mark]

Teaching note: Producers are organisms that make their own food through photosynthesis using sunlight, water, and carbon dioxide. All plants are producers.

(b) Answer: The small bird population would increase at first. [1 mark] Without eagles preying on them, more small birds would survive and reproduce. [1 mark]

Teaching note: This demonstrates predator-prey relationships in food chains. Removing a predator typically causes a population increase in the prey species. However, long-term, the small bird population might crash if they over-consume caterpillars or overpopulate their habitat.

(c) Answer: Decomposers break down dead organisms and waste materials, returning nutrients to the soil for producers to use. [1 mark]

Teaching note: Bacteria and fungi are decomposers in most ecosystems. They recycle nutrients by breaking down complex organic matter into simple substances that plant roots can absorb, completing the nutrient cycle.

Question 15 (5 marks)

(a) Answer: Setup Q. [1 mark]

Explanation: Setup Q has both moisture and warm temperature, which are ideal conditions for mould (fungi) to grow. [1 mark]

Teaching note: Mould growth requires: (1) moisture/water, (2) suitable temperature, (3) food source (bread). Setup Q provides all three optimal conditions. Fungi cannot grow in dry conditions and grow very slowly in cold conditions.

(b) Answer: Setup P is dry / lacks moisture. [1 mark] Mould (fungi) needs water to grow and reproduce. [1 mark]

Teaching note: While both setups have food and suitable temperature, water is essential for fungal life processes including spore germination and nutrient absorption through hyphae.

(c) Answer: To act as a control / to show the effect of temperature on mould growth / to compare with Setup Q to show that lower temperature slows mould growth. [1 mark]

Teaching note: A control or comparison setup ensures that any differences observed are due to the variable being tested. Here, Setup R (cold, wet) compared with Setup Q (warm, wet) isolates temperature as the variable affecting growth rate.

Question 16 (4 marks)

(a) Answer: Venus flytraps grow in soil that is poor in nutrients (especially nitrogen). [1 mark] The insects provide additional nutrients like nitrogen that the plant cannot get enough of from the soil. [1 mark]

Teaching note: Photosynthesis provides glucose (energy) but does not supply minerals. Plants normally absorb nitrates from soil for making proteins and other essential molecules. In nitrogen-poor bog habitats, Venus flytraps supplement their mineral nutrition by digesting insects.

(b) Answer: It would trap fewer insects / might not need to trap insects at all. [1 mark] The plant could obtain enough nitrogen from the soil instead. [1 mark]

Teaching note: This demonstrates how organisms' adaptations relate to their environment. The trapping mechanism is energetically expensive; if soil provides sufficient nutrients, there is no selective advantage to maintaining elaborate traps, and the plant may reduce this behaviour or grow larger through regular photosynthesis alone.

Section C: Open-Ended Questions

Question 17 (5 marks)

(a) [3 marks — 1 mark per correct row]

(Any three correct rows accepted)

(b) [2 marks]

Mushrooms cannot make their own food / they are heterotrophic. [1 mark] They absorb nutrients from decaying matter through their hyphae (thread-like structures), unlike plants which use chlorophyll for photosynthesis. [1 mark] Their "roots" are actually hyphae for absorption, not true roots for anchorage and water uptake like plants.

Teaching note: A common misconception is that anything growing from soil is a plant. Fungi form a separate kingdom because they lack chlorophyll, have cell walls made of chitin (not cellulose), and obtain food by absorption (not photosynthesis).

Question 18 (6 marks)

(a) [2 marks]

Answer: Complete metamorphosis / complete life cycle. [1 mark]

Explanation: The mosquito has four distinct life stages (egg, larva, pupa, adult) that look very different from each other. [1 mark] The larva and pupa live in water and do not resemble the winged adult.

Teaching note: Incomplete metamorphosis (seen in grasshoppers) has three stages: egg → nymph → adult, where the nymph resembles a smaller adult. Complete metamorphosis has a dramatic transformation (pupa stage) between larval and adult forms.

(b) [2 marks]

Mosquitoes need water for their eggs, larvae, and pupae. [1 mark] Without stagnant water, mosquitoes cannot complete their life cycle / reproduce successfully. [1 mark]

Teaching note: Understanding life cycles helps control pests. Targeting the aquatic stages is most effective because mosquito eggs, larvae, and pupae are concentrated in water and cannot escape. Adult flying mosquitoes disperse widely and are harder to eliminate.

(c) [2 marks]

Suggested method: Use mosquito repellent / spray insecticide / install mosquito netting / introduce mosquito-eating fish / genetic modification of mosquitoes / regular cleaning of gutters. [1 mark]

Explanation: Repellents prevent mosquitoes from biting humans; netting blocks entry; fish eat larvae; insecticides kill adults; genetic methods reduce viable offspring. [1 mark]

Question 19 (5 marks)

(a) [2 marks]

The tiny algae living inside corals make food through photosynthesis. [1 mark] The corals depend on this food/nutrients from the algae. Without algae, the corals lose their food source and starve. [1 mark] (This process is called coral bleaching.)

Teaching note: Corals and algae have a mutualistic relationship—algae get protection and minerals from coral tissue; corals get up to 90% of their nutrition from algal photosynthesis. This symbiosis is the foundation of reef ecosystems.

(b) [1 mark]

Pollution from nearby cities; and overfishing. [1 mark] (Both required for full mark)

(c) [2 marks]

For marine life: Fish lose their homes and food sources / biodiversity decreases. [1 mark]

For humans: People who depend on fishing may not catch enough food / loss of income from tourism and fishing. [1 mark]

(Any two valid impacts, one for marine life and one for humans, accepted)

Question 20 (4 marks)

(a) [2 marks]

Venn diagram or table should show:

Or Venn diagram with:

• Producers circle: Green plants only
• Decomposers circle: Bacteria, Fungi only
• No overlap between producers and decomposers
• Rabbits and birds outside both circles

Marking: Correct classification of all seven organisms [1 mark]; clear diagram/table format with logical groupings [1 mark]

(b) [2 marks]

The student would need to change her conclusion. [1 mark] If some bacteria can make their own food using sunlight, then some decomposers (bacteria) can also be producers. This means the groups are not mutually exclusive. [1 mark]

Teaching note: This question tests logical reasoning and flexibility in classification. Scientific understanding evolves with new evidence. Some bacteria (like cyanobacteria/blue-green algae) are photosynthetic and can be considered both producers and decomposers depending on context, showing that biological classifications can have exceptions and overlaps.

Mark Allocation Summary

Duration check: 75 minutes allows approximately:

• Section A: 1 minute per question = 10 minutes
• Section B: 3 minutes per question = 18 minutes
• Section C: 6-8 minutes per question = 25-32 minutes
• Reading and review = 15-20 minutes

This is manageable for prepared P5 students with review buffer.