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

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SA2 Practice Paper - Science Primary 4

Version 2 of 5 — ANSWER KEY

Total Marks: 60 marks

SECTION A: MULTIPLE CHOICE ANSWERS (20 marks)

SECTION B: OPEN-ENDED ANSWERS (40 marks)

Question 21 (2 marks)

(a) Object X is a living thing. (0.5 mark)

Reason: It can move on its own, grow, and respond to changes — all characteristics of living things. (0.5 mark)

Teaching note: Living things show MRS GREN characteristics: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition. Object X shows three key characteristics.

(b) Object Z could be a crystal / ice cube / seed (before germination). (0.5 mark)

Explanation: Crystals grow bigger as more dissolved substance settles on them, but they are not living because they cannot move on their own or respond to stimuli. OR A seed grows into a plant but before it germinates, it does not move or respond. (0.5 mark)

Alternative acceptable answers: A cloud growing bigger (non-living, accumulates water), a stalactite/stalagmite (mineral deposit growing).

Common mistake: Students often think that "growth" alone means living. Must emphasize that living things need MULTIPLE characteristics together.

Question 22 (3 marks)

(a) Leaf B comes from a monocot plant. (0.5 mark)

Explanation: Leaf B has parallel veins — veins that run side by side from base to tip without forming a network. Monocot plants have parallel-veined leaves. (0.5 mark)

Also accept if student identifies Leaf A as dicot with supporting explanation: Leaf A has net-like/reticulate veins, which is a dicot feature. Both approaches valid.

(b) Leaf D is thick and fleshy. (0.5 mark)

This adaptation stores water in the leaf tissue. In dry conditions, water is scarce, so storing water helps the plant survive long periods without rain. The thick surface also reduces water loss through evaporation. (0.5 mark)

Teaching note: Succulent plants like aloe vera and cacti have this adaptation. The fleshy tissue is modified for water storage, not food storage (that's tubers like potatoes).

(c) Having many small leaflets instead of one large leaf allows the leaf to fold up or close when touched (in sensitive plants like mimosa), reducing water loss and damage from strong winds or animals. OR: Small leaflets can turn to follow sunlight better, maximizing photosynthesis. OR: If one leaflet is damaged/eaten, the plant still has many others to continue making food. (1 mark for any valid reason)

Question 23 (3 marks)

(a) Incomplete metamorphosis. (1 mark)

Teaching note: Complete metamorphosis has four stages (egg → larva → pupa → adult) with a pupal stage. Incomplete metamorphosis has three stages with no pupa — the young (nymph) resembles a smaller adult.

(b) The nymph has no wings / very small wing buds, while the adult has fully developed wings. (1 mark)

Alternative valid answers: Nymph cannot reproduce; adult can reproduce. Nymph may have different colouration. Nymph molts several times, adult does not grow more.

(c) Cockroach / dragonfly / praying mantis / termite / lice. (1 mark)

Note: Must be an insect with incomplete metamorphosis. Butterfly/moth/beetle/fly/mosquito have complete metamorphosis and are incorrect.

Question 24 (4 marks)

(a) The sunbird shows the clearest preference. (0.5 mark)

Evidence: 18 sunbirds visited the fruit station, but only 1 visited seeds and 4 visited insects. The difference of 17 between highest and lowest shows strong preference. Compared to sparrow (15 vs 2 vs 3, difference 13) and mynah (more even distribution). (1 mark for clear data comparison)

Marking note: Must name the bird AND use numerical evidence. "Sunbird likes fruits" alone = 0.5 mark maximum.

(b) No, his conclusion is not correct. (0.5 mark)

Explanation: The sunbird barely visited seeds (only 1 bird), and the mynah also preferred other foods. Not all birds eat seeds — the data shows sunbirds prefer fruits. A correct conclusion would be "Some birds eat seeds" or "Sparrows prefer seeds." (1 mark)

Common mistake: Students confuse "all" with "some." Must evaluate the absolute claim against evidence.

(c) Any one of: Repeat the experiment on different days; use more feeding stations; observe for longer time (e.g., several days); use equal amounts of each food type; place stations at same distance from bird nesting areas; count visits by same observer to reduce error. (1 mark)

Question 25 (3 marks)

(a) Both have streamlined bodies / smooth, tapered shapes that reduce water resistance when swimming. (1 mark)

Alternative: Both have limbs modified as flippers/paddles for swimming.

(b) Animal X (Penguin): Bird — it has feathers and lays eggs. (0.5 mark) Animal Y (Whale): Mammal — it has hair (at some stage), gives birth to live young, and feeds babies with milk. (0.5 mark)

Teaching note: Whales are mammals despite looking fish-like. Key distinguishing features: whales have horizontal tail flukes (fish have vertical), breathe air through blowholes, give live birth, nurse with milk. Penguins are birds — they have feathers, lay eggs, and are warm-blooded.

(c) Whales are mammals because: they breathe air through lungs (not gills), they give birth to live young (not eggs), and they feed their babies with milk. Fish have gills, lay eggs, and do not produce milk. (1 mark for any two correct reasons)

Question 26 (3 marks)

(a) Crustacean. (1 mark)

Teaching note: Key features of crustaceans: hard exoskeleton, two pairs of antennae, primarily aquatic, variable leg numbers (crabs have 10 legs including claws). Crayfish, lobster, shrimp are also crustaceans with similar features.

(b) Crab / prawn / shrimp / lobster / crayfish. (1 mark)

Note: Must be a crustacean that is eaten. "Prawn" or "shrimp" acceptable.

(c) The hard outer shell (exoskeleton) protects the animal's soft body from predators and physical damage. It also helps prevent water loss and provides support for muscles to attach to. (1 mark for any valid protective function)

Question 27 (4 marks)

(a) Producer: Cabbage / Tomato plant / Grass (any one = 0.5 mark) Consumer: Caterpillar / Grasshopper / Rabbit / Frog / Bird / Snake / Hawk (any one = 0.5 mark)

(b) The bird population will decrease. (0.5 mark)

Explanation: Birds eat caterpillars and grasshoppers. With fewer caterpillers, birds lose one food source. Even though they still eat grasshoppers, the total available food decreases, so fewer birds can be supported in the garden. (1.5 marks)

Alternative valid prediction: Some birds may leave the garden to find food elsewhere; bird population becomes smaller or less healthy.

(c) A food web shows all the feeding relationships in an ecosystem, not just one chain. (0.5 mark) Organisms often eat more than one type of food and are eaten by multiple predators. If one species is removed, the food web shows alternative pathways, making it more realistic than a simple linear chain. (0.5 mark)

Teaching note: Food chains oversimplify; food webs show interconnectedness and greater stability.

Question 28 (3 marks)

(a) Animal M is the mammal. (0.5 mark)

Reason 1: It has hair/fur on its body. (0.5 mark) Reason 2: It gives birth to live young (not eggs). (0.5 mark)

Teaching note: Warm-blooded alone is not sufficient (birds are also warm-blooded). The combination of hair + live birth definitively identifies mammals.

(b) Salamander / newt / toad / caecilian. (0.5 mark)

Note: All amphibians have moist skin. "Frog" was given in question, so must name a different amphibian.

(c) Being warm-blooded means they can maintain a constant body temperature regardless of the outside temperature. (0.5 mark) This allows them to stay active and hunt or escape predators in cold weather, while cold-blooded animals become sluggish and must warm up in the sun. (0.5 mark)

Question 29 (4 marks)

(a) Most earthworms will be found in the dark compartment. (0.5 mark)

Explanation: Earthworms have no eyes and live underground where it is dark and moist. Bright light can dry out their skin and harm them. They move away from light (negative phototaxis) to stay in dark, damp conditions that keep their skin moist for breathing. (1.5 marks)

Teaching note: Earthworms breathe through their moist skin. If skin dries, they cannot breathe and will die. This is why they surface after rain (waterlogged tunnels) and stay underground in dry weather.

(b) Using 100 earthworms gives more reliable results because: the sample size is larger so random movements of individual worms matter less; the result is less affected by unusual behaviour of a few worms; easier to see a clear pattern/trend. (1 mark for any valid reason)

(c) Amount/volume of damp soil; type of soil; temperature of environment; size of earthworms; same time of day for experiment. (0.5 mark for any valid controlled variable)

(d) Earthworms are living things and should be treated with care/respect. OR Returning them maintains the natural ecosystem where they contribute to soil health. OR It is ethical not to harm animals used in experiments. (0.5 mark)

Question 30 (3 marks)

(a) The dark purple colour indicates the presence of starch. (1 mark)

Teaching note: Iodine solution is a test for starch. Starch is produced during photosynthesis, so its presence shows the leaf has been making food.

(b) Leaf P has stomata on its lower surface where gas exchange occurs for photosynthesis; OR Leaf P was exposed to light and could photosynthesize; OR Leaf Q may have been kept in darkness so could not make starch; OR Leaf Q has fewer/no stomata on the lower surface. (1 mark for any valid, specific reason)

Common mistake: General answer "Leaf P had more light" without explaining the surface difference is insufficient — the question compares lower surfaces specifically.

(c) Plant P is better able to make food. (0.5 mark)

Explanation: Starch is the food that plants make during photosynthesis. The presence of starch in Leaf P shows that photosynthesis occurred. Leaf Q lacks starch, suggesting little or no photosynthesis happened, so the plant has less food stored. (0.5 mark)

Question 31 (4 marks)

(a) Similarity: Both are found in coastal/marine areas; both are found in warm tropical regions; both need clean water to survive. (0.5 mark for valid similarity)

Difference: Mangroves grow along the shoreline/coast (intertidal zone), while coral reefs grow offshore in deeper, clearer seawater; OR Mangroves are plants/trees, coral reefs are made of animals (coral polyps); OR Mangroves are found in muddy/silty water, coral reefs need clear water. (0.5 mark for valid difference)

(b) Mangrove muddy water has very little oxygen. The roots that grow above water (pneumatophores or prop roots) have pores (lenticels) that can take in air directly. (1 mark)

This allows the roots to breathe/get oxygen even when submerged at high tide or when the mud is low in oxygen. Without these special roots, the tree would suffocate. (1 mark)

Teaching note: This is root adaptation for anaerobic (oxygen-poor) conditions. Salt-excreting leaves and vivipary (seeds germinate while attached to parent) are other mangrove adaptations not asked here.

(c) Use cleaner fuels for ships; create designated shipping lanes away from sensitive areas; treat ballast water before release; enforce laws against oil dumping; use double-hulled tankers to prevent spills. (1 mark for any practical, valid suggestion)

Question 32 (4 marks)

(a) Rain trees / shrubs / grass / herbs / flowers (any two = 1 mark; 0.5 each)

Note: Must name plants, not animals. "Trees" alone is vague — specific types from context preferred.

(b) The cat could hunt and catch native animals like birds, lizards, and insects. (0.5 mark)

This reduces the population of these animals. If too many are killed, some species could become rare or disappear from the garden. The cat is not part of the natural food web here. (0.5 mark)

Alternative: Cat waste could introduce diseases; cats compete with native predators.

(c) Fallen leaves decompose to return nutrients to the soil, helping plants grow. (0.5 mark)

They also provide hiding places and food for small animals like insects, earthworms, and lizards. Removing leaves disrupts nutrient cycling and removes habitat, reducing biodiversity. (0.5 mark)

(d) Plant more flowering plants / nectar-producing plants that butterflies feed on; plant host plants that caterpillars eat (like lime leaves for lime butterflies); provide shallow water dishes; avoid using pesticides that kill caterpillars and butterflies. (1 mark for any valid suggestion)

MARK ALLOCATION SUMMARY

Time Estimate: 75 minutes total

• Section A: ~20 minutes (1 min per question)
• Section B: ~45 minutes (3–4 min per question)
• Review: ~10 minutes buffer