Primary 6 PSLE Science Semestral Assessment 2 (End of Year) Paper 3

TuitionGoWhere Practice Paper — Science Primary 6 PSLE

SA2 Version 3 of 5 — Answer Key & Marking Scheme

Section A: Multiple Choice Questions (10 marks)

1. C — Presence of a backbone

• Marking note: Colour, size, and number of body parts are variable and not reliable classification criteria. The presence or absence of a backbone is a fundamental characteristic used to separate vertebrates from invertebrates. [1 mark]

2. A — Organism P

• Marking note: Birds are characterised by having feathers, lungs, and laying eggs. Only Organism P has all three. Organism S has feathers but does not lay eggs (unusual for birds, but based on the table, P is the best answer). [1 mark]

3. C — River

• Marking note: A river is a non-living thing. Mushrooms (fungi), coral (animals), and ferns (plants) are all living organisms. [1 mark]

4. B — They reproduce by spores.

• Marking note: Spirogyra, moss, and fern all reproduce by spores. They do not produce flowers or seeds. Ferns have true roots and stems, but Spirogyra and moss do not, so this is not a shared characteristic. [1 mark]

5. D — They feed their young with milk.

• Marking note: Mammals are characterised by having fur/hair, being warm-blooded, breathing through lungs, and feeding their young with milk. Scales are found in reptiles and fish; gills are found in fish; cold-blooded animals include reptiles, amphibians, and fish. [1 mark]

6. C — Reptile

• Marking note: Following the key: Lizard has a backbone (Go to 2) → No feathers (Go to 4) → Has dry, scaly skin → Reptile. [1 mark]

7. B — Number of cotyledons in the seed

• Marking note: Monocotyledons have one cotyledon; dicotyledons have two. All green plants have chlorophyll and roots, and can photosynthesise — these do not distinguish the two groups. [1 mark]

8. D — Animal Z

• Marking note: Amphibians have moist skin, begin life breathing through gills (young), and develop lungs as adults. They lay eggs, usually in water. Animal Z matches all these features. [1 mark]

9. C — Mushroom

• Marking note: Mushrooms are fungi, which are decomposers. They break down dead organic matter. Grasshoppers are herbivores (primary consumers), eagles are carnivores (secondary/tertiary consumers), and oak trees are producers. [1 mark]

10. C — Crustaceans

• Marking note: An organism found near a pond with a segmented body, no backbone, and many legs is most likely a crustacean (e.g., a water flea or copepod). Insects have 6 legs; myriapods (e.g., centipedes) are typically terrestrial; fish have backbones. [1 mark]

Section B: Short-Answer Questions (25 marks)

11.

(a) They reproduce by spores. / They do not produce seeds. / They do not produce flowers. / They do not have true roots, stems, and leaves (accept for moss and Spirogyra).

• [1 mark] Accept any valid shared characteristic of fern and moss that rose and pine do not share.

(b) They produce seeds. / They have true roots, stems, and leaves. / They are more complex / vascular plants.

• [1 mark] Accept any valid shared characteristic of rose and pine that fern and moss do not share.

(c) Ferns have true roots, stems, and leaves (while mosses do not). / Ferns have vascular tissue (xylem and phloem) for transport, while mosses do not.

• [1 mark] Must refer to a structural complexity difference.

12.

(a) Any two of the following differences (1 mark each):

1. Fish have scales as body covering, while amphibians have moist skin.
2. Fish breathe only through gills, while amphibians can breathe through gills (young) and lungs (adult).
3. Both lay eggs in water — accept if comparing body covering or breathing organ differences.

• [2 marks] Award 1 mark per correct difference. Answers must compare fish vs. reptile using the table.

(b) The dolphin belongs to the mammal group. Dolphins breathe through lungs and give birth to live young, which are characteristics of mammals according to the table.

• [2 marks] 1 mark for correct group (mammal); 1 mark for explanation referencing lung breathing and/or live birth.

13.

(a) The type of leaf margin (smooth vs. toothed/serrated).

• [1 mark]

(b) Leaf Q has a smooth margin, so it goes to step 2, while Leaf R has a toothed margin, so it goes to step 3. They are separated at the first step of the key based on leaf margin type.

• [2 marks] 1 mark for identifying the distinguishing feature (margin type); 1 mark for explaining that they follow different paths in the key.

14.

(a) The producer is grass / plant (the plant that produces leaves).

• [1 mark] Accept "grass" or "plant."

(b) Any two of the following: Snake, Bird, Hawk, Mouse, Lizard, Caterpillar.

• [2 marks] 1 mark per correct consumer. Do not accept grass/plant.

(c) The population of snakes would decrease. Mice are a food source for snakes. Without mice, snakes would have less food available, leading to starvation and a decline in the snake population.

• [2 marks] 1 mark for stating the population would decrease; 1 mark for explaining the loss of food source.

15.

(a) Organism D is most likely a fungus. It has a cell wall and reproduces by spores (like fungi), but it does not have chlorophyll, so it cannot photosynthesise. This matches the characteristics of fungi.

• [2 marks] 1 mark for identifying Organism D; 1 mark for explanation referencing lack of chlorophyll and presence of cell wall/spores.

(b) Organism B is most likely a green plant that produces seeds. It has a cell wall and chlorophyll (so it can photosynthesise), and it does not reproduce by spores — this suggests it reproduces by seeds instead.

• [2 marks] 1 mark for identifying Organism B; 1 mark for explanation referencing chlorophyll (green plant) and not reproducing by spores (implies seed reproduction).

16.

(a) Any one of the following: Fern, Moss, Pine tree, Spirogyra, Algae, Conifer.

• [1 mark] Accept any valid non-flowering plant.

(b) Vertebrates have a backbone, while invertebrates do not have a backbone.

• [1 mark] Must mention backbone/spine.

(c) They reproduce by spores. / They do not produce seeds. / They do not produce flowers.

• [1 mark] Accept any valid shared characteristic of ferns and mosses.

17.

(a) Organism W is an insect. It has 6 legs, an exoskeleton, and no backbone, which are characteristics of insects.

• [2 marks] 1 mark for identifying Organism W; 1 mark for referencing 6 legs and/or exoskeleton.

(b) Organism Y could be a fish or a sea slug / worm-like organism. It has no legs, no backbone, slimy skin, and lives in water — these features are consistent with a fish (no legs, slimy/scaly skin, aquatic, no backbone would be unusual — but given the table, Y has no backbone, so it is more likely an aquatic invertebrate such as a sea slug, leech, or marine worm). Accept any reasonable aquatic invertebrate.

• [2 marks] 1 mark for suggesting a reasonable organism; 1 mark for explaining the reasoning based on the characteristics given.

18.

(a) Molluscs (or Mollusks).

• [1 mark]

(b) Any two of the following (1 mark each):

1. It has a soft body.
2. It has a hard shell.
3. It moves using a muscular foot.
4. It breathes through gills.

• [2 marks] 1 mark per correct characteristic from the description.

Section C: Structured / Open-Ended Questions (15 marks)

19.

(a)

• [3 marks] Award 1 mark for correctly listing all plants (Grass, Crabgrass) and 2 marks for correctly listing all animals (Grasshopper, Earthworm, Butterfly, Ladybird beetle). Deduct ½ mark per missing or misplaced organism (minimum 0).

(b) Any two of the following reasons (2 marks each):

1. The shaded forest floor is more humid / moist, which earthworms and woodlice need to survive as they breathe through their skin / body surface that must stay moist.
2. The shaded forest floor has more dead organic matter / leaf litter, which provides food for earthworms and woodlice (decomposers/detritivores).
3. The shaded forest floor provides protection from direct sunlight and predators, which helps these organisms avoid desiccation and predation.
4. The temperature on the shaded forest floor is cooler and more stable, which suits the survival of these organisms.

• [4 marks] 2 marks per reason. Award 1 mark for the reason and 1 mark for the explanation linking it to the organism's needs.

20.

(a) 1a → 2a → 3b → Dicot

• The sunflower is a plant (1a), it produces flowers (2a), and has two cotyledons (3b), so it is classified as a Dicot.
• [2 marks] 1 mark for correct path; 1 mark for correct final group (Dicot).

(b) 1b → 5a → 6b → 7b → Amphibian

• The frog is an animal (1b), has a backbone (5a), is cold-blooded (6b), and has moist skin (7b), so it is classified as an Amphibian.
• [2 marks] 1 mark for correct path; 1 mark for correct final group (Amphibian).

(c) Limitation: Physical characteristics can be misleading because unrelated organisms may look similar due to convergent evolution (e.g., a dolphin looks like a fish but is a mammal). Some organisms may have features that are not visible externally.

Additional method: Scientists also use DNA analysis / genetic comparison / molecular classification to classify organisms more accurately by examining their genetic material.

• [3 marks] 1 mark for a valid limitation; 1 mark for suggesting an additional method (DNA/genetic analysis); 1 mark for brief explanation of why the method is useful.

(d) Classifying living things helps scientists:

• Organise and make sense of the vast diversity of life on Earth.
• Identify and study relationships between organisms (evolutionary relationships).
• Communicate about organisms using a standard naming and grouping system.
• Predict characteristics of newly discovered organisms based on their group.
• [1 mark] Accept any valid reason. Award 1 mark for a clear, relevant explanation.

Mark Summary

— End of Answer Key —