Primary 6 PSLE Science Semestral Assessment 2 (End of Year) Paper 5

TuitionGoWhere Practice Paper — Science Primary 6 PSLE

SA2 (Version 5 of 5) — Answer Key and Marking Scheme

Total Marks: 80

Section A — Multiple Choice Questions (2 marks each × 10 = 20 marks)

1. B — Number of body parts and type of skeleton

• Marking note: Classification is based on structural/observable biological features, not superficial traits like colour or speed. Size varies within groups and is not a reliable classifier.

2. A — Organism P

• Marking note: Birds are characterised by having feathers, lungs, and laying eggs. Only Organism P has all three. S has feathers but does not lay eggs (unlikely for a bird in this context).

3. C — Green plants

• Marking note: Green plants contain chlorophyll and can make their own food by photosynthesis. Fungi and animals cannot make their own food. Most bacteria cannot photosynthesise (some exceptions exist but are not the focus at P6).

4. B — Ability to conduct electricity

• Marking note: Group 1 contains metals (copper, iron, aluminium) which are good electrical conductors. Group 2 contains non-metals/insulators (wood, plastic, rubber) which do not conduct electricity well.

5. C — They reproduce.

• Marking note: All living things carry out life processes including reproduction. Not all living things can fly (A), have backbones (B), or live on land (D).

6. C — Organism R

• Marking note: Fish have no legs, no wings, and have fins. Organism R fits this description. P is a bird (has feathers and wings). Q has no feathers but has wings — could be a bat. S has no legs, no wings, and no fins — could be a snake or worm.

7. C — The colour of their skin

• Marking note: Skin colour varies widely within species and is not a scientifically valid basis for classification. The other options are standard classification criteria.

8. C — Substance Y

• Marking note: Mercury is a metal with a relatively high boiling point (357°C), is insoluble in water, and conducts electricity. These match the properties of Substance Y.

9. C — Are green and can make food.

• Marking note: Ferns, mosses and flowering plants all contain chlorophyll and can carry out photosynthesis. Only flowering plants have flowers (A) and produce seeds (D). Mosses do not have true roots, stems and leaves (D).

10. A

• Marking note: Fish, frogs, birds, and insects are correctly placed. Insects and crabs are invertebrates (no backbone); earthworms are also invertebrates. Option A is the only one that correctly places all organisms.

Section B — Short-Answer Questions (35 marks)

11. Classification of invertebrates [4]

(a) [1 mark] Number of legs / presence of exoskeleton / body segments / presence of antennae / type of skeleton (any one valid visible feature)

• Acceptable answers: "Number of legs," "body covering," "presence of antennae," "number of body segments"

(b) [2 marks]

• Example answer using "number of legs":
  • Group 1 (6 legs): Grasshopper
  • Group 2 (more than 6 legs or no legs): Crab (10 legs), Spider (8 legs), Earthworm (no legs)
• Marking note: Award 1 mark for each correctly filled group. Groups must correspond to the feature stated in (a). Accept any logical grouping based on a valid feature.

(c) [1 mark] Any other valid feature not used in (a), e.g., "presence of wings," "body shape," "habitat," "type of skeleton"

• Marking note: Must be different from the feature in (a).

12. Vertebrate classification [4]

(a) [2 marks] Vertebrate A is most likely a fish.

• Reason: It has scales, lays eggs, breathes through gills, and is cold-blooded — all characteristics of fish.
• Marking note: Award 1 mark for identifying A, 1 mark for a valid explanation referencing at least two features from the table.

(b) [2 marks] Vertebrate C is a mammal.

• Reasons (any two):
  1. It has fur (body covering of fur/hair).
  2. It gives birth to young alive (does not lay eggs).
  3. It breathes through lungs.
  4. It is warm-blooded.
• Marking note: Award 1 mark for identifying C, 1 mark for giving two valid reasons (½ mark each if only partial).

13. Material classification [4]

(a) [3 marks]

• Example answer:
  • Natural fibres: Cotton, silk, wool
  • Synthetic (man-made) fibres: Nylon, polyester, rayon
• Marking note: Award 1 mark for stating the classification criterion (natural vs. synthetic), 1 mark for correctly listing Group 1, 1 mark for correctly listing Group 2. Accept other valid classifications (e.g., animal-derived vs. plant-derived vs. fully synthetic) if correctly executed.

(b) [1 mark] This classification is useful because it helps us choose the right material for different purposes / understand the properties of materials / know how to care for fabrics (e.g., washing instructions differ).

• Marking note: Accept any reasonable practical explanation.

14. Classification key for invertebrates [3]

(a) [2 marks] Two features to separate jellyfish from others (any two of the following):

1. Body shape (jellyfish has a bell/umbrella shape; others do not)
2. Presence of tentacles (jellyfish has tentacles; others do not)
3. Body symmetry (jellyfish has radial symmetry; others have bilateral symmetry)
4. Skeleton type (jellyfish has no hard parts; starfish has a hard endoskeleton)

• Marking note: 1 mark per valid feature.

(b) [1 mark] Prawn has an exoskeleton / jointed legs / antennae, while snail has a shell / muscular foot / no jointed legs.

• Acceptable answers: "Prawn has an exoskeleton but snail has a shell," "Prawn has jointed legs but snail does not," "Prawn has antennae but snail has tentacles"

15. Plant and fungi classification [6]

(a) [4 marks — 1 mark each]

• W: Flowering plant (angiosperm) — Has chlorophyll, true roots, flowers, and seeds.
• X: Fern — Has chlorophyll, no true roots, no flowers, has spores (not seeds).
• Y: Fungus (e.g., mushroom) — No chlorophyll, no true roots, no flowers, has spores.
• Z: Non-vascular plant (e.g., moss/liverwort) — No chlorophyll stated (Z has no chlorophyll, no spores, no seeds, no true roots, no flowers — this is unusual; accept "bacteria" or "fungus without spores" if reasoned. However, given the table, Z could be a non-photosynthetic organism without spores — most likely a bacterium or a non-spore-producing organism.)
• Revised marking note for Z: Accept "bacteria" or "non-photosynthetic organism" with reasoning. If the student identifies Z as an organism without chlorophyll, spores, or seeds, award the mark.

Clarification for examiners: Organism Z lacks chlorophyll, roots, flowers, spores, and seeds. The most appropriate answer at P6 level is bacteria or a non-photosynthetic organism without spores.

(b) [2 marks] Organism X is a fern.

• Explanation: It has chlorophyll (can make food), has spores but no seeds, and does not have true roots or flowers. These are characteristics of ferns.
• Marking note: 1 mark for identifying X, 1 mark for explanation referencing spores and absence of seeds/flowers.

16. Dichotomous key for leaves [6]

(a) [4 marks] Example key:

1a. Leaf is simple .............................. go to 2
1b. Leaf is compound ........................... go to 3

2a. Leaf margin is smooth ....................... go to 4
2b. Leaf margin is toothed ...................... Leaf Q

3a. Leaf margin is smooth ....................... Leaf R
3b. Leaf margin is toothed ...................... Leaf T

4a. Venation is parallel ........................ Leaf P
4b. Venation is net-like ........................ Leaf U

• Marking note: Award 1 mark per correctly written pair of statements (4 pairs = 4 marks). Accept alternative valid keys. The key must correctly separate all six leaves.

(b) [2 marks] Leaves Q and U are most similar (both are simple leaves with toothed/smooth margins and net-like venation — actually Q and U differ in margin).

• Better answer: Leaves P and U are most similar because they both have smooth margins and simple leaves (they differ only in venation). OR Leaves R and T are most similar because they are both compound leaves with net-like venation (they differ only in margin).
• Marking note: Accept any pair with a valid reason. 1 mark for identifying the pair, 1 mark for a valid reason.

17. Habitat diversity analysis [6]

(a) [2 marks] Habitat Y is most likely a pond.

• Explanation: Habitat Y has a large number of fish (35) and crabs (28), which are aquatic organisms. Habitat X has no fish, suggesting it is a land-based habitat.
• Marking note: 1 mark for identifying Y, 1 mark for explanation referencing fish and/or crabs.

(b) [2 marks] Two abiotic factors:

1. Amount of water / moisture — Habitat X may be drier, reducing insect populations.
2. Temperature — Different temperatures affect insect survival and reproduction.

• Also accept: Light intensity, humidity, wind, soil type, availability of food (if abiotic context is clear).
• Marking note: 1 mark per valid abiotic factor.

(c) [2 marks] Yes, I agree.

• Explanation: Habitat Y has five types of organisms present (insects, birds, fish, crabs, plants) with relatively high numbers across all groups, while Habitat X has no fish at all and fewer types of organisms represented. Habitat Y therefore has greater biodiversity (more variety of species).
• Marking note: Award 1 mark for stating agreement/disagreement with reasoning, 1 mark for using data from the table. Accept "disagree" if supported with valid data reasoning.

18. Material property classification [4]

(a) [2 marks]

• Conductors: Steel nail
• Insulators: Wooden ruler, glass rod, rubber band
• Marking note: 1 mark for each correctly completed group. Steel is a metal and conducts electricity; wood, glass, and rubber are insulators.

(b) [2 marks]

• Example:
  • Property: Flexibility / hardness / transparency / density (any valid property)
  • Group 1 (Flexible): Rubber band
  • Group 2 (Rigid): Wooden ruler, glass rod, steel nail
• Marking note: 1 mark for stating a valid property, 1 mark for correctly grouping the objects. Accept any valid property and correct grouping.

Section C — Structured / Longer-Answer Questions (25 marks)

19. Classification of a newly discovered organism [10]

(a) [1 mark] Amphibian

(b) [2 marks] Two reasons:

1. It has moist, smooth skin and is cold-blooded, which are characteristics of amphibians.
2. It lays eggs in water, and the young breathe through gills while the adult breathes through lungs and skin — this is typical of amphibians (metamorphosis from aquatic young to semi-terrestrial adult).

• Marking note: 1 mark per valid reason. Must reference specific features from the description.

(c) [1 mark] Reptile

(d)(i) [2 marks] Two features:

1. Number of legs (insects have 6 legs; centipedes and millipedes have many legs)
2. Number of body segments / wings present or absent / number of legs per segment

• Acceptable alternatives: Presence of wings, body shape, antennae type, habitat
• Marking note: 1 mark per valid feature that can distinguish the four organisms.

(d)(ii) [4 marks] Example key:

1a. Has 6 legs ................................. go to 2
1b. Has many legs .............................. go to 3

2a. Has wings ................................. Butterfly
2b. Has no wings / has hard wing covers ...... Beetle

3a. Has one pair of legs per segment .......... Centipede
3b. Has two pairs of legs per segment ......... Millipede

• Marking note: Award 1 mark per correctly written branching point (4 branch points = 4 marks). Accept alternative valid keys. Each organism must be correctly identified at the end of a branch.

20. Material properties and classification [10]

(a) [3 marks] Material A is most likely a metal.

• Reasons (any two for 2 marks, plus 1 mark for correct identification):
  1. It is a good electrical conductor (metals conduct electricity well).
  2. It is a good thermal conductor (metals conduct heat well).
  3. It has a high density (7.9 g/cm³, similar to iron/steel).
  4. It is rigid and opaque (typical metallic properties).
• Marking note: 1 mark for identifying A, 1 mark per valid reason (max 2 reasons).

(b) [1 mark] Transparency — Material B is transparent while Material D is opaque.

• Also accept: Density (B = 1.0 g/cm³, D = 0.9 g/cm³) or any other valid distinguishing property from the table.

(c) [2 marks] Material C would be more suitable.

• Explanation: Material C is rigid and has poor thermal conductivity, meaning it would not heat up easily and would protect the user's hand from the heat of the cooking pot. Material D is flexible and also has poor thermal conductivity, but a flexible handle would not be practical for gripping a hot pot.
• Marking note: 1 mark for choosing C, 1 mark for explanation referencing thermal conductivity and/or rigidity. Accept D with valid reasoning about thermal insulation, but note that rigidity is important for a handle.

(d) [2 marks] Two properties supporting glass identification:

1. It is transparent (glass is transparent).
2. It is rigid and has poor electrical and thermal conductivity (glass is an insulator for both electricity and heat).

• Marking note: 1 mark per valid property linked to glass.

(e) [2 marks] Materials A and F have similar properties because they are both metals.

• Explanation: Both materials are good electrical and thermal conductors, are rigid and opaque. These are characteristic properties of metals. Material A (density 7.9 g/cm³) is likely iron or steel, and Material F (density 2.7 g/cm³) is likely aluminium.
• Marking note: 1 mark for stating they are both metals, 1 mark for explanation referencing shared properties (conductivity, rigidity, opacity).

— END OF ANSWER KEY —

Mark Summary

Common Mistakes to Watch For

• Q1: Students may choose "colour" — remind them classification uses consistent structural features.
• Q6: Students may confuse Organism S (no legs, no wings, no fins) with a fish. Emphasise that fish have fins.
• Q11–14: Students may give vague features (e.g., "looks different"). Insist on specific, observable features.
• Q15: Organism Z is unusual; accept reasoned answers. The key point is that it lacks chlorophyll, spores, and seeds.
• Q16: Students may struggle with dichotomous key construction. Remind them each level must have exactly two choices that are opposites.
• Q19: Students may confuse amphibians with reptiles. Key differentiator: amphibians have moist skin and lay eggs in water; reptiles have dry scaly skin and lay eggs on land.
• Q20: Students may not link material properties to real-world applications. Encourage reasoning about why certain properties matter for specific uses.