Primary 5 Science Systems Quiz

Primary 5 Science Quiz - Systems (Answer Key)

Total Marks: 50

Section A: Multiple-Choice Questions (10 × 2 marks = 20 marks)

1. C — Circulatory system

Explanation: The circulatory system (heart, blood vessels, blood) transports oxygen, nutrients, hormones, and waste products throughout the body. The digestive system breaks down food, the respiratory system handles gas exchange, and the nervous system controls body responses.

2. C — Aorta

Explanation: The aorta is the largest artery and carries oxygen-rich blood from the left ventricle to the body. The pulmonary artery carries deoxygenated blood to the lungs; the pulmonary vein carries oxygenated blood from the lungs to the heart; the vena cava carries deoxygenated blood from the body to the heart.

3. A — Right atrium

Explanation: Deoxygenated blood from the body enters the heart via the vena cava into the right atrium. It then flows to the right ventricle, to the lungs via the pulmonary artery, returns via the pulmonary vein to the left atrium, then left ventricle, and out through the aorta to the body.
Visual reference: In the diagram, the vena cava (H) connects to the right atrium (A), shown by blue arrows.

4. C — Allow exchange of gases (carbon dioxide and oxygen)

Explanation: Stomata are tiny pores on the underside of leaves surrounded by guard cells. They open to allow CO₂ in for photosynthesis and O₂ out, and close to reduce water loss. They do not absorb water (roots do), transport nutrients (xylem/phloem do), or provide support (cell walls do).

5. B — Xylem

Explanation: Xylem transports water and mineral salts from roots to leaves (upward, one-way). Phloem transports food (sugars) from leaves to other parts (bidirectional). Cambium produces new xylem and phloem. Epidermis is the protective outer layer.

6. C — Y

Explanation: In a dicot stem cross-section, vascular bundles are arranged in a ring. In each bundle, xylem is on the inner side (towards the centre) and phloem on the outer side. Y is labelled on the inner part of the vascular bundle, representing xylem (larger, hollow cells for water transport).
Visual reference: The diagram shows Y as the inner portion of each vascular bundle with larger cells.

7. C — Takes in oxygen and removes carbon dioxide

Explanation: The respiratory system (nose, trachea, bronchi, lungs) facilitates gas exchange: oxygen enters the blood, carbon dioxide leaves the blood. Digestion is the digestive system's role; waste removal is mainly the excretory system; movement control is the nervous/muscular systems.

8. C — Oxygen diffuses from the alveoli into the blood

Explanation: In the alveoli, oxygen concentration is higher in the air sacs than in the blood, so O₂ diffuses into the blood. Carbon dioxide concentration is higher in the blood, so CO₂ diffuses out of the blood into the alveoli to be exhaled. Diffusion follows concentration gradients.

9. B — The bulb will become dimmer

Explanation: Adding an identical bulb in series increases total resistance. Current decreases (I = V/R), so each bulb receives less current and becomes dimmer. In series, current is the same through all components; voltage splits across bulbs.

10. C — Copper

Explanation: Copper is a metal and an excellent conductor of electricity. Rubber, plastic, and wood are insulators (do not conduct electricity well). Conductors allow current to flow; insulators block current flow.

Section B: Short-Answer Questions (10 × 3 marks = 30 marks)

11. Human Digestive System

(a) Small intestine [1]
(b) The small intestine is where most digestion is completed and where nutrients are absorbed into the bloodstream. [1]
Key points: receives bile and pancreatic juice, villi increase surface area for absorption.
(c) Undigested food (mainly fibre and water) moves into the large intestine (S), where water is absorbed. The remaining waste (faeces) is stored in the rectum and expelled through the anus (T). [1]
Marking note: Must mention large intestine absorbs water and anus expels waste.

12. Composition of Inhaled and Exhaled Air

(a) Carbon dioxide [1]
Explanation: CO₂ increases from 0.04% to 4% (100× increase). Oxygen decreases from 21% to 16% (only ~24% decrease).
(b) Nitrogen is not used or produced by the body during respiration. It is an inert gas that simply passes through the respiratory system unchanged. [1]
(c) The air passages and alveoli are moist. As inhaled air passes through, it picks up water vapour. Exhaled air is saturated with water vapour at body temperature (37°C). [1]
Alternative: "Air is warmed and moistened in the nasal cavity and respiratory tract."

13. Series-Parallel Circuit

(a) Bulb B3 will remain lit (with normal brightness). [1]
Explanation: B2 and B3 are in parallel. If one branch breaks, the other branch is unaffected because it still has a complete circuit.
(b) Both bulbs B2 and B3 will go out. [1]
Explanation: B1 is in series with the parallel combination. If B1 fuses, the main circuit is broken — no current flows anywhere.
(c) The reading on A1 will be greater than the reading on A2. [1]
Explanation: A1 measures total current from the battery. A2 measures current only through B2. In a parallel circuit, total current = sum of branch currents. Since B2 and B3 are identical, current splits equally: A1 = 2 × A2.

14. Root Cross-Section

(a) Structure A: Root hair. Function: Increases surface area for absorption of water and mineral salts from the soil. [1]
(b) Water enters root hair (A) → moves through cortex (B) cell by cell (osmosis) → passes through endodermis → enters xylem (C) in the vascular cylinder. [1]
Key terms: osmosis, cortex, endodermis, xylem.
(c) The central position of xylem provides structural support to the root (prevents collapse) and allows efficient water transport to the stem. It is protected by surrounding tissues (cortex, endodermis). [1]
Alternative: "Xylem vessels are lignified and strong; central placement anchors the plant and resists pulling forces."

15. Seed Germination Experiment

(a) Set-up W only. [1]
(b) Water (moisture), Air (oxygen), and Suitable temperature (warmth). [1]
All three must be present simultaneously.
(c) Set-up Y is in the freezer at -5°C. The temperature is too low for the enzymes in the seed to function. Metabolic reactions (respiration) needed for germination cannot occur at freezing temperatures. [1]
Key concept: Enzymes are temperature-sensitive; low temperature slows/stops metabolic activity.

16. Food Chain in Garden Ecosystem

(a) Grass [1]
Explanation: Grass is a producer (photosynthesises to make its own food using sunlight).
(b) The frog population will decrease. [1]
Explanation: Frogs feed on grasshoppers. Fewer grasshoppers means less food for frogs, leading to starvation, lower reproduction, or migration.
(c) The Sun [1]
Explanation: Sunlight is the original energy source. Producers (grass) capture solar energy through photosynthesis and convert it to chemical energy, which passes through the food chain.

17. Human Respiratory System

(a) Alveoli (air sacs) [1]
(b) Any two of the following: [1]

• Thin walls (one cell thick) for short diffusion distance
• Moist lining for gases to dissolve
• Large surface area (millions of alveoli)
• Rich blood supply (dense capillary network) for rapid transport
  Marking note: Award 1 mark for any two correct features.
  (c) The diaphragm contracts and flattens (moves downwards). [1]
  Explanation: This increases the volume of the chest cavity, decreasing air pressure inside the lungs, so air rushes in.

18. Parallel Circuit

(a) Bulb B2 will remain lit with the same brightness. [1]
Explanation: In a parallel circuit, each bulb has its own complete path to the battery. If one bulb fuses, the other branch is unaffected.
(b) Each bulb in parallel has the same brightness as a single bulb connected to the same battery. [1]
Explanation: In parallel, each bulb receives the full battery voltage (3V). Current through each bulb is the same as a single bulb circuit.
(c) 3V [1]
Explanation: In a parallel circuit, voltage across each branch is the same as the battery voltage.

19. Life Cycle of a Flowering Plant

(a) Pollination [1]
(b) The petals, stamens, and stigma wither and fall off. [1]
Explanation: After fertilisation, their functions are complete. The ovary develops into fruit, ovules into seeds.
(c) Any one of the following: [1]

• By wind (e.g., dandelion, grass)
• By animals (e.g., burrs on fur, seeds in fleshy fruits eaten and excreted)
• By water (e.g., coconut, lotus)
• By splitting/explosion (e.g., rubber tree, balsam)
  Marking note: Accept any valid dispersal method.

20. Pond Food Web

(a) Example: Algae → Tadpole → Small fish → Kingfisher [1]
Other valid chains: Water plants → Water snail → Large fish → Kingfisher; Algae → Water snail → Large fish → Kingfisher.
Marking note: Must have 4 organisms, arrows pointing from prey to predator, starting with a producer.
(b) The algae population may increase. [1]
Explanation: Water snails feed on algae. Removing snails reduces grazing pressure on algae, so algae population grows (unless limited by other factors).
(c) Decomposers break down dead organisms and waste materials, returning nutrients to the environment for producers to reuse. [1]
Key concept: Nutrient recycling; without decomposers, nutrients would be locked in dead matter.

Section C: Structured / Long-Answer Questions (0 × 5 marks = 0 marks)

No Section C questions in this version. All marks allocated to Sections A and B.