From Real Exams Quiz
Primary 6 PSLE Science Systems Quiz
Free P6 PSLE Science Systems quiz, Nemo3 Exam version, with questions, answers, and PSLE-focused practice for Singapore students.
These static practice materials are generated from the site's syllabus and paper-generation workflow, with source and model context shown so students and parents can evaluate the material before use.
Questions
Primary 6 PSLE Science Quiz - Systems
Name: ___________________________
Class: Primary 6 _______
Date: _______________
Score: _______ / 50
Duration: 45 minutes
Total Marks: 50
Instructions:
- Answer all questions.
- For Section A, choose the correct option and write its number (1, 2, 3, or 4) in the brackets provided.
- For Section B and C, write your answers in the spaces provided.
- The number of marks for each question is shown in brackets [ ].
- Diagrams are not drawn to scale unless stated.
Section A: Multiple-Choice Questions (20 marks)
Questions 1 to 10 carry 2 marks each.
1. The diagram below shows the human respiratory system.
Generated diagram for Q1.
Which of the following correctly describes the movement of the diaphragm and ribs during inhalation?
(1) Diaphragm relaxes and moves up; ribs move down and in
(2) Diaphragm contracts and moves down; ribs move up and out
(3) Diaphragm contracts and moves up; ribs move down and in
(4) Diaphragm relaxes and moves down; ribs move up and out
[ ]
2. The table below shows the composition of inhaled and exhaled air.
| Gas | Inhaled Air (%) | Exhaled Air (%) |
|---|---|---|
| Oxygen | 21 | 16 |
| Carbon dioxide | 0.04 | 4 |
| Nitrogen | 78 | 78 |
| Water vapour | Variable | Saturated |
Which of the following statements about the changes in air composition is correct?
(1) Oxygen increases because the body produces oxygen during respiration.
(2) Carbon dioxide increases because it is a product of respiration.
(3) Nitrogen decreases because it is used up during respiration.
(4) Water vapour decreases because the lungs absorb water.
[ ]
3. The diagram below shows a cross-section of the human heart.
Generated diagram for Q3.
Blood that is rich in oxygen and low in carbon dioxide is found in which chamber?
(1) Right atrium
(2) Right ventricle
(3) Left atrium
(4) Left ventricle
[ ]
4. The diagram below shows the human digestive system.
Generated diagram for Q4.
In which part of the digestive system does most absorption of digested food take place?
(1) Stomach
(2) Duodenum
(3) Ileum
(4) Large intestine
[ ]
5. The diagram below shows a plant cell and an animal cell.
Generated diagram for Q5.
Which of the following statements correctly compares the two cells?
(1) Only the plant cell has a nucleus.
(2) Only the animal cell has a cell membrane.
(3) The plant cell has chloroplasts but the animal cell does not.
(4) The animal cell has a large central vacuole but the plant cell does not.
[ ]
6. The diagram below shows the human circulatory system.
Generated diagram for Q6.
Which blood vessel carries deoxygenated blood from the heart to the lungs?
(1) Aorta
(2) Pulmonary artery
(3) Pulmonary vein
(4) Vena cava
[ ]
7. The table below shows the results of an experiment to investigate the effect of light intensity on the rate of photosynthesis in a water plant.
| Distance of lamp from plant (cm) | Number of bubbles produced per minute |
|---|---|
| 10 | 48 |
| 20 | 32 |
| 30 | 18 |
| 40 | 8 |
| 50 | 2 |
Which of the following conclusions can be drawn from the results?
(1) The rate of photosynthesis increases as light intensity decreases.
(2) The rate of photosynthesis decreases as light intensity decreases.
(3) Light intensity has no effect on the rate of photosynthesis.
(4) The rate of photosynthesis is highest at 50 cm.
[ ]
8. The diagram below shows a food chain in a pond community.
Generated diagram for Q8.
If a disease kills most of the water fleas, what will most likely happen to the population of small fish?
(1) Increase, because there is less competition for food.
(2) Increase, because the large fish have less food.
(3) Decrease, because there is less food for the small fish.
(4) Remain the same, because small fish can eat algae directly.
[ ]
9. The diagram below shows the human excretory system.
Generated diagram for Q9.
Which of the following substances is removed by the kidneys and excreted in urine?
(1) Glucose
(2) Oxygen
(3) Urea
(4) Proteins
[ ]
10. The diagram below shows a reflex arc.
Generated diagram for Q10.
What is the function of the interneuron in a reflex arc?
(1) Detects the stimulus
(2) Carries impulses from the receptor to the spinal cord
(3) Processes the impulse and connects sensory neuron to motor neuron
(4) Carries impulses from the spinal cord to the effector
[ ]
Section B: Structured Questions (20 marks)
Questions 11 to 16 carry 2 to 4 marks each.
11. The diagram below shows the human respiratory system during gas exchange in the alveoli.
Generated diagram for Q11.
(a) Name the process by which oxygen moves from the alveolus into the blood. [1]
(b) State two structural features of the alveolus that allow efficient gas exchange. [2]
(c) Explain why the blood leaving the lungs is bright red in colour. [1]
12. The diagram below shows the human digestive system with three organs labelled X, Y, and Z.
Generated diagram for Q12.
(a) In which organ (X, Y, or Z) does most chemical digestion take place? [1]
(b) Organ Y has villi and microvilli. Explain how these structures help in the absorption of digested food. [2]
(c) State the main function of organ Z. [1]
13. The diagram below shows a section through a human heart.
Generated diagram for Q13.
(a) Name the blood vessel that carries oxygenated blood away from the left ventricle. [1]
(b) The wall of the left ventricle is thicker than the wall of the right ventricle. Explain why. [2]
(c) What is the function of the valves in the heart? [1]
14. The diagram below shows an experiment to investigate the effect of carbon dioxide concentration on the rate of photosynthesis.
Generated experimental_setup for Q14.
(a) What is the purpose of adding sodium hydrogen carbonate to the water? [1]
(b) State two variables that must be kept constant to ensure a fair test. [2]
(c) The volume of oxygen collected was measured every 5 minutes for 20 minutes. The results are shown below.
| Mass of NaHCO₃ (g) | Volume of O₂ collected in 20 min (cm³) |
|---|---|
| 0 | 2 |
| 1 | 8 |
| 2 | 18 |
| 3 | 26 |
| 4 | 28 |
Describe the relationship between the mass of sodium hydrogen carbonate and the volume of oxygen collected. [1]
15. The diagram below shows a food web in a forest community.
Generated diagram for Q15.
(a) From the food web, write down one food chain with four organisms. [1]
(b) If all the snakes are removed from the community, explain what will happen to the population of grasshoppers. [2]
(c) State the role of decomposers in this community. [1]
16. The diagram below shows the human nervous system.
Generated diagram for Q16.
(a) Which part of the brain (cerebrum, cerebellum, or medulla) controls involuntary actions such as heartbeat and breathing? [1]
(b) State one difference between a voluntary action and a reflex action. [1]
(c) In a reflex action, the impulse does not travel to the brain before the response occurs. Explain the advantage of this. [2]
Section C: Open-Ended Questions (10 marks)
Questions 17 to 20 carry 2 to 3 marks each.
17. The diagram below shows a plant cell and an animal cell as seen under a light microscope.
Generated diagram for Q17.
(a) Identify one structure present in the plant cell but absent in the animal cell. [1]
(b) State the function of the structure you identified in (a). [1]
(c) The cell membrane is described as partially permeable. Explain what this means. [1]
18. The diagram below shows the human circulatory system with blood samples taken from four blood vessels: A, B, C, and D.
Generated diagram for Q18.
The table below shows the oxygen and carbon dioxide content of the blood samples.
| Blood Sample | Blood Vessel | Oxygen Content | Carbon Dioxide Content |
|---|---|---|---|
| 1 | A | Low | High |
| 2 | B | High | Low |
| 3 | C | High | Low |
| 4 | D | Low | High |
(a) Which blood sample (1, 2, 3, or 4) was taken from the pulmonary vein? [1]
(b) Explain why the blood in the pulmonary artery has low oxygen content and high carbon dioxide content. [2]
19. The diagram below shows an experiment to investigate the conditions needed for photosynthesis.
Generated experimental_setup for Q19.
After 6 hours, a leaf from each setup was tested for starch using iodine solution. The results are shown below.
| Setup | Condition | Iodine Test Result |
|---|---|---|
| P | Sunlight, air | Blue-black |
| Q | Sunlight, potassium hydroxide (absorbs CO₂) | Yellow-brown |
| R | Dark cupboard | Yellow-brown |
| S | Sunlight, sodium hydrogen carbonate (releases CO₂) | Blue-black |
(a) What is the purpose of Setup P? [1]
(b) Explain why the leaf in Setup Q did not turn blue-black with iodine. [2]
20. The diagram below shows a cross-section of a leaf.
Generated diagram for Q20.
(a) Name the layer where most photosynthesis takes place. [1]
(b) Explain how the air spaces in the spongy mesophyll help in gas exchange. [1]
(c) State the function of the guard cells. [1]
End of Quiz
Answers
Primary 6 PSLE Science Quiz - Systems (Answer Key)
Total Marks: 50
Section A: Multiple-Choice Questions (20 marks)
1. Answer: (2) [2 marks]
Explanation: During inhalation, the diaphragm contracts and flattens (moves down), and the external intercostal muscles contract, pulling the ribs up and out. This increases the volume of the thoracic cavity, decreasing pressure so air rushes in. Option (1) describes exhalation. Option (3) has diaphragm moving up when contracted (wrong). Option (4) has diaphragm relaxing but moving down (wrong).
2. Answer: (2) [2 marks]
Explanation: During respiration, glucose is broken down with oxygen to release energy, producing carbon dioxide and water vapour as waste products. Therefore, exhaled air has more CO₂ (4% vs 0.04%) and more water vapour (saturated). Oxygen decreases (21% → 16%) because it is used up. Nitrogen remains unchanged (78%) as it is inert and not used in respiration.
3. Answer: (3) [2 marks]
Explanation: Oxygenated blood (rich in O₂, low in CO₂) returns from the lungs via the pulmonary vein into the left atrium. It then passes to the left ventricle to be pumped to the body via the aorta. The right atrium and right ventricle handle deoxygenated blood.
4. Answer: (3) [2 marks]
Explanation: The ileum (final section of the small intestine) has villi and microvilli that provide a huge surface area for absorption of digested nutrients (glucose, amino acids, fatty acids, glycerol, vitamins, minerals). The stomach mainly digests proteins; the duodenum receives digestive juices but absorption is limited; the large intestine absorbs water and minerals, not most nutrients.
5. Answer: (3) [2 marks]
Explanation: Chloroplasts contain chlorophyll for photosynthesis and are found only in plant cells (and some protists). Animal cells lack chloroplasts. Both cells have a nucleus (1 is wrong). Both have a cell membrane (2 is wrong). Plant cells have a large central vacuole; animal cells have small vacuoles (4 is wrong).
6. Answer: (2) [2 marks]
Explanation: The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs to pick up oxygen. The aorta carries oxygenated blood to the body. The pulmonary vein carries oxygenated blood from lungs to left atrium. The vena cava carries deoxygenated blood from body to right atrium.
7. Answer: (2) [2 marks]
Explanation: As distance increases (10 → 50 cm), light intensity decreases, and bubbles per minute decrease (48 → 2). This shows rate of photosynthesis decreases as light intensity decreases (or increases as light intensity increases). Light intensity is inversely proportional to distance squared.
8. Answer: (3) [2 marks]
Explanation: Water fleas are the food source for small fish. If water fleas decrease, small fish have less food, so their population will decrease. This is a direct trophic relationship: Producer → Primary Consumer → Secondary Consumer.
9. Answer: (3) [2 marks]
Explanation: Urea is a nitrogenous waste product from protein metabolism, filtered by kidneys and excreted in urine. Glucose is normally reabsorbed (not in urine unless diabetic). Oxygen is carried by blood, not excreted. Proteins are too large to be filtered (normally absent in urine).
10. Answer: (3) [2 marks]
Explanation: The interneuron (relay neuron) in the spinal cord receives impulses from the sensory neuron, processes them, and passes them to the motor neuron. It enables a rapid response without involving the brain. Sensory neuron carries impulse to spinal cord (2). Motor neuron carries impulse to effector (4). Receptor detects stimulus (1).
Section B: Structured Questions (20 marks)
11. [4 marks]
(a) Diffusion [1 mark]
Accept: Diffusion of oxygen / gaseous diffusion
(b) Two structural features: [2 marks, 1 each]
- One-cell-thick walls (alveolar and capillary walls) → short diffusion distance
- Large surface area (millions of alveoli) → more space for gas exchange
Also accept: Moist lining (dissolves gases), Good blood supply (maintains concentration gradient)
(c) Oxygen combines with haemoglobin in red blood cells to form oxyhaemoglobin, which is bright red. [1 mark]
Key concept: Haemoglobin + O₂ → Oxyhaemoglobin (bright red); Deoxyhaemoglobin (dark red)
Common mistake: Saying "blood turns red because of oxygen" without mentioning haemoglobin.
12. [4 marks]
(a) Y (Small intestine) [1 mark]
Most chemical digestion occurs in the duodenum (first part of small intestine) where bile, pancreatic juice, and intestinal juices act.
(b) Villi and microvilli: [2 marks]
- Increase surface area tremendously (folding + microscopic projections)
- Thin walls (one cell thick) for short diffusion distance
- Rich blood capillary network to transport absorbed nutrients away, maintaining concentration gradient
- Lacteals for fat absorption
Any two well-explained points for 2 marks.
(c) Absorbs water and mineral salts from undigested food; forms and stores faeces temporarily before egestion. [1 mark]
Accept: Absorption of water; formation of faeces.
13. [4 marks]
(a) Aorta [1 mark]
(b) Left ventricle pumps blood to the whole body (systemic circulation), requiring high pressure to overcome long distance and resistance. Right ventricle pumps only to the lungs (pulmonary circulation), a shorter distance with lower resistance. Thicker wall = stronger contraction = higher pressure. [2 marks]
Key comparison: Systemic vs pulmonary circulation; pressure difference.
(c) Valves prevent backflow of blood, ensuring one-way flow through the heart. [1 mark]
Accept: Ensure blood flows in one direction; prevent mixing of oxygenated and deoxygenated blood.
14. [4 marks]
(a) To provide carbon dioxide for photosynthesis / to vary the concentration of CO₂. [1 mark]
NaHCO₃ dissolves → releases CO₂ in water.
(b) Two constant variables: [2 marks, 1 each]
- Light intensity (lamp distance fixed at 20 cm)
- Temperature (maintained at 25°C)
- Type/size of plant (same Elodea)
- Volume of water (500 ml)
- Duration of each trial (20 minutes)
Any two valid.
(c) As the mass of sodium hydrogen carbonate increases, the volume of oxygen collected increases, but the rate of increase slows down at higher masses (plateaus at 4 g). [1 mark]
Accept: Increases then levels off; positive correlation but not directly proportional; CO₂ becomes non-limiting at high concentrations.
15. [4 marks]
(a) Example food chain (4 organisms): [1 mark]
Grass → Grasshopper → Frog → Snake
Or: Grass → Rabbit → Fox → Hawk; Trees → Deer → Fox → Hawk; Shrubs → Grasshopper → Frog → Hawk, etc.
Must start with producer, end with tertiary consumer, arrows from food to consumer.
(b) Snakes eat frogs. If snakes are removed, frog population increases (less predation). More frogs eat more grasshoppers, so grasshopper population decreases. [2 marks]
Step-by-step: Snakes ↓ → Frogs ↑ → Grasshoppers ↓. This is a trophic cascade.
(c) Decomposers (bacteria, fungi) break down dead organisms and waste, recycling nutrients back into the environment for producers to use. [1 mark]
Key words: Break down dead matter, recycle nutrients, return to soil/air.
16. [4 marks]
(a) Medulla [1 mark]
Controls involuntary actions: heartbeat, breathing, blood vessel diameter, swallowing, vomiting.
(b) Difference: [1 mark]
| Voluntary Action | Reflex Action |
|---|---|
| Conscious control / involves brain (cerebrum) | Automatic / involuntary / does not involve brain initially |
| Slower (decision-making) | Very fast (protective) |
| Learned / chosen | Inborn / innate |
Any one clear difference.
(c) Advantage: Rapid response to protect the body from harm (e.g., pulling hand from hot object) without waiting for brain processing, preventing or reducing injury. [2 marks]
Key points: Speed, protection, bypasses brain.
Section C: Open-Ended Questions (10 marks)
17. [3 marks]
(a) Chloroplast / Cell wall / Large central vacuole [1 mark]
Any one correct structure.
(b) Function: [1 mark]
- Chloroplast: Contains chlorophyll, traps light energy for photosynthesis
- Cell wall: Provides structural support, maintains shape, prevents bursting
- Large central vacuole: Stores water/substances, maintains turgor pressure, supports cell
Match function to structure chosen in (a).
**(c) Partially permeable means the membrane allows some substances (like water, oxygen, carbon dioxide) to pass through freely, but restricts or prevents others (like large molecules, ions) from passing. [1 mark]
Also accept: Selectively permeable; controls movement of substances in/out of cell.
18. [3 marks]
(a) Sample 2 [1 mark]
Pulmonary vein carries oxygenated blood from lungs to left atrium → High O₂, Low CO₂.
(b) The pulmonary artery carries blood from the right ventricle to the lungs. This blood has just returned from the body where oxygen was used up in respiration and carbon dioxide was produced. So it is deoxygenated (low O₂) and high in CO₂. [2 marks]
Key trace: Body cells → Vena cava → Right atrium → Right ventricle → Pulmonary artery → Lungs. At body cells: O₂ used, CO₂ produced.
19. [3 marks]
(a) Setup P is the control — it has all conditions needed for photosynthesis (light, CO₂ from air, chlorophyll, water) to show that photosynthesis occurs normally and starch is produced. [1 mark]
Purpose of control: Baseline for comparison; proves starch production is due to experimental conditions.
(b) Potassium hydroxide absorbs carbon dioxide, so no CO₂ is available for photosynthesis. Without CO₂, photosynthesis cannot occur, so no starch is produced. Iodine test remains yellow-brown (no starch). [2 marks]
Step-by-step: KOH absorbs CO₂ → No CO₂ for photosynthesis → No glucose/starch made → Iodine negative.
20. [3 marks]
(a) Palisade mesophyll [1 mark]
Also accept: Palisade layer; Palisade cells. Reason: Tightly packed, columnar cells with most chloroplasts to trap maximum light.
(b) Air spaces increase surface area for gas exchange and allow rapid diffusion of gases (CO₂ in, O₂ out) between the atmosphere (via stomata) and the photosynthesising cells. [1 mark]
Key: Large surface area, short diffusion path, connects to stomata.
(c) Guard cells control the opening and closing of stomata to regulate gas exchange (CO₂ in, O₂ out) and water loss (transpiration). [1 mark]
Mechanism: Turgid → stomata open; Flaccid → stomata closed.
End of Answer Key
Free quiz and exam paper access
Enter your details to view this paper
Your access is remembered on this device.