Primary 6 PSLE Science Systems Quiz

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Primary 6 Science - Systems (Human Body Systems)

Quiz 01 | Answer Key

Section A: Multiple Choice Questions (2 marks each)

1. B) Heart

The heart is the main organ that pumps blood throughout the body

2. C) To exchange oxygen and carbon dioxide

The respiratory system brings oxygen in and removes carbon dioxide

3. C) Small intestine

The small intestine has villi that increase surface area for nutrient absorption

4. B) Arteries

Arteries carry blood away from the heart; veins carry blood to the heart

5. C) Muscular system

Muscles attached to bones contract to produce movement

Section B: Matching (2 marks each)

6. C (Lungs - Where gas exchange takes place) 7. D (Heart - Pumps blood to all parts of the body) 8. A (Stomach - Breaks down food using acid and enzymes) 9. B (Kidneys - Filters waste from blood to form urine) 10. E (Liver - Produces bile to help digest fats)

Section C: Short Answer Questions (4 marks each)

11. (a) Digestion begins in the mouth. (1 mark)

Mechanical digestion (chewing) and chemical digestion (saliva/enzymes) start in the mouth

(b) The oesophagus is a tube that connects the mouth to the stomach. It transports food from the mouth to the stomach using muscular contractions (peristalsis). (1.5 marks)

(c) In the stomach:

• Food is mixed with gastric juices (acid and enzymes)
• Proteins begin to be broken down
• Food is churned and turned into a semi-liquid called chyme (1.5 marks)

12. Blood circulation pathway:

1. Blood low in oxygen returns to the right atrium of the heart through veins
2. Blood moves to the right ventricle and is pumped to the lungs
3. In the lungs, blood picks up oxygen and releases carbon dioxide
4. Oxygen-rich blood returns to the left atrium of the heart
5. Blood moves to the left ventricle and is pumped out through arteries
6. Blood delivers oxygen and nutrients to all body cells and picks up waste
7. Blood returns to the heart to repeat the cycle (4 marks for complete description)

13. (a) Carbon dioxide builds up in the body when holding breath. (2 marks)

(b) The build-up of carbon dioxide in the blood is detected by the brain. High levels of carbon dioxide signal to the brain that the body needs to breathe to get rid of carbon dioxide and take in fresh oxygen. This creates the strong urge to breathe. (2 marks)

Section D: Structured Questions (5 marks each)

14. (a) The trachea (windpipe) is a tube that carries air from the nose/mouth to the lungs. It is lined with mucus and tiny hairs (cilia) that trap dust and germs. (1 mark)

(b) In the alveoli:

• Oxygen from the air we breathe in passes through the thin walls of the alveoli into the blood capillaries
• Carbon dioxide from the blood passes into the alveoli to be breathed out
• This is called gas exchange (2 marks)

(c) The bronchi divide into many bronchioles and alveoli to:

• Increase the surface area available for gas exchange
• This allows more oxygen to enter the blood and more carbon dioxide to be removed at the same time
• Making breathing/respiration more efficient (2 marks)

15. (a) Blood components and functions:

(0.5 marks each, total 2 marks)

(b) A person with fewer red blood cells would feel tired and weak because:

• Red blood cells carry oxygen to body cells
• With fewer red blood cells, less oxygen is delivered to the cells
• Cells cannot produce enough energy through respiration
• This causes tiredness, weakness, and shortness of breath (2 marks)

(c) If a person has very few platelets:

• Their blood would not clot properly
• They would bleed for longer from cuts and wounds
• They may bruise easily
• Internal bleeding could be dangerous (1 mark)

Section E: Higher-Order Thinking (5 marks)

16. (a) How the digestive and circulatory systems work together:

1. The digestive system breaks down food into small nutrient molecules (like glucose, amino acids, vitamins)

2. These nutrients are absorbed through the walls of the small intestine into the blood capillaries

3. The circulatory system (blood) carries these nutrients throughout the body

4. The heart pumps blood to all parts of the body through arteries and capillaries

5. Nutrients pass from the blood through capillary walls into the body cells

6. Cells use these nutrients for energy, growth, and repair

(3 marks for clear explanation of both systems' roles and how they connect)

(b) If the circulatory system stopped working:

• Nutrients and oxygen would not be delivered to body cells
• Cells would not be able to produce energy through respiration
• Waste products (like carbon dioxide) would not be removed from cells
• Cells would die due to lack of oxygen and nutrients
• This would be fatal to the organism

(2 marks)

Marking Scheme

End of Answer Key