Q: The diagram below shows the blood flow in parts A, B and C of the human body. Which of the following correctly represents the body parts A, B and C?

3. A: lungs, B: heart, C: leg. Blood rich in oxygen flows from A to B — only blood leaving the lungs is oxygen-rich, so A is the lungs. Blood rich in carbon dioxide flows from C back to B — only blood returning from body parts (e.g. the leg) is carbon-dioxide rich, so C is the leg. B receives oxygen-rich blood from A (lungs) and carbon-dioxide-rich blood from C (leg), so B is the heart, which pumps blood to and from both.

Q: Ali began running for a period of time before slowing down to a walk. After walking for a while, he started running again. Which of the graphs below correctly shows how Ali's heart rate changed?

4. Graph 4 — heart rate rises, dips slightly, plateaus lower, then rises again. When Ali runs, his heart rate increases (rises). When he slows down to walk, his heart rate decreases but does not drop to zero — it stays elevated above resting. When he runs again, his heart rate rises again. Graph (4) correctly shows a rise, a dip/drop while walking (but not to zero), then a rise again. Graph (1) misses the initial high then drop; (2) does not show a decrease during walking; (3) wrongly drops to zero.

Q: Jenny wanted to find out if the number of roots affect the amount of water taken in by a plant. Which of the following variable(s) should she keep the same? A. number of roots B. number of leaves C. type of plant D. thickness of stem

3. B, C and D only. The variable Jenny is testing (changing) is the number of roots, so A must be varied — not kept the same. All other variables that could affect water uptake must be kept the same to ensure a fair test: the number of leaves (affects transpiration pull), the type of plant, and the thickness of stem. Therefore B, C and D should be kept the same.

Question 1

The diagram below shows the changes of state of water. Which of the processes E, F, G or H involves heat loss by water?

Accepted Answer

2. G and H only. Processes that involve heat loss (cooling) by water are condensation (water vapour → water, H) and freezing (water → ice, G). E (ice → water, melting) and F (water → water vapour, evaporation/boiling) both involve heat gain. So heat loss processes are G and H.

Question 2

Which of the following are parts of the respiratory system?
A. heart
B. lungs
C. gullet
D. nose
E. mouth

Accepted Answer

2. B and D only. The respiratory system includes the nose, trachea, bronchi, and lungs. The heart belongs to the circulatory system, the gullet (oesophagus) belongs to the digestive system, and the mouth is part of the digestive system. Hence only lungs (B) and nose (D) are parts of the respiratory system.

Question 3

In which of the following part(s) is/are water-carrying tubes found?
A. roots
B. stems
C. leaves
D. flowers

Accepted Answer

4. A, B, C and D. Water-carrying tubes (xylem) are present throughout the entire plant — they run from the roots, up the stem, into the leaves, and into the flowers — so water can be transported to every part of the plant. Therefore the answer is A, B, C and D.

Question 4

The graph below shows the temperature of liquid Y as it is heated. Which of the following statements is true?

Accepted Answer

3. The boiling point of Y is 80°C.. Y is a liquid being heated. From P to Q the liquid's temperature rises to 80°C. From Q to R the temperature stays constant at 80°C even though heat is being added — this is the boiling stage (a liquid cannot be melting). From R to S the temperature rises again (gas being heated). Therefore the boiling point of Y is 80°C. Y is not water because water boils at 100°C; Y is still gaining heat from Q to R (used to change state).

Question 5

Two cups, X and Y, were filled with water at different temperatures. Metal lids were placed on the cups, and both cups were left in a room with a temperature of 30 °C. After some time, water droplets were observed as shown in the diagram below. Which of the following shows the possible temperatures of water in cups X and Y at the start of the experiment?

Accepted Answer

3. X: 40°C, Y: 10°C. In cup X, water droplets formed on the underside of the metal lid (inside the cup) — this means water vapour from the warm water inside condensed on the cooler lid, so the water inside X must be warmer than the surrounding air (40°C > 30°C room). In cup Y, water droplets formed on the outside of the cup — this means water vapour in the warm surrounding air condensed on the cooler outer surface of the cup, so the water inside Y must be cooler than the room (10°C < 30°C). Hence X = 40°C and Y = 10°C.

Question 6

The diagram below shows the blood flow in parts A, B and C of the human body. Which of the following correctly represents the body parts A, B and C?

Accepted Answer

3. A: lungs, B: heart, C: leg. Blood rich in oxygen flows from A to B — only blood leaving the lungs is oxygen-rich, so A is the lungs. Blood rich in carbon dioxide flows from C back to B — only blood returning from body parts (e.g. the leg) is carbon-dioxide rich, so C is the leg. B receives oxygen-rich blood from A (lungs) and carbon-dioxide-rich blood from C (leg), so B is the heart, which pumps blood to and from both.

Question 7

Ali began running for a period of time before slowing down to a walk. After walking for a while, he started running again. Which of the graphs below correctly shows how Ali's heart rate changed?

Accepted Answer

4. Graph 4 — heart rate rises, dips slightly, plateaus lower, then rises again. When Ali runs, his heart rate increases (rises). When he slows down to walk, his heart rate decreases but does not drop to zero — it stays elevated above resting. When he runs again, his heart rate rises again. Graph (4) correctly shows a rise, a dip/drop while walking (but not to zero), then a rise again. Graph (1) misses the initial high then drop; (2) does not show a decrease during walking; (3) wrongly drops to zero.

Question 8

Jenny wanted to find out if the number of roots affect the amount of water taken in by a plant. Which of the following variable(s) should she keep the same?
A. number of roots
B. number of leaves
C. type of plant
D. thickness of stem

Accepted Answer

3. B, C and D only. The variable Jenny is testing (changing) is the number of roots, so A must be varied — not kept the same. All other variables that could affect water uptake must be kept the same to ensure a fair test: the number of leaves (affects transpiration pull), the type of plant, and the thickness of stem. Therefore B, C and D should be kept the same.

P5 Science SA1 2025 — Maha Bodhi

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