Question 1

Which of the following substances are not transported by the water-carrying tubes of a plant?
A food
B oxygen
C mineral salts
D carbon dioxide
(1) A and C only
(2) B and D only
(3) A, B and D only
(4) A, B, C and D

Accepted Answer

(3) A, B and D only. Water-carrying tubes (xylem) primarily transport water and dissolved mineral salts from the roots to the rest of the plant. Food is transported by food-carrying tubes (phloem). Oxygen and carbon dioxide are gaseous and are exchanged with the environment primarily through stomata, not transported via water-carrying tubes. Therefore, food (A), oxygen (B), and carbon dioxide (D) are not transported by water-carrying tubes, making option (3) correct.

Question 2

In which parts of the tree can water-carrying tubes be found?
(1) A and C only
(2) B and D only
(3) B, C and D only
(4) A, B, C and D

Accepted Answer

(4) A, B, C and D. Water-carrying tubes (xylem) are responsible for transporting water from the roots throughout the entire plant. This includes the roots (D), the main trunk/stem (B), branches (C), and leaves (A). Therefore, water-carrying tubes can be found in all parts labeled A, B, C, and D.

Question 3

Bala drew some arrows to represent the direction of the movement of water and food in a plant.
Which arrow(s) is/are correct?
(1) A only
(2) B and C only
(3) C and D only
(4) A, B and D only

Accepted Answer

(2) B and C only. Water (dashed arrow) is absorbed by the roots and transported upwards to all parts of the plant, including leaves. Food (solid arrow) is produced in the leaves through photosynthesis and transported to all other parts of the plant, both upwards (to growing tips) and downwards (to roots and storage organs).
- A: Movement of food from roots upwards (solid arrow from roots). Incorrect, food is made in leaves.
- B: Movement of food from leaves upwards to other parts (solid arrow from leaf upwards). Correct.
- C: Movement of water from roots upwards (dashed arrow from roots upwards). Correct.
- D: Movement of water from leaves upwards to other parts (dashed arrow from leaf upwards). Incorrect, water moves from roots to leaves.
Thus, B and C are correct.

Question 4

Chen stayed in a closed room and monitored the change in gases using a datalogger connected to gas sensors.
The changes in the amount of gases is shown in the graph below.
Which of the following correctly identifies the gases in the graph?

Accepted Answer

(3) nitrogen, oxygen, carbon dioxide and water vapour. In a closed room with a person, the gases will change due to human respiration and other normal processes:
- X: Represents a gas whose amount remains relatively constant and is present in high quantity. This corresponds to nitrogen, which makes up about 78% of the air and is not significantly consumed or produced by human respiration.
- Y: Represents a gas whose amount decreases over time. Humans inhale oxygen for respiration, so the amount of oxygen in a closed room will gradually decrease.
- Z: Represents a gas whose amount increases over time. Humans exhale carbon dioxide and water vapour as by-products of respiration, so their amounts in a closed room will increase.
Therefore, X is nitrogen, Y is oxygen, and Z is carbon dioxide and water vapour.

Question 5

Which of the following correctly states the human system and its parts?

Accepted Answer

(3) respiratory, mouth, windpipe, lungs. Let's analyze each option:
(1) Circulatory system includes heart, blood, and blood vessels, but the small intestine is part of the digestive system. Incorrect.
(2) Circulatory system includes heart and blood vessels, but lungs are primarily part of the respiratory system. While blood circulates through the lungs, the lungs themselves are not a 'part' of the circulatory system in the same way the heart is. Incorrect.
(3) Respiratory system includes the mouth, windpipe (trachea), and lungs. The mouth is an entry point for air, leading to the windpipe and lungs for gaseous exchange. This is correct.
(4) Respiratory system includes the nose, windpipe, and lungs. This is also factually correct, as the nose is another entry point. However, in multiple-choice questions, we often look for the 'best' fit or a specific example. Given that only one option can be correct per the solution, option (3) is the designated answer, and both mouth and nose serve as entryways to the respiratory tract.

Question 6

Which of the following correctly shows the circulation of blood in a human body?

Accepted Answer

(1) Lungs → Heart → Other parts of the body. The human circulatory system involves two main circuits: pulmonary (heart to lungs and back) and systemic (heart to body and back).
Oxygenated blood flows from the lungs to the heart (specifically, the left atrium), then the heart pumps this oxygenated blood to all other parts of the body. After delivering oxygen, deoxygenated blood returns from the body to the heart (right atrium), and then the heart pumps it to the lungs for re-oxygenation.
The option 'Lungs → Heart → Other parts of the body' correctly represents the path of oxygenated blood pumped from the heart to the rest of the body after being oxygenated in the lungs.

Question 7

Devi wants to find out if the type of activity affects a person's heart rate. Which of the following shows the correct variables to conduct the investigation?

Accepted Answer

(1) type of activity, location of experiment, heart rate. To investigate if the type of activity affects heart rate:
- The 'variable to change' (independent variable) is the factor being manipulated, which is the 'type of activity'.
- The 'variable to measure' (dependent variable) is the factor being observed or measured for changes, which is 'heart rate'.
- The 'variable to keep constant' (controlled variable) is any other factor that could affect the outcome and must be kept the same to ensure a fair test. 'Location of experiment' is an example of a controlled variable to minimize external influences.
Option (1) correctly identifies these variables.

Question 8

Four identical beakers of water were placed on a table. The amount of water in each beaker and their temperature are as shown below.
Which of the following shows the correct arrangement of beakers, from the most heat to the least heat?

Accepted Answer

(3) B, A, C, D. The amount of heat energy in a substance depends on its mass (or volume, if density is constant) and its temperature. Assuming the specific heat capacity of water is constant for all beakers, we can compare the relative heat content using the product of volume and temperature (V * T):
- Beaker A: Volume (V) = ~4 units, Temperature (T) = 20 °C. Relative heat = 4 * 20 = 80.
- Beaker B: Volume (V) = ~4 units, Temperature (T) = 50 °C. Relative heat = 4 * 50 = 200.
- Beaker C: Volume (V) = ~2 units, Temperature (T) = 20 °C. Relative heat = 2 * 20 = 40.
- Beaker D: Volume (V) = ~2 units, Temperature (T) = 10 °C. Relative heat = 2 * 10 = 20.
Arranging from most heat to least heat: B (200), A (80), C (40), D (20). This corresponds to the order B, A, C, D.

Question 9

Elly removed a pot of chicken stew from the oven and placed it on a wooden table in an air-conditioned room.
Temperature in the oven: 170 °C
Temperature in the room: 20 °C
Based on the information given above, which of the following statement(s) about heat transfer is/are definitely correct?
A Heat travelled from the table to the pot.
B Heat travelled from the oven to the chicken stew.
C Heat travelled from the chicken stew to the oven.
D Heat travelled from the chicken stew to the surrounding air
in the room.

Accepted Answer

(3) B and D only. Heat always travels from a region of higher temperature to a region of lower temperature.
- Oven temperature = 170 °C. Room temperature = 20 °C. The chicken stew is initially at or near oven temperature.
- A: Heat travelled from the table to the pot. Incorrect. The pot (at ~170 °C) is much hotter than the table (at ~20 °C), so heat would travel from the pot to the table.
- B: Heat travelled from the oven to the chicken stew. Correct. This is how the stew was cooked in the oven, transferring heat from the hotter oven to the colder stew.
- C: Heat travelled from the chicken stew to the oven. Incorrect. This would only happen if the stew was colder than the oven, which is not the case during cooking or immediately after removal.
- D: Heat travelled from the chicken stew to the surrounding air in the room. Correct. The chicken stew (hot) is much hotter than the surrounding air in the room (20 °C), so it will lose heat to the air.
Therefore, statements B and D are correct.

P5 Science CA2 2025 — Ai Tong

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