Question 1

1. In the table below, A, B and C represent the characteristics of the given animals. A tick (✔) shows that the characteristic is present. Which of the following characteristics represent A, B and C?

Accepted Answer

(4) Has feathers, Lays eggs, Can fly. Let's analyze the characteristics given in option (4):
- A: Has feathers
- B: Lays eggs
- C: Can fly

Now, let's check against the ticks in the table and general biological knowledge:
- Eagle: Ticked for A (Has feathers) and B (Lays eggs). Eagles do have feathers and lay eggs. (Although eagles can fly, C is not ticked, which is an inconsistency in the question's table).
- Snake: Ticked for C (Can fly). Snakes do not have feathers, and many lay eggs (B not ticked, an inconsistency). Critically, snakes cannot fly, so C being ticked is a biological inaccuracy in the table for this option.
- Butterfly: Ticked for B (Lays eggs) and C (Can fly). Butterflies do lay eggs and can fly. They do not have feathers (A not ticked), which is consistent.

Despite the inconsistencies for the eagle and snake in the table's ticks, option (4) presents the characteristics for A, B, and C that have some alignment with the animals' properties and the ticks for the most part, especially for the butterfly and 'A' for the eagle. The question is potentially flawed with these inconsistencies, but given option (4) as the intended answer, we prioritize the partial matches.

Question 2

2. The classification chart below shows the characteristics of animals P, Q, R and S. Which of the following animals represent P, Q, R and S?

Accepted Answer

(3) grasshopper, butterfly, frog, mosquito. Let's classify each animal based on the chart:
- P: Young lives on land, 3-stage life cycle. A grasshopper undergoes incomplete metamorphosis with 3 stages (egg, nymph, adult) and lives on land.
- Q: Young lives on land, 4-stage life cycle. A butterfly undergoes complete metamorphosis with 4 stages (egg, larva, pupa, adult) and lives on land.
- R: Young lives in water, 3-stage life cycle. A frog's young (tadpole) lives in water, and it has 3 main stages (egg, tadpole, adult).
- S: Young lives in water, 4-stage life cycle. A mosquito undergoes complete metamorphosis with 4 stages (egg, larva, pupa, adult), and its larval and pupal stages are aquatic (live in water).

Option (3) correctly matches these classifications.

Question 3

3. Diagram 1 shows two seeds planted in a garden. The seeds were watered daily. Diagram 2 shows what happened in the garden after a few months. Based on the diagrams above, which of the following processes have taken place?
A fertilisation
B germination
C pollination
D seed dispersal

Accepted Answer

(4) A, B, C and D. Let's analyze each process:
- A (Fertilisation): For the plants to produce fruits and new seeds (as implied by the growth from seeds to plants with fruits), fertilisation must occur in the flowers.
- B (Germination): The initial seeds planted in Diagram 1 grew into mature plants shown in Diagram 2, which indicates germination has definitely taken place.
- C (Pollination): Pollination is the transfer of pollen necessary for fertilisation, which in turn leads to the development of fruits and seeds. So, it must have occurred.
- D (Seed dispersal): The presence of multiple plants (three) in Diagram 2, originating from only two initial seeds, implies that the initial plants grew, reproduced (fertilisation, pollination), produced new seeds, and those new seeds were dispersed and germinated. Therefore, seed dispersal must have also occurred.
All four processes are necessary to explain the transformation from initial seeds to a garden with multiple fruiting plants.

Question 4

4. Mdm Lim removed the food-carrying tubes from the stem of a plant shown below. The water-carrying tubes remained in the stem. After some time, she observed some changes in the plant. Which of the following is correct?

Accepted Answer

(4) Leaf Y remains green as removing the food-carrying tubes does not affect the process of photosynthesis.. The food-carrying tubes (phloem) transport manufactured food (sugars) from the leaves to other parts of the plant, including fruits and roots. The water-carrying tubes (xylem) transport water and minerals from the roots to the rest of the plant.

- (1) Removing food-carrying tubes means food made by Leaf W cannot be transported *downwards* past the cut. Leaf W remains green because it continues to photosynthesize, not because food is transported *to* it. So, this is incorrect.
- (2) Fruit X is above the removed tubes. Food can still reach it. However, if food cannot reach the roots below the cut, the roots will eventually die, impacting the entire plant. Storing more water is not a direct consequence of phloem removal. So, this is incorrect.
- (3) The stem *above* the cut (Stem Z refers to the area of the cut, which would include the part above the cut where sugars accumulate) would swell because food produced by the leaves cannot be transported downwards past the removal point and accumulates there. Water transport via xylem (water-carrying tubes) is unaffected, so water can still reach the roots. So, this is incorrect.
- (4) Photosynthesis is the process by which leaves make food using carbon dioxide, water, and sunlight. This process occurs in the chloroplasts of the leaves and is independent of the phloem (food-carrying tubes). Removing the phloem will not stop the leaves from performing photosynthesis, so Leaf Y (and other leaves) will continue to make food and remain green. So, this is correct.

Question 5

5. Some scientists wanted to study the digestive system of Animal Z. They fed Animal Z with the same amount of food, A, B and C, according to the table below. Animal Z's digestive system was checked at specific time intervals each day to find out how much of the food remained undigested. The results were plotted in the line graph below. Based on the above results, what can the scientists conclude at the end of the experiment?

Accepted Answer

(4) Different organs of the digestive system digest different types of food at different rates.. Let's analyze the graph and experiment setup:
- The experiment used the 'same amount of food' (A, B, C), so option (2) is incorrect.
- The graph shows distinctly different digestion patterns for Food A, B, and C across organs P, Q, R, S. For example, Food A is largely digested in organ P, while Food B is significantly digested in organ R, and Food C is digested to a lesser extent overall. This indicates that the type of food *does* affect the amount digested, making option (3) incorrect.
- Organ P is very effective for Food A but not for Food B or C. So, organ P is not the 'most effective' at digestion overall, making option (1) incorrect.
- The varying digestion patterns for different food types across the different organs (P, Q, R, S) clearly demonstrate that different organs play distinct roles in digesting different types of food, and they do so at different efficiencies or rates. This aligns perfectly with option (4).

Question 6

6. Zhi Wei performed various physical activities within 30 minutes. The graph below shows the number of times his heart beats per minute over that period. Which of the following statements correctly describes what is happening to Zhi Wei during the period indicated by line PQ on the graph?

Accepted Answer

(3) Zhi Wei's body is releasing an increasing amount of carbon dioxide per minute.. The line PQ on the graph shows an increasing trend in the number of heartbeats per minute. An increasing heart rate indicates that the body is undergoing increased physical activity or exertion.
- Increased physical activity leads to a higher rate of respiration in muscle cells to produce more energy. This process consumes more oxygen and produces more carbon dioxide.
- To supply the increased oxygen demand and remove the increased carbon dioxide, both the breathing rate and heart rate will increase.

Let's evaluate the options:
- (1) Zhi Wei's breathing rate would be increasing, not decreasing, to take in more oxygen and remove more carbon dioxide. So, this is incorrect.
- (2) The heart rate is increasing, meaning the heart is pumping blood at an increasing rate to deliver more oxygen and nutrients to muscles and remove waste products. So, this is incorrect.
- (3) With increased respiration due to activity, more carbon dioxide is produced as a waste product, and thus an increasing amount of carbon dioxide is released per minute. So, this is correct.
- (4) Zhi Wei's body would require an *increasing* amount of oxygen, not the same amount, to support the higher metabolic demands of increased activity. So, this is incorrect.

Question 7

7. Simon studied cells W, X, Y and Z. He listed in the table below the cell parts each cell had. A tick (✔) represents the presence of the cell part. Which cell could be a cheek cell from a human?

Accepted Answer

(1) W. A human cheek cell is an animal cell. The key characteristics of a typical animal cell are:
- Presence of Cytoplasm
- Presence of Cell membrane
- Presence of Nucleus
- Absence of Cell wall (which is found in plant cells)
- Absence of Chloroplast (which is found in photosynthetic plant cells)

Let's examine the characteristics of each cell in the table:
- Cell W: Has Cytoplasm, Cell membrane, Nucleus. Lacks Cell wall and Chloroplast. This perfectly matches the characteristics of a human cheek cell (animal cell).
- Cell X: Has Cytoplasm, Cell membrane, Cell wall, Nucleus. Lacks Chloroplast. This describes a plant cell, such as an onion epidermal cell or root cell, which lacks chloroplasts but has a cell wall.
- Cell Y: Has Cytoplasm, Cell membrane, Cell wall, Nucleus, Chloroplast. This describes a photosynthetic plant cell, like a leaf cell.
- Cell Z: Has Cytoplasm, Cell membrane, Nucleus, Chloroplast. Lacks Cell wall. This combination (chloroplasts without a cell wall) is not characteristic of a human cheek cell or typical plant cells.

Therefore, Cell W is the correct representation of a human cheek cell.

Question 8

9. Isaac decided to study the food relationship among three different types of animals, A, B and C. He created three similar terrariums, X, Y and Z, such that they resembled the natural habitat of the three animals. He then placed a number of the animals in the terrariums in the following manner. For a month, Isaac counted the number of each type of animal in the terrariums every two days. He plotted three graphs, as shown below, to illustrate the results that he had recorded. Based on the graphs, which of the following statements correctly explains a possible food relationship between the animals?

Accepted Answer

(3) B is both a predator and a prey.. Let's analyze the graphs to determine the food relationships:
-   **Terrarium X (A and B):** The number of animal A decreases, while the number of animal B increases. This indicates that B preys on A (A → B). So, A is the prey of B, and B is the predator of A.
-   **Terrarium Y (A and C):** The number of animal A decreases, while the number of animal C increases. This indicates that C preys on A (A → C). So, A is the prey of C, and C is the predator of A.
-   **Terrarium Z (B and C):** The number of animal B decreases, while the number of animal C increases. This indicates that C preys on B (B → C). So, B is the prey of C, and C is the predator of B.

Combining these relationships:
-   A is prey to both B and C.
-   B is a predator of A, and also prey to C.
-   C is a predator of both A and B.

Now let's evaluate the given options:
-   (1) A is the prey of C. (This is correct, as shown by A → C).
-   (2) B is the predator of A. (This is correct, as shown by A → B).
-   (3) B is both a predator and a prey. (B preys on A, and C preys on B. Therefore, B is indeed both a predator and a prey. This is correct).
-   (4) C is the prey of A and predator of B. (C is a predator of A, not its prey. C is a predator of B. So this statement is incorrect because the first part is false).

Since option (3) is definitively correct based on the analysis of all three graphs, it is the best answer. (Note: There might be an issue with the provided answer key if it suggests (4) as correct, as (4) contains a false statement.)

Question 9

10. The table below shows some information about two different organisms, X and Y. Which of the following descriptions correctly matches the information about the two organisms above?

Accepted Answer

(2) Organism X: Stem twines around a support, Stigma hanging outside petals. Organism Y: Sweats very little, Padded feet.. Let's analyze the characteristics given for Organism X and Y:
-   **Organism X:** 'Weak stem', 'Pollinated by wind'. Wind-pollinated plants typically do not have showy flowers (no need to attract insects), and their stigmas (for pollen capture) and anthers (for pollen release) are often exposed or feathery to maximize contact with wind.
-   **Organism Y:** 'Lives in a desert', 'Walks on hot sandy grounds'. Desert animals have adaptations to cope with extreme heat and conserve water. For walking on hot sand, specialized feet are common.

Now, let's evaluate the options:
-   **(1)** Organism X having 'Bright coloured flowers' contradicts wind pollination. Incorrect.
-   **(2)** Organism X: 'Stem twines around a support' is consistent with a weak stem. 'Stigma hanging outside petals' is a classic adaptation for wind pollination, allowing pollen to be easily caught. Organism Y: 'Sweats very little' is a water conservation adaptation for deserts. 'Padded feet' help insulate against or distribute weight on hot sandy grounds. This option provides good matches for both organisms.
-   **(3)** Organism X having 'Has thorns' is not directly implied. 'Feather-like stigma' is consistent with wind pollination. Organism Y having 'Camouflages with the surrounding' is a general adaptation, less specific to 'walks on hot sandy grounds' than padded feet. Less strong than (2).
-   **(4)** Organism X: 'Has climbing stem' is consistent with a weak stem. 'Anthers hanging outside petals' is consistent with wind pollination. Organism Y: 'Active at night' is a good desert adaptation to avoid heat. 'Sharp claws' are for digging or hunting, not specifically for walking on hot sand, making 'padded feet' a better fit for the given information. Less strong than (2).

Option (2) provides the most appropriate and specific adaptations for both Organism X and Organism Y based on the given information.

Question 10

11. A company is mindful of the impact its products have on the environment. Which of the following measures could the company take to be environmentally friendly?
A Using materials that are biodegradable
B Using renewable energy sources to power its plants
C Designing products that are attractive to the customers
D Designing packages that save space during transportation

Accepted Answer

(3) A, B and D only. Let's assess each measure for environmental friendliness:
-   **A (Using materials that are biodegradable):** Biodegradable materials break down naturally, reducing landfill waste and pollution. This is environmentally friendly.
-   **B (Using renewable energy sources to power its plants):** Renewable energy sources (like solar or wind) reduce reliance on fossil fuels, lowering greenhouse gas emissions and air pollution. This is environmentally friendly.
-   **C (Designing products that are attractive to the customers):** This is a marketing strategy aimed at increasing sales; it does not inherently relate to environmental impact. This is NOT environmentally friendly.
-   **D (Designing packages that save space during transportation):** More compact packaging means more products can be transported in fewer trips, reducing fuel consumption, emissions, and logistical environmental footprint. This is environmentally friendly.

Therefore, measures A, B, and D are environmentally friendly. Option (3) is the correct choice.

Question 11

12. The diagram below shows an organism with big eyespots on its body as a form of adaptation. These big eyespots look like eyes on larger animals. Which of the following is correct about the organism's adaptation?

Accepted Answer

(2) Structural, resemble the appearance of larger animals to frighten away predators. Let's break down the type and purpose of the adaptation:
-   **Type of adaptation:** The eyespots are physical markings on the organism's body (wings). Adaptations that are physical features of an organism are classified as **structural adaptations**. Behavioural adaptations involve actions or responses.
-   **Purpose of adaptation:** The question states that these eyespots "look like eyes on larger animals" and their function is to "frighten away predators". This is a form of mimicry, designed to deter predators by making the organism appear larger or more dangerous.

Evaluating the options:
-   Options (1) and (3) incorrectly identify the type as behavioural.
-   Options (3) and (4) incorrectly identify the purpose as camouflage (blending in) rather than frightening away (mimicry).
-   Option (2) correctly identifies the adaptation as **structural** and its purpose as to **resemble the appearance of larger animals to frighten away predators**.

Therefore, option (2) is correct.

Question 12

13. Mr Lee conducted an experiment in a dark room with the set-up below. He switched on the lamp and made an observation one hour later... He observed that the water level P in the glass tube had moved, while the plunger remained at the same place. In which direction did the water level P move and what was the reason for the movement?

Accepted Answer

(3) Down, Oxygen produced during photosynthesis took up the air space.. Let's analyze the experiment:
-   A water plant is placed in a syringe with some air space.
-   A lamp is switched on in a dark room, providing light to the plant.
-   The water plant will carry out photosynthesis, as it has light, water, and implicitly carbon dioxide in the air space.
-   The process of photosynthesis consumes carbon dioxide and produces oxygen.

Now, let's determine the effect on the water level P:
-   As oxygen is produced by the plant, it will be released into the air space above the water in the syringe.
-   This increase in the amount of gas (oxygen) in the sealed air space will increase the pressure inside the syringe.
-   The increased pressure will push the water downwards into the glass tube, causing water level P to move **down**.

Evaluating the options:
-   (1) While the lamp produces heat, the primary reason for the water level change in a photosynthesis experiment is gas exchange. Syringe expansion due to heat would be secondary and might not explain the specific movement of water level P. So, this is incorrect.
-   (2) Food (glucose) produced during photosynthesis is stored or used by the plant; it does not take up air space as a gas. So, this is incorrect.
-   (3) Oxygen produced during photosynthesis *increases the volume of gas* in the air space (effectively 'taking up' more space, or increasing pressure), pushing the water level P down. This is correct.
-   (4) Carbon dioxide is *consumed* during photosynthesis, not produced. If it were consumed, the pressure would decrease, and water level P would move up. So, this is incorrect.

Question 13

14. Ben observed four materials, W, X, Y and Z, and came up with the flowchart below. Based on the flowchart above, which material, W, X, Y or Z, is used to make the shopping bag to carry groceries as shown below?

Accepted Answer

(3) Y. A shopping bag for carrying groceries needs specific properties:
1.  **Does not break easily:** It must be strong enough to hold heavy items without tearing or breaking. Following the flowchart, this means we take the 'No' path from 'Does it break easily?'.
2.  **Flexible:** It needs to be flexible to accommodate items of various shapes, be folded for storage, and handle movement. Following the flowchart, this means we take the 'Yes' path from 'Is it flexible?'.

Following these two conditions in the flowchart, the material that matches is **Y**. Let's trace it:
-   Does it break easily? -> No
-   Is it flexible? -> Yes
-   Result: Material Y

Therefore, material Y is used to make the shopping bag.

Question 14

15. An experiment was set up using a sealed metal container which holds 700cm³ of water and 300cm³ of air as shown below. What observations about the volume of air and the volume and mass of water in the container could be made after 200cm³ of water was removed from the container through the pump?

Accepted Answer

(3) increased, decreased, decreased. Let's analyze the changes after 200cm³ of water is removed:

1.  **Volume of water in the container:**
    -   Initial volume of water = 700 cm³.
    -   Amount removed = 200 cm³.
    -   Final volume of water = 700 cm³ - 200 cm³ = 500 cm³.
    -   So, the volume of water **decreased**.

2.  **Mass of water in the container:**
    -   Since a quantity of water was removed, the mass of water in the container will also **decrease** proportionally.

3.  **Volume of air in the container:**
    -   The container is sealed and has a fixed total internal volume (700 cm³ water + 300 cm³ air = 1000 cm³).
    -   When 200 cm³ of water is removed, that space becomes available within the sealed container.
    -   Gases (like air) expand to fill the entire volume of their container.
    -   The new volume available for air will be the total container volume minus the new water volume = 1000 cm³ - 500 cm³ = 500 cm³.
    -   Since the initial air volume was 300 cm³ and the new volume is 500 cm³, the volume of air **increased**.

Therefore, the correct observations are: Volume of air (increased), Volume of water (decreased), Mass of water (decreased). This matches option (3).

Question 15

16. The diagram below shows a terrarium. After it was created, it was placed near a window undisturbed without opening the cover for a few days. Which of the following did not occur in the terrarium?

Accepted Answer

(3) The plants absorbed water from the damp soil and the soil became dry after a few days.. A terrarium is a sealed ecosystem where the water cycle occurs internally.
-   **(1) Water in the terrarium went through the process of evaporation.** Heat from the window (sunlight) would cause water from the damp soil to evaporate, turning into water vapour. This occurs.
-   **(2) Excess water in the plants was still lost through its leaves as water vapour.** Plants release water vapour through transpiration (a form of evaporation) from their leaves. This occurs.
-   **(3) The plants absorbed water from the damp soil and the soil became dry after a few days.** While plants absorb water, the evaporated water (from soil and transpiration) condenses on the cooler surfaces of the terrarium and drips back down, keeping the soil damp. The water cycle ensures the soil does not become dry over a few days in a sealed terrarium. This statement is incorrect.
-   **(4) Water vapour in the terrarium condensed into tiny water droplets on the sides of the terrarium.** As warm, moist air inside the terrarium comes into contact with the cooler glass surfaces, the water vapour loses heat and condenses into droplets. This occurs.

Therefore, the statement that did not occur is (3).

Question 16

17. Max filled two identical beakers with an equal amount of liquid X and liquid Y each. Both liquids were at the same temperature at the start of the experiment. He left the beakers on a table for one hour. After one hour, he recorded his results in the table shown below. Based only on Max's results, what can he conclude about liquids X and Y?
A Liquid Y evaporates slower than liquid X.
B Both liquids X and Y can evaporate at room temperature.
C Liquid Y can evaporate faster in a room with a lower temperature.

Accepted Answer

(2) A and B only. Let's analyze the results from the table:
-   Liquid X: Started with 150 ml, ended with 20 ml. Amount evaporated = 130 ml.
-   Liquid Y: Started with 150 ml, ended with 140 ml. Amount evaporated = 10 ml.

Now, let's evaluate each conclusion:
-   **A (Liquid Y evaporates slower than liquid X):** In the same time period (one hour), liquid Y evaporated 10 ml, while liquid X evaporated 130 ml. Since liquid Y evaporated significantly less, it evaporates slower than liquid X. This statement is **correct**.
-   **B (Both liquids X and Y can evaporate at room temperature):** The experiment was conducted by leaving the beakers on a table, implying normal room temperature conditions. Both liquids showed a decrease in volume, indicating evaporation occurred. This statement is **correct**.
-   **C (Liquid Y can evaporate faster in a room with a lower temperature):** The experiment was only performed at one temperature (room temperature). There is no data to support how a lower temperature would affect the evaporation rate of liquid Y. Therefore, this statement cannot be concluded from the given results. This statement is **incorrect**.

Based on the results, only conclusions A and B can be made. Thus, option (2) is the correct answer.

Question 17

18. The table below gives some information about A, B, C and D. Which of the following correctly matches water and sound?

Accepted Answer

(3) B, D. First, let's classify A, B, C, and D based on their properties:
-   **A:** Has mass, has definite volume, has definite shape. These are the properties of a **solid**.
-   **B:** Has mass, has definite volume, has no definite shape. These are the properties of a **liquid**.
-   **C:** Has mass, has no definite volume. These are the properties of a **gas** (it fills any container, thus no definite volume).
-   **D:** Has no mass. This describes a form of **energy** (e.g., light, heat, sound).

Now, let's match water and sound:
-   **Water** at room temperature and pressure is a liquid. Therefore, water matches **B**.
-   **Sound** is a form of energy (mechanical energy transmitted through vibrations). Therefore, sound matches **D**.

The correct match is Water corresponds to B, and Sound corresponds to D. This is found in option (3).

Question 18

19. The diagram below shows how the shadow of an object can be cast on a screen using a torch. All the items of the set-up can be moved. Which of the following is correct when the distances x and y are changed?

Accepted Answer

(2) Distance x: remain the same, Distance y: decrease, Shadow height z: decrease. Let's analyze how changes in distances x and y affect the height of the shadow (z):
-   **Distance x (torch to object):** If the torch moves further from the object (x increases), the light rays spread less before hitting the object, resulting in a smaller shadow. If the torch moves closer (x decreases), the light rays spread more, resulting in a larger shadow.
-   **Distance y (object to screen):** If the screen moves closer to the object (y decreases), the shadow becomes smaller. If the screen moves further (y increases), the shadow becomes larger.

Now let's check the options:
-   **(1) x increase (smaller shadow), y decrease (smaller shadow):** Combined effect is a decrease in shadow height. Option states 'remain the same'. Incorrect.
-   **(2) x remain the same (no effect), y decrease (smaller shadow):** Combined effect is a decrease in shadow height. Option states 'decrease'. Correct.
-   **(3) x decrease (larger shadow), y increase (larger shadow):** Combined effect is a large increase in shadow height. Option states 'decrease'. Incorrect.
-   **(4) x increase (smaller shadow), y remain the same (no effect):** Combined effect is a decrease in shadow height. Option states 'increase'. Incorrect.

Therefore, option (2) correctly describes the changes.

Question 19

20. The diagram below shows a dessert called Baked Alaska. It contains ice-cream and cake under a thick layer of well-beaten egg white. The dessert was placed in a very hot oven and baked until the top of the egg white turned brown. It was then removed from the oven, ready to be served. It was observed that the ice cream inside the metal dish did not melt. Which one of the following statements best explains the above observation?

Accepted Answer

(4) Air in the egg white is a poor conductor of heat and it slowed down heat gain by the ice-cream from the surroundings.. The observation that ice cream does not melt in a hot oven implies that there is a good insulating layer protecting it from the high temperature.
-   The dessert has a thick layer of 'well-beaten egg white' (meringue).
-   Well-beaten egg white contains a significant amount of trapped air bubbles.
-   Air is known to be a poor conductor of heat (a good insulator).

Let's evaluate the options:
-   (1) Metal dishes are good conductors of heat. If heat reached the dish easily, the ice cream would melt quickly. So, this is incorrect.
-   (2) Air is a poor conductor of heat (an insulator), not a good conductor. So, this is incorrect.
-   (3) Cake is a component, but its primary role here is not to conduct heat away from the ice cream in a way that would prevent melting in an oven. So, this is incorrect.
-   (4) Air trapped within the egg white acts as an excellent thermal insulator because air is a poor conductor of heat. This insulating layer significantly slows down the transfer of heat from the hot oven to the ice cream, preventing it from melting. This is the correct explanation.

Question 20

21. The diagram below shows four bulbs in a circuit. At which position, A, B, C or D, should a switch be placed so that only two bulbs will remain lighted up when the switch is opened?

Accepted Answer

(2) B. Let's analyze the circuit configuration:
-   The current flows from the battery to a junction.
-   It then passes through Bulb A.
-   After Bulb A, the circuit splits into two parallel branches.
    -   Branch 1: Bulb B in series with Bulb C.
    -   Branch 2: Bulb D.
-   These two parallel branches then rejoin and return to the battery.

So, Bulb A is in series with the parallel combination of (Bulb B in series with Bulb C) and (Bulb D).

Now let's test placing a switch at each position and opening it:
-   **If a switch is opened at position A:** The entire circuit is broken at the main path. No current will flow, so *zero* bulbs will light up.
-   **If a switch is opened at position B:** The branch containing B and C is broken. Current can still flow through Bulb A and through the branch containing Bulb D. Therefore, Bulb A and Bulb D will light up. This results in *two* bulbs lighting up.
-   **If a switch is opened at position C:** Similar to B, the branch containing B and C is broken. Current can still flow through Bulb A and through the branch containing Bulb D. Therefore, Bulb A and Bulb D will light up. This also results in *two* bulbs lighting up.
-   **If a switch is opened at position D:** The branch containing Bulb D is broken. Current can still flow through Bulb A and the branch containing Bulb B and Bulb C. Therefore, Bulbs A, B, and C will light up. This results in *three* bulbs lighting up.

The question asks for a position where only two bulbs remain lighted up when the switch is opened. Both positions B and C satisfy this condition. Since B is an option, we select B.

Question 21

22. Kelly was given three circuits X, Y and Z as shown below. The bulbs and batteries in all the circuits are new and identical. Different objects, A, B and C, are connected in each circuit. Kelly made the following observations in her notebook. Which of the following is possible?

Accepted Answer

(2) Object C is another light bulb.. Let's analyze the observations:
-   **The bulb in circuit X did not light up.** This means that Object A did not allow electricity to flow, indicating that Object A is an electrical insulator. Therefore, option (1) 'Object A is made of metal' (a conductor) is incorrect.
-   **The bulbs in circuits Y and Z lighted up.** This means that Objects B and C allowed electricity to flow, indicating that both Object B and Object C are electrical conductors. Therefore, option (3) 'Object B is an electrical insulator' is incorrect.
-   **The bulb in circuit Y was brighter than the bulb in circuit Z.** This implies that the total resistance in circuit Y was lower than in circuit Z. Since the bulbs and batteries are identical, the difference in brightness must be due to Objects B and C.
    -   If Object C is another light bulb (option 2), it would add additional resistance to circuit Z, making the bulb in Z dimmer compared to circuit Y (assuming Object B is a low-resistance conductor like a wire). This is a plausible explanation. Therefore, option (2) is possible.
    -   If Objects B and C are identical electrical wires (option 4), they would have similar, very low resistances. This would result in the bulbs in Y and Z having similar brightness, contradicting the observation that Y was brighter than Z. Therefore, option (4) is incorrect.

Thus, option (2) is the most plausible explanation.

Question 22

23. The diagram below shows a sky lantern. A sky lantern is made of paper. It has a covered top and an opening at the bottom. Which one of the following correctly shows the energy changes when the candle is lit and the sky lantern rises up into the air?

Accepted Answer

(4) Chemical potential energy → heat energy + light energy → kinetic energy + gravitational potential energy. Let's trace the energy transformations during the lighting and rising of the sky lantern:
1.  **Chemical potential energy:** The candle wax stores chemical potential energy.
2.  **Burning candle:** When the candle is lit, this chemical potential energy is converted into:
    -   **Heat energy:** Primarily heats the air inside the lantern, making it less dense.
    -   **Light energy:** Emitted by the flame.
    -   (A small amount of sound energy is also produced).
3.  **Rising lantern:** The heated air provides lift (buoyancy), causing the lantern to ascend. This upward movement involves:
    -   **Kinetic energy:** Energy of motion as the lantern moves upwards.
    -   **Gravitational potential energy:** Energy gained due to increased height above the ground.

So the complete energy transformation is: Chemical potential energy → Heat energy + Light energy (+ Sound energy) → Kinetic energy + Gravitational potential energy.

Comparing with the options:
-   (1) and (2) start with incorrect initial forms of energy.
-   (3) misses the kinetic energy associated with the upward movement of the lantern.
-   (4) accurately describes the sequence: Chemical potential energy (in the candle) is converted into heat energy (heating the air) and light energy (from the flame), which then leads to kinetic energy (as the lantern moves) and gravitational potential energy (as its height increases). This is the most comprehensive and correct sequence.

Question 23

24. Jay left three identical glasses in rooms A, B and C for an hour. After one hour, the three glasses were removed and left in room D. Five minutes later, Jay noticed water droplets form on the outer surface of glass B but not on glasses A or C. If the room temperature of all the rooms, A, B, C and D are different from one another, which of the following is definitely correct?

Accepted Answer

(1) Room B is the coldest room.. Condensation (water droplets forming on the outer surface of a glass) occurs when the surface of the glass is at or below the dew point of the surrounding air. This means the glass must be cold enough to cool the water vapour in the air to its condensation temperature.

-   Water droplets formed on glass B in Room D: This indicates that glass B was significantly colder than the air in Room D. For glass B to be this cold, Room B (where it was initially left for an hour) must have been cold enough to cool the glass significantly.
-   No water droplets formed on glasses A or C in Room D: This suggests that glasses A and C were not as cold as glass B when placed in Room D, or at least not cold enough to cause condensation.

Therefore, to be the only glass cold enough to cause condensation, glass B must have been the coldest of the three glasses initially. This implies that **Room B was the coldest room** among A, B, and C.

Let's evaluate the options:
-   (1) Room B is the coldest room. This aligns with our deduction, as it explains why only glass B was cold enough to cause condensation.
-   (2) Room D is the warmest room. We only know Room D's temperature was warmer than glass B's temperature; we cannot conclude it's the warmest overall without more information.
-   (3) Room A is colder than room D. Since glass A did not show condensation in room D, glass A was likely not significantly colder than room D (or not as cold as glass B). This doesn't mean Room A is colder than Room D. It could be warmer or similar.
-   (4) Room C is as warm as room D. Similar to Room A, we cannot conclude this from the lack of condensation on glass C.

Thus, the only statement that is definitely correct is (1).

Question 24

25. Tanya carried out an experiment as shown below. Based on the information given above, which of the following statements are true?
A The spring started moving because of elastic spring force.
B Frictional force caused the spring to change its direction.
C The force applied by Tanya caused the spring to change its size.
D Gravitational force caused the spring to stop moving upwards.

Accepted Answer

(4) A, C and D only. Let's analyze each statement:
-   **A (The spring started moving because of elastic spring force):** In Step 2, Tanya compresses the spring, storing elastic potential energy. When released in Step 3, this stored energy is converted into kinetic energy, causing the spring to move upwards due to the elastic restoring force. So, A is **true**.
-   **B (Frictional force caused the spring to change its direction):** Frictional force always opposes motion. While it would slow down or stop the spring's vertical movement, it would not cause it to change direction from vertical to horizontal. So, B is **false**.
-   **C (The force applied by Tanya caused the spring to change its size):** In Step 2, Tanya pushes the spring down by 2cm, compressing it. This compression directly changes the length (size) of the spring. So, C is **true**.
-   **D (Gravitational force caused the spring to stop moving upwards):** As the spring moves upwards, gravitational force (its weight) continuously acts downwards, opposing its upward motion. This opposing force causes the spring to decelerate, eventually stop at its highest point, and then fall back down. So, D is **true**.

Therefore, statements A, C, and D are true. Option (4) is the correct choice.

Question 25

26. Sam used some ice-cream sticks and rubber bands to make a catapult as shown in the diagram below. A small container is attached at the end of the inclined ice-cream stick to hold a piece of stone. When the inclined ice-cream stick is pushed down, the rubber bands are stretched. When it is released, the stone will propel forward and travel in the air for a certain distance before dropping to the ground. Which of the following is correct?

Accepted Answer

(3) Some kinetic energy in the stone is converted to heat energy as it moves in the air.. Let's analyze the energy transformations involved in the catapult:
-   When the stick is pushed down, the rubber bands are stretched, storing **elastic potential energy**.
-   When released, this elastic potential energy is converted into **kinetic energy** of the stick and stone.
-   As the stone travels in the air, its kinetic energy is further converted into **gravitational potential energy** (as it gains height) and some is lost due to air resistance.

Now, let's evaluate each statement:
-   (1) The stone will have gravitational potential energy as its height above the ground changes while it travels in the air. So, this is false.
-   (2) Just before the stone reaches the ground, gravity has been accelerating it downwards, so it will have its maximum kinetic energy (just before impact). So, this is false.
-   (3) As the stone moves through the air, it experiences air resistance (a form of friction). This air resistance converts some of the stone's kinetic energy into other forms of energy, primarily **heat energy** (due to friction with air particles) and some sound energy. So, this is true.
-   (4) When the inclined ice-cream stick is released, the stretched rubber bands *contract*, *releasing* their stored elastic potential energy and converting it into kinetic energy. Therefore, the potential energy in the rubber bands *decreases*, it does not increase. So, this is false.

Therefore, option (3) is correct.

Question 26

27. A mixture of materials P and Q was poured into machine Z. This machine can separate materials based on their magnetic properties. The arrows show the direction the belts on the rollers are moving in. Based on the diagram above, which of the following statements is true?

Accepted Answer

(3) Material Q is a magnetic material.. The machine separates materials based on their magnetic properties.
-   As the mixture of P and Q moves on the first belt and passes over roller X:
    -   Material P falls off the belt earlier, following a typical trajectory of a non-magnetic material or one not strongly attracted to the roller.
    -   Material Q, however, stays attached to the belt for longer, following its curvature around roller X before being directed to the second belt. This behavior indicates that Material Q is attracted to roller X.

Let's evaluate the options:
-   (1) The fact that separation occurs at roller X (with Q being attracted) strongly implies that roller X contains a magnet. While it's possible roller Y also contains a magnet, the separation for magnetic properties is shown occurring at X. So this could be true, but (3) is a more direct observation about the material.
-   (2) If Material P were magnetic, it would be attracted to roller X and follow the belt's path like Material Q. Since it falls off early, Material P is a non-magnetic material. So, this is false.
-   (3) Material Q's behavior of sticking to the belt around roller X is characteristic of a material attracted by a magnet. Thus, Material Q is a magnetic material. So, this is true.
-   (4) The machine's stated function is to separate based on magnetic properties, not weight. We cannot infer anything about the relative weights of P and Q from this diagram. So, this is false.

Therefore, the most accurate statement based on the diagram and the machine's purpose is (3).

P6 Science SA2 2019 — Ai Tong

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P6 Science SA2 2019 — Ai Tong

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