Question 1

Study the animals in group A and B, as shown below.
Which of the following describes the animals in group A and B?

Accepted Answer

B. Group A: Covered with hair (No), Lay eggs (Yes). Group A consists of a chicken and a penguin. Both are birds. Birds do not have hair (they have feathers) and they lay eggs. Option B correctly states 'Group A: Covered with hair (No), Lay eggs (Yes)'.

Question 2

Bala has butterflies of three different stages. Each was placed separately into similar containers, A, B and C. Each container has 15 g of leaves and 15 g of nectar as shown below.
The results after five days are shown in the table below.
Which of the following shows the correct stage of the butterfly in each container?

Accepted Answer

C. Container A: pupa, Container B: larva, Container C: adult. Different stages of a butterfly have different dietary needs:
- Larvae eat leaves.
- Adults eat nectar.
- Pupae do not eat.
Comparing the results:
- Container A: 15 g of leaves left, 15 g of nectar left. Nothing was eaten, so the organism is a pupa.
- Container B: 5 g of leaves left, 15 g of nectar left. Leaves were eaten, so the organism is a larva.
- Container C: 15 g of leaves left, 5 g of nectar left. Nectar was eaten, so the organism is an adult.
Therefore, the correct stages are Container A: pupa, Container B: larva, Container C: adult, which matches option C.

Question 3

Study the two flowers as shown below.
After one month, both flowers A and B developed into fruits.
Which of the following statement(s) is/ are correct?
A Only flower B can produce pollen grains.
B Both flowers have male and female reproductive organs.
C Ovules from both flowers can develop into seeds after fertilisation.

Accepted Answer

C. A and C only. Let's analyze each statement:
- Flower A has a pistil (female reproductive organ) but no stamens (male reproductive organs). Flower B has both pistil and stamens.
- Statement A: Since Flower A lacks stamens, it cannot produce pollen grains. Flower B has stamens and can produce pollen. So, statement A is correct.
- Statement B: Flower A only has female reproductive organs. Flower B has both male and female reproductive organs. Thus, it's incorrect to say both have male and female reproductive organs.
- Statement C: Both flowers developed into fruits, which implies that fertilization occurred, and their ovules developed into seeds. So, statement C is correct.
Therefore, statements A and C are correct, which corresponds to option C.

Question 4

In a power disruption, Bala was trapped in a lift. The ventilation fan stopped working, no air can enter or leave the lift. After one hour, he started to feel unwell.
Which of the following statement(s) describe(s) what was happening to Bala?
A Bala's breathing rate increases.
B The amount of oxygen entering Bala's lungs decreases.
C The amount of carbon dioxide entering Bala's lungs decreases.

Accepted Answer

C. A and B only. Let's analyze each statement in a sealed environment:
- Statement A: As oxygen levels decrease and carbon dioxide levels increase due to respiration, Bala's body would try to compensate by increasing his breathing rate to maximize gas exchange. So, A is correct.
- Statement B: With no fresh air entering, oxygen is consumed by Bala's respiration. The concentration of oxygen in the lift decreases, so the amount of oxygen entering his lungs with each breath, and subsequently transferred to his blood, decreases. So, B is correct.
- Statement C: Carbon dioxide is produced by Bala's respiration. In a sealed environment, its concentration in the lift would increase. This would reduce the concentration gradient for CO2 to diffuse out of Bala's blood into his lungs for exhalation. Therefore, the *net amount* of carbon dioxide leaving Bala's blood and lungs would decrease (it becomes harder to expel CO2). However, if 'entering Bala's lungs' means inhaled CO2, then it would increase. Given that C implies a negative effect leading to feeling unwell, the interpretation of reduced net expulsion of CO2 from the body via the lungs is more fitting. But B is more straightforwardly correct.
Given that the typical options in such questions are that oxygen decreases and carbon dioxide increases, and breathing rate increases, A and B are definitively correct. Option C is ambiguously worded but often in physiology, 'entering lungs' for CO2 refers to its diffusion from blood into the alveolar space for expulsion. If the ambient CO2 concentration rises, this gradient reduces, leading to less CO2 effectively 'entering' the lungs for removal. However, it's common for these questions to treat C as false because the *inhaled* CO2 *concentration* increases. Assuming A and B are the most robustly correct statements, 'A and B only' (option C) is the most scientifically sound choice among the provided options.

Question 5

Study the characteristics of fruit A and B of different plants below.
Below are three maps showing the distribution of seeds.
Which of the following maps correctly matches how the seeds of fruit A and B are dispersed?

Accepted Answer

B. Fruit A: map Y, Fruit B: map Z. Fruit A shows a small, winged seed, which is characteristic of wind dispersal. Map Y shows seeds widely dispersed in the direction of the wind, which is consistent with effective wind dispersal.
Fruit B shows a large, fleshy fruit with a single large seed. Such fruits are typically dispersed by gravity (dropping near the parent plant) or by animals. Map Z shows seeds clustered tightly around the parent plant, which is characteristic of gravity dispersal.
Therefore, Fruit A (wind dispersal) matches Map Y, and Fruit B (gravity/animal dispersal) matches Map Z. This corresponds to option B.

Question 6

Mable prepared two set-ups as shown below.
What will be the colour of the leaves of plants C and D after a few days?

Accepted Answer

B. Leaves of plant C: turned blue, Leaves of plant D: remained green. Let's analyze each plant's setup:
- Plant C: Only the food-carrying tubes (phloem) have been removed. The water-carrying tubes (xylem) are intact. Since blue-coloured water is available, it will be absorbed by the roots and transported via the xylem to the leaves, causing the leaves to turn blue.
- Plant D: Both food-carrying and water-carrying tubes have been removed. This means no water can be transported to the leaves. Consequently, the blue-coloured water will not reach the leaves. The leaves will remain green initially (before wilting and eventually turning brown due to lack of water).
Therefore, the leaves of Plant C will turn blue, and the leaves of Plant D will remain green. This matches option B.

Question 7

The diagrams below show two different cells, A and B.
Which of the following statements about cell A and cell B is correct?

Accepted Answer

D. Only certain substances can move in and out of both cells.. Cell A is an animal cell (roundish, no cell wall or chloroplasts). Cell B is a plant cell (rectangular, with cell wall and chloroplasts).
- Statement A: Animal cells (A) do not have a fixed shape. Plant cells (B) have a fixed shape due to the cell wall. So, this statement is incorrect.
- Statement B: Only plant cells (B) have chloroplasts and can perform photosynthesis. Animal cells (A) cannot. So, this statement is incorrect.
- Statement C: Both animal cells (A) and plant cells (B) can reproduce by cell division. So, this statement is incorrect.
- Statement D: Both animal cells (A) and plant cells (B) have a cell membrane. The cell membrane is selectively permeable, meaning it controls which substances can move in and out of the cell. So, this statement is correct.

Question 8

The diagrams below shows how blood flows in the body of a fish and a human.
At which parts A, B, C or D, is the blood rich in oxygen in the fish and human respectively?

Accepted Answer

B. Fish: A, Human: D. Let's analyze blood flow for each:
- Fish circulation: Blood is pumped from the heart to the gills. In the gills, oxygen is absorbed from the water, making the blood oxygen-rich. This oxygenated blood then flows from the gills directly to the body tissues (Part A in the diagram, leading to 'body'), where oxygen is delivered. So, in fish, part A has oxygen-rich blood.
- Human circulation: Blood is pumped from the heart to the lungs. In the lungs, oxygen is absorbed, making the blood oxygen-rich. This oxygen-rich blood (Part C in the diagram) returns to the heart, which then pumps it to the rest of the body through arteries (Part D in the diagram, leading to 'body'). Both C and D contain oxygen-rich blood, but D represents the blood being distributed to the body, which is a key location of oxygen-rich blood for tissue supply.
Therefore, Part A in the fish and Part D in the human represent locations of oxygen-rich blood, which corresponds to option B.

Question 9

Which part of the human digestive system does not have any digestion taking place?

Accepted Answer

B. Part (2) (Esophagus). Let's identify the parts and their digestive functions:
- Part (1) represents the mouth/pharynx. Digestion begins in the mouth with mechanical (chewing) and chemical (salivary amylase for starch) digestion.
- Part (2) represents the esophagus. The esophagus is a muscular tube that transports food from the pharynx to the stomach via peristalsis. No digestion (mechanical or chemical) occurs here.
- Part (3) represents the stomach. Mechanical digestion (churning) and chemical digestion (pepsin for proteins) occur here.
- Part (4) represents the small intestine. This is the primary site for both chemical digestion of carbohydrates, proteins, and fats, and absorption of nutrients.
Thus, the esophagus (Part 2) is the only part listed where no digestion takes place.

Question 10

Study the food web below.
Which of the following shows how populations of A and B are immediately affected if population of C is wiped out by a disease?

Accepted Answer

A. Population A: increases, Population B: decreases. Based on the food web:
- Plant is eaten by A and B.
- A is eaten by C.
- C is eaten by E.
If population of C is wiped out:
- Effect on A: C is a predator of A. If C is removed, A will have fewer predators. Therefore, the population of A will immediately increase.
- Effect on B: A and B both eat Plant. If A's population increases due to the removal of C, then A will consume more Plant. This increased consumption by A will reduce the availability of Plant for B. Therefore, the population of B will immediately decrease due to reduced food supply.
Thus, population A increases and population B decreases, which matches option A.

Question 11

Snake R is well-adapted to survive in its habitat. The rattle at its tail will make a sound when it is alarmed.
Which of its adaptions are grouped under the correct heading?

Accepted Answer

C. Structural: Sharp fangs to inject poison into its prey, Behavioural: Wait silently to attack. Structural adaptations are physical features, while behavioural adaptations are actions or ways of behaving.
- 'Sharp fangs' are a structural adaptation. The function 'to inject poison into its prey' is enabled by this structure and involves a behaviour, but the fangs themselves are structural.
- 'Wait silently to attack' is an action, thus a behavioural adaptation.
Let's evaluate the options:
- A: 'Wait silently to attack' is behavioural, not structural. 'Shake its rattle...' is behavioural. Incorrect grouping.
- B: 'Shake its rattle...' is behavioural, not structural. 'Forked tongue to sense changes' describes the function of a structural part but 'sense changes' is a behaviour. Incorrect grouping.
- C: 'Sharp fangs' are structural. Linking it to 'inject poison into its prey' is often accepted as describing the function of the structural adaptation. 'Wait silently to attack' is a clear behavioural adaptation. This option is the most accurately grouped.
- D: Headings are swapped. Incorrect.

Question 12

Susan collected equal amount of water from point A and B of a river. She found three types of organisms, X, Y and Z in her water samples.
The factories discharged substance W into the river.
Susan wanted to find out the effect of substance W on the organisms.
Based on her results, which of the following is a possible conclusion?

Accepted Answer

D. W is useful to Y, W is harmful to X, W has no effect on Z. Point A is upstream (before substance W), and Point B is downstream (after substance W). By comparing the populations at Point B to Point A, we can determine the effect of substance W.
- Organism X: Population decreased from 100 at A to 5 at B. This means substance W is harmful to X.
- Organism Y: Population increased from 40 at A to 80 at B. This means substance W is useful to Y.
- Organism Z: Population remained 70 at both A and B. This means substance W has no effect on Z.
Therefore, the conclusion is: W is useful to Y, W is harmful to X, and W has no effect on Z. This matches option D.

Question 13

Ravi has a potted plant that had been placed in the dark for two days. He then tied a clear plastic bag with a substance which absorbs carbon dioxide around leaf A of his potted plant.
Then he placed the potted plant in the sun for another two days before plucking leaf A and B to test for starch. The iodine solution turned dark blue on leaf B but remain yellowish brown on leaf A..
Which of the following is the aim of Ravi's experiment?

Accepted Answer

B. To find out if carbon dioxide is needed for photosynthesis.. The experiment is designed to test the necessity of a specific factor for photosynthesis using a control (Leaf B) and an experimental group (Leaf A).
- The plant was destarched (placed in dark) to ensure any starch present at the end of the experiment was newly produced.
- Both Leaf A and Leaf B were exposed to sunlight.
- Leaf A was deprived of carbon dioxide by the CO2 absorber inside the plastic bag.
- Leaf B was exposed to atmospheric carbon dioxide.
- The results (no starch in Leaf A, starch in Leaf B) indicate that the presence of carbon dioxide allowed Leaf B to photosynthesize and produce starch, while its absence prevented Leaf A from doing so.
Therefore, the aim of the experiment is to determine if carbon dioxide is needed for photosynthesis.

Question 14

The diagram below shows a pond habitat.
Which of the following statements is correct?

Accepted Answer

D. There are 10 populations of living organisms.. Let's identify the different populations of living organisms shown or implied in the pond habitat:
Producers:
1.  Water plants (e.g., lily pads)
2.  Land plants (where the caterpillar is)
3.  Algae/Plankton (implied food source for tadpoles)
Consumers:
1.  Caterpillars
2.  Dragonflies
3.  Fish
4.  Tadpoles
5.  Frogs
6.  Birds
7.  Smaller flying insects
So, there are 3 populations of producers and 7 populations of consumers.
- Total living organisms = 3 (producers) + 7 (consumers) = 10 populations.
- Option A: There are 3 (not 4) populations of producers.
- Option B: There are 7 (not 5) populations of consumers.
- Option C: There are 7 populations of consumers. (This statement is correct based on the count, but option D is also correct and more comprehensive).
- Option D: There are 10 populations of living organisms. (This is correct, summing producers and consumers).
Since multiple choice questions usually have only one best answer, and 10 populations encompass both producers and consumers, D is often the intended correct answer if C is also technically true.

Question 15

The diagram below shows a crow dropping small pebbles into a cylinder to obtain water to drink.
As the pebbles are dropped into the cylinder, the water level increases.
Which of the following is a reason why the water level increases?

Accepted Answer

D. The pebbles take up the space in the water.. When pebbles are dropped into the water, they displace an amount of water equal to their own volume. Since the pebbles occupy space (have volume), the water level rises to accommodate them.
- A: While pebbles have mass, it is their volume that causes the water level to rise by displacement.
- B: The mass of the water does not change; only pebbles are added.
- C: The volume of the water itself does not increase; it is the total volume occupied by water and pebbles that increases.
- D: This correctly explains that the pebbles occupy space, displacing the water and causing its level to rise.

Question 16

Tom placed two sealed containers that were fully filled with air and sand into a swimming pool.
Which of the following diagrams shows the correct positions of containers, A and B, in the swimming pool?

Accepted Answer

A. Container A: floating at surface, Container B: at bottom. The position of an object in water depends on its density relative to water.
- Container A is fully filled with air. Air is much less dense than water. Therefore, container A will float on the surface of the water.
- Container B is fully filled with sand. Sand is much denser than water. Therefore, container B will sink to the bottom of the swimming pool.
Option A correctly depicts Container A floating and Container B sinking.

Question 17

The amount of electrical energy used by a refrigerator can be greatly reduced by observing good conservation practices.
Which of the following action(s) help(s) to conserve electricity?
A Minimizing the opening of door.
B Putting hot food into the refrigerator.
C Setting the refrigerator to the lowest temperature.

Accepted Answer

A. A only. Let's evaluate each action:
- A Minimizing the opening of the door: This reduces the exchange of cold air inside with warm air from the room, meaning the refrigerator's cooling system has to work less to maintain the desired temperature, thus saving electricity. (Correct)
- B Putting hot food into the refrigerator: This introduces a significant amount of heat into the refrigerator, forcing its cooling system to work harder and longer to cool the food and the internal space, thereby using more electricity. (Incorrect)
- C Setting the refrigerator to the lowest temperature: This requires the refrigerator's cooling system to work harder to achieve and maintain a colder internal temperature, consuming more electricity. (Incorrect)
Therefore, only action A helps to conserve electricity.

Question 18

The diagram below shows Nila bouncing a basketball.
Which of the following statements is incorrect?

Accepted Answer

D. The gravity acting on the ball is greater as it drops than when it bounces up.. The question asks for the *incorrect* statement.
- A: Nila applies a push force to dribble the basketball downwards. (Correct)
- B: When the ball hits the ground, it changes direction from downwards to upwards. (Correct)
- C: Nila applies a force to push the ball downwards, thereby changing its direction of motion. (Correct)
- D: Gravity is a force that acts constantly on the ball due to its mass and the Earth's gravitational field. The magnitude of gravitational force remains essentially constant whether the ball is moving up or down, as long as its mass and distance from the Earth's center do not significantly change. Therefore, this statement is incorrect.

Question 19

Xiao Ming pulled a block of wood across three different surfaces as shown below.
Xiao Ming recorded the force needed to pull the block across these three surfaces in the table below.
Which of the following is the changed variable of the experiment?

Accepted Answer

A. The type of surfaces. In an experiment, the changed variable (or independent variable) is the factor that is intentionally altered by the experimenter to observe its effect.
- Xiao Ming pulled the block across *three different surfaces* (X, Y, and Z). This indicates that the type of surface was the factor being changed.
- The mass of the block was kept constant (same block).
- The reading on the spring balance and the amount of force used to pull the block are the measured outcomes (dependent variables), not the changed variable.

Question 20

Based on his results, which of the following is true?

Accepted Answer

C. More force is needed to pull the block on Y than on Z.. The force needed to pull the block indicates the amount of friction present; a greater force means greater friction and a rougher surface.
- Force for X = 20 units
- Force for Y = 16 units
- Force for Z = 14 units
Let's evaluate the options:
- A: Z has a rougher surface than X. Force for Z (14) is less than force for X (20), so Z is smoother than X. (Incorrect)
- B: The force needed to pull the block on Y (16) is not the most; X (20) is the most. (Incorrect)
- C: More force is needed to pull the block on Y (16 units) than on Z (14 units). This is true (16 > 14). (Correct)
- D: There is less friction acting between the block and Y (16 units) than the block and Z (14 units). This is false; 16 units implies more friction than 14 units. (Incorrect)

Question 21

In a factory, a pile of metal pieces travels along a moving rubber belt. When these pieces reaches the end of the belt where the magnet roller is, they get separated into two piles, A and B.
What are the two main forces used to separate the metal pieces into pile A and pile B respectively?

Accepted Answer

A. Pile A: magnetic force, Pile B: gravitational force. At the end of the conveyor belt, a magnet roller is used for separation.
- Magnetic metal pieces will be attracted by the magnet roller, causing them to stick to the belt for longer and fall off at a point further away from the initial drop-off, forming Pile A. So, magnetic force is responsible for Pile A.
- Non-magnetic metal pieces (or those not strongly attracted) will not be held by the magnet. They will follow the natural trajectory as they leave the belt, falling into Pile B primarily due to the force of gravity.
Therefore, magnetic force separates pieces into Pile A, and gravitational force separates pieces into Pile B.

Question 22

Jeremy needs to inflate two identical balls. He pumps 20 units of air into ball A and 40 units of air into ball B.
He observed that the inflated ball A and ball B have the same size after different amount of air has been pumped into them.
What conclusion can Jeremy make from the above observation?

Accepted Answer

D. Air can be compressed.. Both balls are identical and end up the same size (occupying the same volume). However, Ball B contains twice the amount of air (40 units) compared to Ball A (20 units).
- If a larger quantity of air can fit into the same volume, it means the air is being squeezed into a smaller space than it would normally occupy. This demonstrates the property of compressibility.
- A: While air has mass, this experiment primarily demonstrates volume changes under pressure, not mass.
- B: Air is a form of matter, so this statement is incorrect.
- C: Air takes the shape of its container and does not have a definite shape. This statement is incorrect.
- D: The ability to fit different amounts of air into the same volume proves that air can be compressed.

Question 23

Mei Qi is in a well-lit room, standing in front of a mirror as shown in the diagram below.
Mei Qi can see her own reflection in the mirror. Which of the following item(s) will Mei Qi also be able to see in the mirror?

Accepted Answer

D. teddy bear and spider only. To see an object in a mirror, the light rays from the object must reflect off the mirror and enter Mei Qi's eyes. This means the object must be within the mirror's field of view from Mei Qi's perspective.
- The diagram shows Mei Qi looking into the mirror. The teddy bear is placed somewhat centrally in front of her. The spider is hanging relatively close to the mirror on her left side. These positions make it highly probable for their reflections to be within her line of sight reflecting off the mirror.
- The lamp is on the ceiling (likely above the mirror's direct reflective area for Mei Qi's eye level), and the dog and ball are further to her right and might be outside the effective field of view of the mirror for her, especially if the mirror is not very wide.
Therefore, the teddy bear and spider are the most likely items for Mei Qi to also see in the mirror, which corresponds to option D.

Question 24

Tisha conducted an experiment by heating substance X. At the start, substance X was a solid at 28°C. After 15 minutes of heating, substance X reached a temperature of 110°C as shown below.
Based on Tisha's experiment, which of the following is possible?

Accepted Answer

D. Melting point of X: 60°C, Boiling point of X: 150°C. From the experiment, we know:
1.  Substance X was a solid at 28°C. This means its melting point (MP) must be *above* 28°C.
2.  After heating, it became a liquid at 110°C. This means its boiling point (BP) must be *above* 110°C (otherwise it would have boiled away and become a gas by 110°C).
Let's check the options based on these two conditions (MP > 28°C and BP > 110°C):
- A: MP = 20°C (Not > 28°C). Incorrect.
- B: MP = 28°C (Not strictly > 28°C; if it melts at 28°C, it would be a mixture of solid and liquid or just melted at 28°C). BP = 100°C (Not > 110°C). Incorrect.
- C: MP = 30°C (Correct, > 28°C). BP = 100°C (Not > 110°C). Incorrect, it couldn't be liquid at 110°C if its BP is 100°C.
- D: MP = 60°C (Correct, > 28°C). BP = 150°C (Correct, > 110°C). This option is consistent with both observations.
Therefore, option D is the only possible set of melting and boiling points.

Question 25

Xuan Wen set up a circuit with objects, X, Y and Z as shown.
She recorded her observations in the table below.
In which of the following circuit(s) will both bulbs remain lit?

Accepted Answer

D. circuit B and C only. First, determine the properties of X, Y, and Z from the initial experiment:
- Bulb B1 (with Y) does not light up -> Y is an insulator.
- Bulb B2 (with X) lights up -> X is a conductor.
- Bulb B3 (with Z) lights up -> Z is a conductor.
Now, evaluate each circuit option to see if both bulbs light up:
- Circuit A: The two bulbs and object Y are all in series. Since Y is an insulator, it breaks the circuit, and no current will flow. Neither bulb will light up.
- Circuit B: The circuit diagram shows the current flowing through a first bulb, then through X, then splitting into two parallel paths (one through a second bulb, one through Y), and then these paths rejoin. Since X is a conductor and Y is an insulator, current will flow through X and the second bulb (as it's in parallel with Y, which is open). Both bulbs will light up.
- Circuit C: The circuit diagram shows the current flowing through X, then splitting into three parallel paths (one through a first bulb, one through Y, one through Z). These paths rejoin, then the current flows through a second bulb. Since X and Z are conductors, and the first bulb is also a conductor (filament), current can flow through these paths. Even though Y is an insulator, the current can bypass it via the parallel paths through the first bulb and Z. So, both bulbs will light up.
Therefore, both Circuit B and Circuit C will have both bulbs lit, which corresponds to option D.

Question 26

Ali has a toy car that works on batteries.
His observations are shown below.
Which of the following circuits is used in Ali's toy car?

Accepted Answer

C. Circuit 3. Let's analyze the observations to deduce the control logic:
1.  Switch A only: Wheels spun (Headlamp off, Siren off).
2.  Switch B only: Headlamp lit, Siren sounded (Wheels did not spin).
3.  Both A and B: Headlamp lit, Siren sounded, Wheels spun.
From this, we can conclude:
- Switch A controls only the wheels.
- Switch B controls both the headlamp and the siren.
Now let's examine the circuits:
- Circuit (1): Switch A controls wheels. Switch B controls headlamp. Siren is in series with wheels controlled by A. This contradicts observation 1 (siren would sound with A only). Incorrect.
- Circuit (2): Switch A controls headlamp. This contradicts observation 1 (headlamp off with A only). Incorrect.
- Circuit (3): Switch A is in series with the wheels. Switch B is in series with a parallel combination of the headlamp and the siren. This perfectly matches all observations:
    - A only: Wheels spin.
    - B only: Headlamp and siren activate.
    - A and B: All three activate.
- Circuit (4): Switch A controls siren. This contradicts observation 1 (siren off with A only). Incorrect.
Thus, Circuit (3) is the correct circuit.

Question 27

A hot air balloon uses hot air to rise. The burner with fuel is lighted. As the fuel burns, the hot air balloon floats up into the sky.
Which of the following best represents the energy conversions involved in making the hot air balloon float into the sky when the fuel is burnt?

Accepted Answer

B. chemical potential energy → heat energy → kinetic energy (fuel) (flame) (moving hot air). Let's trace the energy conversions:
1.  Fuel: The fuel (e.g., propane) stores chemical potential energy.
2.  Burning: When the fuel burns, its chemical potential energy is converted primarily into heat energy (manifested as flame).
3.  Hot air: The heat energy from the flame is transferred to the air inside the balloon, making it less dense and causing it to rise. This rising motion is kinetic energy of the hot air, which lifts the balloon.
So, the sequence is Chemical potential energy (fuel) → Heat energy (flame) → Kinetic energy (moving hot air/balloon). This matches option B.
Option C is incorrect because light energy is a minor byproduct; heat is the primary useful energy form for lift. Options A and D are incorrect as they start with gravitational potential energy, which is a result of the lift, not the initial energy source.

Question 28

Thomas has a set-up below.
After a while, Thomas observed water droplets forming on the underside of the basin.
What should Thomas do in order to increase the number of water droplets formed on the underside of the basin?

Accepted Answer

A. Basin: Add ice cubes, Beaker: Add more water at 100°C. Water droplets form due to condensation. Condensation is maximized when there is a greater amount of water vapor and a colder surface for the vapor to condense upon.
- To increase water vapor: The water in the beaker should be hotter, increasing its evaporation rate. Adding more water at 100°C to the beaker (initially 70°C) would significantly increase the water temperature and thus the amount of water vapor.
- To make the condensation surface colder: The water in the basin (initially 10°C) should be made colder. Adding ice cubes to the basin would lower its temperature, providing a colder surface for condensation.
Let's evaluate the options:
- A: Basin: Add ice cubes (makes surface colder). Beaker: Add more water at 100°C (increases water vapor). This combination optimizes both factors for increased condensation. (Correct)
- B: Basin: Add ice cubes (good). Beaker: Add ice cubes (bad, decreases water temperature and thus evaporation). (Incorrect)
- C: Neither action significantly changes the temperatures to promote more condensation. (Incorrect)
- D: Basin: Add more water at 100°C (makes surface hotter, reducing condensation). Beaker: Add ice cubes (bad, decreases evaporation). (Incorrect)
Therefore, option A is the best way to increase the number of water droplets.

P6 Science SA2 2019 — Tao Nan

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P6 Science SA2 2019 — Tao Nan

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