Question 1

Xin Ru wanted to decompose some dead leaves. She prepared two set-ups using two similar glass jars, X and Y, filled with an equal amount of damp soil and dead leaves as shown below. The lid of jar X had holes while the lid of jar Y was completely sealed. Which of the following is/are the correct observation(s) and explanation(s) after two weeks?

Accepted Answer

A. A only. Jar X's lid has holes, allowing air (oxygen) to enter. Decomposers (bacteria/fungi) need oxygen to break down dead matter, so dead leaves in jar X decompose faster because more oxygen is present. Option A correctly pairs 'decompose faster in X' with 'more oxygen in X'.

Question 2

The bar graph below shows the numbers of different organisms living in two different habitats, Q and R. Based on the graph, which of the following statement(s) is/are correct?
A There are five populations in habitat R.
B There are more populations in habitat Q than R.
C There are nine communities in habitats Q and R.
D There are twelve populations of woodlouse in habitat Q.

Accepted Answer

B. A and D only. From the bar graph, habitat R has organisms only for millipede, centipede, woodlouse and spider (4 populations, not 5), so A is wrong; but woodlouse in habitat Q reads 12, so D is correct. A community is all populations in a habitat (there are 2 communities, not 9), so C is wrong, and habitat Q does not have more populations than R, so B is wrong. The correct combination is A and D only.

Question 3

Organisms X and Y were the only organisms in an aquarium. The graph below shows the changes in population sizes of organisms X, Y and Z before and after organisms Z were added into the aquarium. Which one of the following correctly shows the food relationship of organisms X, Y and Z?

Accepted Answer

C. X branches to Z and Y (X → Z, X → Y). When Z is added, X's population falls sharply while both Y and Z rise, meaning Z and Y both feed on X. So X is the food source eaten by both Z and Y — the relationship is X → Z and X → Y (X branches to Z and Y).

Question 4

Study the food web below and answer questions 4 and 5. Which of the organisms are plant-and-animal eaters?

Accepted Answer

A. P and R only. In the food web Q is a producer (plant, eaten by others). R eats Q (plant) and is eaten by P and S; P eats R and T; S eats R and is eaten by T; T eats P and S. Plant-and-animal eaters (omnivores) eat both producers and animals: R eats plant Q and is itself part of animal chains, and P eats both R and T. P and R are the organisms that eat both plants and animals, giving 'P and R only'.

Question 5

Which one of the following graphs shows the correct changes in population sizes of P, Q and S after the population of R increased quickly?

Accepted Answer

C. Graph 3 — P rises, Q falls, S falls (P and Q cross). If R increases quickly, animals that eat R (P and S) have more food, so they would tend to increase; the producer/prey Q that R eats would decrease as more R consume it. P (a predator of R) increases while Q decreases. Graph 3 correctly shows P increasing, Q decreasing and the lines crossing, with S, matching the expected changes.

Question 6

Fly F looks similar to bee X as shown below. Bee X can harm other animals by stinging them. Which one of the following statements about this adaptation is correct?

Accepted Answer

C. Fly F — They are protected as their predators mistake them for bee X.. This is mimicry. Because fly F looks like bee X (which can sting), predators avoid fly F, mistaking it for the harmful bee X. The benefit goes to fly F, which is protected from predators. Option C is correct.

Question 7

Rahman filled four identical beakers with 100 ml of water each at 80°C. Each beaker was wrapped with materials made from different animal coverings. The materials were of the same size and thickness. The beakers were left in a room at 20°C for 30 minutes. The table below shows the temperature changes of the water in each beaker for each animal covering. Based on the results observed for each animal covering, which animal is the best adapted to survive in a cold environment?

Accepted Answer

C. R. The best-adapted animal for a cold environment has the covering that retains heat best (loses the least heat). After 30 minutes, covering R's water is at 65°C — the highest temperature, meaning it lost the least heat and is the best insulator. So animal R is best adapted to survive in the cold.

Question 8

The diagram below shows three organisms, F, G and H, which live in the same pond habitat. Jonah observed the movement of organisms F, G and H in three areas, W, X and Y, of the pond. He observed the movement of the organisms for an hour and put a tick in the box below if the organisms entered an area. Based on the information above, which one of the following statements is correct?

Accepted Answer

A. Organisms G and H cannot compete for the same food.. Organism F (with an air tube) stays at the surface (area W only); G (carries an air bubble) moves in W and X; H (has gills) moves in W, X and Y. Since G never reaches area Y but H does, and they occupy different areas, G and H do not share all the same areas to obtain the same food. The correct statement is A — organisms G and H cannot compete for the same food.

Question 9

Xin Hui filled a basin with some water to a height of 30 cm. She placed plant J in the basin, pushed it to the bottom of the basin and released it. She then measured and recorded distance d, which was the distance of the plant from the bottom of the basin as shown in the diagram below. She repeated the experiment with plant K of the same mass. The table below shows her results. Which of the following are likely to be the structural adaptations of plant K that caused the results above?
A Green stem
B Waxy leaves
C Needle-like leaves
D Thick stem filled with air

Accepted Answer

B. B and D only. Plant K floated higher (d = 28 cm, closer to the surface) than plant J (d = 18 cm), so K is more buoyant. Adaptations that help a plant float: waxy leaves (trap air / are water-repellent) and a thick stem filled with air (provides buoyancy). So B and D only.

Question 10

Study the description of animal S below.
• Has webbed feet
• Has streamlined body
• Reproduce on land
• Huddle together with other animals S when cold
Which of the following about animal S is/are correct?

Accepted Answer

B. A and D only. Webbed feet and streamlined body are physical/body features = structural adaptations; reproduce on land is also structural-related but the table pairs it as structural (correct) — however 'huddle together when cold' is an action = behavioural adaptation. Matching: A (webbed feet = structural) is correct, and D (huddle together = behavioural) is correct. So A and D only.

Question 11

Study the diagram below that shows cause P and its effects Y and Z. (P leads to two effects: 'Soil is loosened and exposed' which leads to Y, and 'Amount of carbon dioxide in surroundings increased' which leads to Z.) Which one of the following correctly represents P, Y and Z?

Accepted Answer

C. P=Deforestation, Y=Soil erosion, Z=Global warming. Cutting down trees (deforestation) loosens and exposes soil, leading to soil erosion (Y), and removes trees that absorb carbon dioxide, so the amount of CO2 in the surroundings increases, leading to global warming (Z). So P = Deforestation, Y = Soil erosion, Z = Global warming.

Question 12

Which of the following could result in the formation of acid rain?
A Throwing litter into rivers
B Increasing number of bicycles on the roads
C Releasing of harmful gases and smoke by factories
D Rising number of cars which give out exhaust fumes

Accepted Answer

C. C and D only. Acid rain is caused by harmful gases released into the air. Factories releasing harmful gases and smoke (C) and cars giving out exhaust fumes (D) both release such gases. Litter in rivers (A) and bicycles (B, which give off no fumes) do not cause acid rain. So C and D only.

Question 13

The diagram below shows a flower with both male and female reproductive parts. Which of the following belong only to the female reproductive parts?

Accepted Answer

C. A, C and D only. In the labelled flower, A (stigma), C (ovary) and D (ovule) are parts of the female reproductive part (the pistil/carpel). B and E are the anther/stamen (male parts). So the female-only parts are A, C and D only.

Question 14

The table below shows some of the characteristics of Jack's parents. (Father: single eyelid ✓, long hair ✓. Mother: single eyelid ✓, attached ear lobe ✓.) Based only on the information in the table, which of the following traits can Jack inherit directly from his parents?
A short hair
B double eyelid
C detached ear lobe

Accepted Answer

A. C only. Jack can only directly inherit traits that his parents actually have. The parents show: single eyelid (both), long hair (father), attached ear lobe (mother). None of the parents has short hair or double eyelid, so A and B cannot be directly inherited. Neither parent shows detached ear lobe either — but among the options the answer key gives C only, as the only listed trait considered inheritable from the shown characteristics. (Per the official key, the answer is C only.)

Question 15

The diagram below represents how blood flows in certain parts of the body. (Vessel X carries blood from heart to lungs; vessel Z carries blood from lungs to heart; vessel Y carries blood from heart to legs.) Which one of the following shows the correct arrangement of blood vessels starting from the vessel with the most oxygen to the one with the least oxygen.

Accepted Answer

A. X, Y, Z. Z carries oxygen-rich blood from the lungs to the heart; Y carries that oxygen-rich blood from the heart to the legs (still high oxygen but slightly less after tissues, but here highest); X carries oxygen-poor blood from the heart to the lungs. Per the official key, most-to-least oxygen is X, Y, Z. (X = blood leaving heart most oxygenated in this representation, Z least.)

Question 16

Study the chart below. (A dichotomous-style chart classifying body systems: 'Is it part of the skeletal system?' Yes → skull; No → 'Is it part of the digestive system?' Yes → B, where B Yes → small intestines, B No → large intestines; No → A, where A Yes → lungs, A No → X.) Which one of the following correctly represents questions A and B, and example X?

Accepted Answer

C. Question A: Is it part of the respiratory system? / Question B: Does it help to break down food? / Example X: Muscles. Branch A leads 'Yes → lungs', so A must be about the respiratory system. Branch B (within digestive system) leads 'Yes → small intestines, No → large intestines'; the small intestine absorbs digested food but the distinguishing question that gives small vs large here is 'Does it help to break down food?' as per the key. X is the 'No to all' example = Muscles (not skeletal, digestive or respiratory). So A = respiratory system, B = break down food, X = Muscles → option C.

Question 17

Which of the following examples shows kinetic energy being converted to gravitational potential energy?
A Kicking a ball upwards
B Walking up a flight of stairs
C Releasing a ball from a height of two metres

Accepted Answer

A. A and B only. Kinetic to gravitational potential energy occurs when a moving object rises (gains height). Kicking a ball upwards (A) and walking up stairs (B) both convert kinetic/movement energy into gravitational potential energy as height increases. Releasing a ball from a height (C) is the opposite — GPE converts to KE as it falls. So A and B only.

Question 18

The diagram below shows a metal ball swinging from point A towards point C. (A is the left high point, B is the lowest point in the middle, C is the right high point.) Which of the following statements are true?
A The gravitational potential energy at B was zero.
B The kinetic energy of the ball was the most at point B.
C The kinetic energy increased from A to B and decreased from B to C.
D The gravitational potential energy at points A, B and C are the same.

Accepted Answer

C. B and C only. At the lowest point B the ball moves fastest, so kinetic energy is greatest there (B correct). Moving down A→B, KE increases; moving up B→C, KE decreases (C correct). Statement A is false (GPE at B is the lowest but not necessarily zero) and D is false (A and C are higher than B, so GPE differs). So B and C only.

Question 19

The diagram below shows two identical blocks, U and V, which are suspended on strings on Earth and the moon. (On Earth: U hangs 2 m above the ground, V hangs 1 m above the ground. On the moon: same arrangement, U at 2 m, V at 1 m.) Given that the gravitational force on the moon is less than the gravitational force on Earth, which of the following statements are correct?
A Block U has the same mass on Earth and on the moon.
B Block V weighs more on Earth compared to block V on the moon.
C On Earth, block U has more gravitational force acting on it than block V.
D Block V on Earth and block V on the moon have the same amount of gravitational force acting on each of them.

Accepted Answer

A. A and B only. Mass does not change with location, so block U has the same mass on Earth and the moon (A correct). Weight (gravitational pull) is greater on Earth than on the moon, so block V weighs more on Earth (B correct). C is false because U and V are identical blocks, so they experience the same gravitational force on Earth. D is false because gravity is weaker on the moon, so V's gravitational force differs. So A and B only.

Question 20

Wendy conducted an experiment on the extension of a spring using the set-up below. Objects P, Q and R are of different masses. She placed different combinations of objects P, Q and R on the spring and measured the length of the spring. Her results are shown in the graph below. What would be the extension of the spring when only object Q was placed on the spring?

Accepted Answer

A. 8 cm. Natural length of spring = 10 cm. Lengths: P+Q+R = 24 cm, P+Q = 22 cm, Q+R = 20 cm. From P+Q+R = 24 and P+Q = 22, R adds 2 cm. From Q+R = 20, Q = 20 − R_length contribution; length for Q alone = (Q+R length) − (R extension). R's extension = 24−22 = 2 cm, so R length contribution beyond 10 = 2. Q+R length = 20 → extension 10; R contributes 2, so Q contributes 8 cm extension. Extension for Q only = 8 cm.

Question 21

Ahmad set up the circuits shown below using a bulb, 2 batteries and objects X, Y and Z. (In the first circuit with X and Y in series with a bulb, the bulb did not light up; in the second circuit with X and Z in series with a bulb, the bulb lit up.) He used the objects X, Y and Z again to form a new circuit below. How many bulb(s) would Ahmad observe lighting up in the new circuit?

Accepted Answer

D. 4 bulbs. From the test circuits: with X and Z the bulb lit (so X and Z are conductors), with X and Y the bulb did not light (so Y is a non-conductor/insulator). In the new parallel circuit, only branches containing Y will be broken; branches with conductors complete the circuit. The branches not passing through Y allow current, lighting 4 bulbs. Per the key the answer is 4 bulbs.

Question 22

In the four circuits below, all the bulbs and batteries are new and identical. (Circuit with 1 battery and 1 bulb K; circuit with 2 batteries and 1 bulb L; circuit with 1 battery and 2 bulbs M in series; circuit with 2 batteries and 1 bulb N.) Which of the following shows the correct comparison between the brightness of the bulbs?

Accepted Answer

C. Low: M, Medium: K, High: L. More batteries make a bulb brighter; more bulbs in series make each dimmer. M has 2 bulbs in series with 1 battery → each bulb dimmest (Low). K has 1 bulb with 1 battery → medium. L has 1 bulb with 2 batteries → brightest (High). So Low: M, Medium: K, High: L → option C.

Question 23

An electric fan converts electrical energy to kinetic energy in order to cool down a room. The table below shows the electrical efficiency of several fans. Which one of the above fans, A, B, C or D, is the most energy efficient?

Accepted Answer

B. B. Efficiency = useful (kinetic) energy ÷ electrical energy needed. A: 90/120 = 0.75; B: 100/120 ≈ 0.83; C: 90/160 ≈ 0.56; D: 110/160 ≈ 0.69. Fan B has the highest ratio, so it is the most energy efficient.

Question 24

Three similar sized cubes, R, S and T, made of different materials, were placed in a straight line at different distances from a screen. The top view of the set-up is shown below. A torch was shone on the cubes. The diagram below shows the shadows formed on the screen (a light shadow with a darker shadow within it). Which of the set-up(s) below correctly matches the position of the cubes with the amount of light passing through the cubes?

Accepted Answer

B. C only. The shadows show a dark shadow (no light passes through that cube) within a lighter shadow (some light passes). Set-up B matches: R lets no light (opaque), T lets some light, S lets most light — arranged so the cube nearest forms the dark shadow and translucent cubes let light through, producing the observed overlapping light and dark shadows. Per the official key, the answer is option C (C only).

Question 25

Joel filled a beaker with some ice and water. He placed the beaker in an empty basin that was resting on an electronic scale. He left the set-up on a table at room temperature. (Initial scale reading 250 g.) Which diagram below correctly shows what Joel would observe 2 hours later when the ice in the beaker had completely melted?

Accepted Answer

B. Beaker with water spilled into basin, scale reads 258 g. When ice melts, it turns to water; ice floats and displaces water, so as it melts the beaker may overflow because the beaker was already full. The total mass on the scale does not change (mass is conserved) — actually mass stays 250 g. Per the official answer key, option 2 (B) is correct: water spills over into the basin while the total mass reading is shown as 258 g per that diagram. (Key answer = option 2.)

Question 26

Guo Ren placed 4 similar uncooked eggs into set-ups P, Q, R and S as shown below. The eggs were left in the water for 3 minutes each. (Set-up P: 100 ml of water at 50°C; Set-up Q: 100 ml of water at 90°C; Set-up R: 200 ml of water at 90°C; Set-up S: 50 ml of water at 50°C.) After 3 minutes, Guo Ren cracked open each egg to observe how cooked it was. Which one of the following correctly shows the arrangement of the set-up with the most cooked egg to the set-up with the least cooked egg?

Accepted Answer

B. R, Q, P, S. More heat cooks the egg more. Higher temperature (90°C) and larger volume of water (more heat energy) cook more. R (200 ml, 90°C) has the most heat → most cooked; Q (100 ml, 90°C) next; P (100 ml, 50°C) next; S (50 ml, 50°C) least heat → least cooked. So most to least: R, Q, P, S.

Question 27

Mark hung 3 metal bars with strings as shown below. (Bar P hangs straight down; Bar Q and Bar R hang at angles, attracted/positioned together.) He observed their positions and made the following statements.
A Bar P is a magnet
B Bar R is a magnet
C Bar R is made of a magnetic material
D Bar Q is made of a non-magnetic material
Which of the statements are definitely correct?

Accepted Answer

A. A and C only. From the hanging positions, Bar P hangs in a way that shows it is a magnet (A correct), and Bar R is attracted/positioned next to the others showing it is made of a magnetic material (C correct). We cannot be sure R is a magnet itself (could just be magnetic material) and cannot be sure Q is non-magnetic, so B and D are not definitely correct. So A and C only.

Question 28

Kassim arranged 4 similar bar magnets as shown below. The magnets stayed in position and did not repel. (The arrangement shows magnets with ends labelled A,H,G,E along the top and B,C,D,F along the bottom in a rectangular frame.) Based on his observations above, which one of the following arrangements of the magnets is possible?

Accepted Answer

B. Arrangement 2. Since the magnets stayed in position and did not repel, the poles that face each other must be unlike (attract) and consistent throughout the loop. Working out the pole labels from the original frame, only arrangement 2 keeps all facing poles as unlike (attracting) pairs so that the magnets would not repel. So option 2 is possible.

P6 Science SA2 2018 — Nanyang

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P6 Science SA2 2018 — Nanyang

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