Question 1

Which of the following is/are the unit of life for all living things?
A: cell
B: tissue
C: organ

Accepted Answer

A. A only. The cell is the smallest basic unit of life for all living things. Tissues and organs are made up of many cells, so they are not the fundamental unit of life.

Question 2

Study the characteristics of P, Q, R and S below. (For each of P, Q, R and S the table records whether it can move from place to place, reproduce, produce its own food and respond to changes.) Which of them is/are definitely living thing(s)?

Accepted Answer

C. R and S only. A definite living thing must be able to reproduce and respond to changes (and grow). R (no move, reproduces, makes own food, responds) is a plant and S (moves, reproduces, no own food, responds) is an animal — both definitely living. P and Q cannot reproduce, so they are not definitely living.

Question 3

Study the diagram below. Which part(s) of the above flower is/are definitely not needed for pollination and fertilisation to take place?

Accepted Answer

B. Q only. Pollination and fertilisation require the reproductive parts (stamen/anther and pistil/stigma and ovary). The part labelled Q (the petal) only serves to attract insects and is not directly involved in pollination or fertilisation, so it is definitely not needed.

Question 4

The diagram below shows the 4 stages in the life cycle of an organism. The cycle shows: from A it takes 2-3 weeks to reach B; from B 'fertilization' leads to C; from C it takes 8 days to reach D; from D it takes 4 weeks back to A. Identify the correct stages in the above life cycle.

Accepted Answer

B. A=pupa, B=adult, C=egg, D=larva. The arrow labelled 'fertilization' must lead to the egg, so C = egg. After 8 days the egg becomes the larva (D), after 4 weeks the larva becomes the pupa (A), and after 2-3 weeks the pupa becomes the adult (B), which then mates (fertilization) producing eggs again.

Question 5

Which of the following body systems work together with the reproductive system in humans for the growth and birth of the baby?
A: Skeletal system
B: Muscular system
C: Digestive system
D: Circulatory system
E: Respiratory system

Accepted Answer

D. A, B, C, D and E. All the systems are needed: the digestive system provides nutrients, the respiratory system provides oxygen, the circulatory system transports these to the baby, and the skeletal and muscular systems support and aid the birth process, so all five work together.

Question 6

Which of the following are similarities between digestion and decomposition?
A: Both provide nutrients for survival.
B: Both require bacteria and fungi to take place.
C: Both break matter down into simpler substances.
D: Both break dead matter up into smaller substances.

Accepted Answer

A. A and C only. Both digestion and decomposition break matter down into simpler substances (C) and release/provide nutrients (A). B is wrong because digestion does not require bacteria and fungi, and D is wrong because digestion does not act only on dead matter.

Question 7

Alison filled bag A with starch solution and immersed it into the iodine solution as shown below. When the iodine solution comes into contact with starch, the iodine solution would change from brown to dark blue. After one day, she observed that the content in bag A turned dark blue while the content in the beaker remained brown. Which part(s) of a cell is/are similar in function to bag A?
A: cell wall
B: cell membrane
C: cytoplasm

Accepted Answer

B. B only. Bag A allowed the small iodine particles to enter but kept the large starch particles inside (only the inside turned blue). This selective, partially-permeable control of what enters and leaves is the function of the cell membrane.

Question 8

Ahmad studied a small habitat and constructed a food web which consisted of four organisms A, B, C and D. He described the food relationship as shown in the box below: 'A eats B, C and D', 'B is eaten by A and D', 'D is eaten by C'. Which organism in the food web above obtains its energy directly from the Sun?

Accepted Answer

B. B. The organism that obtains energy directly from the Sun is the producer, which is not described as eating any other organism. B is only ever 'eaten by' others and never eats anything, so B is the producer (plant).

Question 9

The diagram below shows how blood flows from one organ to another through blood vessels A, B, C and D in a human body (lungs ↔ heart ↔ large intestine, with vessel A from lungs to heart, B from heart to large intestine, C from large intestine to heart, D from heart to lungs). Blood samples W, X, Y and Z were collected from the blood vessels shown above. The graph below shows the amount of digested food present in each blood sample. Which blood vessel was the blood sample W most likely taken from?

Accepted Answer

B. B. Sample W has the greatest amount of digested food. According to the official answer key this corresponds to blood vessel B (blood travelling from the heart to the large intestine).

Question 10

Zachary wanted to investigate how digestion takes place in the body. He took samples of food as it passed through five parts, A, B, C, D and E, of the digestive system as shown below. He plotted the amount of undigested food at the five parts on a graph below. Which line best represents the relative amount of undigested food in the various parts of the human digestive system?

Accepted Answer

C. Line (3). Undigested food should decrease gradually as it passes from the mouth, with the largest drop occurring across the small intestine (around parts C to D) where most digestion and absorption happen, then levelling off. Line (3) best shows a moderate decrease with the steepest fall at the small intestine.

Question 11

Hamid had 4 water samples, A, B, C and D, collected from different parts of the same river. Using the same amount of each water sample, he set up the following apparatus using the same amount of water plant. He placed the 4 set-ups near a window for 3 days. At the end of the experiment, Hamid compared the amount of oxygen produced by the water plants and recorded his observation in the table (A=14 cm³, B=20 cm³, C=18 cm³, D=10 cm³). Hamid made the following conclusions:
A: The water plants in all the water samples photosynthesized at different rates.
B: The water samples used affected the rate of photosynthesis of the water plants.
C: The water is not polluted at the parts of the river where water samples B and C were collected from.
D: The rate of photosynthesis of the water plants was dependent on the amount of sunlight that reached each plant.
Based on Hamid's experimental results above, which of his conclusions are correct?

Accepted Answer

A. A and B only. Different volumes of oxygen show the plants photosynthesised at different rates (A), and since only the water sample was changed, the water sample affected the rate (B). C cannot be concluded (pollution was not tested) and D is wrong because sunlight was kept the same (it was the controlled variable, not the one changed).

Question 12

Joseph carried out an experiment to find out if the brightness of the light will affect the amount of gas produced. He set up the apparatus as shown below. In order to ensure a fair test, he should only change the ______.

Accepted Answer

D. distance between the lamp and the glass jar. To test how brightness of light affects gas produced, the variable changed must be the brightness. Brightness is varied by changing the distance between the lamp and the glass jar; all other factors (type and amount of plant, amount of water) must be kept the same.

Question 13

Mr Quek noticed some mealybugs feeding on a plant in the Community Garden. He made the following observations: The mealybugs damaged the plant while feeding on the plant sap. There were many black ants crawling all over the plant. The ants were feeding on the honeydew or waste produced by the mealybugs. Ladybugs appeared on the plant after a few days and were seen feeding on the mealybugs. The ants were seen attacking the ladybugs. Based on the interactions as stated above, which one of the following correctly states the relationship between the different organisms?

Accepted Answer

C. Both organisms benefitted: mealybug and ant; Only one benefitted: mealybug and plant. The ant and mealybug both benefit (mutualism): the ant gets honeydew to feed on and the mealybug is protected by the ants. Between the mealybug and the plant, only the mealybug benefits (it feeds on sap and damages the plant), so only one organism benefits.

Question 14

The diagram below shows a model of a food chain: Food producers → Primary consumers → Secondary consumers → Tertiary consumers, with decreasing mass of organisms along the chain (greatest mass of organisms at the producers, least mass at the tertiary consumers). The graph below shows the masses of the organisms W, X, Y and Z that form a food chain in a lake at the Gardens by the Bay. Based on the given information above, deduce which part of the food chain each organism belongs to.

Accepted Answer

C. Food producer=Y, Primary=W, Secondary=X, Tertiary=Z. Mass decreases along the food chain, so the organism with the greatest mass is the producer and the smallest mass is the tertiary consumer. From the graph the masses are Y (~950 g) > W (~350 g) > X (~150 g) > Z (~50 g), giving producer Y, primary consumer W, secondary consumer X and tertiary consumer Z.

Question 15

One way of measuring water quality in rivers is by examining the types of fish, insects and other invertebrates that the water will support. Different aquatic animals are able to tolerate different levels of pollutants. As the level of pollutants increases, the number of sensitive animals will decrease and the number of tolerant animals will increase. The chart shows the tolerance of some aquatic organisms to pollutants (bloodworm = most tolerant, then leech, then freshwater shrimp, then fish = least tolerant). During a random check, an environmental officer counted the number of individual organisms in water samples taken from 4 different rivers and recorded his results in the table (River A: bloodworm 4, leech 5, freshwater shrimp 5, fish 3; River B: 2, 2, 6, 5; River C: 6, 4, 2, 0; River D: 8, 5, 0, 0). Arrange the rivers from the most polluted to the least polluted.

Accepted Answer

D. D, C, A, B. More tolerant organisms (bloodworm, leech) and the absence of sensitive organisms (fish) indicate more pollution. River D (most bloodworms, no shrimp, no fish) is most polluted, then C (high bloodworm, no fish), then A and B which still support fish — A has fewer shrimp/more bloodworm than B, so order is D, C, A, B (least polluted).

Question 16

Study the flow chart below carefully. (The chart classifies a Material: first 'Does it absorb water?' — if Yes, 'Is it light?' Yes → A, No → B; if No, 'Is it light?' Yes → C, No → D.) Refer to part R of the shoes as shown below. Which of the letter, A, B, C or D, matches with the material used to make part R of the shoe?

Accepted Answer

C. C. Part R is the rubber sole of the shoe. The sole does not absorb water (so follow the 'No' branch) and it is light, so following the chart this gives the letter C.

Question 17

The table below shows three tests, A, B and C, that can be carried out on an object to find out whether it is a magnet (A: Can it be attracted to another magnet?; B: Does it come to a rest pointing in N-S direction when suspended freely?; C: Can it repel another magnet?). Which of the test(s) can be used to confirm that the object is a magnet without using another magnet?

Accepted Answer

A. Test B only. Tests A and C both require a second magnet (to attract or repel). Only Test B — suspending the object freely and seeing if it rests pointing in the North-South direction — can be carried out on the object alone, and only a magnet behaves this way, so Test B only.

Question 18

A shadow is formed because ______.
A: light can be blocked.
B: light can be reflected.
C: light can be absorbed.

Accepted Answer

B. C only. According to the official answer key the accepted response is 'C only' — a shadow forms where light is absorbed (not transmitted) by an opaque object, so light does not reach that area.

Question 19

Why is air classified as a matter?
A: Air has mass.
B: Air occupies space.
C: Air can be compressed.

Accepted Answer

B. A and B only. Matter is anything that has mass and occupies space. Air has mass (A) and occupies space (B), so it is classified as matter. Being compressible (C) is not part of the definition of matter.

Question 20

The table below shows the melting points of substances P, Q, R and S (P = 49°C, Q = 15°C, R = 23°C, S = 5°C). At which temperature will two of the above substances be at its liquid state?

Accepted Answer

C. 20°C. A substance is liquid when the temperature is above its melting point. At 20°C, Q (m.p. 15°C) and S (m.p. 5°C) are liquid (2 substances), while R (23°C) and P (49°C) are still solid. So 20°C gives exactly two substances in the liquid state.

Question 21

Andy recorded the volume of four objects and the volume of water the objects can displace when put into a measuring cylinder (W: object volume 20 cm³, water displaced 20 cm³; X: 40 cm³, 10 cm³; Y: 60 cm³, 30 cm³; Z: 80 cm³, 5 cm³). Andy studied the water tank used for flushing a toilet bowl in his house as shown below. After flushing, water enters and re-fills the tank. The tank will stop filling when the water reaches level L. Based on the results above, which object W, X, Y or Z should Andy put inside the water tank so that he would use the least water to flush the toilet?

Accepted Answer

C. Y. To use the least water, the object must take up the most space below water level (i.e. displace the most water). The volume of water displaced is the submerged volume: W=20, X=10, Y=30, Z=5 cm³. Y displaces the most (30 cm³), so it occupies the most space and the tank needs the least water to reach level L.

Question 22

Li Fei was holding a metal spoon with a cube of ice as shown. After some time, she felt that the spoon was cold. Which one of the following correctly explains why Li Fei felt that the spoon was cold?

Accepted Answer

C. The spoon lost heat to the ice and gained heat from her hand.. Heat flows from a hotter region to a colder region. The spoon is colder than the hand, so heat flows from her hand into the spoon (spoon gains heat from her hand) — that is why her hand feels cold. The ice is colder than the spoon, so the spoon loses heat to the ice.

Question 23

Four steel rods of equal thickness but different lengths were heated to the temperatures indicated in the diagrams below (A: 20 cm at 60°C; B: 15 cm at 50°C; C: 15 cm at 60°C; D: 10 cm at 40°C). Ali wanted to investigate if the amount of heat the object has is affected by the mass of the object and its temperature. Which one of the following should he compare?

Accepted Answer

A. A, B and C only. To investigate the effect of mass, keep temperature the same and vary length: A (20 cm) and C (15 cm) are both at 60°C. To investigate the effect of temperature, keep mass the same and vary temperature: B (15 cm, 50°C) and C (15 cm, 60°C). So comparing A, B and C lets both variables be tested.

Question 24

David stirred a white solid in some water and it became a clear liquid. He then poured the clear liquid into a container. Finally, he placed a cardboard boat in the container filled with the clear liquid. At first, the boat looked wet. Then he placed the boat on a table. After a few days, David observed a white coat on the boat. The above observation is possible due to ______.

Accepted Answer

C. evaporation. The white solid dissolved in water to form a solution. When the wet boat was left on the table, the water evaporated and left the dissolved solid behind as a white coat on the boat. This is due to evaporation.

Question 25

Study the water cycle below. (Cycle: clouds → (S) → rain → (P) → water bodies → (Q) → water vapour → (R) → clouds.) Which one of the following statements about the water cycle is true?

Accepted Answer

B. There is energy conversion at Q.. According to the official answer key the correct statement is that there is energy conversion at Q. Q is the change from water in the water bodies to water vapour (evaporation), during which energy is taken in/converted.

Question 26

Abby has an electric circuit as shown below (a battery and a lighted bulb in a circuit with two open clips). He did the following:
1. Joined the clips and measured the brightness of the bulb.
2. Added an object between the clips and measured the brightness of the bulb.
3. Compared the brightness of the bulb between steps 1 and 2.
4. Repeated steps 2 and 3 for three other objects.
Which one of the following is a possible observation?

Accepted Answer

B. Object: bulb — the brightness of the bulb is dimmer compared to no object between the clips.. Adding a second bulb in series with the original bulb increases the resistance of the circuit, so less current flows and the original bulb becomes dimmer. So the observation 'bulb → dimmer' is the possible one.

Question 27

Study the four electrical circuits as shown below. All the batteries and bulbs are similar. In which circuits will the bulbs be of the same brightness?

Accepted Answer

C. A, C and D only. Circuit A has one bulb across the battery (full brightness). Circuits C and D have bulbs connected in parallel, so each bulb still receives the full battery voltage and lights at the same brightness as in A. Circuit B has two bulbs in series (dimmer). So A, C and D have bulbs of the same brightness.

Question 28

Which of the following effects of forces are true?
A: A force may change the shape of an object.
B: A force can change the speed of a moving object.
C: A force can change the direction of a moving object.
D: A force can change the size of a gas trapped in a balloon.

Accepted Answer

D. A, B, C and D. A force can change the shape of an object (A), change the speed of a moving object (B), change the direction of a moving object (C), and compress a gas to change its size/volume in a balloon (D). All four statements are true.

Question 29

The diagram below shows two 40 kg students ready to dive into the pool. Student A stands on a platform 4 m above the water and Student B stands on a higher platform 8 m above the water (heights are marked on scales: 2 m, 4 m for A's side; 2 m, 4 m, 6 m, 8 m for B's side). Which one of the following is a possible aim for the experiment?

Accepted Answer

B. To find out if amount of potential energy will affect the depth of the dive.. Both students have the same mass (40 kg) but stand at different heights. The only variable changed is the height, which changes the amount of potential energy. So the aim is to find out if the amount of potential energy affects the depth of the dive.

Question 30

Some students wanted to find a suitable fabric to make a bathmat. They placed the fabric on a ramp and put a weight on it to represent a person standing on it. They raised the height until the weight started to slide off the fabric. The results were as shown below (Fabric P: weight slid off at height 8 cm; Fabric Q: weight slid off at height 17 cm). Based on the results obtained, which fabric will be more suitable for making the bathmat and why?

Accepted Answer

D. Fabric Q — There is greater friction between the mat and the feet.. Fabric Q allowed the weight to be raised to a greater height (17 cm) before the weight slid off, meaning there is greater friction between the fabric and the weight (the person's feet). Greater friction between the mat and the feet makes Q safer and more suitable for a bathmat.

P6 Science SA2 2016 — Rosyth

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P6 Science SA2 2016 — Rosyth

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