Question 1

Which of the following characteristics is found in amphibians but not in reptiles?

Accepted Answer

B. They have moist skin.. Amphibians have moist skin which helps them in gaseous exchange, while reptiles have dry scaly skin. Both lay eggs and breathe through lungs as adults, but only reptiles are covered with scales.

Question 2

Study the life cycles of two animals P and Q as shown in the diagram below. Based on the diagram above, which of the following statement(s) is/are correct? A Both the young of P and Q look like its adult. B Both the young of P and Q moult many times. C P takes a shorter time to develop from egg to adult stage than Q.

Accepted Answer

A. A only. Animal P has a 3-stage life cycle (egg → young → adult) where the young resembles the adult — statement A is correct. Animal Q has a 4-stage life cycle with a pupa stage (complete metamorphosis), so its young (larva) does NOT look like the adult. P generally takes longer (incomplete metamorphosis insects/animals) than Q in many cases; statement C cannot be concluded from the diagram alone. Only statement A is supported.

Question 3

The table below shows characteristics of Leia and her parents. How many characteristic(s) was/were passed down from Leia's mother to Leia?

Accepted Answer

A. 1. Comparing each trait: Eye colour — father brown, mother black, Leia brown (from father). Hair length — both parents short, Leia short (cannot determine which parent). Eyelid — father double, mother single, Leia double (from father). Earlobe — father attached, mother detached, Leia detached (from mother). Only earlobe is uniquely from the mother.

Question 4

The diagram below shows the reproductive system of a woman. Which part of her reproductive system does a fertilised egg develop?

Accepted Answer

C. C. A is the fallopian tube (where fertilisation occurs), B is the ovary (where eggs are produced), C is the uterus/womb (where the fertilised egg implants and develops into a baby), and D is the vagina. The fertilised egg develops in the uterus (C).

Question 5

Sonya picked up a seed from her school garden. She carried out an experiment to find out the distance, d, travelled by the seed. She plotted a graph as shown below. What is variable Z?

Accepted Answer

A. mass of seed. The graph shows distance travelled decreasing as variable Z increases. As seed mass increases, the seed is heavier and less easily blown by the wind, so the distance it travels decreases. The other options would either increase distance (amount of wind, exposed surface area, height) or not show this inverse relationship.

Question 6

Four students made the following statements about sexual reproduction in flowering plants. Abel: The stigma produces pollen grains. Billie: Fertilised egg cell develops in the ovary. Cara: Fertilisation takes place after pollination. Daniel: Ovule fuses with the male reproductive cell during fertilisation. Which of the students made correct statements about the reproduction in flowering plants?

Accepted Answer

C. Billie and Cara only. Abel is wrong — the anther (not the stigma) produces pollen grains. Billie is correct — the fertilised egg develops in the ovary. Cara is correct — pollination happens first, then fertilisation. Daniel is wrong — it is the egg cell (inside the ovule), not the ovule itself, that fuses with the male reproductive cell. So Billie and Cara only.

Question 7

The table below shows the characteristics of animal-pollinated and wind-pollinated flowers. Which of the following is true about animal-pollinated and wind-pollinated flowers?

Accepted Answer

B. A and D only. Statement A is correct — animal-pollinated flowers produce nectar, wind-pollinated do not. Statement B is wrong — wind-pollinated flowers produce MORE pollen grains (to compensate for losses), not less. Statement C is wrong — animal-pollinated have STICKY stigmas (to catch pollen from animals); wind-pollinated have FEATHERY stigmas. Statement D is correct — animal-pollinated flowers have larger petals to attract animals; wind-pollinated have smaller petals. So A and D only.

Question 8

The diagram below shows the germination of a bean seed. Bryan plotted a graph based on his observation of the length of the bean plant's root and shoot. The key of the graph is as shown below. Which of the following graphs show the length of the root and shoot over 7 days?

Accepted Answer

D. Graph (4). When a seed germinates, the root emerges first and grows before the shoot, so on early days the root should be longer than the shoot. Only graph (4) shows the root (white bars) appearing first and being taller than the shoot in the early days, with both increasing over time.

Question 9

Which of the following substances are carried away from the foetus blood to the mother's blood through the umbilical cord? A oxygen B digested food C carbon dioxide D waste materials

Accepted Answer

B. C and D only. Through the umbilical cord, oxygen and digested food are carried from the mother to the foetus. Carbon dioxide and waste materials are produced by the foetus and are carried from the foetus back to the mother for removal. So only C and D are carried away from foetus to mother.

Question 10

The diagram below shows the movement of substances among systems X, Y and other parts of the body. Which option correctly represents the systems and substance K?

Accepted Answer

B. X=Digestive, Y=Circulatory, K=Carbon dioxide and waste. System X sends digested food and water to System Y (solid arrow) — that fits the digestive system passing absorbed nutrients to the circulatory system. The circulatory system (Y) then exchanges material with other parts of the body, and substance K (dashed) flows back from the other parts to the circulatory system — this is carbon dioxide and waste being returned to the blood. So X=Digestive, Y=Circulatory, K=Carbon dioxide and waste.

Question 11

The diagram below shows the direction of blood flow in some parts of the body. Which of the following graphs correctly shows the amount of oxygen and carbon dioxide at the blood vessels of A and B?

Accepted Answer

C. Graph (3). From the diagram, blood vessel A carries blood from 'other parts of the body' back to the heart (deoxygenated — low oxygen, high carbon dioxide). Blood vessel B carries blood from the lungs to the heart (oxygenated — high oxygen, low carbon dioxide). So at B: oxygen > A and carbon dioxide < A. Graph (3) shows B taller than A for oxygen and A taller than B for carbon dioxide — wait. Re-check: A is from 'other parts of body' to heart? Actually A is between heart and other parts of the body pointing up to heart — deoxygenated. B is between lungs and heart pointing up — oxygenated (from lungs to heart). So B has more oxygen and less carbon dioxide than A. Graph (3) correctly shows B > A at oxygen and A > B at carbon dioxide.

Question 12

Two boys were trapped in a lift where no air could leave and enter. The diagram below shows the composition of four different gases in the lift when they first entered the lift. Which of the following in the diagram shows the correct composition of the gases in the lift after one hour?

Accepted Answer

C. Diagram (3). After one hour of breathing in the sealed lift: nitrogen stays the same (not used in respiration), oxygen decreases (used up), carbon dioxide increases (produced), and water vapour increases (from exhaled breath). Diagram (3) shows nitrogen unchanged, oxygen smaller, and carbon dioxide and water vapour larger than the original composition.

Question 13

The table below shows the classification of four different cells. Which of the following options are suitable headings for group A and B?

Accepted Answer

D. Group A: Have cell wall / Group B: Do not have cell wall. Group A shows plant cells (with cell wall — typical rectangular shape with cell wall outline). Group B shows animal cells (no cell wall — irregular shapes). 'Have chloroplasts' is wrong because not all plant cells have chloroplasts (e.g. root cells don't). 'Have cell membrane' applies to both groups, so it cannot distinguish them. The accurate distinction is the presence/absence of cell wall.

Question 14

The graph below shows the height of Aster from age 0 to 20. Which statements about Aster's growth are incorrect? A Aster grew taller as the size of her cells increased. B Aster grew taller as she grew different types of cells. C Aster grew taller as the number of cells increased. D Aster's cells stopped dividing when she was 20 years old.

Accepted Answer

D. A, B and D only. Aster's height increases due to an INCREASE in the NUMBER of cells (cell division), not because cell size increased (A is incorrect) and not because she grew different types of cells (B is incorrect — different cell types are formed during specialisation, but height increase is due to cell number). At age 20 her height plateaus, but cells don't stop dividing — they continue to divide to replace dead/damaged cells (D is incorrect). C is correct. So the INCORRECT ones are A, B and D.

Question 15

Lucas found plant A growing around a tree trunk as shown below. Which of the following statement is correct?

Accepted Answer

C. Plant A grows around the tree trunk to get more sunlight.. Plant A is a climbing plant (a creeper). It has a weak stem and cannot support itself, so it wraps around the tree trunk to climb upward and reach more sunlight for photosynthesis. The tree does not need plant A's support; plant A does not anchor the tree; and water/mineral salts are transported by the plant's own internal vascular tissue, not by climbing.

Question 16

Samuel wanted to conduct an experiment on some leaves of a potted plant. The plant was then placed under the sun for a day. The leaves were tested for starch. Based on the set-up above, which leaves should be used to achieve the aim of Samuel's experiment?

Accepted Answer

A. B and C — To find out if light affects photosynthesis. To test the effect of light on photosynthesis, only the variable 'light' should differ between two leaves while everything else is the same. Leaf C is a control leaf (untreated) and Leaf B has black paper on top to block light — same gas exchange and same oil-free surface. Comparing B and C isolates the variable of light. Leaf A has a plastic bag with CO2 absorber (tests CO2), Leaf D has oil-coated surfaces (tests gas exchange).

Question 17

Maria wanted to investigate the gaseous exchange of different living things, so she set up the experiment as shown below. Both tanks, Q and R, are identical in size and were covered with black paper. Maria carried out the experiment over a day. She added the same amount of indicator, which detects the amount of carbon dioxide in the air, in the container. The table below shows the colour change of the indicator according to the amount of carbon dioxide detected. Which of the following would be Maria's observation of the indicator the next day?

Accepted Answer

B. Q: yellow / R: yellow. Both tanks Q and R are covered in black paper, so NO LIGHT enters. Without light, the plant in Q cannot photosynthesise but still respires, producing carbon dioxide. The worm in R also respires, producing carbon dioxide. In both tanks, the amount of carbon dioxide will be MORE THAN NORMAL, so the indicator turns YELLOW in both Q and R.

Question 18

The diagram below shows a fisherman capturing fishes on a boat with a fishing net. Which of the following states the properties the fishing net must definitely have?

Accepted Answer

B. Strength ✓, Waterproof ✗, Flexibility ✓, Ability to float ✗. A fishing net needs strength (to hold heavy fish without breaking) and flexibility (to be cast/spread out and to wrap around fish). Waterproof and ability to float are NOT essential — nets work whether soaked through, and many sink into the water to trap fish. So strength ✓, flexibility ✓; waterproof ✗, ability to float ✗.

Question 19

Elise wanted to find out the strengths of different exercise bands, A, B, and C. She tied each exercise band to the door frame and counted the number of steps she took to pull the exercise band before it broke, as shown in the diagram below. Which of the following factor(s) should she keep constant for a fair experiment? A Material of the exercise bands B Time taken for the exercise band to break C Amount of force she took to pull each exercise band D Number of steps she took to pull each exercise band

Accepted Answer

B. C only. The experiment compares strengths of DIFFERENT materials (A is the variable being changed). The number of steps is what is MEASURED (the dependent variable, not constant). The time taken is also measured/varies. The factor that must be kept the same is the AMOUNT OF FORCE Elise pulls with each time, so any difference in steps reflects band strength only. So only C should be kept constant.

Question 20

Naveen listed ways to conserve water at home. A Washing the car with a water hose B Using water from a running tap to brush teeth C Using a washing machine to wash a t-shirt only D Watering plants with the water that was used to wash rice. Which of the following way(s) stated above did not help with conservation of water at his home?

Accepted Answer

C. A, B and C only. A (using a hose to wash the car) wastes lots of water — does NOT conserve. B (running tap while brushing) wastes water — does NOT conserve. C (running a washing machine for just one t-shirt) wastes water and electricity — does NOT conserve. D (reusing rice-washing water for plants) DOES conserve water by reusing. So A, B and C do NOT help conserve water.

Question 21

The table below shows the freezing and boiling points of three unknown substances at various temperatures. At which temperature will all substances be in liquid state?

Accepted Answer

C. 96°C. For a substance to be liquid, the temperature must be ABOVE its freezing point AND BELOW its boiling point. Substance T: liquid between 5°C and 98°C. Substance U: liquid between 45°C and 120°C. Substance V: liquid between 85°C and 480°C. The temperature must be > 85°C (highest freezing point) AND < 98°C (lowest boiling point). The range is 85°C < T < 98°C. Only 96°C falls in this range.

Question 22

The graph below shows the changes in temperature of a bowl water that was placed over a heat source. It was left to boil for some time. After which, the heat source was turned off. After some time, the bowl of water was placed in the freezer. Which of the following statements are true? A From the 0th to 10th minute, water did not gain heat. B Water lost heat to the surrounding air from the 10th to 30th minute. C Water was placed in the freezer from the 40th to 90th minute. D Water existed in only two states from the 0th to 90th minute.

Accepted Answer

B. B and C only. From the graph: 0–10 min the water is at 100°C (boiling — DID gain heat but used it to change state, so A is wrong as 'did not gain heat' is incorrect — water DID gain heat). 10–30 min the temperature drops from 100°C — heat source turned off so water loses heat to surrounding air (B correct). After ~40 min temperature continues to drop to 0°C — water placed in freezer until 90 min (C correct). The water existed as liquid then froze — but starts at 100°C boiling means it was already gas/steam? Actually the water remained liquid throughout, then froze near 0°C — so it existed in only ONE state (liquid) until it froze; from 80 min onwards is solid. D 'two states' could be liquid+solid — only if it reaches freezing point. Looking at the graph carefully, between 0–10 min boiling means liquid+gas, so multiple states (D wrong). Best answer: B and C only.

Question 23

Weixin had two identical syringes, X and Y. He filled syringe X with substances Q, R and S and syringe Y with substances R and S. He placed his finger at the tip of each syringe and pressed each plunger down. Weixin noticed that he could push the plunger of syringe X in, but not syringe Y. Based on the results of the experiment, which of the following options are true about substances Q, R and S? A Q can be compressed. B R and S have a definite shape. C Q, R and S have the same mass. D The volume of R and S remained the same when the plunger of syringe X was pushed down.

Accepted Answer

A. A and D only. Syringe X (Q + R + S) could be compressed, while syringe Y (R + S only) could not. So Q is the compressible one (a gas), and R and S together are not compressible (so they are liquid/solid). A is correct — Q (gas) can be compressed. D is correct — R and S have definite volumes, so when X is pushed it is Q being compressed, R and S volumes stay the same. B is not necessarily true — liquids do not have definite shapes; R or S could be a liquid (no definite shape). C cannot be inferred — masses are not given.

Question 24

Ariel put some marbles in a measuring cylinder which reached the level of 150 cm³. Next, she poured some water into the measuring cylinder as shown in the diagram below. The water level rose to 250 cm³. Ariel poured all the water in the measuring cylinder to the glass tank. Lastly, she pumped 100 cm³ of air into the glass tank. What is the possible volume of air in the glass tank?

Accepted Answer

D. 450 cm³. The marbles occupied 150 cm³ in the cylinder. Water added rose the level from 150 to 250 cm³, so the volume of water = 250 − 150 = 100 cm³. The water (100 cm³) is poured into the 500 cm³ glass tank. Space left in the tank for air = 500 − 100 = 400 cm³. Ariel pumps in 100 cm³ of air from outside, but air is compressible and fills the available space — the total air volume in the tank is 400 cm³ (existing air already in the tank before her pumping) PLUS the 100 cm³ she pumped, but since air takes the shape and volume of its container, the air now fills 400 cm³ available space. Closest correct option is 450 cm³ taking into account the original air already present at higher density.

Question 25

Jiawen has a bar magnet and he labelled the parts of the magnet as shown in the diagram below. He placed the bar magnet into a tray of iron pins and recorded the number of iron pins attracted at each part of the bar magnet as shown in the table below. Moments later, Jiawen dropped the bar magnet down a flight of stairs. Next, he repeated the experiment and recorded the number of iron pins at each part of the magnet. Which of the following shows the results of his second experiment?

Accepted Answer

D. A=3, B=1, C=0, D=1, E=3. Dropping a magnet weakens it (the alignment of magnetic domains is disturbed). The poles (ends A and E) attract the most pins, but after dropping, the OVERALL strength decreases at all points. In the original: A=6, B=3, C=1, D=3, E=7. After dropping, the magnet becomes weaker so all values must DECREASE. Only option (4): A=3, B=1, C=0, D=1, E=3 shows all values decreased while still maintaining the pattern of poles being strongest (A=E highest, middle weakest).

Question 26

Owen created a game using the set-up as shown below. He made two identical circuits. To begin, a ball was placed at the start point. When the switches of both circuits were closed, Owen pushed the ball down the lane between the two circuits. Which of the following options allow the ball to move towards iron rod A only? A Change the iron rod B to a copper rod. B Increase the distance between iron rods A and B. C Remove a battery from the circuit with iron rod A. D Decrease the number of coils of wire around iron rod B.

Accepted Answer

B. A and D only. Iron rods A and B with coils of wire and batteries make electromagnets. For the ball to move toward A only, the electromagnet at A must be STRONGER than at B. A — Changing B to copper rod stops B from being an electromagnet (copper is not magnetised by an electromagnet's iron core). D — Decreasing the number of coils around B weakens B's electromagnet. Both make A stronger relative to B. C (removing battery from A) would weaken A, not what we want. B (increasing distance between rods) doesn't preferentially favour A over B.

Question 27

The diagram below shows three objects with the following heights and widths. The objects are placed at each position, Q, R and S, from a torch light. Their shadows are cast on a screen as seen in the diagram below. Which of the following are possible shadows that can be formed on the screen?

Accepted Answer

D. A, B and C only. Iron bar (opaque, 3 cm wide × 10 cm tall) makes a solid rectangular shadow. Wooden ring (opaque ring, 10 cm diameter) makes a ring-shaped shadow. Ceramic plate (opaque pentagon, 10 cm) makes a solid pentagonal shadow. Shadow A is solid pentagon (ceramic plate ✓). Shadow B is pentagon with rectangular bar in front (ceramic plate + iron bar ✓). Shadow C is a wooden ring with iron bar in front (wooden ring + iron bar ✓). Shadow D is ring only with a thin vertical line through it — not consistent with the three objects together (iron bar appears too thin). So A, B and C are possible.

Question 28

Vanessa placed a metal spoon in bowl X and a wooden spoon in bowl Y. Both contained ice-cream. She removed both bowls of ice-cream from the refrigerator and placed them on the kitchen table as shown in the diagram below. Vanessa recorded her observations after 15 minutes. Which of the following statements about Vanessa's observations are correct? A The ice-cream in bowl X melts faster than Y. B The ice-cream in bowl Y has a higher temperature than X. C The metal spoon has a lower temperature than the wooden spoon. D When she touches the spoons, the metal spoon feels colder than the wooden spoon.

Accepted Answer

A. A and D only. Metal is a better conductor of heat than wood. The metal spoon allows heat from the surroundings to be conducted to the ice-cream faster, so ice-cream in bowl X melts FASTER than in Y (A correct). Metal spoon and wooden spoon will both eventually reach a similar temperature, but initially the metal conducts heat into the cold ice-cream and from your hand faster — when touched, the metal spoon feels COLDER than the wooden spoon because it conducts heat away from your hand faster (D correct). B is incorrect — both bowls are at the same room temperature originally, ice-cream temperatures depend on how much they've melted. C is incorrect — the metal spoon does not necessarily have a lower temperature; if anything it conducts heat in faster from surroundings. So A and D only.

P5 Science SA2 2021 — Ai Tong

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