Question 1

Similar seeds were placed in four identical bottles, M, N, O and P, at room temperature as shown.
In which set-up(s) would the seeds most likely germinate?

Accepted Answer

P only. Seeds require water, warmth, and oxygen to germinate. Let's analyze each setup:
M: Has water (for moisture) and dry cotton wool (allows oxygen), but the seeds are submerged in water, which may limit oxygen. 
N: Has liquid to absorb oxygen, meaning there is no oxygen available for the seeds. So, seeds will not germinate.
O: Has dry cotton wool, meaning there is no water for the seeds. So, seeds will not germinate.
P: Has damp cotton wool (provides water) and air (provides oxygen). This setup provides all necessary conditions for germination (water, oxygen, and room temperature for warmth). 
Therefore, only seeds in setup P would most likely germinate.

Question 2

The diagrams show two flowers from the same plant. Some parts of flower A and flower B are removed as shown below.
Which of the following is correct?

Accepted Answer

anther and filament; Stigma and style; Flower A can undergo pollination.. Let's analyze the flower parts and processes:
Pollination is the transfer of pollen (from anther) to the stigma.
Fertilisation is the fusion of male and female gametes (after pollen reaches the ovule).

Flower A has its anther and filament (male reproductive parts) removed. It still has its stigma and style (female reproductive parts). For Flower A to undergo pollination, it needs to receive pollen from another flower. Since its stigma and style are intact, it can receive pollen, hence undergo pollination.

Flower B has its stigma and style (female reproductive parts) removed. It still has its anther and filament (male reproductive parts). Flower B cannot receive pollen (no stigma) or undergo fertilisation (no stigma/style/ovary), but it can produce pollen. If it still has its anthers, it can contribute to pollination by providing pollen, but it cannot undergo pollination itself if pollination is defined as receiving pollen.

Let's evaluate the options based on the provided conclusions:
(1) Flower A can undergo fertilisation. (Incorrect, it can undergo pollination but needs an ovary to fertilise, which is not stated if it is removed or not. Fertilization usually happens after pollination and if the stigma/style/ovary is intact). Flower A has stigma and style, but if the anther/filament are removed, it cannot self-pollinate. It can be cross-pollinated. Fertilization requires a stigma and style (which it has) AND an ovary (which is assumed present if it's a female flower part). However, the critical part missing from Flower A is the anther/filament, so it cannot self-pollinate.
(2) Flower B can undergo pollination. (Incorrect. Flower B has its stigma and style removed, so it cannot receive pollen, which is the act of pollination from its perspective).
(3) Flower A can undergo pollination. (Correct. Flower A has its stigma and style intact, allowing it to receive pollen from another flower (cross-pollination). The anther/filament are removed, meaning it cannot self-pollinate, but it can still be pollinated).
(4) Flower B can undergo fertilisation. (Incorrect. Flower B has its stigma and style removed, so it cannot receive pollen to initiate fertilization, nor can it contain an ovule for fertilisation without those parts).

Question 3

The table below shows the physical characteristics of Mr Tan and his family.
Based on the table, which of the following statements are true?
A Gerald and Carissa inherited their hair type from their father.
B Gerald inherited his hair colour and eye colour from his mother.
C Carissa inherited her hair length and hair colour from her father.

Accepted Answer

A and B only. Let's analyze each statement:
**A Gerald and Carissa inherited their hair type from their father.**
Mr Tan (father) has wavy hair type. Mrs Tan (mother) has straight hair type.
Gerald (son) has wavy hair type. Carissa (daughter) has wavy hair type.
Both Gerald and Carissa have wavy hair, which matches their father's hair type. So, statement A is true.

**B Gerald inherited his hair colour and eye colour from his mother.**
Mr Tan (father) has black hair colour and black eye colour.
Mrs Tan (mother) has brown hair colour and brown eye colour.
Gerald (son) has brown hair colour and brown eye colour.
Gerald's hair colour and eye colour match his mother's. So, statement B is true.

**C Carissa inherited her hair length and hair colour from her father.**
Mr Tan (father) has short hair length and black hair colour.
Carissa (daughter) has short hair length and black hair colour.
Carissa's hair length and hair colour match her father's. So, statement C is true.

Therefore, statements A, B, and C are all true.

Question 4

Which of the following statements regarding sexual reproduction in humans are true?
A The sperm cell is produced by the testes.
B The unfertilised egg will develop in the womb.
C Fertilisation occurs when a sperm fuses with an ovary.
D The developing baby will obtain digested food from the mother.

Accepted Answer

A and D only. Let's analyze each statement:
A The sperm cell is produced by the testes. (True. Testes are the male reproductive organs responsible for sperm production.)
B The unfertilised egg will develop in the womb. (False. An unfertilised egg will not develop in the womb; it will typically be shed during menstruation. Only a fertilised egg (zygote) implants and develops in the womb.)
C Fertilisation occurs when a sperm fuses with an ovary. (False. Fertilisation occurs when a sperm fuses with an egg cell, usually in the fallopian tube, not the ovary itself. The ovary produces the egg.)
D The developing baby will obtain digested food from the mother. (True. The developing baby (fetus) receives nutrients, including digested food, oxygen, and antibodies, from the mother's blood via the placenta and umbilical cord.)

Therefore, only statements A and D are true.

Question 5

Tessa wants to find out the effect of overcrowding on the growth of a balsam plant.
She set up some pots shown below for the experiment.
Which three pots should she use to carry out a fair test?

Accepted Answer

B, D and E. For a fair test to investigate the effect of overcrowding (number of seeds) on plant growth, all other variables must be kept constant. These variables include the type of soil and the amount of soil. The only variable that should change is the number of balsam seeds.

Let's examine the pots:
Pot A: 10 seeds, garden soil, 100g soil
Pot B: 50 seeds, garden soil, 200g soil
Pot C: 30 seeds, sandy soil, 200g soil
Pot D: 30 seeds, garden soil, 200g soil
Pot E: 10 seeds, garden soil, 200g soil
Pot F: 30 seeds, sandy soil, 100g soil

We need to find three pots where the 'Type of soil' and 'Amount of soil' are the same, but the 'Number of balsam seeds' differs.

Let's check the options:
(1) A, B and D:
   A: 10 seeds, garden, 100g
   B: 50 seeds, garden, 200g
   D: 30 seeds, garden, 200g
   The amount of soil is different between A and B/D (100g vs 200g). Not a fair test.

(2) A, C and F:
   A: 10 seeds, garden, 100g
   C: 30 seeds, sandy, 200g
   F: 30 seeds, sandy, 100g
   Both soil type and amount of soil vary. Not a fair test.

(3) B, C and E:
   B: 50 seeds, garden, 200g
   C: 30 seeds, sandy, 200g
   E: 10 seeds, garden, 200g
   The type of soil is different between B/E and C (garden vs sandy). Not a fair test.

(4) B, D and E:
   B: 50 seeds, garden, 200g
   D: 30 seeds, garden, 200g
   E: 10 seeds, garden, 200g
   In this set, the 'Type of soil' is consistently 'garden' and the 'Amount of soil' is consistently '200g'. The 'Number of balsam seeds' varies (50, 30, 10), allowing Tessa to investigate the effect of overcrowding. This is a fair test.

Therefore, pots B, D, and E should be used.

Question 6

The diagram below shows the layout of a stage for a shadow puppet performance.
Three puppets of the same height were placed behind the screen at the start of the performance. The audience observed the following image on the screen.
Which of the following shows the correct positions of puppets A, B and C?

Accepted Answer

Image showing puppet B far from light source, puppet C moderately far, puppet A close to light source, all in a row.. In shadow puppet performances, the size of the shadow cast on the screen depends on the distance of the puppet from the light source and the screen. The closer the puppet is to the light source, the larger its shadow will be, assuming the screen is at a fixed distance.

The observed image on the screen shows:
- Shadow of puppet A: Largest shadow.
- Shadow of puppet B: Smallest shadow.
- Shadow of puppet C: Medium-sized shadow.

Since all puppets are of the same height, their shadow sizes are determined by their distance from the light source. To cast the largest shadow (A), the puppet must be closest to the light source. To cast the smallest shadow (B), the puppet must be furthest from the light source. Puppet C, with a medium shadow, must be at a medium distance.

Therefore, the order from furthest from the light source to closest to the light source should be B, C, A.

Let's check the options:
Option (1) shows A, B, C positions from furthest to closest to the light source. Incorrect.
Option (2) shows B, A, C positions from furthest to closest to the light source. Incorrect.
Option (3) shows C, B, A positions from furthest to closest to the light source. Incorrect.
Option (4) shows B, C, A positions from furthest to closest to the light source. This matches the required order.

P5 Science CA1 2025 — Ai Tong

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