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CIE iGCSE Co-Ordinated Science B15.3 Sexual reproduction in plants Exam Style Questions Paper 4

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Question

(a) Plants and bacteria are made of cells.
State two ways the plant cells and bacterial cells are similar and two ways that they are different.
(b) (i) Plant cells can divide by mitosis.
Complete the sentence about mitosis.
The exact replication of ……… occurs before mitosis.
(ii) Plants can reproduce by sexual reproduction.
State one advantage and one disadvantage of sexual reproduction.
advantage ……
disadvantage ……
(c) (i) In plants, the flower contains both the male and female gametes.
Fig. 1.1 is a diagram of an insect-pollinated flower.
Identify the parts labelled A and B in Fig. 1.1.
(ii) The parts labelled C and D in Fig. 1.1 would be different in a wind-pollinated flower.
Describe these differences.
(d) State the type of cell division that produces gametes.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic B2.1 — Cell structure (Part (a))
• Topic B16.2 — Cell division / Mitosis (Part (b)(i))
• Topic B15.2 — Sexual reproduction (Part (b)(ii))
• Topic B15.3 — Sexual reproduction in plants (Part (c)(i) & (c)(ii))
• Topic B16.2 — Cell division / Meiosis (Part (d))

▶️ Answer/Explanation

(a) Similar:
1. Both have a cell wall surrounding the cell membrane.
2. Both contain ribosomes for protein synthesis and DNA as genetic material.
Both plant and bacterial cells share basic structural features like a cell wall, cell membrane, cytoplasm, and ribosomes.

(a) Different:
1. Plant cell wall is made of cellulose; bacterial cell wall is made of peptidoglycan (sugars and amino acids).
2. Plant cells have chloroplasts and a vacuole; bacterial cells lack these organelles.
Plant cells have membrane-bound organelles like chloroplasts and a nucleus, whereas bacterial cells have circular DNA and plasmids without a nucleus.

(b)(i) chromosomes
DNA replication occurs before mitosis to ensure each daughter cell receives an identical set of chromosomes.

(b)(ii) Advantage: Produces genetic variation in offspring.
Disadvantage: Takes longer than asexual reproduction as offspring develop from fertilised eggs.
Sexual reproduction promotes diversity through gamete fusion, but requires more time and energy compared to asexual methods.

(c)(i) A – stigma ; B – style
The stigma is the receptive surface for pollen grains, and the style is the stalk connecting the stigma to the ovary.

(c)(ii) C: In wind-pollinated flowers, petals are dull/small/absent and have no scent.
D: Anthers are hanging outside the flower to release pollen easily into the wind.
Wind-pollinated flowers lack bright colours and nectar, and their anthers are exposed for efficient pollen dispersal by air currents.

(d) meiosis
Meiosis is the reduction division that produces haploid gametes from diploid cells, halving the chromosome number.

Question

Fig. 3.1 is a magnified image of a plant root tip viewed using a light microscope.
(a) At X in Fig. 3.1, there are 37 cells across the width of the root tip. The actual width of the root tip at X is \(1.2\text{ mm}\). Calculate the average size of the cells in the root tip in \(\mu\text{m}\).
(b) Fig. 3.1 shows a zone in the root tip where cells become specialised. Tick (✓) one box to identify a type of specialised cell made in the root.
☐ ciliated cells
☐ neurones
☐ phloem cells
☐ sperm cells
(c) Fig. 3.1 shows a zone in the root tip where cells divide so the root can grow.
(i) State the type of cell division needed for growth.
(ii) During this type of cell division, the number of chromosomes is maintained in each daughter cell. Describe two processes in cell division that ensure that the chromosome number is maintained.
(d) A different type of cell division takes place in the ovary and anther of flowers to make gametes.
(i) Fig. 3.2 is a diagram of a wind-pollinated flower.
On Fig. 3.2, draw a label line and the letter A to identify one anther.
(ii) The anthers produce male gametes. Complete the sentences about male gametes in plants.
Male gametes in plants are called ______________ grains.
During production of male gametes, the chromosome number is halved from ______________ to haploid.
Male gametes produced are all genetically ______________.
A nucleus of a male gamete will fuse with the nucleus of an ovule. This process is called ______________.
(iii) Describe one advantage of sexual reproduction to a population of plants in the wild.

Topic codes:

• Topic B2.2 — Size of specimens (Part (a))
• Topic B2.1 — Cell structure / Specialised cells (Part (b))
• Topic B16.2 — Cell division: Mitosis (Part (c))
• Topic B15.3 — Sexual reproduction in plants (Part (d))
• Topic B16.2 — Cell division: Meiosis (Part (d)(ii))

▶️ Answer/Explanation

(a) Average cell size = Actual width ÷ Number of cells

= \(1.2\text{ mm} \div 37 = 0.0324\text{ mm}\)
= \(0.0324 \times 1000 = 32.4\ \mu\text{m}\)

(b) ☑ phloem cells

Phloem cells are specialised cells that transport sucrose and amino acids in plants. They are formed from meristem tissue in the root tip.

(c)(i) Mitosis is the type of cell division needed for growth.

(c)(ii) Two processes that maintain the chromosome number:

1. Replication of DNA / chromosomes occurs before division begins.
2. Separation of chromosomes into two identical sets, with each daughter cell receiving one complete set.

Alternative: cells only divide once / splits into two daughter cells with the same chromosome number.

(d)(i) The anther should be labelled on Fig. 3.2. In a wind-pollinated flower, anthers are typically found hanging outside the flower on long filaments.

(d)(ii) Male gametes in plants are called pollen grains.

During production of male gametes, the chromosome number is halved from diploid to haploid.
Male gametes produced are all genetically different.
A nucleus of a male gamete will fuse with the nucleus of an ovule. This process is called fertilisation.

(d)(iii) One advantage of sexual reproduction to a population of plants in the wild:

Sexual reproduction produces genetic variation among offspring. This allows the population to adapt to changes in the environment and increases the chances of survival if conditions change.
Alternative: spreads offspring through dispersal of pollen / seeds.

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