krit.club logo

Reproduction - Explain pollination, fertilisation, and seed/fruit formation in flowering plants

Grade 9CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Pollination: The transfer of pollen grains from the anther of a stamen to the receptive stigma of a carpel. It is classified into Self-pollination (same flower or same plant) and Cross-pollination (different plants of the same species).

•

Pollen Germination: Once a pollen grain lands on a compatible stigma, it absorbs nutrients and produces a pollen tube that grows down through the style toward the ovary.

•

Fertilisation: The process where the male gamete released from the pollen tube fuses with the female gamete (egg cell) present inside the ovule to form a zygotezygote.

•

Zygote Development: The zygotezygote divides multiple times to form an embryo within the ovule. The embryo consists of the radicle (future root) and plumule (future shoot).

•

Seed Formation: The ovule develops a tough coat and gradually converts into a seed. The seed contains the embryo and stored food (endosperm or cotyledons).

•

Fruit Formation: Triggered by hormonal changes after fertilisation, the ovary grows rapidly and ripens to form the fruit, while other floral parts like petals, sepals, and stamens usually wither and fall off.

•

The ploidy level changes during reproduction: Haploid (n)+Haploid (n)→Diploid (2n)\text{Haploid (n)} + \text{Haploid (n)} \rightarrow \text{Diploid (2n)}.

📐Formulae

Male Gamete (n)+Female Gamete (n)→FertilisationZygote (2n)\text{Male Gamete (n)} + \text{Female Gamete (n)} \xrightarrow{\text{Fertilisation}} \text{Zygote (2n)}

Ovule→Post-FertilisationSeed\text{Ovule} \xrightarrow{\text{Post-Fertilisation}} \text{Seed}

Ovary→Post-FertilisationFruit\text{Ovary} \xrightarrow{\text{Post-Fertilisation}} \text{Fruit}

Zygote→Embryo→Seedling\text{Zygote} \rightarrow \text{Embryo} \rightarrow \text{Seedling}

💡Examples

Problem 1:

During an experiment, a student removes the stamens from a bisexual flower before they mature. Will this flower be able to produce fruit? Explain the conditions.

Solution:

Yes, it can still produce fruit if cross-pollination occurs.

Explanation:

Since the stamens (male parts) are removed, self-pollination is impossible. However, if pollen grains from another flower of the same species reach the stigma via agents like wind or insects, fertilisation\text{fertilisation} can still occur, leading to the formation of a zygote\text{zygote} and subsequently a fruit.

Problem 2:

Identify the ploidy of the following: Pollen grain, Egg cell, and Zygote.

Solution:

Pollen grain: nn, Egg cell: nn, Zygote: 2n2n.

Explanation:

Gametes (pollen and egg) are produced through meiosis and are haploid (nn). When they fuse during fertilisation, they restore the diploid number (n+n=2nn + n = 2n) in the zygote.

Problem 3:

A flower has 20 ovules in its ovary. How many pollen grains are minimally required for all ovules to develop into seeds?

Solution:

2020 pollen grains.

Explanation:

Each ovule contains one female gamete. To fertilise one female gamete, one pollen tube carrying male gametes is required. Therefore, for 2020 ovules, at least 2020 pollen grains must germinate on the stigma.