5- Sexual reproduction in plants

List the parts of a plant involved in reproduction.

• Stamen (anther + filament, male part makes pollen)

• Carpel (stigma, style, ovary, ovule, female part contains egg cells)

• Petal

• Sepal (leaf looking bit under petals)

• Receptacle

• Peduncle

Where are male gametes produced in flowering plants and what are they called?

Microspores found in the anthers, inside the pollen sacs.

Where are female gametes produced in flowering plants and what are they called?

Megaspores produced in the ovule, inside the ovary.

 

What are the steps of pollen formation (microsporogenesis)?

1. Diploid microspore mother cells/ microsporophytes in the anther undergo meiosis. They form four haploid microspores.

2. Haploid microspores undergo mitosis to mature into pollen grains. Pollen grains consist of two nuclei - the generative nucleus and the pollen tube nucleus - and a protective coating.

The generative nucleus will divide once more by mitosis to form two haploid male gametes, but only after the pollen grain lands on a female stigma and germinates.

What are the steps of ovum formation/ megasporogenesis?

1. Diploid megaspore mother cells/ megasporocyte in the ovule undergo mitosis, forming four haploid megaspores, but the division is uneven with one megaspore containing almost all the cytoplasm of the mother cell.

The other three megaspores are very small and disintegrate.

2. The remaining megaspore grows until it fills most of the ovule and its nucleus divides three times by mitosis to form eight haploid nuclei.

3. Membranes then form splitting the embryo sac into seven cells: one female gamete, two polar nuclei sharing the most of the cytoplasm and five smaller cells (3 antipodal cells and 2 synergids which help the generative nucleus reach the egg cell).

What is a microspore mother cell?

A diploid cell that undergoes meiosis to produce four haploid microspores (pollen grains).

What does each pollen grain contain after mitosis?

A generative nucleus (→ two male gametes) and a tube nucleus.

What is the embryo sac?

The female gametophyte containing the egg cell, synergids, antipodal cells, and the polar nuclei.

What is a megaspore mother cell?

A diploid cell undergoing meiosis to form four megaspores, one of which becomes the embryo sac.

What are the stages of fertilisation in plants?

Pollen grain composed of the pollen tube nucleus and the generative nucleus adheres to the stigma, where it subsequently germinates.

The pollen tube grows down the style via the secretion of digestive enzymes which digest the surrounding tissue and use it as a source of nutrients.

The pollen tube grows through the micropyle into the embryo sac.

The generative nucleus of the pollen divides by mitosis to produce two sperm cells which enter the embryo sac.

Double fertilisation occurs: one of the male gametes fuses with the female nucleus to form a diploid zygote and the other male gamete fuses with two polar nuclei to form a triploid endosperm nucleus which serves as a source of nutrients for the embryo.

What is pollination?

Transfer of pollen from an anther to a stigma.

What happens during pollen tube formation?

The tube nucleus forms a pollen tube through the style, carrying the generative nucleus into the ovary.

 

What is one key difference between fertilisation in mammals vs flowering plants?

Flowering plants have double fertilisation