D3 Sexual Reproduction in flowering plants SL

Bisexual/hermaphroditic flowers

Flowers that have both male and female reproductive structures.

Unisexual flowers

Flowers that have either male or female reproductive structures.

Perfect flower

A flower that contains both male and female reproductive structures.

Imperfect flower

A flower that only contains one sexual reproductive organ, either male or female.

Pistil/carpel

The female reproductive part of a flower. It’s centrally located and typically consists of: the ovary, the style, and the stigma. The ovary contains the ovules. Inside each ovule is the embryo-sac with seven cells and eight haploid nuclei.

Stamen

The male structures of a flower, consisting of two parts: a tube-like filament and a sac-like anther. Pollen grains are present within the anther, which are released once mature.

Pollination

The transfer of pollen grains from the anther (stamen) to the stigma (pistil) of a flower. It is a step before the fertilisation and can occur via modulators: wind, water, or animals.

Synergids

Two supporting cells in the ovule that help guide the pollen tube to the egg.

Micropyle

A small opening in the ovule of a flowering plant through which the pollen tube enters, allowing sperm cells to reach the egg for fertilisation. It enables double fertilisation by giving access to both the egg and central cell.

Features of insect pollinated flowers

Nectar, bright colors, and strong scents to lure insects, sticky pollen to ensure that it sticks to the body of an insect.

Triple fusion

The process where the second sperm nucleus fuses with the central cell (which consists of 2 haploid nuclei), resulting in a triploid cell(3n) which gives rise to endosperm.

Double fertilisation

The entire process of fertilisation and triple fusion which is only seen in flowering plants.

Endosperm

The tissue that surrounds the developing embryo of flowering plant seeds and nourishes them.

Central cell

A cell in the ovule that contains two haploid polar nuclei; fuses with the second sperm cell during fertilisation to form the triploid endosperm.

Generative cell

A cell within the pollen grain that divides mitotically to form two sperm cells.

Ovule

The structure within the ovary of a flower that contains the female gamete (egg cell), synergids, and micropyle. After fertilisation, it develops into a seed.

Ovary

The base of the carpel containing ovules; becomes the fruit after fertilisation.

Pollen tube

A tube formed by the tube cell of a germinating pollen grain; grows down the style to allow sperm to reach the ovule.

Cross-pollination

The transfer of pollen grains from one flower on one plant to the stigma of another flower on another plant. It can be transferred by water, wind, or animals. It increases genetic diversity.

Features of wind-pollinated flowers:

No nectar-producing glands, small flowers, exposed anthers that dangle loosely from the filament, feathery stigma to catch the pollen, and light small pollen grains that are produced in large amounts.

Self-pollination

The transfer of pollen grains to the stigma of the same flower or to the stigma of another flower on the same plant. It’s unfavourable as it doesn’t increase genetic diversity.

Self-incompability

The inability of hermaphroditic plants to produce zygotes after self-pollination due to the failure in any of these stages: pollen germination, growth of the pollen tube, fertilisation, and emrbyo development.

Germination

The development of the seed, which begins with the uptake of water by the seed and is completed when the radicle emerges from the seed. In order for a seed to go through this process, there should be enough water, oxygen, and favourable temperature.