Reproduction in Flowers

A flower is considered a hermaphrodite. This means it has bot a male and female reproductive system. A flower consists of sepals, the receptacle, and the parts the receptacle bears such as the stamen and carpel. The purpose of a flower is to assist a plant in fertilization.

The parts of the flower, from bottom to top:

1. pedicel (the root of the flower)

2. receptacle (bears the stamen and carpel)

3. sepal (protects the flower when in bloom)

4. nectary (found at the base of the flower, attracts insects to flower)

5. petals (large, scented, brightly colored to attract insects)

6. ovary (houses many ovules, becomes a fruit after fertilization, produces ova)

7. ovules (contain eggs, called ova, which are to be fertilized by pollen grains. they become the seed after fertilization)

8. ovum (egg waiting to be fertilized by pollen grain)

9. style (holds the stigma in place at the best angle for the flower to get fertilized)

10. stigma (sticky surface that collects pollen to fertilize the plant)

11. filament (holds the anther at the best position to deliver pollen to the stigma)

12. anther (creates the pollen grains and delivers them to the stigma)

3.2. Pollination and agents of pollination

Pollination is the transfer of pollen from the anther to the stigma of a plant. There are two types:

• cross pollination: the transfer of pollen from the anther of one plant to the stigma of another

• self-pollination: the transfer of pollen from the anther of a plant to the stigma of the same plant or a flower on the same plant
  

Agents of pollination:

There are two main types, wind and insect.

3.3. Difference between wind-pollinated and insect-pollinated flowers

3.4. Process of fertilization and fruit development

Fertilization is the process in which the male and female gamete fuse to form a zygote.

In plants, fertilization occurs in these steps:

1. Two pollen grains land on the stigma

2. The pollen grains travel through the style all the way around to what is known as the micropyle of the seed through a pollen tube. They enter the seed through the micropyle by releasing a digestive enzyme called 

3. The two pollen grains enter the ovule, one goes to fertilize the ovum, while the other fertilizes the polar nuclei (to form endosperm)

4. The ovule develops into a seed, and the ovary a fruit

When an ovule is fertilized, the plant loses all of its flowery parts: stamen, carpel and sometimes the sepal remains (e.g eggplant).

The ovary then develops into a fruit, which can either be succulent (bright and juicy) or dry, while the ovule develops into a seed.

There are three layers of a fruit, all of them combined are known as the pericarp.

• Exocarp (outside layer)

• Mesocarp (middle layer)
  Endocarp (inner layer)

After fertilisation, a zygote is formed. This zygote divides by mitosis to form a baby root (radicle), a baby shoot (plumule) and a cotelydon.

3.5. Fruit/seed dispersal mechanisms

There are four main method of seed dispersal

Animal

• bright and attractive fruits, succulent, enticing animals to bite

• when animals eat these foods, the seeds are protected and they are either spat out (mango) or excreted (cucumber)

• there are also fruits that have hooks that attach themselves to an animals fur to transport around (caster oil seed)

Wind:

• plants adapted for this type of dispersal are often very light

• have wing like features or feathery extensions 

• e.g. poui seed

Water

• have a waterproof exocarp that allows them to float downstream

• e.g. coconut

Mechanical

• plants just automatically open along points of weakness to eject seeds 

• e.g. read pea pod