Sexual Reproduction in Plants

Objective

This topic gives an overview of; 

  • Sexual Reproduction 
  • Pollination
  • Fertilisation
  • Fruits and Seed Formation
  • Seed Dispersal

 Modes of Reproduction 

Most plants have roots, stems and leaves. These are called the vegetative parts of a plant. After a certain period of growth, most plants bear flowers. You may have seen the mango trees flowering in spring. It is these flowers that give rise to juicy mango fruit we enjoy in summer. We eat the fruits and usually discard the seeds. Seeds germinate and form new plants. So, what is the function of flowers in plants? The flowers perform the function of reproduction in plants. Flowers are the reproductive parts of a plant. A flower may have either the male part or the female part or both male and female parts.

There are several ways by which plants produce their offspring.These are categorised into two types: (i) asexual, and (ii) sexual reproduction.

Sexual Reproduction

You have learnt earlier the structure of a flower. You know that the flowers are the reproductive parts of a plant. The stamens are the male reproductive part and the pistil is the female reproductive part.

The flowers which contain either only the pistil or only the stamens are called unisexual flowers. The flowers which contain both stamens and pistil are called bisexual flowers. Corn, papaya and cucumber produce unisexual flowers, whereas mustard, rose and petunia have bisexual flowers.Both the male and the female unisexual flowers may be present in the same plant or in different plants.

Could you identify the anther and the filament of a stamen? . Anther contains pollen grains which produce male gametes. A pistil consists of stigma, style and ovary. The ovary contains one or more ovules. The female gamete or the egg is formed in an ovule. In sexual reproduction a male and a female gamete fuse to form a zygote.

Pollination

Generally pollen grains have a tough protective coat which prevents t hem from drying up. Since pollen grains are light, they can be carried by wind or water. Insects visit flowers and carry away pollen on their bodies. Some of the pollen lands on the stigma of a flower of the same kind. The transfer of pollen from the anther to the stigma of a flower is called pollination. If the pollen lands on the stigma of the same flower it is called self-pollination. When the pollen of a flower lands on the stigma of another flower of the same plant, or that of a different plant of the same kind, it is called cross-pollination.

Fertilisation

The cell which results after fusion of the gametes is called a zygote. The process of fusion of male and female gametes (to form a zygote) is called fertilisation . The zygote develops into an embryo.

Fruits and Seed Formation

After fertilisation, the ovary grows into a fruit and other parts of the flower fall off. The fruit is the ripened ovary. The seeds develop from the ovules. The seed contains an embryo enclosed in a protective seed coat.

Some fruits are fleshy and juicy such as mango, apple and orange.Some fruits are fleshy and juicy such as mango, apple and orange. Some fruits are hard like almonds and walnuts.

Seed Dispersal

In nature same kind of plants grow at different places. This happens because seeds are dispersed to different places. Sometimes after a walk through a forest or a field or a park, you may have found seeds or fruits sticking to your clothes.

What do you think will happen if all seeds of a plant were to fall at the same place and grow there? There would be severe competition for sunlight, water, minerals and space. As a result the seeds would not grow into healthy plants. Plants benefit by seed dispersal. It prevents competition between the plant and its own seedlings for sunlight, water and minerals. It also enables the plants to invade new habitats for wider distribution.

Seeds and fruits of plants are carried away by wind, water and animals. Winged seeds such as those of drumstick and maple ,light seeds of grasses or hairy seeds of aak (Madar) and hairy fruit of sunflower , get blown off with the wind to far away places. Some seeds are dispersed by water. These fruits or seeds usually develop floating ability in the form of spongy or fibrous outer coat as in coconut. Some seeds are dispersed by animals, especially spiny seeds with hooks which get attached to the bodies of animals and are carried to distant places. Examples are Xanthium and Urena.

Some seeds are dispersed when the fruits burst with sudden jerks. The seeds are scattered far from the parent plant. This happens in the case of castor and balsam.
 

 

Summary

  • Sexual reproduction involves the fusion of male and female gametes.
  • The male gametes are found inside the pollen grains and female gametes are found in the ovule.
  • Pollination is the process of transfer of pollen grains from the anther of one flower to the stigma of the same or another flower.
  • Pollination is of two types, self-pollination and cross-pollination. In self-pollination, pollen grains are transferred from the anther to the stigma of the same flower. In cross-pollination, pollen grains are transferred from the anther of one flower to the stigma of another flower of the same kind.
  • The fusion of male and female gametes is called fertilisation..
  • Fertilised egg is called zygote. Zygote develops into an embryo..
  • Fruit is the mature ovary whereas ovule develops into a seed, which contains the developing embryo.
  • Seed dispersal is aided by wind, water and animals.
  • Seed dispersal helps the plants to (i) prevent overcrowding, (ii) avoid competition for sunlight, water and minerals and (iii) invade new habitats

 

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