How Do Organisms Reproduce

Some plants reproduce asexually but the majority of the flowering plants reproduce sexually. Both male and female gametes are produced by flowers, which is the reproductive part of the plant. Sexual reproduction takes place in flowers in plants. The main parts of a flower are:

• Receptacle,
• Sepals,
• Petals,
• Stamen
• Carpel/Pistil: It comprises of three parts:
  1. Stigma: It is the top most part of a flower.
  2. Style: It is the long tube which connects stigma to the ovary.
  3. Ovary: It contains a lot of ovules. It is the part of the plant where the seed formation takes place.

Based on whether a flower consist of stamen or pistil or both can be either unisexual or bisexual. Rose, China rose are bisexual flowers is composed of all the four parts whereas, the plants like papaya and cucumber produce only unisexual flowers.

PROCESS OF SEXUAL REPRODUCTION IN PLANTS

The sexual reproduction in plants takes places in the following steps:

• Stamen, the male organ of flower makes the male gametes (male sex cells) of the plant. These male gametes are present in pollen grains. The filament supports the anther.

• Carpel or pistil, the female organ of a flower makes the female gametes (female sex cells) of the plant. These female gametes are present in ovules. The alternatives for the female gametes present in ovules are ‘ova’, ‘egg cells’ or just ‘eggs’.

• The male gametes present in pollen grains fertilise the female gametes( or egg cells) present in ovules.

• The ferilised eggs cells grow within ovules and become seeds.

• Under suitable conditions of water, warmth, air and light, the seeds produce new plants on germination.

POLLINATION IN PLANT

It is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. In this way, male gametes in pollen grains fuse with egg in the ovule to form a zygote. Depending on the pollen landing, pollination can be classified into two types-

• Self-Pollination: It is the process when the pollen grains from the anther of a flower are transferred to the stigma of the same flower (or another flower on the same plant)
• Cross Pollination: It is the process when the pollen grains from the anther of a flower on one plant are transferred to the stigma of a flower on another similar plant.

Pollination takes place with the help certain agents so called pollinators such as insects, water, birds, the wind, etc.

FERTILISATION IN PLANT

Zygote is formed when pollen gets transferred to stigma and the male gametes from pollen grains release and fuses with egg in the ovule. This process of fusion of gametes is called fertilization and the zygote thus formed, divides and develops into an embryo, and later into a seed. The ovary develops into a fruit.

FORMATION OF FRUITS AND SEEDS

The ovule of the flower develops a tough coat around it and is gradually converted into a seed. The ovary of flower develops and becomes a fruit (with seeds inside it).

GERMINATION OF SEEDS

The beginning of the growth of seeds is called germination of seeds.