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Sexual Reproduction in Plants
Reproductive Parts of a Flower:
Flowers of some plants possess either only a male reproductive part called the stamen or a female reproductive part called the pistils. Such flowers are called unisexual flowers. It is likely that both male and female flower is present in the same plant or in different plants.
Examples of plants containing unisexual flowers are corn, papaya, and cucumber.
While some plants contain both male and female reproductive parts within the same flower and hence are called bisexual flowers. Examples are rose, mustard, and petunia.
The stamen contains Anther sitting on top of a filament. The anther contains pollen grains which produce male gametes. Likewise, a pistil contains a stalk called style, a stigma, and an ovary containing ovules. These ovules produce female gametes called eggs. In sexual reproduction, the male gametes and female gametes fuse to form a zygote.
What is Pollination?
The pollen grains present in the male flower travel across to plants containing female flowers with the help of mediums such as air and water. As pollens are light in weight and consist of a hard protective coating, they are not damaged easily while traveling.
The pollens fall on the sticky tip, the stigma of the female flower resulting in a phenomenon called Pollination. The pollens then travel through the stalk, and stigma and reach the ovules where female gametes, the egg present.
There are two different types of pollination occurring in nature
i) self-pollination, which occurs when pollen from an anther lands on the stigma of the same plant
ii) cross-pollination, which occurs when pollen from an anther lands on the stigma of a different plant
(Figure 7.5.1). Cross-pollination results in a diversity of the traits present in a plant.
What is Fertilization?
The process of fusion of male and female gametes is defined as fertilization. Once the pollen reaches the ovules of a female flower, it results in the fusion of the egg and the pollen resulting in the formation of a zygote. The zygote then develops into an embryo.
Fruit and Seed Formation
As the embryo develops, it is enclosed within a hard protective coating. This hard protective coat is called a seed. The ovary of the flower develops into a fruit and other parts of the flower fall off gradually. The fruit ripens eventually and is plucked off. In some plants, the ovary develops into a fleshy fruit like mango and apple, while some develop into hard fruit like almonds and walnuts.
Seed Dispersal:
The distribution of seeds into different places is called seed dispersal. Seed dispersal is essential to growing healthy plants otherwise; it would result in competition for necessary elements such as sunlight, water, and minerals. Hence, the medium through which seeds are dispersed is water, air, and birds. In this way, plants grow in different habitats and adapt themselves to the environment.
Some seeds are light and have a wing-like structure to be carried off by the wind, for example, maple seeds. While some seeds are enabled to float in water for example coconut. Birds and other animals also contribute to the dispersal of seeds by eating the fruit and throwing away the seeds in a place where they migrate. In the case of castor plants, it is observed that there is a sudden burst of the fruit resulting in the scattering of seeds distantly from the parental plant. In this way, the seeds are dispersed and result in the growth of a new plant.