Sexual reproduction is the production of a new organism from two parents by making use of their gametes or sex cells. Plants also have male and female sex organs. These sex organs in plants are carried within the flower and the seeds which are inside a fruit. Such plants are called angiosperms or flowering plants as they reproduce by sexual reproduction method.
Most of the plants contain reproductive organs of both male and female in the flowers. The same flower has both male and female reproductive organs. Such flowers make male and female gametes and ensure that fertilisation takes place so that new seeds are formed for the reproduction of plant.
Parts of a Flower
Steps for sexual reproduction in plants
Various Parts of a Flower
Stamen: Male reproductive organ of a plant.
Carpel: Female reproductive organ of a Plant. Carpel is also known as Pistil.
There are flowers which are called unisexual. This is because they have either stamens or carpels. Flowers of papaya and watermelon are examples of unisexual flowers. And the flowers which have both male and female sex organs are called bisexual. Flowers of hibiscus and mustard plant are called bisexual flowers.
In order to make a new seed male gamete present in a pollen grain units with the female gamete present in the ovule. This process takes place in two steps.
When pollen grains from the anther are transferred to the stigma of a carpel, it is called pollination. This is important because it is due to pollination that male gametes are able to combine with female gametes. Pollination is done by insects like bees, butterflies and birds, wind and water.
There are two types of pollination, self-pollination and cross-pollination. When pollen grains from one flower carried to the stigma of the same flower or to another flower of the same plant, it is called self-pollination. And when pollen grains from a flower of one plant are carried to the stigma of a flower of another similar plant, it is called cross-pollination.
Insects help in pollination. This happens when an insect sits on a flower of one plant to suck nectar then the pollen grains from anther stick to its body. Now, when this insect flies and sits on the flower of another similar plant then the pollen grains are transferred and they stick to the stigma of the flower of another plant. This way insects help cause cross-pollination. Wind too helps in cross-pollination.
After pollination, next step is fertilisation. In this step, male gametes present in pollen grains joins with the female gametes present in ovule.
When the pollen grain falls on stigma it bursts open and a pollen tube grown which moves through the style towards the ovary and enters ovule. Male gamete moves down through the pollen tube. The tip of pollen tube bursts open in the ovule and the male gamete come out. In the ovule, male gamete combines with the nucleus of female gamete and fertilised egg is formed. This fertilised egg is called zygote.
Fertilisation in a Flower.
Formation of fruits and seeds
In the ovule, the fertilised egg divides several times to form an embryo. A tough coat is developed around the ovule and it gradually develops into a seed. The ovary of flower develops to become a fruit which contains seeds inside it. Other parts of the flower like sepal, stamen, stigma and style become dry and fall off. Fruit takes place of the flower. Seed is protected by the fruit. Some fruits are soft and juicy while the other fruits are hard and dry.
A fruit contains seed of the plant inside it.
The seed is the reproductive unit of a plant. With this seed new plant can be grown as the seed contains baby plant and food for the baby plant inside it. The part of the baby plant in seed which grown into leaves is called plumule and the part which develops into roots is called radicle. The part of the seed which stores food for the baby plant is called cotyledon. The baby plant inside a seed is in a dormant state. It is only when we provide it with suitable environment like water, air, light, etc., it germinates and a new plant grows. Wheat grains, gram, corn, peas, beans etc., are examples of seeds.
Parts of a Seed
Germination of seeds
The seeds obtained from a plat are in dry and dormant state. It is only when they get water, air, soil, etc., that they begin to grow into a new plant. The beginning of the growth of a seed is called germination of seeds.
The germination of a seed begins when it absorbs water, swells and bursts through the seed coat. It is with the help of water that enzymes function in the seed. The enzymes digest stored food and make it soluble. With the help of soluble food radicle and plumule grow.
Seeds germinate under suitable conditions to produce new plants. These pictures show the germination of a bean seed to form a new bean plant.
First the radicle of the seed grows to form roots. These roots grow inside soil and absorb water and minerals from the soil. After this plumule grows upwards and shoots are formed. These shoots develop green leaves. The leaves begin to make food with the process of photosynthesis and gradually a whole new plant is developed.