Molecular biology, one of the Biology Topics, focuses on the study of biological molecules.
Main Parts of a Flower and Its Functions
Flowers are perhaps the most beautiful part of a plant. Different plants have different types of flowers. Flowers are of many sizes, shapes and colours. The flowers have different smells. But some of the flowers do not have any smell. Some of the common flowers are : Rose, Bougainvillea, Jasmine, Lily, Sunflower and Marigold. The flower is that part of a plant which contains the reproductive organs. The main function of flowers is to produce fruits and seeds. All the flowers have the same basic parts.
The main parts of a flower are : Sepals, Petals, Stamen and Pistil. The main parts of a flower are shown in Figure.
(i) The green, leaf-like parts in the outermost circle of a flower are called sepals (see Figure).
The sepals protect the flower when it is in the form of a bud in the initial stage. Sepals may either be separate from one another or joined together.
(ii) Inside the sepals are the petals of a flower (see Figure). Petals are the most attractive part of a flower. Petals of flowers can be of different colours, shapes and sizes. The petals can be red, blue, green, orange, pink, white, or any other colour. The petals of some of the flowers have natural scents in them due to which they smell very nice. Petals also attract insects. The ring of colourful petals in a flower protects the reproductive organs of the flower (like stamen and pistil). Petals may be either separate from one another or joined together to form a tubular flower.
In many flowers, the number of petals is equal to the number of sepals in it. For example, the buttercup flower has 5 green sepals and an equal number of 5 petals. In some flowers, however, the number of petals is not equal to the number of sepals. In such flowers, the number of petals is much more than the number of sepals. For example, the rose flower has 5 green sepals but the number of petals is much more than five. Thus, the number of petals and sepals in a flower is not always equal.
(iii) Just inside the petals of a flower, there are many little stalks with swollen tops. These stalks with swollen tops are called stamens (see Figure). The stamen is the male part of a flower.
The stamen is actually made up of two parts : a filament and an anther. The stalk of stamen is called filament and the swollen top of stamen is called anther (see Figure). The anther contains a yellow powder-like substance called pollen (or pollen grains). If we cut the anther of a flower horizontally with a blade, we can see the pollen grains in it (see Figure). The pollen grains contain male sex cells of a plant. There are many stamens in a flower. They form a ring around the female part of the flower called pistil.
(iv) In the centre of a flower, there is a flask-shaped organ. This flask-shaped organ of a flower is called pistil (see Figure). The pistil is the female part of a flower. A pistil is made up of three parts : stigma, style and ovary. The top part of a pistil is called stigma (see Figure). Stigma is very sticky so that pollens can stick to it. The middle part of a pistil is called style. It is a tube which connects stigma to ovary. The swollen part at the bottom of the pistil is called ovary. The ovary contains tiny, egg-like structures called ovules. If we cut the ovary of a flower vertically with a blade and observe with a magnifying lens, we will see tiny egg-like structures inside the ovary.
These tiny, egg-like structures are ovules (see Figure). The ovary may contain one or several ovules. The ovules contain female sex cells of a plant. The female organ ‘pistil’ is surrounded by a number of male organs called ‘stamens’. Please note that the female part of a flower called ‘pistil’ is also known as ‘carpel’. In most plants, the stamens and pistils (male and female parts) are present in the same flower. In some plants, however, stamens and pistils are present in separate flowers.
How are fruits and seeds formed?
A fruit is that part of a plant which contains the seeds. Apples, oranges, plums, lemons, and tomatoes, are all fruits. They all have seeds inside them [see Figure (A)]. The pea pod is also a fruit. The peas inside it are seeds [see Figure (b)],
We will now describe how fruits and seeds are formed from flowers.
The fruits and seeds are formed from flowers by the process of pollination and fertilisation. The transfer of pollen grains from anther of a stamen to the stigma of a pistil is called pollination. Pollination is done by insects, wind and water. In other words, the pollen grains are carried from the anther of a stamen to the stigma of a pistil by insects (like bees), blowing wind, and falling water.
When the pollen grains fall on stigma, they move down through the tube called style and reach the ovary. In the ovary, the male sex cells present in pollens join with the female sex cells present in ovules. The joining together of male and female sex cells is called fertilisation. After fertilisation, the ovules grow and become seeds. The ovary of flower grows and becomes a fruit (with seeds inside it). A fruit protects the seeds. The other parts of the flower dry up and fall off.
The wheat grains, gram (chana), corn (makka), peas, pulses, and beans, which we use as food are all seeds of their respective plants. All these seeds can germinate under suitable conditions to produce new plants. For example, when we sow wheat seeds in the fields, they grow to give new wheat plants (or wheat crop).