How Flowers Turn Into Fruits and Seeds

A flower becomes a fruit and forms seeds through the processes of pollination and fertilisation, followed by changes in the ovary and ovules. This article explains these steps as taught in ICSE Class 6 Biology, including what pollination is, the difference between self- and cross-pollination, the agents that help in pollination, and how fertilisation leads to fruit and seed formation. You will also learn about the features of insect- and wind-pollinated flowers and the functions of fruits.

Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same or another flower of the same species. There are two main types: self-pollination and cross-pollination. In self-pollination, pollen from the anther is transferred to the stigma of the same flower or another flower on the same plant. In cross-pollination, pollen is transferred from the anther of one plant to the stigma of a flower on a different plant of the same species. Self-pollination ensures that even if pollinators are absent, seeds can still form, which is its main advantage. Cross-pollination, on the other hand, produces healthier and more varied offspring, which is its advantage. For example, in a field of mustard plants, some flowers may self-pollinate if wind or insects do not visit, while others may cross-pollinate when insects carry pollen between plants. A common misconception is that all flowers need insects for pollination, but some can self-pollinate without any external help.

Agents of pollination are the means by which pollen is transferred from one flower to another. The main agents are insects, wind, water, and other animals. Insect-pollinated flowers are usually brightly coloured, have a sweet smell, and produce nectar to attract insects like bees and butterflies. Their pollen grains are often sticky or spiky so they attach easily to insects. Wind-pollinated flowers, in contrast, are often small, dull-coloured, and have no scent or nectar. Their pollen is light and produced in large quantities so it can be carried by the wind. For example, grass flowers are wind-pollinated and have long, feathery stigmas to catch airborne pollen, while hibiscus flowers attract insects with their colour and scent. Some students think all colourful flowers are insect-pollinated, but some water plants rely on water as the agent of pollination.

Fertilisation in a flower occurs when a male gamete from a pollen grain fuses with the egg cell inside an ovule. After pollination, the pollen grain on the stigma grows a pollen tube down through the style toward the ovary. The male gamete travels through this tube and enters the ovule, where it joins with the egg cell to form a zygote. This zygote will later develop into an embryo inside the seed. For example, in a pea plant, after pollen lands on the stigma, a pollen tube forms, and the male gamete reaches the ovule to fertilise the egg. Some students confuse pollination with fertilisation, but pollination is just the transfer of pollen, while fertilisation is the actual fusion of male and female gametes.

After fertilisation, several changes occur in a flower. The ovary enlarges and ripens to become the fruit, while each fertilised ovule develops into a seed. The wall of the ovary becomes the pericarp, which has three layers: epicarp (outer), mesocarp (middle), and endocarp (inner). The other parts of the flower, like petals and stamens, usually dry up and fall off. Fruits have two main functions: they protect the seeds and help in their dispersal. For example, in a mango, the fleshy part we eat is the mesocarp, and the hard stone inside is the endocarp protecting the seed. Some students think all fruits are sweet and edible, but many fruits, like chillies or cotton, are not eaten but still protect and disperse seeds.