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Class 6 Science Notes on Structure and Functions of Plant Parts - Part 2

Check Part  1 of the lesson.

The Flower

Flower is the most important part of the plant. It is the reproductive part of the plant and is meant for giving rise to new plants. It has a stalk known as pedicel. Some flowers do not have pedicel and such flowers are called sessile.

Parts of a flower

A flower has four parts. These are:
  1. Calyx: The outermost whorl made of green leaf-like protective structure called sepal.

  2. Corolla: The next inner whorl made of brightly coloured structures called petals that attract insects.

  3. Stamens: This is the third inner whorl that consists of swollen structures called anthers that are present on the tip of thread-like filaments. Anthers produce powdery substance called pollen grains that contain the male reproductive cells.
  4. Carpel (pistil): This is the innermost whorl and is the female part of a flower. It consists a swollen base called ovary and a long tubular structure called style that ends with a knob-like part called stigma. Ovary contains ovules which has female reproductive. After fertilisation, ovary changes into a fruit and ovules change into seeds.

Types of flowers

There are two types of flowers based on the presence of male / female part.
  1. Bisexual flower: A flower that has both stamens and carpels i.e male and female reproductive parts. E.g. hibiscus flower, mustard flower.

  2. Unisexual flower: Flowers that have only one reproductive part i.e. either only stamen or only carpel. E.g. flower of cucumber plant.

Functions of flower

  • Flower is the most important part of the plant as it takes part in reproduction.
  • It leads to the formation of fruit and seeds that grow into new plants on germination.

Sexual Reproduction in plant

  • Flowers help in the sexual reproduction in plants.
  • Pollen grains contain the male reproductive cells (male gametes) and ovule contains a single large egg cell / female reproductive cell (female gamete).
  • A male gamete is small in size and contains a nucleus and little cytoplasm. While a female gamete is large and has a nucleus with more cytoplasm.

Pollination

The process of transfer of pollen grains from a ripe anther to the stigma is called pollination. There are two types of pollination:
  1. Self-pollination: When the pollination takes place between the same flower or flowers of the same plant.

  2. Cross-pollination: When the pollination takes place between the flowers of different plants of the same species.

Agents of pollination

There are different agents that help in pollination. Wind, water, insects, birds or other animals are some of the agents of pollination. Insects like butterflies, bees, moths etc are the most common agents of cross-pollination.

Fertilisation

The fusion of male gamete and the female gamete is known as fertilisation.

What happens during fertilisation

  • Pollen grains that fall on the stigma develop pollen tubes that grow downwards through the style till it reaches the ovule.
  • The male gamete moves through the pollen tube and enters into the ovule where it fuses with the female gamete.
  • The process of fertilisation is completed with the fusion of male and female gamete.

Formation of fruit and seeds

The following changes take place after fertilisation:
  • The flower loses its brightness and the sepals, petals and stamen fall off.
  • The fertilised ovary grows bigger in size till it changes into a fruit. The ovary wall changes into fruit wall and the ovules change into seeds.
  • Thus fruit and seeds are formed as a result of fertilisation.

Structure of fruit

A fruit is a ripened ovary formed after fertilisation. It consists of two parts:
  1. The fruit wall called the pericarp.
  2. Seeds that developfrom ovules.
A fruit may contain only one fruit like a mango or many seeds like apple.

Functions of fruit

  • Fruit stores the food prepared by the plant.
  • It protects the seeds from unfavourable conditions and from animals.
  • It helps in the dispersal of seeds which is essential for the healthy growth of a plant.

Seed

A seed consists of 3 parts:
  1. A protective layer called the seed coat.
  2. One or two cotyledons separated by an embryo and contain food for the developing baby plant.
  3. An embryo contains the baby plant. It has two distinct parts - plumule and radicle.
  4. On germination of the seed, the plumule grows into shoot system and radicle grows into root system.

Dispersal of seeds

The process by which seeds / fruits get carried away to distant places from their parent plant with the help of special features, by various agents, is called dispersal of seeds.

Why is dispersal of seeds essential

Dispersal of seeds is essential as it helps in preventing the over-crowding of seeds at one place and thus helps in the healthy growth of the new plants.

Wind, water and animals are the agents that help in the dispersal of seeds.

Dispersal by wind

Seeds that are dispersed by wind develop fine wing-like / hair-like structures which help them to get carried away by wind. E.g. dandelion seeds, cotton seeds etc.

Dispersal by water

Seeds like coconut and lotus are light in weight. They float on the surface of water and get dispersed by water currents.

Dispersal by animals

Most of the fruits / seeds are eaten by animals and are dispersed by animals. Humans, animals and birds eat the fleshy part of the fruits and drop the seeds far away from the mother plant. Thus animals help in the dispersal of seeds.

Some seeds develop sharp hooks, stick to the body of animals and thus get dispersed to distant places.

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