Sexual Reproduction in Flowering Plants: Introduction, Parts of a Flower

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Introduction to Sexual Reproduction

  • Sexual reproduction can be defined as the production of a new organism from two parents by making use of their gametes or sex cells.

  • It involves the production of male and female gametes.

  • The transfer of the male gamete to the female ovules is known as the process of pollination.

  • In case of most of the plants, reproductive organs of both male and female are present in the flowers.

  • Once the pollination occurs, it is followed by the fertilization and the ovules growing seeds within a fruit.

Flowering Plant

Flowering Plant

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Parts of a Flower

Parts of a Flower

Parts of a Flower

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Receptacle

  • It lies above the flower stem.

  • All other parts of the flower are attached at the receptacle.

Sepals

  • Green leaf-like parts present on the outer most part of the flower.

  • They help in protecting the flower.

  • When all the sepals of a flower come together, it is known as Calyx.

Petals

  • These are the colorful leaves of a flower.

  • When all the leaves of a flower come together, it is known as corolla.

  • They attract insects for pollination.

  • The main function is to protect the reproductive organs present at the center of a flower.

Stamen

  • These are the male reproductive organ of a plant.

  • Anther and filament are the two parts.

    • Stalk of stamen is called filament.

    • Swollen top is called an anther.

  • A flower contains a lot of stamens within it.

Carpel

  • It is the female reproductive organ.

  • It is present at the center of a plant.

  • Pistil can be defined as the female organ of a plant.

It is made up of three parts:

  • Stigma: Top portion of the carpel is known as stigma.

  • Style: The center portion of the carpel is known as style.

  • Ovary: The bottom-swollen portion of the carpel is called ovary.

Steps Involved in Sexual Reproduction in Plants

  • Stamen, which is the male organ of a flower, helps in making male gametes of the plant.

  • Carpel is the female organ of a flower, which helps in making female gametes or egg cells of the plant.

  • The female gametes are fertilized by the male gametes.

  • Thereafter the fertilized cells grow into ovules and become seeds.

  • On germination, these seeds become new plants.

Pollination

Transferring pollen grains from the male anther of a flower to the female stigma.

Types of Pollination

Autogamy

  • This is the transfer of the dust grains from the anther to the stigma of a similar flower.

  • Anthers and stigma lie near each other in such flowers.

Xenogamy

This means the transfer of dust grains from anther to the stigma of an alternate plant.

Geitonogamy

Transfer of dust grains from the anther to the stigma of the diverse flower within the same plant.

Chasmogamous Flowers

These are the flowers with uncovered anthers and stigma.

Cleistogamous Flowers

Flowers which do not open.

Agents of Pollination

Anemophily

Pollination occurring due to the impact of wind.

Hydrophily

Pollination occurring due to the impact of water.

Zoophily

Pollination due to the impact of creatures.

Fertilization

  • In this process, the male gamete in pollen grains and female gametes in ovule join each other.

  • The male gametes move down through the pollen tube.

  • The male gamete comes out as soon as the tip of pollen tube bursts open in the ovule.

  • The male gamete combines with the nucleus of female in the ovule leading to the formation of a fertilized egg.

  • The fertilized egg is known as zygote.

Double Fertilization

  • This is the fertilization occurring in angiosperms.

  • One vegetative and two generative cells form into a male gamete with the development of pollen grains.

  • The pollen tube creates leaves germ pore.

  • Pollen tube can be distinguished into:

    • Porogamy: The passage of dust tube through micropyle.

    • Chalazogamy: The passage of dust tube through chalaza.

    • Misogamy: Section of dust tube through integument or funicle.