REPRODUCTION IN PANTS Class 7 Chapter 12

 INTRODUCTION-

Living organisms have a limited lifespan. Unless they are not going to form new organism, they will finish. Their continuity of life will be lost. So, fertile organisms form new organism of same kind either by self or by the help of other individual of same species. The process of formation of similar types of organisms by existing organism is called reproduction.

    There are two types of reproductions-

     (a) Asexual Reproduction – New organism is formed by single parent. It is common in plants     

          and animals.

     (b) Sexual Reproduction- New organism is formed by two parents. It is common in plants     

          and animals.

A. ASEXUAL REPRODUCTION IN PLANTS - New organism is formed by a single parent. It occurs by following methods-

1. Vegetative Propagation- The vegetative parts of plant is used to grow the new organism. e. g.- Roots in case of Sweet Potato and Mint, Stem in case of Strawberry and Chrysanthemum, Modified stem in case of Potato tubers, Leaves in case of Bryophyllum and African violet is used to develop new organism.

Vegetative Propagation also occurs by artificial methods like- Cutting, Grafting, Layering and Tissue culture. It is very useful for fruit yielding plants.

2. Budding- Bud is an asexual reproductive structure. This is an outgrowth of mother body in which a nucleus is found. The bud grows to form the new organism. e.g. – Yeast (A Fungus)

3. Fragmentation- Fragments are small asexual reproductive structures formed by fragmentation of mother body. Each fragment grows into a new organism. e. g.- Spirogyra

 

4. Spore Formation- Spores are small asexual reproductive structures that germinate to form new organism. Spores are formed in large number. They float in air and on finding suitable surface for germination, they form new organisms. The germinating surface must contain organic matter and water. e. g.- Ferns (Pteridophytes) and Fungi like Rhizopus, Mucor, Penicillium, Agaricus (Mushroom) etc.

B. SEXUAL REPRODUCTION IN PLANTS-   The reproduction in which two parents, one male and one female are required to form the new organism is called as sexual reproduction.

Flower is the reproductive part of the plant. The complete flowers have all the four whorls but incomplete flowers have less than four parts. It has male part called stamen and female part called pistil (or carpel). Stamen forms pollen grains that contain male gametes. Carpel has ovary that contains eggs.

Uni-sexual and Bisexual Flowers- Those incomplete flowers which have either pistil or stamen are called uni-sexual flowers. e. g.-Papaya, Maize, Cucumber etc.

Those flowers which have both pistil as well as stamen are called as bisexual flowers. e. g.- Rose, china-rose, mustard, marigold, lotus etc.

Pollination- The transfer of pollen grains from anther to the stigma is called pollination. There are two types of pollinations-

A. Self fertilization

B. Cross fertilization

When transfers of pollen grains occur from anther to the stigma of same flower, it is called as self fertilization. When transfers of pollen grains occur from anther to the stigma of different flower, it is called as cross fertilization.

On stigma, pollen grains germinate to form pollen tube in which male gametes are found. The pollen tube moves below inside the ovary for fertilization.    

Fertilization- The fusion of male gamete with female gamete to form zygote is called fertilization. As a result of fertilization, single celled zygote is formed.

Formation of Fruits and Seeds- As a result of fertilization some post-fertilization changes starts. The ovary changes into fruit and ovules change into seeds. So, fruit is ripened ovary.

Seed- The seed develops from the fertilized ovules. They have an outer protective covering called seed coat. The Seed has either one cotyledon or two cotyledons. Cotyledons are nutritive cells that give food to developing radical and plumule.

Seed Germination- The seeds can remain in dormant stage for many months to many years. On finding suitable conditions, the seed germinate to form radicle and plumule. The small embryo develops into radicle and plumule. The root system develops from radicle and shoot system develops from plumule.

Seed Dispersal- The method of going of seed from one place to other by an agent is called seed dispersal. The agents to seed dispersal can be- air, wind, water, animals including humans, bats, explosion etc.

Some seeds have hairy structures and wings so they are carried away by wind to other place.