CBSE CLASS 7-Reproduction in Plants -CHAPTER NOTE

 

All living organism including plants, is to create offspring for the next generation.

Most plants have roots, stems and leaves. These parts are called the vegetative parts of a plant.

After a certain period of growth, most plants bear flowers and gives fruits.

When we eat fruit we discard the seeds in it. Seeds germinate and form new plants.

All living organisms have a characteristic to produce same kind of living organisms.

Production of new individuals from a parent is known as reproduction.

Flowers perform the function of reproduction in plants. Flowers are the reproductive parts.

MODES OF REPRODUCTION

There are several ways by which plants produce their offspring. These are categorized into two types:

1.        Asexual reproduction

2.       Sexual reproduction

Asexual reproduction

·         In asexual reproduction we only need one parent to produce a offspring.

Vegetative propagation: It is a type of asexual reproduction in which plant reproduce by the help of different vegetative parts like roots, stem, leave etc.

Budding:

·         Yeast grow and multiply every few hours if sufficient nutrients are made available to them.

·         Yeast is a single-celled organism.

·         A small bulb-like projection emerging out from the yeast cell is called a bud.

·         A bud gradually grows in mature state and gets detached from the parent cell.

·         A new yeast cell grows, matures and produces more yeast cells.

·         A few times, another bud arises from the bud forming a chain of buds.

·        This process continues and a large number of yeast cells are produced in a short time.

Fragmentation

·         Green patches in ponds, or in other stagnant water bodies. These are the algae.

·         When a algae gets  water and nutrients algae grow and multiply rapidly  by fragmentation.

·         An alga breaks  into two or many fragments. These pieces grow into new individuals.

·         This process continues and cover a large area in a short period of time.

       Spore formation

·         A fungi on bread piece grow from spores which are present in the air.

·         When spores burst out they keep floating in the air.

·         As they are light they can cover long distances.

·         Spores are asexual reproductive bodies. Each spore is covered by a hard protective coating to withstand unfavorable conditions such as high temperature and low humidity. that is why , they could survive for a long time. Under a favorable and good condition, a spore germinates and develops into a new individual. Example:- moss and ferns 

SEXUAL REPRODUCTION

·         Flowers are reproductive parts of a plant. Stamens are male reproductive part and pistil is female reproductive part.

·         Flowers which have either stamen or pistil are called unisexual flower. Ex- Corn, papaya and cucumber produce unisexual flowers,

·         Flowers which has both stamen and pistil are called bisexual flowers. Ex- mustard, rose and petunia.

·         Both Reproductive parts male and female unisexual flowers may be present in the same plant or in different plants.

·         Anther has 'pollen grains' which produce male gametes.

·         A pistil has three parts style, stigma and ovary. 

·         Ovary contains one or more ovules.

·         Female gametes are formed in an ovule.

·         In the sexual reproduction a male and a female gamete fuse to form a zygote.

Pollination

·        Pollination is a process of transferring pollen grains from the male anther of a flower to the female stigma.

Plants can be:

  • Self-pollinating -  the plant which can fertilize itself
  • Cross-pollinating - the plant which needs a vector (a pollinator or the wind) to get the pollen to another flower of the same species.

Fertilization

·         The process in which male and female gametes fuse to form a zygote is called fertilization.

·         The zygote develops into an embryo.

FRUITS AND SEED FORMATION

·         After the process of fertilization, the ovary grows into a fruit and other parts of the flower fall off.

·         The fruit is the ripened ovary.

·         The seeds develop from the ovules. The seed contains an embryo  which is enclosed in a protective seed coat.

SEED DISPERSAL

·       The process in which seed disperse to different places is called seed dispersal.

·         Seed dispersal is done by wind, water and animal. It help the plants to (i) prevent overcrowding, (ii) avoid competition for sunlight, water and minerals and (iii) invade new habitats.