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Reproduction in Plants Class 7 Science Notes - Chapter 12

Reproduction in Plants Class 7 Science Notes - Chapter 12

Preview of the chapter

All living species, including plants and animals, have the ability to produce new individuals during the course of their lives. Reproduction is the process of creating a new organism from an existing organism (or the parent) of the same species. The new people created are carbon replicas of their parents. The process of reproduction is a crucial biological process that is required for the survival of the species.

Thus, reproduction keeps life going, which is not only necessary for an organism's survival but also for the perpetuation and preservation of the species because it increases the number of members in a species.  

Introduction

Reproduction

Different organisms reproduce in a different way. In plants, there are two different methods of reproduction:

  1. Asexual reproduction
  2. Sexual reproduction
Asexual Reproduction

Asexual reproduction refers to the process of producing new members of the same species with just one parent involved. Asexual reproduction in plants leads in the generation of progeny or new plants that lack seeds or spores.

Asexual reproduction in plants occurs through the following methods:

  1. Vegetative propagation
  2. Budding
  3. Fragmentation
  4. Spore formation

Sexual Reproduction


Asexual Reproduction in Organisms

  • Asexual reproduction allows organisms to give birth to new species without the need for gamete fusion.
  • There is only one parent participating.

Fission

  • Unicellular organisms like amoebas, paramecium, and other similar species engage in this particular form of asexual reproduction.
  • The division of a single parent cell produces two or more daughter cells.
  • The two are as follows:
  • One parent cell divides into two daughter cells in a process known as binary fission. such as an amoeba or paramecium
  • Multiple Fission: the division of a single parent cell into numerous daughter cells. (Example: Plasmodium) 



Fragmentation

  • Some algae (Spirogyra) that are present in waterbodies reproduce by fragmentation.
  • In this- method, the body of the parent breaks into small pieces called fragments and each fragment grows up to become a new plant.
  • Fragmentation of parent body occurs when they are matured.

Budding

  • A daughter individual is created in this procedure from a tiny projection on the parent body known as a bud. Most yeasts that resemble fungi reproduce by budding. If given enough nutrition and favorable conditions, yeast will grow and reproduce within a few hours.


Spore Formation

  • Some fungi, such as bread mould, reproduce asexually by producing spores.
  • Spores are tiny, spherical bodies that are found in the air and have a thick protective wall to shield them from harmful elements.
  • The spores explode and germinate when favorable conditions are present, creating new plants.



Vegetative Propagation

In this type of asexual reproduction, the roots, stems, leaves, and buds are used to create new plants. as in roses and bryophyllum

Reproduction in Plants

  • The reproductive organ of a plant is its flower. They assist plants in produce fruits and seeds through sexual reproduction.
  • When a flower reproduces sexually, the male part of the flower produces a male cell, which fuses with a female cell created by the female part of the flower.
  • These cells are known as gametes, and through the process of fertilization, they come together to produce a zygote.
  • Anthers create the male gamete, or pollen grains, whereas pistils produce the female gamete, or ovule.
  • Male and female gametes come together during pollination, combine during fertilization, and form fruit and seeds to create a new plant.

Pollination

Pollination is the process by which pollen grains move from the stigma of a pistil to the anther of a stamen. There are two ways to pollinate plants:

(i) Self-pollination: This process occurs when a pollen grain from an anther of one flower travels to the stigma of that same bloom. Bisexual flowers typically self-pollinate.

(ii) Cross-pollination: This process is referred to as cross-pollination when pollen grains from the anther of one flower or plant are transferred to the stigma of another flower from the same plant or from a different plant of the same species. Insects, wind, water, creatures, birds, etc. all have a role in this transmission to another plant.


Zygote

  • A zygote is formed when a male and a female gamete unite during sexual reproduction.
  • In the case of plants, the male gametes in pollen grains fuse with the female gamete, i.e. the egg.
  • This fusion is known as fertilization, and the cell that results from it is known as a zygote.

Fertilisation

  • The process in which the male gamete fuses with the female gamete to form a new cell (called zygote) is called fertilisation.
  • When the pollens are deposited on the stigma of the pistol, it begins to germinate.
  • After some time, a long pollen tube is developed from the pollen grain which passes through the style towards the female gametes in the ovary.
  • The male gametes move down the pollen tube and the tube enters the ovule present inside the ovary.
  • The tip of pollen tube bursts and the male gamete comes out of the pollen tube.
  • Inside the ovary, the male gametes fuse with the female gametes present in the ovule to form a fertilised egg cell which is called zygote.
  • The zygote develops into an embryo which is a part of a seed that develops into a new plant.

Embryo

  • The zygote further develops to form the embryo.
  • In animals, the embryo grows into an adult.
  • In Plants, the embryo further gives rise to shoot system and root system.

Fruits and Seed Formation

  • Following fertilization, the ovary develops into the fruit and the ovule into the seeds.
  • Parts of the ovule develop into the seed covering, also known as the seed coat.
  • Fruits are matured ovaries from flowers.
  • Which safeguards the seed.

Seed Dispersal

  • Plants produce an abundance of seeds.
  • As a result, some external agencies transport the seeds to distant locations.
  • The seeds and fruits are transported by many means, including wind, water, birds, and some animals.

Dispersal by Wind or Air
Seeds with wing or hair-like structure are easily carried away by the wind, such as maple, drumstick, Madar, oak, cottonseed, and grasses, orchids, and begonia. These seeds can be dispersed away from their natural habitat.

Dispersal by Water
Water lily, lotus, chestnut (singhara) and coconut seeds are dispersed through water, allowing them to float and drift along its flow. The coconut fruits have a fibrous outer coat, allowing them to be carried away by flowing water.

Dispersal by Birds
Birds eat fruits and seeds, which are dispersed through their faeces. Digestion enzymes help dissolve the hard seed coat and release it, allowing the seeds to germinate. Examples include neem seeds.

Dispersal by Animals
Seeds of Xanthium and Urena plants are attached to the animal's fur and dispersed when they move to a distant place, such as when the animal rubs their body surface.

Dispersal by Explosion or Bursting of Fruits

Fruits can break open and scatter seeds far away from their parent plants due to an explosion mechanism, such as when castor plants burst suddenly with a jerk and spread the seeds far away. Balsam fruit is also dispersed through this mechanism.

Germination of Seed

The process through which seeds begin to grow is known as seed germination. When the seed coat splits, a root and plumule grow downward, resulting in the formation of a seedling. This seedling grows quickly and eventually develops into a new plant that produces seed and fruits. This cycle continues to create more children in order to ensure the survival of a species.














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