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Chapter 28 – Reproduction

The following Topics and Sub-Topics are covered in this chapter and are available on MSVgo:

Introduction

Have you ever wondered where you came from? Or why does the offspring of a zebra look like a zebra, and not take after a dolphin? To answer all these questions, we need to understand the process of Reproduction.

  • Reproduction is the process by which an organism, single-celled or multicellular, can produce biologically similar offspring. The chain of life on earth exists due to Reproduction, by the passing of genes from parents to their offspring.

There are two major types of Reproduction:

  1. Asexual Reproduction: In this process, a single parent divides to form new offspring that are genetically identical to itself. There is no fusion of sex cells or gametes.
  2. Sexual Reproduction: In this process, two parents with different genetic materials come together to form a zygote, and produce an offspring that is similar but not genetically identical.

Modes of Asexual Reproduction

  • Fission
  • Budding
  • Fragmentation
  • Vegetative propagation
  • Regeneration
  • Spore formation

1. Fission: In unicellular organisms, Reproduction happens through fission or the cleaving or splitting of the single cell.

There are two types of fission – 

a. Binary Fission: During cell division, when sufficient food and moisture are available, many single-celled bacteria and protozoa divide into two halves called daughter cells, each containing a nucleus. This process is called binary fission. In amoeba, binary fission can take place in any plane, while in Leishmania, fission takes place in a particular orientation.

b. Multiple Fission: When there is an inadequate supply of food and moisture, and unfavourable temperature, unicellular organisms reproduce by multiple fission. During this process, the organism develops a cyst around itself, and its nucleus divides into many new daughter nuclei, each surrounded by a membrane. When the conditions are favourable, the cyst breaks and the daughter cells are released—Eg. in plasmodium and Entamoeba.

2. Budding: In this process, a bud or an outgrowth is produced at a certain site in the parent’s body. This outgrowth develops into a new organism but remains attached to the parent’s body until fully matured. Later, it detaches and leaves behind scar tissue. Yeast and hydra reproduce via budding. In hydra, regenerative cells are used as a bud develops into an outgrowth due to repeated cell division at a specific site.

3. Fragmentation: An important mechanism in multicellular organisms, fragmentation involves the splitting of an organism into different fragments, each of which is capable of being developed and matured into a matured identical fully-grown individual—Eg. in fungi, lichens, plants, etc.

4. Vegetative propagation: In this process, parts of a plant, like leaves, root and stem are used for the production of new plants. There are two types of Vegetative propagation: Natural and Artificial.

In Natural Vegetative propagation – 

  • leaves of a plant may get detached and develop into new plants
  • bulbs, like daffodils, form lateral buds from the base of their mother bulb. From this, new smaller bulbs are produced.
  • rhizomes or root-like stems grow horizontally just below the soil’s surface. New roots form at the nodes, and the shoots grow upwards to form new plants. E.g. in root ginger and iris
  • tubers are underground, enlarged structures that store food. Small buds or ‘eyes’, like in potatoes, develop over the surface and produce shoots that grow in a new plant.
  • horizontal stems or runners grow above the ground, e.g. strawberry. Tiny plantlets crop up along the runners, and where they touch the ground, roots are formed. When the plant is matured, it breaks away from the parent.

In Artificial Vegetative propagation – 

  • Cuttings: A cutting or a piece is taken from the mother plant and made to grow into a new plant. For, e.g. root cuttings with buds are pressed into the soil, after which they produce new shoots.
  • Grafting and budding: A piece of the stem (grafting) or a single bud (budding), called a scion, is joined to a stem of the plant, called the rootstock. It is often used to produce fruit trees with more than one kind of fruit growing on the same stem.
  • In Tissue culture, fragments of plants are treated with hormones in a favourable growing medium. These hormones facilitate the growth of callus, from which a seedling grows. A large number of identical seedlings can be produced in this manner.

5. Regeneration: In organisms like Planaria and Hydra, it is observed that if you cut them in several pieces, each part will grow into a new organism. This process is known as regeneration.

6. Sporogenesis or Spore Formation: During an inadequate supply of food and moisture, knob-like structures are formed on an organism. This is called spore-formation. The structures begin to grow when the conditions turn favourable. The spores that develop into new organisms are enclosed within sporangia and are covered by thick walls. When they come in contact with moisture, they begin to grow—Eg. in fungi, algae, plants, etc.

  • Reproduction in Plants
  • Reproduction in Animals

Reproduction in Plants

Reproduction in plants takes place both sexually and asexually. A majority of the flowering plants reproduce sexually. The reproductive part of the plant is the flower. You have already studied the various parts of plants are – 

  • Petals
  • Sepals
  • Stamen (male reproductive part)
  • Pistil/Carpel (female reproductive part)

Stamen: Stamen is the male reproductive part that consists of the anther (a sac-like structure that produces and contains pollen) and filament (support for the anther).

Pistil: Pistil is the female reproductive part that comprises three components- stigma, style, and ovary.

  • Stigma is the topmost part of a flower.
  • The style is the long tube that connects the stigma to the ovary of the plant.
  • The ovary is the part where seed formation takes place. It contains many ovules.

When a flower contains either stamen or pistil, it is unisexual. E.g. papaya, watermelon. When a flower has both stamen and pistil, it is bisexual. E.g. hibiscus, mustard.

Pollination 

Reproduction in plants takes place via the process of pollination. The process of transferring pollen from the anther (male part) to the stigma (female part) is called pollination. 

It can occur in two ways:

  1. Self-Pollination: When the pollen transfer takes place between the anther and stigma of the same flower.
  2. Cross-Pollination: When the pollen transfer takes place between the anther and the stigma of different flowers of the same plant or different plants of the same species.

Usually, pollination takes place with the help of agents like insects, birds, wind, water, etc. These are called pollinators.

Fertilization

When the male gametes in pollen grains fuse with the egg in the ovule, a zygote is formed. This process of fusion is called fertilization. The zygote then divides and grows into an embryo, and later into a seed. The ovary becomes a fruit.

Reproduction In Animals

Sexual Reproduction in Animals

The process in which male and female gametes fuse to form a new individual is called sexual Reproduction. Let us see how the process of Reproduction takes place and what are the reproductive organs in males and females.

Reproductive Organs

The male reproductive organs include a pair of testes, sperm ducts, and a penis. The testes produce sperms, which are tiny and consist of a head, a middle piece, and a tail.

The female reproductive organs include a pair of ovaries, oviducts, and uterus. The ovaries produce the eggs or the ova. The development of the baby takes place inside the uterus. A mature egg is released into the oviduct every month.

Process of Sexual Reproduction in Animals

Fertilization

During sexual intercourse, the sperm enters the vaginal passage and reaches upwards in the oviduct, where it may encounter an egg. The nuclei of the egg and the sperm fuse to form a single nucleus. Thus, a zygote is formed. This process is called fertilization.

Development of Embryo

The fertilized egg or zygote divides many times to form a ball of cells, called the developing embryo. The cells then form different tissues and organs, and the embryo gets embedded or implanted in the lining of the uterus. This process is called implantation. The embryo gets nutrition from the mother’s blood with the aid of a special tissue called the placenta. When all the body parts of the embryo start being prominent, it is called a foetus. The child takes nine months to develop fully.

Reproduction is how the population can increase on the earth. The rate of birth and the rate of death determines the size of a population.

What are the types of Reproduction?

  1. Asexual Reproduction: In this process, a single parent divides to form new offspring that are genetically identical to itself. There is no fusion of sex cells or gametes.
  2. Sexual Reproduction: In this process, two parents with different genetic materials come together to form a zygote, and produce an offspring that is similar but not genetically identical.

What is Reproduction?

  • Reproduction is the process by which an organism, single-celled or multicellular, can produce biologically similar offspring. 

How does Reproduction happen?

  1. Asexual Reproduction happens when a single parent divides to form new offspring that are genetically identical to itself.
  2. Sexual Reproduction happens when two parents come together to form a zygote and produce an offspring that is similar but not genetically identical.

What does Reproduction mean?

  • Reproduction means a process by which both unicellular and multicellular organisms can produce biologically similar offspring and carry on the chain of life.

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High School Physics

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