How do Organisms Reproduce? | Class 10 CBSE | Web Notes | Part 2 - Modes of Reproduction Used by Single Organisms

MODES OF REPRODUCTION USED BY SINGLE ORGANISMS

The modes of reproduction by various organisms depend on their body design.
Creation of new generations from a single individual is called asexual reproduction.
Types of asexual reproduction: Fission, fragmentation, regeneration, budding, vegetative propagation, and spore formation.

It is the cell division of unicellular organisms to form new individuals. E.g., many bacteria and protozoa.
It is of two types: Binary fission and Multiple fission.

In this, the parent cell divides into two daughter cells. E.g., Amoeba, Leishmania.
In Amoeba, binary fission takes place in any plane.
Some unicellular organisms have complex body organisation. E.g., Leishmania (cause kala-azar), have a whip-like structure. Here, binary fission occurs in relation to these structures.

In this, some single-celled organisms divide into many daughter cells. E.g., Plasmodium (malarial parasite).

In this, an organism simply breaks up into smaller pieces (fragments), and they grow into new individuals. E.g., Spirogyra (greenish, filamentous multicellular structures seen in ponds or lakes).
All multicellular organisms cannot simply divide cell-by-cell because the cells are organised as tissues and organs. Here, different cell types perform different functions. So, reproduction is also performed by a specific cell type. It can grow, proliferate, and make other cell types.

In this, a differentiated organism is cut into many pieces, and they grow into separate individuals. E.g., Hydra and Planaria.
During regeneration, some specialised cells proliferate to form a cell mass. From this, different cells develop to form various cell types and tissues.
However, regeneration is not the same as reproduction, since most organisms do not normally depend on regeneration for reproduction. Also, many organisms use this only to regenerate lost parts.

In this, a new organism is developed from a small part of the parent’s body. E.g., Hydra, Yeast, etc.

Dissolve about 10 gm sugar in 100 mL of water.
Take 20 mL of this solution in a test tube and add some yeast granules. Put a cotton plug on the mouth of the test tube and keep it for 1–2 hours in a warm place.
Put a drop of yeast culture from the test tube on a slide and cover with a coverslip. Observe under a microscope. We see yeast reproducing by forming buds.
Organisms such as Hydra use regenerative cells for budding. In Hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. Buds develop into tiny individuals and, when fully mature, detach from the parent body and become new individuals.

In this, plant parts like roots, stems, and leaves develop into new plants under appropriate conditions.

It is used in layering or grafting to grow plants like sugarcane, roses, or grapes for agricultural purposes.
Plants raised by this method can bear flowers and fruits earlier than those produced from seeds.
Seedless progenies can be produced. E.g., banana, orange, rose, jasmine, etc.
All plants are genetically similar to the parent plant.

Cut a potato into small pieces such that some pieces contain a notch or bud and some do not.
Place them on some wet cotton on a tray.
After a few days, potato pieces with buds give rise to fresh green shoots and roots.

In Bryophyllum, buds produced in the notches along the leaf margin fall on the soil and develop into new plants.

It is a method of growing tissues or cells from a plant in an artificial medium. Cells are divided rapidly to form a callus (a small group of cells). It is transferred to another medium containing hormones for growth and differentiation. Then, the plantlets are placed in the soil. They grow into mature plants.
Thus, many plants can be grown in disease-free conditions. This technique is commonly used for ornamental plants.

It is present in organisms like bread mould (Rhizopus).
Keep a slice of wet bread in a cool, moist, and dark place.
Observe it for a week.
A layer of white mass of thread-like structures is seen on the slice. It is the hyphae of Rhizopus.
Hyphae include some blob-on-a-stick structures. They are involved in reproduction. The blobs (sporangia) contain cells (spores) that can develop into new Rhizopus.
Spores are covered by thick walls that protect them until they come into contact with a moist surface and can begin to grow.

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