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- Reproduction is the biological process by which new individual organisms (offspring) are produced from parents.
- The ability to produce offspring or new individuals of the same species through a sexual or asexual process is an important characteristic of all living beings. A new individual normally goes through a period of growth and development before it reaches a stage when it can reproduce.
Necessity of Reproduction:
- All living thing eventually die. They may be killed by other organisms (predators) or may die of diseases or old age.
- To perpetuate their species individuals produce new ones of their own kind before they die.
- This ensures the continuity of life, unbroken from generation to generation.
Types of Reproduction:
- There are two basic types of reproductions, namely asexual and sexual.·
- Asexual reproduction is a process in which the organism reproduces on its own without the help of another individual. There is only a single parent. No gametes are involved. Usually, asexual reproduction takes place when there is plenty of food available and condition are good for growth.
- Sexual reproduction is a process in which two parents, a male and female, are needed to produce a new individual. In this process male gamete from the male parent and female gamete from female parent fuse together to produce offspring.
- Amoeba is a single-celled organism found in water and in moist soil on land or can also be found as a parasite of other organisms.
- It reproduces by splitting into two.The process by which an organism reproduces by dividing into two cells from a single cell is called binary fission.
- In this process, the nucleus splits or divides into two and then the cells split across the middle forming two identical cells. These are the two new daughter cells.
- Paramecium also divides by binary fission.
- Yeast is a single-celled organism.
- It reproduces by sending a small outgrowth from the cell, called a bud. The nucleus of the parent cell divides into two and one is sent into the bud. The bud grows and eventually separates from the parent cell.
- Sometimes the new cells start budding before it has broken away from the old cell, giving rise to a chain of cells.
- Hydra is a multicellular organism that reproduces by budding.
- A new Hydra grows out from the side of the parent body. It develops tentacles and a mouth and eventually breaks away from the parent body and becomes a separate individual.
- Mushrooms, moulds, ferns and mosses reproduce by this method.
- They produce tiny spherical cells called spores that develop into new individuals.
- Spores are light and hence can float in the air. They have thick wall due to which they can withstand unfavourable conditions. Under favourable conditions, spores develop into the new plants.
- In mosses and ferns, the spores are produced inside special structures called capsules.
Spores of Fern
Spores of Mosses
- In this method, the parent body breaks into pieces and each piece can grow into a new individual. Starfish with a portion of a central disc can regenerate and become entirely new starfish.
- Regeneration also take place in planaria, in which even the posterior part of the animal regenerates a head to produce a new planaria.
Regeneration in Star Fish
Regeneration in Planaria
- This type of reproduction takes place in some lower plants such as spirogyara and animals such as flatwarms and sponges.
- The mature organism break up into two or more pieces or fragments. The fragments grow into complete organisms.
- In many plants the vegetative parts like root, leaf or stem may grow into new plants. The new plant comes from a single parent plant and is the same as the parent.The method of reproduction through vegetative parts is called vegetative propagation or vegetative reproduction.
In some plants the main plant may send out a side branch or runners from which roots grow down into soil. In this method the stem lengthens and creep along the ground and forms roots at intervals thus giving rise to new plants. When the new plant develops completely, the parts joining the new plants wither away, e.g. strawberry and some species of grass.
By underground stem:
Some plants store food in their organs like stem, leaves, roots. These plants develop non-green, under ground perennial stems. e.g. bulbs (onion, gladiola); rhizome (ginger); or underground stem tuber (potato). They store starch during the summer months. These plants give rise to aerial shoots that growduring favourable conditions. During unfavourable conditions, the aerial shoots die and the underground stems remain dormant. Once the conditions become favourable, they produce new aerial shoots. They produce new plants the following year. These organs asexually reproduce new plants year after year and so are called perrenating (through the year) organs.
In plants such as carrot, turnip and radish, the taproots may become swollen with food. These plants are biennial plants they grow vegetatively during the first year and store food. In the second year of growth, they produce flowers and seeds, at the end of which they die. Buds present at the base of the old stem just above the taproot act as organs of perennation and vegetative propagation.
In Bryophyllum, new plants are produced from leaves, which have buds on their margins. These buds give rise to new plants.
Advantages of Vegetative propagation:
- As the new generation produced by asexual reproduction is exactly same as the parent (clone), the good qualities of a race or variety can be preserved indefinitely. With other methods there may be blending of characters in next generation.
- Plants grown this way require less time mature than those grown from seeds.
- In their early stages of growth, plants developed by vegetative reproduction usually need less attention than plants grown from seeds.·
- If plants have poor viability or prolonged seed dormancy, then vegetative propagation is a rapid, easier and a less expensive method of multiplying plants.
- When due to new soil and new environmental conditions, the seed germination fails then vegetative propagation is the best wave to cultivate.
- This method is useful for the plants which produce less number of seeds. e.g. Bermuda grass.
- Banana, seedless grapes, oranges, rose and jasmine have lost their seeds producing capacity. They can be multiplied by vegetative propagation only.
- There uniformity in crops grown by this method, and they flower and fruit simultaneously in the entire field.·
Disadvantages of Vegetative propagation:
- It leads to overcrowding.
- Due to lack of genetic variation, the adaptability of plants to the environment is limited and so they gradually lose vigour and become prone to diseases.
Asexual Reproduction in Plants : Artificial Methods
Artificial vegetative propagation:
- Vegetative methods offer many advantages. As the new generation produced by asexual reproduction is exactly same as the parent (clone), the good qualities of a race or variety can be preserved indefinitely. If plants have poor viability or prolonged seed dormancy, then vegetative propagation is a rapid, easier and a less expensive method of multiplying plants.
Methods of Artificial Vegetative Propagation Used in Agriculture and Horticulture:
- The process of growing plants using artificial method is called artificial propagation.
- In this method a young branch is bent and pressed into moist soil. After some time roots develop from the covered part. This is called a layer.
- Now the branch can be cut from the parent and a new plant is produced .
- This method is used to propagate plants such as jasmine, black raspberries.
- In this method a healthy young branch with a few nodes and internodes is cut off and most of its leaves are removed.
- Now the cut end is stuck into some good moist soil. Care is taken that the soil remains moist. The cutting will then develop roots, and grow into a new plant.
- This method is used to propagate plants like rose, sugarcane and pineapple.
- This is a common method employed in horticulture to develop new varieties.
- It involves removing a twig or bud of plant (called the scion) and inserting or tying it over the cut stem of another plant (called the stock). The stock should have an extensive root system under the soil.
- The two cut surfaces are bound together and the joint is covered with wax to prevent evaporation and to stop infection. The tissues of the stock and scion join together to form one plant, During this process the stock supplies essential nutrients to the scion.
- By this method desirable features of any two plants can be combined.
- For example a high-yielding variety of a fruit is grafted to another of the same species for known for its resistance to diseases, to get a disease resistant, high-yielding variety.
- Many varieties of mango (Alhanso), for example, are produced by grafting.
- This is a modern method of vegetative reproduction.
- In this method a piece of tissue is cut from the plant the removed tissue is called explant. The explant is kept in nutrient medium under controlled condition. This tissue grows into mass of cells called callus. Cells of callus are separated and each cell can give a new plant. These cells are called plantlets. Now the plantlets are grown in pot of soil.
- Plants like chrysanthemum and orchids have been propagated by this method.
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