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Asexual Reproduction, Reproduction in Organisms (12th, Biology, Lesson-1)

In this method, a single individual (the parent) is capable of producing offspring. In many animals, for the process of reproduction, impregnation i.e. the meeting of sperm with the egg is necessary, but there are some such organisms in which reproduction takes place without impregnation, it is called parthenogenesis either asexual reproduction also say.

 जीवों में जनन (12th, जीव विज्ञान, Lesson-1) 

As a result, the offspring that are produced are not only identical to each other, but also exact copies of their parents. Are these offspring likely to be genetically identical or different? The term clone is used in such morphological and genetic variant It is used to describe similar individuals.

Asexual Reproduction, Reproduction in Organisms (12th, Biology, Lesson-1)

Let us see how widespread asexual reproduction is among different groups of organisms. Asexual reproduction is common in single-celled organisms and in plants and animals with relatively simple organisations. In protists and monerans, the organism or parent cell divides in two by mitosis to give rise to new individuals (Figure 1.2). Thus, cell division itself is a mode of reproduction in these organisms.

Figure 1.2 Cell division in a unicellular organism: (a) Budding in
yeast; (b) binary fission in amoeba

Many single-celled organisms reproduce by binary fission, where a cell divides into two halves and each rapidly develops into an adult (eg, amoeba, paramecium). In yeast, division is uneven and small buds are produced that are initially attached to the parent cell, which eventually detach and mature into new yeast organisms (cells). Under adverse conditions the amoeba withdraws its pseudopodia.

and secretes a three-layered hard covering or cyst around itself. This phenomenon is called NCStation. When favorable conditions return, the amoeba divides by several fragments and produces several minute amoeba or pseudopodiospores; The wall of the cyst ruptures, and the spores are released into the surrounding medium to form many amoebas. This phenomenon is known as sporulation.

Members of the kingdom fungi and simple plants such as algae reproduce through specialized asexual reproductive structures (Figure 1.3). The most common of these structures are zoospores which are usually microscopic motile structures. other normal asexuals reproduction The structures are conidia (penicillium), buds (hydra) and gemules (sponge). You have studied about vegetative reproduction in plants in Class XI. What do you think – is vegetative reproduction also a type of asexual reproduction?

Why are you saying this? Does the term clone apply to the offspring produced by vegetative reproduction? While in animals and other simple organisms the term asexual is used explicitly, in plants, the term vegetative reproduction is often used. In plants, units of vegetative propagation such as runners, rhizomes, suckers, tubers, offsets, bulbs are all capable of giving rise to new offspring (Figure 1.4). These formations are called vegetative propagation.

Obviously, since no two parents are involved in the formation of these structures, the process involved is asexual. In some organisms, if the body is broken down into separate pieces (fragments), each fragment develops into an adult capable of producing offspring (eg, hydra). This also asexual reproduction There is a mode of this called fragmentation. You must have heard about the plight of water bodies or ‘Terror of Bengal’. This aquatic plant is nothing but ‘Water Hyacinth’, which is one of the most invasive weeds to grow wherever there is standing water.

It removes oxygen from the water, which kills the fish. You will learn more about this in chapters 13 and 14. You might find it interesting to know that this plant was introduced to India because of its beautiful flowers and the shape of the leaves. Since it can spread vegetatively at an unprecedented rate and spread throughout the water body in a short period of time, it is very difficult to get rid of them.

Do you know how plants like potato, sugarcane, banana, ginger, dahlia are cultivated? Have you seen small plants emerge from the buds (eyes) of potato tubers, from the rhizomes of bananas and ginger? When you try to carefully determine the place of origin of new plants in the plants listed above, you will see that they always arise from nodes present in the modified stems of these plants. When the bales come into contact with moist soil or water, they root and produce new plants.

Similarly, apical buds emerge from the grooves on the margins of the leaves of Bryophyllum. This potential is fully utilized by gardeners and farmers for commercial propagation of such plants. It is interesting to note that asexual reproduction is the common mode of reproduction in organisms that have relatively simple organizations such as algae and fungi and they occur just before the onset of unfavorable conditions. reproduction are transferred to the sexual method. Find out how sexual reproduction enables these organisms to survive in adverse conditions. Why is sexual reproduction favored in such circumstances? Asexual (vegetative) as well as sexual modes of reproduction are exhibited by higher plants. On the other hand, only sexual mode of reproduction is present in most of the animals.

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