How Do Organisms Reproduce? - 1

The thread-like structures on which sporangia develop are called hyphae. Their scientific name is sporangiophore.

Disease-free plants can be produced by tissue culture. In this technique, we can take few healthy cells and selectively multiply them to form new plants under sterile and aseptic conditions. But, in grafting or layering or cutting, the chances of having diseased plants are there because the cells cannot be selectively chosen in these and at any time, the pathogens may attack them.

Vegetative propagation means formation of new plants from vegetative parts.

We know that apple, pear and peach have seeds. It is only banana that is seedless and has lost the capacity to produce seeds. In case of apple, the ability to produce seeds is there but they may not be viable.

Binary (Bi means two) fission produces only two daughter cells and occurs repeatedly, generation after generation, in short time intervals. This fast reproduction is possible only under favourable conditions of temperature, food and humidity. But under unfavourable conditions like high or low temperature, low humidity or lack of food, multiple fission occurs.

On being cut, the two parts of hydra can regenerate the other part because it is a simple organism. Bud also helps it in reproduction, but on being cut, regeneration ability plays the role. The two parts cannot be two individuals unless they regenerate. Lastly, hydra does not produce spores as it reproduces by budding.

Regeneration is carried out by specialized cells, which can proliferate at a fast rate. Also, they can form all the different cells that are required to form the body part that the organism needs to regenerate. Broken cells may not proliferate while “all cells” cannot have the above mentioned specialized features. Differentiated cells take up a fixed role and may not be able to produce all the cells required in regeneration.

To develop a whole body from a fragment is possible by proliferation (i.e. repeated division and consequent growth) of cells. This is called regeneration. On the contrary, in budding, a complete organism forms a new individual from a bud, and in fission, the cells divide into two. Fusion is said to occur when two cells combine to mix their traits (like in bacteria) and it is uncommon.

Spores are the microscopic structures formed during the life cycle of many fungi. Each spore, upon falling on suitable substratum (medium on which an organism depends for deriving its food), grows into a complete organism, which can later divide and form a complete colony. Spore-bearing structures are called sporangia and they are present on stalks called sporangiophores.
Capsules refer to dry and indehiscent fruits. When they split, seeds fall out from them.
Cysts are hard covered bodies formed under unfavourable conditions in bacteria and they produce daughter cells, and not spores. Similarly, buds also do not bear spores as buds are bulging outgrowths of the parent body which, after maturation, detaches itself from the parent body and develops into a new individual. Buds and spores are two different means of asexual reproduction.

Leishmania has a specific organisation of body. It has a whip-like flagella on one end. Due to this, when its fission occurs, it divides the body such that both get the flagella (duplicated). This is possible in binary fission, but not in multiple fission, which will require the division to occur in different planes.

Plasmodium grows rapidly inside a human body and for this, it divides by multiple fission because binary fission will produce less number of organisms. Since it is a unicellular organism, so regeneration and spore formation do not occur in Plasmodium.

Sexual reproduction involves two parents and their gametes fuse to form a new individual. Thus, formation of gametes is a part of sexual reproduction. Fission, regeneration and spore formation are all asexual methods of reproduction.

Ornamental plants are very delicate and some of their features make them valuable. It is desired that during their propagation, there should be no change in those traits and also they should remain free from any disease. Both these requirements are met by tissue culture technique. In addition, it helps to produce a large-scale commercial yield. Budding, fragmentation and regeneration cannot serve all these purposes together because they are slow and cannot ensure disease free progeny.

Asexual reproduction involves only one parent and its cells divide by mitosis (without any change in chromosomes number). Thus, there is no change in genetic makeup of new cells, and the offsprings are identical to parents. Since this method of reproduction involves simple cell division (without any change in number or traits of chromosomes), so it is faster than sexual method. Thus, here only option (3) is incorrect.

Multiple fission, regeneration and spore-formation, all require the formation of a large number of new cells by repeated division of initial or few cells. But in binary fission, only one division occurs and produces two daughter cells. Thus, binary fission is the fastest mode of reproduction. In fact, cells are known to produce daughter cells in twenty minutes of time from their own birth by binary fission.

At the cellular level, reproduction refers to the formation of new cells. It can occur, if a new cell gets nucleus and nucleus contains DNA molecules. DNA is the genetic material, which is passed from one generation to another.
Thus, for reproduction, DNA material is to be duplicated. Hence, DNA is the biochemical basis of reproduction. On the contrary options (1), (2) and (3), which refer to different cells like RBC, WBC and neuron have no role in the process of reproduction.

The leaves of Bryophyllum plant help in vegetative propagation. The notches of these leaves contain vegetative buds, which can grow to produce roots and small shoots that later make a new plant. Its roots, stem or flowers have no such vegetative buds to take part in the reproduction process.

'Bread molds' are a type of fungi and reproduce by spore formation. In asexual reproduction, the mold makes spores inside a sporangium. When the spores are ready to leave and spread more molds, the sporangium breaks open and lets the spores float out. In sexual reproduction, its hyphae touch the hyphae of another Rhizopus mycelium. When they fuse, they make round balls called zygospores. After some time, the zygospore makes another sporangium, which then makes spores. During this sexual process, genetic recombination takes place, as with all eukaryotes. 

Higher plants have complex structures and they have specialised parts to perform asexual (vegetative) reproduction. For example, leaves, stem, roots, etc. This formation of new organism from vegetative parts of a plant is called vegetative propagation. On the contrary, spore formation, budding and regeneration are reproductive methods found in lower organisms or plants.

An unorganized mass of cells is called callus. When it is treated with suitable hormones, it forms tiny root and shoot, which are called rootlet and shootlet, respectively. At this stage, it is called a plantlet.