Question

Cell division is a continuous process. Explain?

Answer 1

Hint: Cell division is the means of reproduction in unicellular organisms whereas it is the means of tissue growth and maintenance in multicellular organisms. In adults, cell divisions are involved in renewing old tissues rather than growth. Therefore millions of cells undergo continuous replacement at the same time in our body.

Complete answer:
Cell division is known to be a process through which a parent cell divides. There are several types of cell division that are known to us and vary among different types of organisms. Organisms have evolved over a period of time to develop different and more complex forms of cell division.
Most prokaryotes, basically bacteria, use binary fission for reproduction. This includes the division of the parent cell into two cells or daughter cells and these daughter cells in turn divide during their adult stage. On the other hand, eukaryotes of all shapes and sizes use mitosis to divide. In this, a cell undergoes division to divide into two cells that are replicas of each other and have the same number of chromosomes. This type of cell division is good for basic growth, repair, and maintenance(refer to the image below for various stages in mitosis). Eukaryotes which have the ability to reproduce sexually rather use a special form of cell division called meiosis or reduction division. In meiosis cell division a cell divides into four cells that have half the number of chromosomes and this provides genetic diversity.

Additional information:
The skin cells in our body are constantly being sloughed off and replaced but the mature differentiated cells do not divide in this particular case. Their population is renewed by the division of immature stem cells only. But on the other hand, certain other cells, such as those found in the liver, mature cells remain capable of division to allow growth or regeneration after injury.
In contrast to the specific patterns exhibited by normal cells, other different cells are sometimes incapable of division or are stopped from dividing by certain molecules produced by surrounding cells. As a result of this, some tissues have a greatly reduced capacity to renew damaged or diseased cells mainly in the adult stage. Examples of such types of tissues include heart muscle cells, nerve cells of the central nervous system, and lens cells in mammals. Therefore, the maintenance and repair of these types of cells are limited.
So, mainly mitosis helps us grow while meiosis makes us all look unique.

Note:
External factors can influence cell division, and depends on:
-Availability of raw materials can affect cell division. If not enough raw materials are present then cell division may not take place.
-Radiation can change DNA molecules which will result in a modified DNA sequence.
-Toxins can damage cell DNA.
-Viruses
-Drugs