Cell Cycle and Cell Division Test - 5

Cell growth results in disturbing the ratio between the nucleus and the cytoplasm. It therefore becomes essential for the cell to divide to restore the nucleo-cytoplasmic ratio. Cell becomes stable when N/C ratio is 1.

Mitosis is called equational division. Since the parent cells are haploi so mitosis will lead to restoration of chromosome number in haploid cells.

Since, in mitosis the number of chromosomes in the parent and progeny cells is the same, it is also called as equational division.

In plant cells, wall formation starts in the centre of the cell and grows outward to meet the existing lateral walls. The formation of the new cell wall begins with the formation of a simple precursor, called the cell plate which hardens to give rise to middle lamella.

The middle lamella cements the tertiary walls of two adjacent plant cells. It is formed out of materials of cell plate.

Astral body are formed of microtubules. Astral bodies are produced by centriolar division proir to start of  during cell division and attach with centromere of the chromosome during.

In plant cell, mitosis cell division is generally controlled by cytokinin hormone. It increase the rate of cell division leading to increased cell production. Auxinis also required for cell division in plant.

During mitosis ER and nucleolus begin to diappear at late prophase stage indicated the beginning of next phase. It happens due to increased divisional activities of nucleus.

In animal cell, cytokinesis takes place by furrow which appears at the margins of plasma membrane and gradually deepens towards the central part of the cell. Ultimately the furrow divides the cell into two halves. This method of cytokinesis is known as cleavage cytokinesis.

Colchicine is an alkaloid used in plant breeding for doubling of chromosomes by inhibiting cytokinesis. It is also called as mitotic poison. It is extracted from the bark of plant belonging to genus Colchicum.