Question

Karyoplasmic index (KI) is
a. $\dfrac{{Vn}}{{Vn - Vc}}$
b. $\dfrac{{Vn}}{{Vc - Vn}}$
c. $\dfrac{{Vc}}{{Vn}}$
d. $\dfrac{{Vn}}{{Vn + Vc}}$

Answer 1

Hint: The karyoplasmic index deals with the relationship between the size of the nucleus and the size of the cell.

Complete answer:
The karyoplasmic index deals with the relationship between the nucleus size and the cell size. So, here the answer will be $\dfrac{{Vn}}{{Vc - Vn}}$.

We know that growth and reproduction are fundamental characteristics of all living cells. All living cells divide to produce daughter cells. These daughter cells again divide and the division goes on and on. Two types of cell division occur in an organism, that is, mitosis (it produces two diploid daughter cells) and meiosis (it produces four haploid daughter cells).

Mitosis was proposed by Walther Flemming in 1882. It was seen that two daughter cells that were produced after the mitotic division were identical to the mother cell as well as to each other. As a result, two causes for the occurrence of mitosis were recorded. The first one was the kern-plasma theory and the second one was the surface volume ratio.

The kern plasma theory was given by R. Hertwig in 1903. According to this theory, the process of mitosis occurs due to the disturbance in the karyoplasmic index. In other words, a definite relation as to size normally exists in every cell between the mass of nuclear material and that of cytoplasm.

The karyoplasmic index is given by a formula,
$KI = \dfrac{{Vn}}{{Vc - Vn}}$
Where,
Vn is the volume of the nucleus
Vc is the volume of cell
Vc-Vn is the volume of cytoplasm

It is seen that the karyoplasmic index of the small cell is high as they have less cytoplasm. This means that the nucleus controls the activity of cytoplasm in the small cell very effectively but in the case of a large cell, the nucleus cannot control the activity of cytoplasm which causes a disturbance in the karyoplasmic index and as a result, the cell divides into two daughter cells.

Hence option B is the right answer

Additional information:
The nuclear-cytoplasmic ratio, that is, the N:C ratio is the ratio of the size of the nucleus of a cell to the size of the cytoplasm of that cell. This ratio tells us about the maturity of the cell because as the cell matures the size of its nucleus decreases. In addition to that, an increase in this ratio also tells us about cancer cells (as the increased ratio means that the cell is dividing rapidly).

Note: The nucleus is responsible for the entire metabolism of the cells. To ensure efficient metabolism, the equilibrium between the surface area and the size of the cell and between the size of the nucleus and volume of the cytoplasm should be maintained.