Question

What will happen if you are provided with root-tips of onion in your class and are asked to count the chromosomes, which of the following stages can be observed easily?
A. Telophase
B. Anaphase
C. Prophase
D. Metaphase

Answer 1

Hint: Division of cells refers to the formation of two or more than two cells from a single cell. Cell division can be easily observed in the root tip cells of onion. Chromosomes divide during the division phase of the cell cycle. The chromosomes are at their maximum condensation during the metaphase because they are maximum thick and visible here.

Complete answer: The phases of the M-phase are as follows:
a. Prophase: It is the longest phase. The nuclear membrane and nucleolus gradually disappear. Chromosomes condense and become short and thick. They are easily visible. Each chromosome breaks into two parts longitudinally and both the parts are closely packed. The centriole pairs move towards the opposite poles and astral rays formation starts.
b. Metaphase: Chromosomes attain maximum condensation here. Both the chromatids separate except at the centromere. All the chromosomes arrange on the equatorial plate. The astral rays further grow and attach with the centromere of each chromosome from both sides. As the chromosomes are at their maximum condensation here, so this is the best stage for chromosomal study. This is because they are maximum thick here and hence best visible.
c. Anaphase –
It is the shortest phase. During anaphase, there is a shrinkage in the traction fibers. This generates a pulling force. This in return breaks the chromosome into two chromatids. These chromatids gradually move towards the opposite poles. In this phase, the shape of the chromosomes is studied. The chromosomal decondensation is maximum here.
d. Telophase –
In telophase, the chromatids of both the sides finally reach the opposite poles. The chromosomal decondensation continues. The nuclear membrane and nucleolus gradually reappear. The astral rays disappear. And finally, two nuclei are formed in a cell.
Hence, the correct answer is option (D).

Note: The process of cell division has two parts. These are karyokinesis and cytokinesis. The karyokinesis the division of the nucleus whereas the cytokinesis is the division of the cytoplasm. The karyokinesis comprises of the following four stages in the order –
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase