Question

Human cells in cell culture show a cell cycle to be completed in approximately
(a) 48 hours
(b) 24 hours
(c) 24 minutes
(d) 24 seconds

Answer 1

Hint: A growing and dividing cell passes through a definite cycle of events, known as the cell cycle. Interphase forms nearly ninety percent of the duration of the cell cycle.

Complete answer:
Cell division is the process by which a cell divides to form two equal daughter cells that resemble the parent. The cell cycle is the sequence of events that occur during cell growth and cell division. It represents the orderly and cyclic sequence of events, processes, and phases between two successive cell divisions. It is completed in two steps; interphase and M- phase.
In the cell cycle interphase is the period between the end of one division to the beginning of the next cell division. It is known as the resting phase. In the case of human beings, it is around 24 hours then the M phase takes place.

Additional Information:
- During cell division, the cellular material gets exactly doubled and almost equally distributed between the incipient daughter cells.
- The length of the cell cycle varies with different kinds of cells. The cell cycle involves coordinated marshaling of several cellular events.
- Some of them are continuous and some are discontinuous. Cell division is always coordinated with cell growth and DNA duplication.
So, the correct answer is '(b) 24 hours'.

Note:
- Eukaryotic cell cycle involves five major events; centrosome cycle, chromosomal cycle, nuclear cycle, cytoplasmic cleavage, and cell duplication.
- A standard eukaryotic cell cycle consists of four non- overlapping linear phases namely ${ G }_{ 1 }$, S,${ G }_{ 2 }$, and M. ${ G }_{ 1 }$ and ${ G }_{ 2 }$are the first and second gap phases during which DNA synthesis does not occur.
- A is the synthetic phase, characterized by active DNA synthesis. M is the mitotic phase of the division phase during which the cell division occurs. ${ G }_{ 1 }$, ${ G }_{ 2 }$ and S collectively represent the non- dividing phase of the cell cycle, often called interphase.