Q.What is the average cell cycle span for a mammalian cell?

A mammalian (human) cell growing in culture completes one full cell cycle in about 24 hours on average.

• This is only a typical figure, not a fixed rule.
• The duration varies from one organism to another and even between different cell types in the same organism.
• Of these 24 hours, the actual division (M phase) takes only about one hour, while interphase occupies more than 95 per cent of the time.
• By comparison, a yeast cell can finish an entire cycle in roughly 90 minutes.

The cell cycle is the ordered sequence of events by which a cell grows, copies its genome and finally splits into two daughter cells. A convenient way to measure how long this takes is to study human cells grown in culture, because they divide in a fairly regular manner.

Such cells complete one full cell cycle in about 24 hours on average. It is worth being clear about what this figure does and does not mean:

• It is an average value, not a constant for all life. The length of the cycle differs from one organism to another, and even different cell types within the same organism can take different amounts of time.
• Yeast cells, for instance, run through an entire cell cycle in only about 90 minutes, which is far quicker than a human cell.

Method 1 — Identifying the average cell cycle span

1. Recall that the question asks for a TYPICAL/AVERAGE duration, not an exact universal constant — cell-cycle length varies by organism and cell type.
2. The standard reference point used in NCERT biology is a MAMMALIAN CELL GROWN IN CULTURE, since these divide regularly enough to measure.
3. Such a cell completes one full cycle (Interphase + M Phase) in about 24 hours.
4. Break that 24 hours down: M Phase (the visible division) takes only about 1 hour; Interphase (G1+S+G2, the growth/DNA-replication/preparation phase) takes the remaining time — over 95% of the cycle.
5. State the answer with this context: about 24 hours on average, of which ~1 hour is division and the rest is interphase.

[!ANSWER] About 24 hours for a mammalian cell in culture.