Lesson 3 of 13 · 5 min
Quiescent stage and which cells divide
NCERT §10.1.1
Their grandfather, recovering from a heart problem, asks why heart muscle does not just grow back the way a cut on the skin heals. Diya takes the question to the cell cycle.
The lesson in notes
In short
Some cells of adult animals do not seem to divide at all, heart cells for example, and many others divide only now and then, to replace cells lost to injury or cell death.
Cells that stop dividing leave G1 and enter an inactive stage of the cycle called the quiescent stage, G0.
Cells in G0 stay metabolically active but no longer multiply, unless the organism needs them to and calls them back into division.
In animals, mitosis is seen only in diploid somatic cells. The exception NCERT names is the male honey bee, whose haploid cells divide by mitosis.
Plants, by contrast, can show mitosis in both haploid and diploid cells, as the alternation of generations in plants requires.
Plants keep growing all their lives because their meristematic tissues keep dividing, while most cells elsewhere in the plant do not.