Q1.
When you get a small cut on your skin, it heals after a few days. When hair fall out, new hair grow back. How does this happen?
Answer
Because cells in the body grow and divide to replace old, dead or damaged cells.
damaged cell removed
→ nearby healthy cell copies its DNA
→ divides by mitosis into 2 identical daughter cells
→ new cells fill the gap and the wound closes
→ nearby healthy cell copies its DNA
→ divides by mitosis into 2 identical daughter cells
→ new cells fill the gap and the wound closes
- Skin cells and the cells at the base of a hair follicle divide continuously, because these tissues are worn away all the time.
- The daughter cells are genetically identical to the parent, so the new skin is real skin and the new hair is the same kind of hair.
- Division stops once the gap is filled and the new cells touch their neighbours — this is contact inhibition.
Why it happens: notice what growth is not. Our body does not grow because cells swell up; a cell can grow only up to a certain size, because beyond it the membrane's surface area cannot supply the volume inside. Growth and repair therefore happen by making more cells, not bigger ones. Roughly a few hundred billion cells — about 1 per cent of all the cells in the body — are replaced every single day.
Did you know? Cells that divide constantly are also the ones most affected by treatments that block cell division. That is why chemotherapy, which targets rapidly dividing cells, often causes hair loss.