A banyan tree keeps spreading and thickening for hundreds of years.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A banyan tree keeps spreading and thickening for hundreds of years. Rekha is years old, and she stopped growing taller at , yet her skin and blood cells are still being replaced. Explain both facts.
Need a reminder? The key ideaShow
Growth is an increase in mass and in the number of cells. A living thing grows from inside, by cell division; a non-living thing grows only by material added on its outside. Plants grow all their life, animals up to a certain age. In a one-celled organism, growth and reproduction are one event: after divisions, one cell gives .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The tree. In a plant, cell division goes on in some tissues all through its life, so the tree keeps getting taller and wider.
Step 2. Rekha's height. In animals, growth in size happens only up to a certain age.
Step 3. Her new cells. Cells still divide in some tissues to replace cells that are lost, such as skin and blood cells. This keeps her body the same size; it does not make it bigger.
Answer: plants grow all their life; animals grow up to an age, but they keep replacing lost cells.
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