animals which die with age, explain it biologically plzz?

Answer 1

The general deterioration of organs and tissues is one of the main issues. Bones become weaker, the immune system is less able to fight off infection, reactions get slower etc etc (see source below). If a pack animal become too old slow it may be shunned by the others and be left on its own where its chances of survival are further reduced.

There can be other reasons though too. For example some animals wear down their teeth as they feed and slowly produce more. There is not an infinite supply of tooth though! Eventually they will all be worn down and the animal will be unable to produce anymore and therefore will not be able to eat.

Hope that helps

Answer 2

The other answers have it basically right. The ultimate reason is probably that in a world of limited resources, after we have some number of kids there really isn't any compelling reason for us to put energy and effort into body maintenance. So pieces of us start breaking down faster and faster until something critical fails, at which point we die.

Answer 3

As anything ages, its organs get slower and slower, There body makes more mutated genes, which causes different diseases.
A Human body as an average age of about 80-100 years. After that organs start failing. Body is a machine and has its limits.