It's some change in the conditions around the organism, which the organism can detect and respond to. A change in temperature, more light, or something physically poking the organism are examples.
A high biodiversity tally may indicate that some of its organisms may be able to survive drastic environmental changes. If there weren't at least a few organisms that contribute to biodiversity, most of the biotic Earth would be gone by now.
For example, woolly mammoths were unable to adapt to the up-and-coming warmth of the poles. Because they lacked biodiversity among their species, all of them died out and weren't able to adapt to the heat.
I hope I helped!
That's a component of a phospholipid, which is a lipid.
