The ultimate purpose of a living organism is to be happy. Most do that by not starving and being alive. Humans are a little complex. Everybody’s looking for something.
That’s an interesting view. I’m not entirely sure what you mean by purpose though. Regardless of what exactly you mean though, why would it be the purpose of a plant or animal to be happy? Aren’t animals the product of a process that selects for survival, not happiness? What gives them this purpose?