Because a food chain is based on one certain thing in the ecosystem ....if the entire ecosystem was in it it would be a food web which is food chains from an ecosystem linked together
Hope that helps
Species change over time. -The mechanism that produces the change is natural selection: the differential survival and reproduction of individuals based on variation in their traits. Natural selection acts on individuals but individuals do not evolve; their descendants do.
Till this day We are always learning more and more so I think this can be helpful for future vaccines of diseases
I can answer when you say if you are talking about cells or no