Must all ecosystems have quaternary consumers? why or why not?

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?

Contrast how pollination is different among gymnosperms and angiosperms.

The embryos of a bird, a reptile, and a mammal are similar in appearance. how does comparing the physical appearance of embryos of different species support the theory of evolution? a. it shows that these organisms share a common ancestor. b. it provides evidence that these organisms eat the same foods.c. it shows that these organisms share the same habitat.d. it provides evidence that these organisms suffered a genetic mutation.