why are oceans least productive?

Why are the tropical rain forests most productive?

Why is it necessary to excrete waste products?

Even though a very few cells in a C_4 plant carry out the biosynthetic - Calvin pathway, yet they are highly productive. Can you discuss why?

Even though each pollen grain has two male gametes, why are at least 10 pollen grains and not 5 pollen grains required to fertilise 10 ovules in a particular carpel?

What are chrysophytes? Why they are considered as the chief producers in the ocean?

Why are green plants not found beyond certain depth in the ocean?