What is the primary role of the respiratory system in living organisms?
a. to make carbon dioxide
b. to obtain oxygen
c. to use up nitrogen
d. to find hydrogen

In addition to seeds, which of the following characteristics are unique to the seed-producing plants? a) sporopollenin b) lignin present in cell walls c) pollen d) use of air currents as a dispersal agent e) megaphylls

Pl as time goes by and water goes through the water cycle again and again, the amount of water on earth: increases decreases ostays the same goes up and down

Is genetic diversity the same as genetic variation?