Which of these valves prevents a backflow of blood into the left atrium?
aortic valve
tricuspid valve
mitral valve

If many different species live in an ecosystem, this the ecosystem to fill its a. populations b. niches c. producers d. communities

Which of the following is the best definition for the process of photosynthesis? a.) plants digest sugars to make energy. b.) plants use oxygen and glucose to make carbon dioxide. c.) plants use sunlight and carbon dioxide to make sugars. d.) plants use sunlight to make chlorophyll and chloroplasts.

How does the carbon cycle involve an exchange of carbon