Which gas makes up 78 percent of our atmosphere? It can be used by plants only when transformed by bacteria or lightning. oxygen
nitrogen
hydrogen
carbon

Biomass can be used to generate electricity. biomass relies heavily on agricultural crops. plants release carbon dioxide and water in combustion. plants use photosynthesis to originally generate the energy that is needed. the chemical energy of these plants all started with what energy source?

When you run, you begin to breathe heavier and faster. your heart beats more quickly, bringing more oxygen to your cells. which organ systems are working together here?

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.