The tiny hollow air sacs where oxygen exchange occurs are

A. lymph nodes.

B. capillaries.

C. alveoli.

D. bronchioles.

Bacteria in root nodules change nitrogen gas into what form?

We have all seen the moon shining at night, whether it is a small sliver or a large full moon. What causes the moon to shine the way it does? A) The tilt of the Earth on its axis. B) The rotation of the Earth on its axis.

How does pH affect enzyme action?

With which two parts of the earth system is a climatologist involved?

Which is the result of a seasonal change? A. Baby bear growing larger B. Rabbits changing fur color C. Trout disappearing due to acid rain D. Forest shrinking due to logging

During which storage stage of the cell cycle is the dna copied

Why do planets travel in elliptical orbits?

The __nervous system carries impulses from the central nervous system to the heart and other organs. autonomic somatic cerebral muscular

Can be used by cells to store energy, form biological membranes, and serve as chemical messengers

How is the formation of natural gas related to the formation of coal and petroleum?