the plasma membrane a. is rigid and impermeable b. is free of proteins c. is permeable to ions and polar molecules d. is composed mostly of cholesterol e. controls the contents of the cell

bilayer

Explanation:

The plasma membrane is SEMIpermeable, it can allow certain materials like nonpolar molecules to pass though its membrane so choice A is wrong. Choice B is also wrong because the plasma membrane is a phospholipd bilayer, meaning it has proteins. Choce C isn't correct  because cholesterol is not composing most of the membrane.

Choice E is your best answer because the most important function of the plasma membrane is to control what enters and exits the cell.

Hope this helps and makes sense to you! Good luck.

the answer is trees if i'm not mistaken

4.) metal

"-the movement of carbon from the nonliving environment into living things and back to the environment

-carbon is the essential component of proteins, fats, and carbohydrates (which make up all organisms)

-carbon exists in air, water, and living organisms

-producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis

-bacteria in the atmosphere cycles through the system in filtration units

-in cellular respiration, carbon is released back into the atmosphere as carbon dioxide

-some carbon is stored in limestone (forming one of the largest "carbon sinks" on earth)

-largest carbon reservoir on earth= limestone

-carbon stored in the bodies of organisms as fat, oils, or other molecules may be released into the soil or air when the organism dies

-this may form deposits of coal, oil, or natural gas (fossil fuels, which increased the atmospheric carbon dioxide)

-fossil fuels store carbon left over from bodies of organisms that died millions of years ago

-they are located in the surface of earth, deep within the earth and beneath the ocean floor."