20. The primary molecule of the cell (plasma) membrane is known as a .

21. Because the interior of the lipid bilayer contains the nonpolar , only small nonpolar substances are able to diffuse directly across the cell membrane.

Proteins within the cell membrane serve different functions. List four examples of membrane proteins found within the cell below:

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both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.