Two amino acids unite by forming a(n) bond between them and releasing a molecule of . The union of many amino acids forms a macromolecule called a .

Which properties describe all matter?

4. how does a phospholipid behave in water? the phosphate head does not mix with water; the fatty acid tails do. the phosphate head and the fatty acid tails mix with water. the phosphate head and the fatty acid tails do not mix with water. the phosphate head mixes with water; the fatty acid tails do not.

What kinds of molecules can pass through the cell membrane without any problem?