Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? select all that apply.

water
ions
proteins
oxygen
carbon dioxide
lipids
sucrose

There are few cells in the body that do not undergo mitosis: most somatic cells divide regularly, some more than others. take for example the cells that line the digestive tract. these cells must be frequently replaced because they are constantly eroded by the movement of food through the tract. what mechanism(s) is/are in place to ensure that these cells are exact copies of the mother cell