All life is composed of cells (page 74)

• About 100 trillion in the case of a human body.

Cells tend to be quite small, (page 75)

• limited by the distance to which substances must diffuse through the cytoplasm and also by the surface-to-volume ratio as cell size increases.

• Small cells have relatively more surface with which to interact with the environment.

The cell cytoplasm is bounded by the plasma membrane. (page 76)

• The plasma membrane is a double layer of modified fat molecules called a lipid bilayer.

Protein-lined passageways (page 77)

• through the bilayer allow chemicals to enter and leave the cell.

The simplest cells are bacteria, (page 79)

• called prokaryotes because they lack a nucleus.

• The key characteristic shared by all bacterial cells is that they lack internal compartments.

All nonbacterial cells contain a nucleus (page 80)

• at some point and are called eukaryotes.

• The interior of eukaryotic cells is occupied by an extensive membrane system that creates many subcompartments within the cytoplasm.

The cell’s hereditary information, (page 82)

• contained within chromosomes, is isolated within the nucleus.

• Proteins are assembled in the cytoplasm on complexes called ribosomes.

• Cells carry out oxidative metabolism within bacteria-like organelles called mitochondria.

All cells transport water and other molecules (page 92)

• across their plasma membranes.

• Molecules move randomly through the cell by diffusion. Molecules diffuse down concentration gradients, thus tending to equalize concentrations.

• Osmosis occurs when water molecules are able to move through a membrane and other polar molecules are blocked.

Selective transport of molecules (page 95)

• can occur via facilitated diffusion or via active transport with the expenditure of ATP.

• The proton pump is a major active transport channel.