Passive Transport:

* Simple Diffusion: Molecules move from an area of high concentration to an area of low concentration, following the concentration gradient. This doesn't require energy. Examples include the movement of oxygen into cells and carbon dioxide out of cells.

* Facilitated Diffusion: Molecules move across the membrane with the help of transport proteins. These proteins act like channels or carriers, facilitating the movement down the concentration gradient. This also doesn't require energy. Examples include the movement of glucose and amino acids into cells.

* Osmosis: The movement of water across a semipermeable membrane from an area of high water concentration to an area of low water concentration. This is driven by the difference in water potential.

Active Transport:

* Primary Active Transport: Molecules move against their concentration gradient, requiring energy directly from ATP hydrolysis. This is often mediated by pumps, which bind to the molecule and use ATP to change their shape and move the molecule across the membrane. Examples include the sodium-potassium pump, which pumps sodium out of cells and potassium into cells.

* Secondary Active Transport: The movement of one molecule against its concentration gradient is coupled to the movement of another molecule down its concentration gradient. This is indirectly powered by ATP, as the gradient of the "driving" molecule is established through primary active transport. An example is the movement of glucose into the cell, coupled to the movement of sodium down its concentration gradient.

Other Mechanisms:

* Endocytosis: The cell membrane engulfs large particles or molecules and brings them into the cell.

* Exocytosis: The cell releases large particles or molecules from the cell by fusing vesicles containing them with the cell membrane.

The specific mechanism used depends on the size and nature of the molecule being transported, as well as the needs of the cell.