Cell Membrane Transport

Study Notes

The cell membrane is selectively permeable, allowing some substances to pass through while restricting others.
The cell's survival depends on maintaining the difference between intracellular and extracellular material.

Substances like enzymes, glycogen, and potassium ions are found in higher concentrations inside the cell.
Sodium, calcium, and chloride ions are found in greater concentrations outside the cell.

Molecules can pass through the cell membrane in four ways: directly through the phospholipid membrane, through membrane channels, via carrier molecules, and through vesicles.
Simple diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.
Osmosis is the diffusion of solvent or water molecules through a selectively permeable membrane.
Filtration utilizes pressure to push substances through a membrane.
Active transport moves substances against a concentration gradient, requiring a carrier molecule and energy.
Endocytosis refers to the formation of vesicles to transfer particles and droplets from outside the cell to inside.

Lipid-soluble molecules like oxygen, carbon dioxide, and steroids pass through the cell membrane readily.
Small, non-lipid-soluble molecules like water and urea can diffuse between phospholipid molecules.

Cell membrane channels are large protein molecules that allow certain molecules to pass through based on size, shape, and charge.
Examples include sodium channels, potassium channels, and chloride channels.

Large polar molecules like glucose and amino acids are transported across the cell membrane by carrier molecules.
Carrier molecules are proteins that extend from one side of the cell membrane to the other, binding to specific molecules to be transported.
Each carrier molecule transports a specific type of molecule.

Vesicles are membrane-bound sacs that can transport large non-lipid-soluble molecules, small pieces of matter, and even whole cells across the cell membrane.
Vesicles can fuse with the cell membrane, allowing their contents to cross the cell membrane.