Active Transport: What Can Cells Do When Diffusion Doesn’t Work? M. Schultz

The Cell Membrane is Selectively Permeable Only small molecules with a neutral charge get across easily. They only flow from high to low concentrations. A cell can’t use diffusion if it needs to get in large or charged molecules. it needs to get molecules from low to high concentrations.

+ + Polymer + + + + - Monomer + + + Small and neutral molecules get into and out of the cell easily.

The Cell Membrane Animation

Facilitated Diffusion: A Type of Passive Transport This does not require energy, but it does require a helper because the molecule the cell wants to get in is too big to fit through the membrane just anywhere. This is how you get glucose into your cells.

Glucose Transporter Animation

Active Transport I. This requires energy (ATP) on the part of the cell. II. The cell needs to use active transport when A. The molecule is too large and the membrane has to change shape. B. The cell needs to pump materials against the concentration gradient (from low to high).

Endocytosis: A Type of Active Transport Some molecules are just too big to get past the membrane even with special helpers. Animation

There are two types of Endocytosis I. Phagocytosis is taking in large solid particles. II. Pinocytosis is taking in large amounts of liquid.

Exocytosis: Another Type of Active Transport This is when a cell spits out large particles of waste.

Sodium Potassium Pumps: A Type of Active Transport The cell must use pumps when it is trying to get materials from where there is a low concentration to a side where there is a higher concentration. This is movement against the concentration gradient. Animation