Diffusion

Movement of particles from high to low concentration

Facilitated Diffusion

Particles diffuse through a transport protein

Osmosis

Diffusion of Water only

Red Blood Cell Link

Plant Cell Link

Note: diffusion and osmosis are both passive, i.e. energy from ATP is not used.

Active Transport

Active transport is the energy-demanding transfer of a substance across a cell membrane against its concentration gradient, i.e., from lower concentration to higher concentration.

Special proteins within the cell membrane act as specific protein ‘carriers’. The energy for active transport comes from ATP generated by respiration (in mitochondria).

Major examples of Active Transport

 Re-absorption of glucose, amino acids and salts by the kidney.
Sodium/potassium pump in cell membranes (especially nerve cells)

Endo/exocytosis

This is the movement of very large molecules (or particles, bacteria or other organisms) across the cell membrane. It involves the fusion of vesicles (containing the target/victim) with the cell membrane e.g. bacteria entering macrophages. Substances destined for secretion are packaged in the Golgi body first.

Pumps

Na+/K+ pump

Using ATP as energy, transport proteins pump materials across the membrane.

Steps

1.     3 Sodium bind from inside the cell to a protein

2.    A molecule of ATP binds to the protein

3.    The protein changes shape and opens to the outside.

4.    Sodium is released, and Potassium binds to protein from outside.

5.    The protein returns to original shape and releases the potassium

Sodium Pump Video