Cell Biology : Plasma Membrane Structure and Transport

• Lipid bilayer + embedded proteins
• Selectively permeable - controls movement of substances
• Phospholipid bilayer

==> Hydrophilic head - water soluble

==> Hydrophobic tails - water insoluble

• Bilayer - Two layers
• Basic structure of cell membranes

Membrane Transport

Based on the permeability a membrane is said to be:
1. Permeable: If a substance passes readily through the membrane
2. Impermeable: If a substance does not pass through the membrane
3. Selectively permeable: If the membrane allows some of the substances
to pass through but does not allow all the substances to pass through it.

Substances are transported across the membrane either by:
1. Passive Transport or 2. Active Transport

1. Passive Transport

• Cross membrane with no energy
• movement from high concentration to low

Diffusion

• Diffusion is the movement of molecules from an area of high concentration to an area of low concentration

Osmosis

• Osmosis is the passage of water across a membrane from an area of high concentration to an area of low concentration

2. Active Transport

• Requires chemical energy to cross(ATP)
• Movement from low concentration to high

Related Items Cell Biology