transport across membranes

Fluid mosaic model

Mixture and movement of phospholipids, proteins, glycoproteins and glycolipids

Hydrophilic heads

Phosphate group has charge which attracts it to water

Hydrophobic tail

Fatty acid has no charge and so repels water

Cholesterol

• Restricts lateral movement of other components

• Membrane less fluid at high temperatures so prevents water and dissolved ions leaking out

Peripheral proteins

Mechanical support or connect to make glycoproteins/glycolipids act as cell recognition

Integral proteins

Protein carriers or channel proteins involved in transport

Protein channels

Form tubes that fill with water to enable water soluble ions to diffuse

Carrier proteins

Bind with larger molecules e.g. glucose and change shape to transport them

Partially permeable

Only lipid soluble substances e.g. hormones and very small molecules e.g CO2 can enter by simple diffusion

Isotonic solution

When water potential of a solution is the same as the cell within solution

Hypotonic

Water potential of solution is more positive(closer to 0)

Animal cells in this solution may burst and plant cells become turgid (cell wall)

Hypertonic

Water potential of solution is more negative than cell

Animal and plant cells become shrivelled