BIOLOGY - CELL BIOLOGY - 1.2 Transport across membranes

Describe the cell membrane

It is semi-permeable and only certain molecules are able to psss through it⁶⁹

Passive transport

Diffusion

Osmosis

Diffusion

The movement of molecules from a higher concentration to a lower concentration, down a concentration gradient

Requires no energy

Why do substances have to diffuse across the cell membrane?

To get in and out of a cell

They can only do this because the membrane has many pores in it

concentrations

Substance concentrated - more sugar particles, less water particles

substance diluted - more water particles, less sugar particles

Concentration gradient

Importance of diffusion to cells

Diffusion allows cells to get materials it needs to survive, and remove waste products

There is always a higher concentration of useful substances outside the cell.

Substances which leave the cell by diffusion are waste products which are constantly produced by the cell.

There is always a higher concentration of waste products inside the cell

Examples of useful substances

Glucose

Amino acids

Oxygen

Examples of waste products

Carbon dioxide

Urea

Importance of diffusion in lungs

Oxygen diffuses from the lungs to blood

Carbon dioxde diffuses from blood to the lungs