Biology B3 Revision

Substances get in and out of cells through Diffusion, Osmosis and Active Transport.

Diffusion and Osmosis involve substances moving from an area of high concentration, to low concentration. BUT, a cell may need to take a substance AGAINST a concentration gradient- this is called ACTIVE TRANSPORT.

 Active transport uses energy from respiration to carry substances over a cell membrane using a protein.

Active transport is found in:

-Glucose moving from kidney to blood

- Mineral Ions in soil moving into plants.

The lungs exchange oxygen (needed for AEROBIC respiration), and carbon dioxide (a product of respiration).

Aerobic respiration=

Oxygen + Glucose > Carbon Dioxide + Water + Energy

The lungs have millions of tiny air sacs named ALVEOLI, which increase the surface area of the lungs greatly.

They also have a rich blood supply, a steep concentration gradient with movement of gases, they are moist to aid diffusion, and the cells around the alveoli are very thin, so gases do not have to travel far.