Active Transport & Diffusion

Diffusion is the separation of the particles, resulting in a net movement from a region of a higher concentration to a region with a lower concentration. The greater the difference in concentration, the faster the rate of diffusion. (concentration gradient)

Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane.

the movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.

1. Having a large surface area that is thin, to provide a short diffusion path

2. (in animals) having an efficient blood supply

3.(in animals, for gaseous exchange) being ventilated

• the alveolus:
• Large surface area
• Thin Walls. Alveolar walls are one cell thick....gases diffuse across a small distance