Diffusion and Osmosis

HideShow resource information
  • Created by: Lauren
  • Created on: 12-03-13 20:27


Substances move in an out of cell membranes by diffusion. Diffusion is the movement of a substance from a region of high concentration to a region of low concentration. Particles move about in lots of different directions. This is called random movement. Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.

The rate of diffusion is increased when:

-there's a greater surface area of the cell membrane 

-there's a greater difference between concentrations(steeper gradient)

-the particles have a shorter distance to travel.

Diffusion in Plants

Carbon Dioxide and oxygen move in and out of plants through their leaves.

During the day:

-carbon dioxide is used up in photosynthesis. The concentration inside the leaves is lower than the concntration outside the leaves.

-carbon dioxide diffuses into plants through the stomata on the bottom of their leaves.

-oxygen, a product of photosynthesis, diffuses from the plant into the atmosphere.

At night, photosynthesus stops. Oxygen diffuses into leaf cells and carbon dioxide diffuses out of leaf cells 

The stomata on the underside of leaves are specially adapted to: 

-open: to help increase the rate of diffusion of carbon dioxide and oxygen

-close: to prevent excessive water loss in drought conditions.


Osmosis is the diffusion of water from high concentration of water (dilute solution)to low concentration of water through a partially permeable membrane. Osmosis is a special type of diffusion involving water molecules. Plant cells are surrounde by  membranewhich allows water to move in and out of the cells. Water and solute molecules move…


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Exchange of materials resources »