B2 - Diffusion and Osmosis

Cells have to constantly...

• replace substances which are used up.
• remove other substances.

Give an example for replacing substances and an example for removing substances.

• Replacing substances: food and/or oxygen.

• Removing substances: carbon dioxide and waste products.

These substances can pass into and out of cells by...

• Diffusion
• Osmosis

What is diffusion?

Diffusion is the spreading of the particles of a gas, or any substance in solution, which results in a net movement from a region where they are at a higher concentration, to a region where they are at a lower concentration.

What passes through cell membranes by diffusion? And why?

Oxygen required for respiration passes through cell membranes by diffusion.

The greater the difference in concentration, the...

The greater the difference in concentration, the faster the rate of diffusion.

Osmosis is...

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

The membrane allows...

The membrane allows the passage of water molecules, but not solute molecules because they are too large.

Osmosis will gradually dilute the more concentrated solution. For example... 

For example, at root hair cells water moves from the soil into the cell by osmosis, along a concentration gradient.