Notes – 6.1

Diffusion and Osmosis

6.1 The Structure and Function of the Cell Membrane

• The cell membrane has many functions.– protection– obtaining food– ridding wastes– communication– interaction with other

cellsA soap bubble is like a cell membrane.

6.1 The Structure and Function of the Cell Membrane

• The cell membrane is made of several types of molecules.

6.1 Diffusion• Molecules move across the cell membrane by a process called

diffusion.• Diffusion is the movement of molecules from areas of greater

concentration to areas of lesser concentration.

6.1 Diffusion• Molecules move

into or out of the cell until there is an equal number on both sides of the cell membrane.

6.1 Diffusion• Water molecules are

small enough to pass through the cell membrane by diffusion.

• Osmosis is the diffusion of water across the cell membrane.

6.1 Other types of transport• Larger molecules

like sugars, starches, and proteins sometimes diffuse through protein channels.

6.1 Active transport• Active transport is a process that allows molecules to move

across the cell membrane from lower to higher concentrations.

• To do this requires energy.

6.1 Other types of transport

• A cell can take in large particles of food by “engulfing” them.

6.1 Why are cells so small?• To understand why the volume of a cell increases

faster than its surface area, let’s imagine a perfectly square cell.

6.1 Why are cells so small?• Which cell type has a higher volume to

surface area ratio?

Now do your Amoeba Sisters –

Osmosis & Diffusion worksheet