1. The diagram represents a biochemical process.
Which molecule is represented by X?
Oxygen (3) protein
(2) starch (4) ATP

2. Molecules naturally “spread out” from high to low concentration.
This is called diffusion.

3. Diffusion requires no extra energy.

4. What if a barrier gets in the way?

5. What if a barrier gets in the way?

6. What if a barrier gets in the way?
It depends on the barrier.

7. What if a barrier gets in the way?
It depends on the barrier.

8. Sometimes molecules pass through.

9. Sometimes molecules pass through.

10. Sometimes molecules pass through.
This is called passive transport.

11. Sometimes molecules pass through.
This is called passive transport.

12. For example, they are always permeable to water.
Cell membranes are permeable to some things and impermeable to other things.
Cell
membrane
For example, they are always permeable to water.
Cell membranes are semi-permeable.

13. SIZE usually determines if the molecules diffuse across a cell membrane.
This is why food must be digested first. Large food molecules cannot fit!

14. This is called facilitated diffusion.
Some larger molecules can diffuse through “tunnels” called channel proteins.
This is called facilitated diffusion.

15. If molecules are too large they cannot diffuse at all.
Let’s see…