Diffusion Osmosis Active Transport Endocytosis Exocytosis This lesson is all about how a cell can move materials into and out of itself.

Diffusion is the distribution of a solute in a solvent from an area of high concentration to low concentration, without adding energy, until a uniform distribution is achieved.

This solution has a uniform concentration. Can diffusion occur? What is diffusion?

This orange dot is an area of high concentration. What will happen to it? What is diffusion?

Observe the molecules of the “orange dot”. What will happen to them? What is the process called? When will diffusion stop? Why? Would this happen faster in a hot solvent or a cold solvent? Why? Where is the energy for diffusion coming from? How does the temperature of the solvent affect diffusion?

This is a divided container. What will happen when the separating wall is removed? Why?

The dotted line represents a porous separator (it has holes in it). How will that affect diffusion?

It still diffused, just as before, but all other things being equal, it took more time.

How is this different? How will it affect diffusion?

Osmosis is like diffusion, in that no outside energy is involved and materials tend to move from high concentration to low concentration, but it is different in that a membrane is involved which controls to some degree which things may cross the membrane, so complete mixing may not occur. A membrane may stop certain things from crossing.

The “bags” represent a membrane. Why did it expand? What was at lower concentration inside the bag? Did the red dots diffuse out? Why?

Is this cell membrane affecting diffusion of the red material?

Diffusion occurs in membranes through pores, which act like simple holes like in the barrier we saw before.

Cells can facilitate diffusion of selected molecules through osmosis. Why would they want to not be uniform in their treatment of all their molecules?

In active transport, the cells expend energy to obtain certain molecules and bring them inside the cell membrane.

In endocytosis, the cell surrounds the desired material and grows around it,until the material is incorporated into the cell. This is particularly helpful for getting large things that cannot pass through the pores of the membrane.

Use your knowledge of language arts and of endocytosis to define exocytosis. The diagram above shows what is happening. Analyze this. Why would a cell do this?

Secretion describes the use of exocytosis by a large number of cells.