1. Exchange with the Environment
The Cell in Action
Exchange with the Environment

2. What would happen if a factory’s power was shut off?
Or their supplies never arrived?
Or they couldn’t get rid of its garbage?
Have a discussion about the importance of everything operating correctly and the flow of things in and out of a working factory.

3. Cells are like factories
Both need to obtain energy and get things in (nutrients) and out (wastes)
These things keep the cell healthy and able to divide
Cells dividing is what allows organisms to grow
What part of the cell controls the things in and out of the cell??
CELL MEMBRANE!

4. What is Diffusion?
Diffusion- the movement of particles from regions of higher density to regions of lower density
Let’s visualize it
Prior to class, make some clear gelatin in a clear cup. For a demo, place some kind of dye over the top of the gelatin. Observe and discuss the diffusion that takes place.
For another demonstration, with the desks, make two boxes with a small “hallway” in-between, but block the hallway with something. Place as many students that can fit into one of the boxes, but place only 2 in the other box. The point is to make one area very dense and the other not very dense. Tell the students to move around, like atoms do. Then, remove the barrier between the two boxes and see where the students go. More than likely, students crammed in the dense area will spread out where they have more room. Use the results of this demonstration to discuss diffusion- particles moving from a higher density area to a lower density area.

5. Diffusion of water Let’s see it in action!!
The diffusion of water is called osmosis
Osmosis- the diffusion of water through a semipermeable membrane
Semipermeable??
Semi – partially
Permeable- accessible/permeable/passable
It means only certain substances can pass through
“Let’s see it in action” is a link to a descriptive animation of osmosis

6. The Cell and Osmosis Cells need a certain amount of water in them
Not too much and not too little!
If red blood cells could burst if they had too much water
Plants wilt if they don’t have enough water in their cells

7. Moving Small Particles
Small particles (like sugars) cross the cell membrane through passageways called channels
The channels are made of proteins
They pass through the channels by either active or passive transport

8. Passive Transport Let’s see it!
Passive transport- the movement of substances across a cell membrane without the use of energy by the cell
Examples: diffusion and osmosis

9. Active transport Let’s see it!
Active transport- the movement of substances across the cell membrane that requires the cell to use energy
Usually is particles moving from an area of low concentration or an area of high concentration
Or…low density to high density
Refer back to the demo using students as desks for props. Ask them if it would take more energy to move to the lower density area or to scrunch yourself into the area of higher density.
Let’s see it!

10. Moving Large Particles
Small particles cross the cell membrane by
Diffusion
Active transport
Passive transport
Large particles use the processes called endocytosis and exocytosis

11. Endocytosis
Endocytosis- the process by which a cell membrane surrounds a particle and encloses the particle in a vesicle to bring the particle into the cell
Vesicle- sacs formed from pieces of cell membrane
cell
PROTEIN

12. Exocytosis
Exocytosis- the process in which a cell releases a particle by enclosing the particle in a vesicle that then moves to the cell surface and fuses with the cell membrane
Things like wastes..EXIT (EXO) the cell

13. Endocytosis and Exocytosis
Let’s see it in action!!

14. Review Describe diffusion How is osmosis different than diffusion?
Why is osmosis important for cells?
Describe passive transport
Is it high to low concentration or low to high?
Does it require energy?
Describe active transport
Describe endocytosis
Describe exocytosis

15. Review
How would the following materials get through a cell membrane and into a cell
Pure water
Sugar entering a cell with a high concentration of particles
Sugar entering a cell with a low concentration of particles
A protein
How would wastes get out of a cell?