1. Diffusion and Osmosis: How does stuff get into and out of a cell?
The Cell in its Environment
Ch 7, Section 2
L3 Biology

2. Molecules are always moving
Molecules move randomly and bump into each other and other barriers

3. Diffusion
Movement of molecules from an area of high concentration to an area of lower concentration
Continues until equilibrium is reached.

4. Diffusion

5. Diffusion
Occurs without control or energy use – it is called Passive Transport
Affected by:
Size of molecules
Size of pores in a membrane
Temperature
Stirring

7. Simple Diffusion

8. Cell Membranes are Semipermeable
Let some molecules pass through and not others.
Small molecules pass through – ex: water
Large molecules can’t pass through – ex: proteins and complex carbohydrates

10. Which molecules will diffuse?1 2 3 4 5 6

11. How long does diffusion continue?
Until equilibrium is reached:
This means there will be an equal distribution of molecules throughout the space – this is why odors smell strong at first, then seem to disappear

12. Osmosis – A Special kind of Diffusion
Diffusion of water across a selectively permeable membrane
Cytoplasm is a solution of water and solutes (stuff dissolved in the water).
Water moves into and out of cells because of the different concentrations of the solutes.
Different kinds of cells react differently to osmosis, depending on the solution they are in:

13. Blood in different solutions:

15. Active Transport – uses carrier molecules to move molecules from an area of lower concentration to an area of higher concentration

16. Endocytosis
Very large molecules or substances must enter the cell by the membrane pinching inward:

17. Pinocytosis
The cell takes in liquid droplets and forms a vacuole

18. Phagocytosis
The cell takes in large particles

19. Exocytosis
The cell gets rid of secretions or wastes

20. Phagocytosis in action – phagocyte (white blood cell) going after a bacteria cell
The End