1. The Cell and its Environment
Key Concepts:
How do most small molecules cross the cell membrane?
Why is osmosis important to cells?
What is the difference between passive transport and active transport?

2. Key Terms Selectively permeable Diffusion osmosis Passive transport
Active transport

3. Diffusion Main method by which small molecules move across the cell
membrane
Diffusion: process by which molecules move from an area of higher concentration to an area of lower concentration.
Concentration – amount of a substance in a given volume
What causes diffusion
Caused by movement of molecules, the more molecules in an area, the more collisions which cause the molecules to spread out.
Eventually they will be spread evenly throughout an area

4. Diffusion Until they are spread out evenly
Molecules move from high to low concentration

5. Diffusion of Oxygen
Cell membrane is selectively permeable, allows certain materials to pass through but not others
Allows oxygen from water to pass through
More oxygen in water, moves from high concentration to low, so it diffuses into cell

6. Osmosis
Osmosis: the diffusion of water across a selectively permeable membrane
Many cell processes depend on osmosis
Osmosis and Diffusion
Water molecules move
from area of high
concentration through a
membrane to an area of
low concentration

7. Effects of Osmosis
If cell is in solution with same concentration of water, it will retain its normal shape and size.

8. Effects of Osmosis
If cell is in water solution in which concentration of water outside the cell is less ( lots of solutes like sugar or salt), water will move by osmosis out of the cell and the cell will shrink.

9. Effects of Osmosis
If the cell is in a water solution with little salt or sugar, the concentration of water outside the cell is higher, water will move by osmosis into the cell and the cell will swell.

10. Effects of Osmosis

11. Cell Transport
Passive transport – movement of materials through a cell membrane without using cellular energy
Active transport – movement of materials through a cell membrane using cellular energy
Cell must use energy during active transport, but not during passive transport

12. Transport Proteins
Transport proteins pick up molecules outside the cell and carry them in using energy
Carry molecules out the same way
Ex. Sodium (Na), potassium (K), calcium (Ca)

13. Transport by Engulfing
Cell membrane surrounds a particle, once engulfed the membrane wraps around the particle and forms a vacuole

14. Why Cells are Small
Size of cell is related to the movement of materials into and out of cells
As cell’s size increases, so does the distance to the center of cell, materials in the cell move by the streaming of cytoplasm, In a large cell it would take a long time to move substances from the membrane to the center of the cell
If a cell grew too large it couldn’t function very well

15. Cell Size