1. The Cell and Its Environment
Pg. 32

2. The Cell Membrane
The cell is separated from the outside world by the cell membrane. The cell membrane is selectively permeable, which means that some substances can pass through, while others cannot. (oxygen, food, waste)

3. Diffusion
Method by which small molecules move across the cell membrane.
Molecules move from an area of higher concentration to an area of lower concentration.
Concentration: the amount of a substance dissolved in a liquid.
Ex) 1g of sugar in 1 L of water = 1 g/L sugar concentration
Diffusion is caused by the movement of molecules.
*Oxygen enters the cell via diffusion.

4. Osmosis
The diffusion of water across the cell membrane. (High concentration to low)

5. Active Transport
Diffusion and Osmosis occur automatically without expending the cell’s energy.
Passive Transport
Active transport uses transport proteins to force materials to move either out of or into the cell. (Low concentration to high)
Requires energy
Calcium, Sodium, Potassium
Engulfing: The cell surrounds a food particle with the cell membrane and traps it in a vacuole.

6. Why Cells are Small
Increased size means that more cytoplasm is located farther from the membrane.
This means it takes longer for materials to move around the cell. => Less efficient energy usage, poor waste disposal.

7. Homework
Workbook Pg. 10~20
Due Monday