1. Warm Up
What is meant by concentration gradient? Which direction do materials diffuse across the gradient?
What is passive transport?
What are two examples of passive transport?

2. 3.5 Active Transport, Endocytosis, and Exocytosis

3. Moving against the concentration gradient
Cells need some materials that cannot passively diffuse across the membrane
Proteins can help transport materials against the concentration gradient.
These proteins are often called pumps

4. Active Transport
Drives molecules across a membrane from a region of lower concentration to higher concentration (opposite of passive transport, different from facilitated diffusion)
Uses transport proteins
Requires energy
Allows cells to get necessary materials regardless of concentration gradient

5. Transport Proteins Found in membrane
Most change shape when they bind to a specific molecule
What do we call a change in shape?
Some bind to only one type of molecule, some bind two different kinds
Those that bind two may move both types in the same direction or in opposite directions

6. Transport Proteins: key point
Using energy to move molecules against the concentration gradient
Most use energy from a molecule called ATP (adenosine triphosphate)
In what ways are active transport proteins similar to enzymes?

7. Vesicles
A cell can use energy to move a large substance or large amount of a substance in a vesicle
Allows substances to enter/exit a cell without crossing through the membrane

8. Endocytosis Large molecules or liquids are engulfed by the membrane
Something like a little capsule forms
The capsule breaks off inside of the cell forming a vesicle
Vesicle fuses with lysosome which breaks down the membrane capsule and allows contents to be released into cell

9. Phagocytosis Type of endocytosis Literally means “cell eating”
Key role in immune system
Macrophages are special white blood cells that perform an interesting form of phagocytosis
Video: watch the macrophage engulf invaders

10. Exocytosis Opposite of endocytosis
Release of substances from cell by way of a vesicle fusing with the membrane
Example: every move you make!
nerve impulses travel along nerve cells as an electrical signal
This electrical signal must be converted into a chemical signal to jump the small gap between nerve cells
These chemicals are stored in vesicles
Video clip: endocytosis and exocytosis