1. Cell Transport
All cells must maintain HOMEOSTASIS (balance). What types of substances must be balanced in a cell?

2. First Step: Cell Membrane
Cell membrane is semi- or selectively permeable – not all molecules can pass through.

3. Concentration gradient
The difference in concentration of a given molecule between two points is called the concentration gradient.
The larger the gradient, the greater the net movement of the molecules.
Molecules continue to move until evenly distributed (gradient = 0).

4. Diffusion
Diffusion occurs whenever molecules move from areas of high concentration to low concentration.
The movement is caused by the random kinetic energy of the molecules, so does not require any energy input.

5. Passive Transport Does not require energy.
Molecules move from high concentration to low concentration.
Three major types:
Simple Diffusion
Osmosis
Facilitated Diffusion
Slide by D Regelski
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6. Simple Diffusion across a Membrane
Molecules pass directly through lipid bilayer.
Molecules generally small with little or no electrical charge (O2, CO2, H2O, etc.).

7. Facilitated Diffusion
Molecules move through special proteins.
Move from high concentration to low.
Does not require energy.

8. Osmosis Special type of diffusion.
Involves water moving across a selectively permeable membrane.
Very important in living organisms.

9. Tonocity
During osmosis, water moves from high concentration to low concentration.
Water is called a solvent, molecules dissolved in water are called solutes.
There are three terms to describe the direction in which water molecules will move during osmosis:
Hypotonic
Isotonic
Hypertonic

10. Hyper- and Hypotonic Hypo = less solute Hyper = more solute
These are relative terms like “greater than” or “less than”
Water moleclue
Solute molecule

11. Effects of Tonicity on Cells

12. Active Transport
Moves molecules against their gradient (from low to high concentration).
This requires energy.
Two major types:
Carrier Proteins
Endocytosis

13. Carrier Proteins
Special membrane proteins that use energy to move molecules across the membrane.

14. Endocytosis
Process by which large molecules or large volumes of liquid are taken into cells.
Endo- means inside, cytosis refers to cell
Phagocytosis = “cell eating”
Pinocytosis = “cell drinking”
Requires energy.

15. Phagocytosis Cell membrane folds around and brings particle into cell.
The membrane around the particle pinches off and forms a vesicle.
The vesicle will eventually fuse with a lysosome for digestion.

16. Pinocytosis Cell membrane folds around and brings liquid into cell.
The membrane around the liquid pinches off and forms a vesicle.

17. Exocytosis
The opposite of endocytosis is called exocytosis (exo = outside).
This is what happens to the packages produced by the Golgi bodies that leave the cell.
Cell Membrane