1. Chapter 6.3: Membranes regulate the traffic of molecules
College Prep Biology
Mr. Martino

2. 6.3 Cell Membranes
Cell membranes make the E in chemical bonds available for metabolic reactions
Kinds and amounts of substances different on either side of membrane – membrane is selectively permeable
CO2, O2, water, and small nonpolar molecules move easily across
Large, polar molecules and ions do not move freely across
These require various proteins

3. Concentration Gradients
Brownian Motion – continuous random movement of particles due to temp. differences
Concentration gradient: the difference in conc. of particles on one side of a membrane as opposed to the other

4. Diffusion
Diffusion: the tendency for particles to move from areas of high concentration to areas of low conc.
Molecules naturally move “with” conc. Gradient
Diffusion is fastest when gradient is steep

5. Active transport: requires E to move substances across a membrane
Transport protein pumps the substance against the conc. gradient
Usually use ATP

7. Movement of Water Osmosis: the diffusion (passive transport) of water
Hypertonic Solution: has a higher conc. of solutes than the cell
Water will leave cells and cells will shrivel
Hypotonic Solution: had a lower conc. of solutes than the cell
Water will rush into cells and cells will swell

8. Turgor (hydrostatic) pressure: the internal force pushing outward in plant cells
Cell wall prevents the uptake of too much water
Isotonic Solution: the conc. of particles inside the cell is = to the conc. of the particles outside the cell
Movement continues – just no net movement

10. Endocytosis and Exocytosis
Exocytosis: process of how cells export bulky materials from the cytoplasm
Ex. Tear and insulin formation
Endocytosis: process of how cells import macromolecules
Phagocytosis: cellular eating
Pinocytosis: cellular drinking
Receptor-mediated endocytosis: highly specific due to receptor proteins