1. Topic 4
Membrane transport

2. Cell Membrane

3. Obj 13,14
Simple Diffusion
Particles move from areas of high concentration to areas of low concentration
Diffusion across a membrane
Occurs as long as the particle can move through that membrane
Concentration gradient
Differences in concentration with in a solution or across a cell membrane
Drives diffusion

4. The diffusion of solutes across membranes
Obj 13,14

5. Osmosis Obj 15 Movement of water over a semipermeable membrane
Driven by a solute concentration gradient
*Review* – Solutions
Homogenous mixture
Solute dissolved in a solvent
Universal Biological solvent
Water!
Solutes – usually a collection of biological molecules
Glucose
Amino acids
Electrolytes

6. Osmosis *Result* *Important*
Low solute concentration
High Water Concentration
High solute concentration
Low Water Concentration
*Result*
Water moves over the membrane until solute concentration is the same on both sides
Homeostasis!
*Important*
Solute particle is too big to cross the membrane
Water is small enough
Time

7. Osmosis in Cells
Obj 19
Isotonic – cell and external environment have the same solute concentration
No net water movement
Hypertonic environment – external environment has a high solute concentration (low water concentration)
Water moves out of the cell
Hypotonic environment – external environment has a low solute concentrations (high water concentration)
Water moves into the cell
*Terms used to compare solutions*

8. Water balance in living cells Plant vs Animal
Obj 19
Water balance in living cells Plant vs Animal
Start with Plants for G block

9. Passive Transport Obj 15 Movement of substances without energy
Driven by a concentration gradient
Two types…
Simple Diffusion (objective 13)
Substances move through the phospholipid membrane
Facilitated Diffusion
Requires a transport protein
Ion Channel (Tunnel)
Protein changes shape (boat lock)

10. Active Transport Obj 16 Transport Protein Needed Energy required
Substances moved against the concentration gradient
Glucose into a cell (sometimes)
Electrolytes (Sodium-Potassium Pump)

11. Passive and Active transport Summary

12. Selective Permeability
OBJ 17, 19
Selective Permeability
Passes freely through the membrane
Needs a special protein transporter
Needs to use other methods to pass through
Polarity and Size
Nonpolar molecules (steroids, N2, O2)
Some very small polar molecules (water, ethanol, etc)
Small polar molecules (amino acids, sugars, etc)
Large polar molecules (proteins)
Electric Charge
No charge
Charged atoms (H+ or Ca+)
Endocytosis
Exocytosis (Active Transport)
Passive or Active
Passive Transport
Active
Transport

13. The contractile vacuole of Paramecium: an evolutionary adaptation for osmoregulation
Start here with G (Active Transport)

14. Endocytosis “Enter” Obj 17
Active transport of substances from the extracellular fluid
Requires energy
Forms a vesicle inside the cell
3 types
Phagocytosis
Solid particles
Cellular “eating”
Pinocytosis
Liquids/dissolved substances
Cellular “drinking”
Receptor-mediated endocytosis
Vesicle forms in the presence of a specific substance
Exocytosis with C block

15. Obj 17
Exocytosis “Exit”
Active transport of substances to the extracellular fluid
Energy required
Excretory vesicles formed by the golgi apparatus