Types of Transport Across Cell Membranes 1

Passive Transport ▪ Does not require energy ▪ Substances move from high to low ▪ Solutes move down the concentration gradient ▪ Examples: oxygen, water, carbon dioxide 2

Types of Passive Transport 3

Diffusion ▪ Movement of substances (except water) across a cell membrane 4

Diffusion of Liquids 5

Osmosis ▪ Diffusion of water across a membrane ▪ Moves from HIGH water concentration (low solute) to LOW water concentration (high solute) 6 Diffusion across a membrane Semipermeable membrane

Diffusion of H 2 O Across A Membrane ▪ High water potential = low solute concentration ▪ Low water potential = low solute concentration 7

3 Types of solutions ▪ Isotonic ▪ Hypotonic ▪ Hypertonic ▪ THINK IN TERMS OF SOLUTE CONCENTRATION NOT WATER CONCENTRATION!!!! 8

Cell in Isotonic Solution 9 CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O The cell is at _______________. equilibrium ENVIRONMENT NO NET MOVEMENT

Cell in Hypotonic Solution 10 CELL 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O What is the direction of water movement?

Cell in Hypertonic Solution 11 CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT

Ways to Remember Solutions ▪ “SALT SUCKS” ▪ Water wants to join the party 12

Think about it: ▪ Why do you cook onions before you salt them? ▪ Why did pioneers use salt to cure their meats (remember no refrigerators) 13

Cytolysis & Plasmolysis ▪ Cytolysis – Cells swell and burst ▪ Plasmolysis – Cells shrink and shrivel 14

Osmosis in Red Blood Cells 15 Isotonic Hypotonic Hypertonic

16 hypotonichypertonic isotonic hypertonicisotonic hypotonic

Facilitated Diffusion ▪ Doesn’t require energy ▪ Uses transport proteins to move material from a high to low concentration ▪ Examples: Glucose or amino acids moving from blood into a cell. 17

18 Proteins Are Critical to Membrane Function

19 Types of Transport Proteins ▪ Channel proteins are embedded in the cell membrane & have a pore for materials to cross ▪ Carrier proteins can change shape to move material from one side of the membrane to the other

20 Channel Proteins

21 Carrier Proteins ▪ Carrier proteins change shape to move materials across the cell membrane

Active Transport ▪ Requires energy or ATP ▪ Moves materials from LOW to HIGH concentration ▪ AGAINST concentration gradient 22

Active transport Example ▪ Sodium/ Potassium pump ▪ Pumping Na + (sodium ions) out and K + (potassium ions) in against strong concentration gradients. 23

24 Sodium-Potassium Pump

Types of Active Transport 25

Exocytosis ▪ Molecules moved out of the cell 26

27 Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

Endocytosis ▪ Molecules moved into of the cell ▪ 2 types 28

Pinocytosis ▪ Most common form ▪ Moves dissolved molecules into cell ▪ Cell “drinking” 29

30 Example of Pinocytosis pinocytic vesicles forming mature transport vesicle Transport across a capillary cell (blue).

Phagocytosis ▪ Used to engulf large molecules to bring into cell ▪ Cell “eating” 31

32 Phagocytosis About to Occur

33 Phagocytosis Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)