2 of 22

Functions of Membranes

1. Protect cell

2. Control incoming and outgoing substances

3. Maintain ion concentrations of various substances

Selectively permeable - allows some molecules in, others are kept out
ALL THIS MAINTAINS HOMEOSTASIS (internal balance)

3 of 22

Phospholipid Bilayer

4 of 22

Fluid Mosaic Model

5 of 22

Methods of Transport Across Membranes

1. Diffusion

2. Osmosis

3. Facilitated Diffusion

4. Active Transport

6 of 22

Proteins

Membrane movement animation

Polar heads love water & dissolve.

Non-polar tails hide from water.

Carbohydrate cell markers

Fluid Mosaic Model of the cell membrane

7 of 22

Types of Cellular Transport

Passive Transport

cell doesn’t use energy

Diffusion
Facilitated Diffusion
Osmosis

Active Transport

cell does use energy

Protein Pumps
Endocytosis
Exocytosis

high

low

This is gonna be hard work!!

high

low

Weeee!!!

Animations of Active Transport & Passive Transport

8 of 22

Diffusion

Movement of molecules from an area of high concentration to an area of low concentration.

Movement from one side of a membrane to another, un-facilitated

10 of 22

Passive Transport: � Diffusion

Diffusion: random movement of particles from an area of high concentration to an area of low concentration.

(High to Low)

Diffusion continues until all molecules are evenly spaced (equilibrium is reached)-Note: molecules will still move around but stay spread out.

http://bio.winona.edu/berg/Free.htm

Simple Diffusion Animation

11 of 22

Osmosis: diffusion of water through a selectively permeable membrane
Water moves from high to low concentrations

Water moves freely through pores.
Solute (green) too large to move across.

Osmosis animation

Passive Transport: � Osmosis

13 of 22

Tonicity is a relative term

Hypotonic Solution - One solution has a lower concentration of solute than another.
Hypertonic Solution - one solution has a higher concentration of solute than another.
Isotonic Solution - both solutions have same concentrations of solute.

14 of 22

Plant and Animal Cells put into

various solutions

15 of 22

Hypotonic Solution

Hypotonic: The solution has a lower concentration of solutes and a higher concentration of water than inside the cell. (Low solute; High water)

Result: Water moves from the solution to inside the cell): Cell Swells and bursts open (cytolysis)!

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions

16 of 22

Hypertonic Solution

Hypertonic: The solution has a higher concentration of solutes and a lower concentration of water than inside the cell. (High solute; Low water)

Result: Water moves from inside the cell into the solution: Cell shrinks (Plasmolysis)!

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions

shrinks

17 of 22

Isotonic Solution

Isotonic: The concentration of solutes in the solution is equal to the concentration of solutes inside the cell.

Result: Water moves equally in both directions and the cell remains same size! (Dynamic Equilibrium)

Osmosis Animations for isotonic, hypertonic, and hypotonic solutions

18 of 22

Types of Transport

19 of 22

Facilitated diffusion: diffusion of specific particles through transport proteins found in the membrane

Transport Proteins are specific – they “select” only certain molecules to cross the membrane
Transports larger or charged molecules

Facilitated diffusion (Channel Protein)

Diffusion (Lipid Bilayer)

Passive Transport: �Facilitated Diffusion

Carrier Protein

http://bio.winona.edu/berg/Free.htm

20 of 22

High Concentration

Low Concentration

Cell Membrane

Glucose

molecules

Protein

channel

Passive Transport: Facilitated Diffusion

Go to Section:

Transport Protein

Through a 🡪

Cellular Transport From a-

High

Low

Channel Proteins animations

21 of 22

Types of Active Transport

Endocytosis: taking bulky material into a cell

Uses energy
Cell membrane in-folds around food particle
“cell eating”
forms food vacuole & digests food
This is how white blood cells eat bacteria!

22 of 22