Diffusion and Osmosis

Warm Up

DEFINE DIFFUSION

Outline

• Learn the concepts of: – Diffusion, osmosis, semi-

permeable membrane, isotonic, hypertonic, & hypotonic

• Plant/animal cells exposure to water – Hypertonic Env.

– Hypotonic Env.

– Isotonic Env.

Diffusion • Solute molecules moving from

an area of high concentration to an area of low concentration

– Random motion drives diffusion

– Movement is based on kinetic

energy (speed), charge, and mass of molecules

– Equilibrium is reached when

there is an even distribution of solute molecules

2

3

1 4

(water)

Osmosis

• Movement of water through a semi-permeable membrane

– Semi-permeable: permeable to solvents (WATER), but not to large molecules

– High [water] to low [water]

• Dissolved molecules (i.e. glucose, starch) are called solutes

• REMEMBER:

Water = solvent

Glucose, Starch = solutes

Effect of Water on Cells

• Hypertonic Environment

– High [solute], low [water]

• Hypotonic Environment

– High [water], low [solute]

• Isotonic Environment

– [water] = [solute]

Isotonic

Hypotonic Hypertonic

Osmosis in Living Cells

Cellulose in cell wall

Osmosis in Red Blood Cells

Isotonic

Hypotonic

Hypertonic

Crenation

Effect of Water on RBC

Diffusion and Osmosis

Warm Up

DEFINE OSMOSIS

INTRO

• Organisms are constantly responding to their environment.

• Homeostasis = ability of an organism to maintain a constant internal condition despite external environmental changes.

INTRO

– Cell Membrane is selectively permeable to different substances

– Some substances use energy to transport across a membrane, while others don’t need energy to move across cell.

Passive Transport

• Movement across the cell membrane that does NOT REQUIRE ENERGY from the cell.

• Concentration Gradient = A difference in the concentration of a substance across a space

Passive Transport

• Equilibrium = A condition in which the concentration of a substance is equal throughout a space.

• Diffusion = The movement of a substance from an area of high concentration to an area of low concentration caused by the random motion of particles of the substance.

Passive Transport

• If diffusion is allowed to continue, equilibrium results!

• The non-polar interior of the cell membrane’s lipid bilayer repels ions and polar molecules and prevents substances from diffusing across the cell membrane.

• Small or non-polar molecules can diffuse across the cell membrane down their concentration gradient.

Water Diffuses Into & Out of Cells

By Osmosis

• Osmosis = The diffusion of water through a selectively permeable membrane.

• Involves the movement of water down its concentration gradient.

• Type of passive transport!

Water Diffuses Into & Out of Cells

By Osmosis

• The direction of the water movement across the cell membrane depends on the concentration of free water molecules in the cytoplasm and in the fluid outside of the cell.

3 Possibilities for Direction of Water

Movement

1. H2O MOVES OUT – cell shrinks! HYPERTONIC SOLUTION

2. H2O MOVES IN – cell swells!

HYPOTONIC SOLUTION

3. NO H2O MOVEMENT – cell remains same size

ISOTONIC SOLUTION

3 Possibilities for Direction of Water

Movement

If swelling is left unchecked, cell could BURST!

How do cells deal with this?

• Plant cells – rigid cell walls and contractile vacuoles

• Animal cells – remove dissolved particles from cytoplasm – Increases free H2O molecules inside of cell

• Example: Common remedy for a sore throat is to gargle with salt water. WHY?

Proteins Help Some Substances Cross the Cell Membrane

• Transport Proteins – CHANNELS – provide polar passageways through which substances can move across the cell membrane.

• Selective! – only specific substances are allowed to pass! (sugars, amino acids)

Facilitated Diffusion

• Carrier Proteins = Transport protein that carries a specific substance across a cell membrane.

• Facilated Diffusion = When carrier proteins are used to transport specific substances (amino acids/sugars) DOWN their concentration gradient.

Facilitative Diffusion

• http://highered.mcgraw-

hill.com/olc/dl/120068/bio02.swf

Diffusion and Osmosis Day 3 Notes

Warm Up

What is the

difference between active and passive

transport?

4:2 Active Transport

• Some substances are transported against the concentration

gradient.

Active Transport

• Active transport = Transport of a substance across a cell membrane against its concentration gradient.

• Requires the cell to use energy – supplied by ATP

Vesicles Move Substances Across

Membranes

• Endocytosis = The movement of a substance into a cell by a vecisle

• Exocytosis = The movement of a substance by a vesicle to the outside of the cell

• Endocytosis • Exocytosis