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Notes Cell Membrane Diffusion


Cell Boundaries

The Cell Membrane

The Cell Membrane

Thin, flexible barrier

Regulates what enters and leaves

Protects and supports

aka: Phospholipid Bilayer .

Consists of: hydrophilic head

(water liking) and a hydrophobic tail.

(water avoiding)

Phospholipid Bilayer: Fluid Mosaic Model

Also has

Proteins – doorways

Carbohydrates – name tags

Cholesterol – keeps membrane flexible

Therefore referred to as a “fluid mosaic” of different molecules.

Cell Boundaries

The Function of the

Plasma Membrane

The Cell Membrane

Cells want nutrients

Cells get rid of wastes

Two ways:

Passive Transport

– No Cell Energy (ATP) needed

Active Transport

– Cell Energy (ATP) required

Passive Transport - Diffusion

Passive Transport – Facilitated


Passive Transport - Osmosis

The diffusion of water molecules through a cell membrane.

Concentration gradient depends on amount of dissolved particles (like salt) inside and outside the cell.

Isotonic Solution

Concentration of a dissolved substance

(solute) is the same inside and outside the cell.

Isotonic = Dynamic equilibrium.

Cell stays same size.

Isotonic Solution

Hypotonic Solution

Concentration of the solute is low outside the cell and higher inside the cell.

Water moves INTO the cell.

Cell gets BIG like the

O in hyp

O tonic

Hypotonic Solution

Hypertonic Solution

Concentration of the solute is higher outside the cell and lower inside the cell.


E xits the cell.

Think of the “E” in hyp

E rtonic

Cell shrinks.

Hypertonic Solution


Draw and Label Figure 23, 24 and 25 on page 204-205.

Complete the Osmosis worksheet.