Cell MembranesOsmosis and Diffusion

Functions of Membranes1. Protect cell2. Control incoming and outgoing substances3. Maintain ion concentrations of various

substances4. Selectively permeable - allows some

molecules in, others are kept out

Phospholipid Bilayer

Fluid Mosaic Model

Solutions• Solutions are made of solute and a solvent

• Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today.

• Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.

Methods of Transport Across Membranes

1. Diffusion -passive transport - no energy expended

2. Osmosis - Passive transport of water across membrane

3. Facilitated Diffusion - Use of proteins to carry polar molecules or ions across

4. Active Transport- requires energy to transportmolecules against a concentration gradient – energy is in the form of ATP

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

Diffusion

Osmosis

Tonicity is a relative term• Hypotonic SolutionHypotonic Solution - One solution has a

lower concentration of solute than another.

• Hypertonic SolutionHypertonic Solution - one solution has a higher concentration of solute than another.

• Isotonic SolutionIsotonic Solution - both solutions have same concentrations of solute.

Plant and Animal Cells put into various solutions

Types of Transport

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