Cell Membranes Osmosis and Diffusion

Functions of Membranes 1. Protect cell 2. Control incoming and outgoing substances 3. Maintain ion concentrations of various substances 4. Selectively permeable - allows some molecules in, others are kept out

Phospholipid Bilayer

Fluid Mosaic Model

Blood-Brain Barrier Allows some substances into the brain, but screens out toxins and bacteria Substances allowed to cross include: water, CO 2, Glucose, O 2, Amino Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.

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 2. Osmosis- Passive 3. Facilitated Diffusion- Passive 4. Active Transport- definitely NOT Passive

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 transport molecules 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

Diffusion in Action

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.

Type of Solutions – Salts Suck Diffusion and Osmosis are both types of PASSIVE TRANSPORT - that is, no energy is required If the concentration of solute (salt) is equal on both sides, the water will move back in forth but it won't have any result on the overall amount of water on either side. "ISO" means the same

The word "HYPO" means less, in this case there are less solute (salt) molecules outside the cell, since salt sucks, water will move into the cell. The cell will gain water and grow larger. In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting In animal cells, the cell may be in danger of bursting, organelles called CONTRACTILE VACUOLES will pump water out of the cell to prevent this.

The word "HYPER" means more in this case there are more solute (salt) molecules outside the cell, which causes the water to be sucked in that direction. In plant cells, the central vacuole loses water and the cells shrink, causing wilting. In animal cells, the cells also shrink. In both cases, the cell may die. This is why it is dangerous to drink sea water - its a myth that drinking sea water will cause you to go insane, but people marooned at sea will speed up dehydration (and death) by drinking sea water. This is also why "salting fields" was a common tactic during war, it would kill the crops in the field, thus causing food shortages.

Plant and Animal Cells put into various solutions

Types of Transport

Diffusion Lab We are using plastic baggies as the cell membrane - It is selectively permeable The solute is either the starch solution or the iodine solution What is the solvent?

Membrane Permeability Solute is eosin-starch-chloride solution Solvent is Water Indicator for presence of starch is IKI Starch is made of amylose and amylopectin – amylopectin is insoluble Iodine is not very soluble in water, but with KI it forms a I 3 - (triiodine ion) which is soluble. I 3 - combines with the amylose and the starch molecule turns blue-black.

Test for Starch Elmhurst College Website