Cell Membranes The cell membranes purpose is to
Cell Membranes
�The cell membrane’s purpose is to control what goes in and what goes out of a cell �The cell membrane also provides protection and support
The Lipid Bilayer �The cell membrane is made up primarily of two sheets of lipids called the lipid bilayer �In addition to lipids, some carbohydrates and proteins are embedded in the bilayer. Because of these embedded molecules we refer to the lipid bilayer as a fluid mosaic.
Concentration �How does a cell membrane control what enters and exits a cell? �The concentration of the liquids on either side of the membrane is the key.
�Concentration is the measure of the amount of “stuff” (solutes) in any given amount of a solvent. �Concentration = mass of solute / volume of solvent. � 8 grams of an salt in 2 liter of water gives us a concentration of 4 g/L.
Which of these is more concentrated for sugar? � 2 gallon of iced tea with one spoonful of sugar � 3 gallons of iced tea with two spoonfuls of sugar
Which of these is more concentrated for sugar? � 3 gallons of iced tea with two spoonfuls of sugar
Diffusion �http: //www. uh. edu/phar 2362/animations/simple_diff usion. html
Diffusion �Diffusion is the random spreading out of molecules �In diffusion molecules move from areas of high to areas of low concentration
�The cell membrane is only permeable to some substances. It is selectively permeable. �Diffusion can only occur across a cell membrane if that membrane is permeable to the solute in question.
Osmosis �Cell membranes usually permeable to water, so a special kind of diffusion called osmosis can occur. �Osmosis is diffusion of water. �Osmosis moves water from high concentration of water to low concentrations of water.
Concentration of Water �If a water solution is highly concentrated for a solute, it has a low concentration of water.
Which of these is more concentrated for iced tea? � 2 gallon of iced tea with one spoonful of sugar � 3 gallons of iced tea with two spoonfuls of sugar
Which of these is more concentrated for iced tea? � 2 gallon of iced tea with one spoonful of sugar
Where will salt move?
Where will water move?
Transport �When substances move across a cell membrane we call it transport �There are 2 types of transport �Passive �Active
Passive Transport � No energy � Moves from high to low concentration
Facilitated Diffusion �Special protein channels allow substances to pass through a membrane �High to low concentration
Active Transport �Uses energy �Requires transport protein �Low concentration to high concentration
Tonicity Hypotonic Solution – concentration is lower
Tonicity Isotonic Solution – concentration is equal
Tonicity Hypertonic Solution – concentration is higher
Why can’t we drink sea water? �Salt water is hypertonic to our cells
Water intoxication �Drinking extremely large amounts of water in a short time period can lead to death �Our cells are hypotonic to pure water
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