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Cell Membrane and TransportHOW THE CELL ABSORBS AND EXCRETES VARIOUS MOLECULES
Cell MembraneCell membrane separates the components of a cell from its environment (what surrounds the cell) and controls the passage of materials into and out of a cell.Composed of a phospholipid bilayer (75-95%), and proteins (5-25%). Hydrophilic heads-
Hydrophobic tails-
Attracted to water
Repelled from water
Membrane ProteinsMembrane proteins are used for
CommunicationI.D. TagAnchorsGatesPumps
Cell Membrane Structure Fluid Mosaic Model- molecules and proteins are “free floating” along the phospholipid bilayer.
Fluid Mosaic Model
3 Types of Proteins Found in Cell MembraneChannel Proteins- allow molecules or ions to enter the cell. They can be open or gated.Receptor Proteins- relay information from outside the cell to inside the cell. Marker Proteins- act as the name tag of the cell.
Factors Affecting TransportMolecules size and chargeThe cell membrane is permeable to small neutral molecules, H2O, gases, and lipids.The cell membrane is impermeable to charged molecules. Proteins are needed to
move these across the membrane.
Concentration gradientMolecules like to move from areas of high concentration to areas of low
concentration
Electrical gradientThe inner membrane of the cell is slightly negative (-) to the outer surface of the cell.Therefor (+) charged molecules will be attracted into the cell.
Concentration Gradient- the difference in concentration across a space.
High HighLow Low• “Down” concentration gradient.
No energy needed.• “Against” concentration gradient.
Requires energy.
Passive Transport Active Transport
Moving Down the Concentration Gradient
Moving molecules down their concentration gradient is known as
Passive Transport. The cell uses no energy to move the molecules.
Processes that used passive transport are…DiffusionOsmosisFacilitated Diffusion
Diffusion Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration.
When the concentration of molecules is the same throughout the space it occupies they are in a state of Equilibrium.
No energy needed
Osmosis Osmosis is the process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration.
The direction of movement of water molecules depends on the relative concentration of solutes on the two sides of the semi-permeable membrane.
There are three osmolality's◦ Hypotonic◦ Hypertonic◦ Isotonic No energy needed
Hypotonic SolutionsWhen the concentration of solute molecules outside the cell is lower than the concentration inside the cell, the solution outside the cell is hypotonic to the cytosol.Water molecules will have a net movement into the cell causing the cell to swell.The force that water molecules exert against the cell wall is called osmotic pressure.If a cell takes in to much water it can burst. This is termed cytolysis.
Hypotonic Solution
Plant cell Animal Cell
Hypertonic SolutionsWhen the concentration of solute molecules outside the cell is higher than the concentration in the cytosol, the solution outside is hypertonic.Water will have a net movement out of the cell causing the cell to shrivel.
Plasmolysis is when osmotic pressure is lost due to water leaving the cell. This is what causes plants to wilt.
Hypertonic Solutions
Animal CellPlant Cell
IsotonicWhen the concentration of solutes outside and inside the cell are equal, the outside solution is said to be isotonic to the cytosol.There will be no net movement.
Isotonic Solutions
Animal CellPlant Cell
5% Solute95% Water
10% Solute90% Water
What will happen to the cell?
10% Solute90% Water
10% Solute90% Water
What will happen to the cell?
30% Solute70% Water
10% Solute90% Water
What will happen to the cell?
Facilitated DiffusionThis type of transport is for molecules that may not be soluble or are to large to pass through the membrane pores.Requires protein channels or carrier proteins which move the molecules down their concentration gradient.Protein channels are specific to one type of moleculeSome are always open, others are gated and require a trigger to open and close.
No energy needed
