Cell Membrane/Plasma Membrane Separates the cell from the
non-living outside environment Without a cell membrane there could
be no cell Performs two functions: 1.It separates the cell from its
outside environment 2.It enables communication and movement of the
materials between the cell and its environment
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Transport across the Cell Membrane Selective permeability cell
membrane allows some substances to pass through but keeps others
out (Border control, Customs, Airport security) So the cell
membrane is selectively permeable or semi-permeable Cell membrane
can also control if the transport of these molecule is fast or
slow
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Fluid Mosaic Model Cell membranes are made up of lipids Protein
molecules float within the lipid molecules of the cell membrane
This arrangement of molecules in constant motion is called the
fluid mosaic model
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The role of Proteins Two Types: Transport proteins and Receptor
proteins Transport proteins: Enable much of the transport or
movement of materials across the cell membrane. Sometimes called
carrier proteins. Receptor proteins: function as receptor molecules
receive signals from the outside and transmit the signal to the
inside of the cell enabling communication between cells
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Semi-permeable materials that can pass and materials that
can't
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Passive Transport Molecules are always in motion They naturally
move from high to low concentrations The difference in
concentration between two areas is called a concentration
gradient
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Solute A substance that is being dissolved to make a solution
In the case of sugar and water it is the sugar because it is being
dissolved in the water
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Solvent A liquid that is dissolving another substance to make a
solution In the case of sugar and water it is the water because the
water is dissolving the sugar
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Diffusion Diffusion The random movement of molecules down the
gradient or from high to low concentration Example: Perfume
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How Does Diffusion Work? Pores in the cell membrane allow these
materials to pass thru Diffusion happens automatically if the
membrane is permeable to that molecule and there is a difference in
concentration on either side This is called passive transport
because no energy is used by the cell to move these molecules
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Hypertonic Solution Higher concentration of solutes outside the
cell Higher concentration of water inside the cell Water moves out
of cell and cell shrinks
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Hypotonic Solution Higher concentration of solutes inside the
cell Higher concentration of water outside the cell Water moves
into the cell and cell expands
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How Diffusion Works Continued... They continue to move from
high amounts to low amounts until there is an even amount of each
side this is called equilibrium or isotonic
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Equilibrium (Isotonic) Diffusion will continue until there is
the same concentration of water and solute molecules on each side
of the cell this is called isotonic
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Function of Diffusion in the Cell This is how cells get food
and oxygen
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Osmosis Osmosis movement of water across cell membrane. - The
movement of water continues until there is the same amount of water
on both sides of the membrane this is called equilibrium.
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Why Does Osmosis Happen in Cells? Cells are surrounded by water
so there must be the same amount of water inside as outside the
cell.
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Question Worth Homework Pass: What happens to a plant when its
cells lose too much water? Answer: Plants wilt! Plant cell membrane
pull away from cell walls in a process called plasmolysis
