Download - Cell Boundaries
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Cell Boundaries
7-3
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Cell Membrane
• Cell membrane = – controls what enters and leaves the cell– provides protection and support– Receives chemical signals
• All cell membranes are made up of a double layer known as a lipid bilayer.
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Outsideof cell
Insideof cell(cytoplasm)
Cellmembrane
Proteins
Proteinchannel Lipid bilayer
Carbohydratechains
Section 7-3The Structure of the Cell Membrane
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Cell Walls
• Cell wall = provides support and protection for the cell
• the cell wall is found in plant and fungi cells not animal cells
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Measuring concentration• The cytoplasm of a cell contains many different
substances in water
• The substances dissolved in the solution are called solutes
• The concentration of a solution is the mass of the solute in the volume of solution– Example: 12 grams of salt in 4 liters of water is 12g/3L– The concentration is 3g/L
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Diffusion
• In a solution molecules move constantly and randomly
• Diffusion = molecules tend to move from an area of high concentration to an area of low concentration to spread out
• When the concentration in the solution is the same throughout it is at equilibrium
• Diffusion happens without having to use energy
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Osmosis• Many substances can diffuse across the membrane bus
some are too large or strongly charged and cannot cross. – Water moves easily across the membrane
• Osmosis = is the diffusion of water through a selectively permeable membrane
• Water will move across the membrane until equilibrium is reached, at that point the concentration of water and solute will remain the same. This will mean they are isotonic
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• Isotonic = same strength (equal amounts)• Hypertonic = above strength (more solute)• Hypotonic = below strength (less solute)
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Effects of Osmosis on Cells
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Facilitated Diffusion
• Some molecules, such as Glucose, move across the cell membrane through protein channels
• Facilitated diffusion= is when a protein in the cell membrane helps a molecule move across it
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HighConcentration
LowConcentration
CellMembrane
Glucosemolecules
Proteinchannel
Section 7-3 Facilitated Diffusion
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Active Transport
• Active transport is when a cell uses energy to “pump” molecules across the membrane against the concentration gradient
• Moving molecules from a low concentration to a high concentration
• Requires energy!!
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Molecule tobe carried
Moleculebeing carried
Energy
Section 7-3
Active Transport
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Endocytosis
• Endocytosis = is the process of taking material into the cell by means of infoldings, or pockets of the cell membrane
• Endo = In
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Endocytosis – two types
• Phagocytosis: extensions of cytoplasm surround a particle and package it within a food vacuole
• Pinocytosis: tiny pockets form around the cell membrane, fill with fluid, and pinch off to form vacuoles
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Exocytosis
• exocytosis: the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.
• Exo = Out