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Agenda 10/27Cell Membrane and Homeostasis
2.1 Relate cell parts/organelles (plasma membrane) to their functions. Explain the role of cell membranes as a highly selective barrier (diffusion, osmosis, facilitated diffusion, active transport).
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Homeostasis– Maintaining a relatively constant internal environment
Cells need the proper concentration of nutrients and water, and to eliminate wastes.
The cell membrane is selectively permeable – it allows some things to pass through,
while blocking other things.
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Structure of the Cell Membrane
Phospholipid bilayer – two sheets of phospholipids.
Embedded with proteins and strengthened with cholesterol molecules.
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What’s a Phospholipid? 2 fatty acid chains, a phosphate group,
and a glycerol.– Hydrophilic heads face out
– hydrophobic fatty acids hang inside.
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Fluid Mosaic Model The parts of the cell membrane form a
fluid that can move more or less freely. The cell membrane is a “mosaic” in that
it is composed of several different parts
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Cell Membrane
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Cellular Transport Diffusion – movement of particles from
an area of high concentration to an area of low concentration.– Continues until an equilibrium is reached
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Osmosis
Diffusion of water across a selectively permeable membrane.
Occurs until water is balanced on both sides of the membrane.
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AquaporinsAquaporins Water Channels Protein pores used during
OSMOSIS WATERMOLECULES
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Cellular Transport [1] Passive transport – no energy is
needed to move particles (from high to low concentration).
– Facilitated diffusion –proteins act as tunnels allowing particles to cross the cell membrane
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Cellular Transport [2] Active transport – energy is
needed to move particles across the membrane (from low to high concentration).
1. Transport (or carrier) proteins
2. Endocytosis (endo- = into; cyto- = cell)
3. Exocytosis (exo- = out)
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Active Transport: Transport Proteins
Allow movement of particles against the concentration gradient (from low to high)
Carrier proteins –protein changes shape to open and close passages across membrane.
Carrier Protein
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Active Transport: Endocytosis
Movement of larger
particles INTO the cell
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ExocytosisMovement of larger
particles OUT of the cell
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Osmosis
Diffusion of water across a selectively permeable membrane.
Occurs until water is balanced on both sides of the membrane.
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Solutions
Solute: substance that is dissolved into something else
Solvent: the substance the solute is dissolved into
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Cell Concentrations
Hypertonic solutions – more dissolved solute.
Hypotonic solutions – less dissolved solute.
Isotonic solutions – the same dissolved solute.
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Osmosis
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Osmosis in Cells
Animal Cells- – Crenation- cell shrivels as water leaves– Lysis- cell bursts when too much water
enters Plant Cells-
– Turgor Pressure- pressure of full central vacuole pressing out on cell wall- when low, plant wilts
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Osmosis in Cells
Contractile vacuoles – expel excess water from bacterial cells that live in water to keep cells from bursting.
Turgor pressure – water pressure in a plant cell (central vacuole). Loss of turgor pressure causes wilting.
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Membrane Proteins
1. Determine what particles can pass through the membrane.
2. Serve as enzymes.3. Act as markers inside and outside of
the cell (communication).
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Can you identify the cell parts?
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