2 State StandardStandard 1.a. – Cells are enclosed within semi-permeable membranes that regulate their interaction with their surroundings
3 Membrane FunctionForms a boundary between living cells and their surroundings.Controls the movement of molecules into and out of the cell- Selective permeability – allows some substances to cross more easily than others and blocks passage of some substances altogether
4 Membrane Function3. Takes up substances the cell needs and disposes of the cell’s wastes. 4. Membranes can contain enzymes that function in various chemical reactions.
5 Membrane Structure The plasma membrane is 8 nm thick. It is mainly made up of phospholipids and proteins.
6 Membrane Structure carbohydrate protein cholesterolc Phospholipid bilayer
7 Membrane phospholipids Phospholipids have a hydrophilic head and two hydrophilic tails.
8 Membrane phospholipids The phospholipids form a bilayer- The hydrophilic heads face outward and the hydrophobic tails face inwardHydrophobic tails
9 Membrane ProteinsMembrane proteins are found within the phospholipid bilayerThey can extend all the way through the bilayer – integral proteinsThey can be found embedded on either surface – peripheral proteinsPhospholipidbilayerIntegral ProteinPeripheral protein
11 Some proteins transport substances across the membrane by forming channels or by physically moving them across the membrane.
12 Membrane Proteins Functions of membrane proteins include: Transport of substances across the membraneJoin cells to one anotherAct as enzymesBind to chemical messengers from other cellsAct as identification tags so cells can recognize one anotherAttach to cytoskeleton and the extracellular matrix
13 Membrane cholesterol and carbohydrates Cholesterol is found within the phospholipid bilayerIt helps stabilize the phospholipidsCarbohydratesLocated on outer layer of membrane onlyBound to proteins (glycoproteins) or phopholipids (glycolipids)Act as identification tags for cell cell recognition
15 Fluid Mosaic Model The membrane is a fluid mosaic Fluid – the phospholipids and the proteins drift within the membraneMosaic – the diversity of proteins found within the membrane and the arrangementof these proteins in the membrane
17 Transport Across the Membrane DiffusionThe tendency of particles of any kind to spread from regions of high concentration to regions of low concentrationRequires no energy, results from the random motion of atoms and molecules.
18 Transport Across the Membrane Passive TransportSubstances diffuse through the membrane without work by the cellThey spread from areas of high concentration to areas of lower concentrationAt equilibrium the molecules continue to move but there is no net change in the concentration on either side of the membraneMolecule of dyeMembraneEQUILIBRIUM
19 Transport Across the Membrane Osmosis is the passive transport of waterWater travels from an area of lower solute concentration to an area of higher solute concentration
20 Transport Across the Membrane Hypertonic- the solution with the higher solute concentrationHypotonic- the solution with the lower solute concentrationWater moves from the hypotonic solution to the hypertonic solution.
21 Transport Across the Membrane Water continues to cross the membrane until the solute concentrations are equal on both sides of the membraneIsotonic- solutions with equal solute concentrationsWater molecules continue to move across the membrane but at the same rate in both directions
22 Osmosis Problems – Draw a diagram illustrating the problem, identify the solutions as hyper, hypo or isotonic, and show the direction osmosis will occur1. A cell containing 2% solute is placed in a solution containing 10% solute.2. A candy containing 15% solute is placed in a solution containing 12% solute.3. A cell containing 7% solute is placed in a solution containing 9% solute.4. A candy containing 10% water is placed in a solution containing 90% water.5. A fish contains 95% water lives in freshwater that contains 68% water.
23 How Does Osmosis Affect Cells? Distilled Water3x SalineInduces turgor in cellsInduces turgor in animal cellsMakes plant cell pull away from cell wallMakes plant cell lyseMakes animal cell lyseMakes animal cell shrivel
24 How Does Osmosis Affect Cells? Explain the different outcomes of adding distilled water to the plant and animal cells.Which conditions best model the effects of drought on plant cells? Explain your answer.Hypothesize why plants grow better when the water surrounding their cells is slightly hypotonic to the cell.
25 Water balance between cells and their surroundings is crucial to organisms Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution.
26 Transport Across the Membrane Small non-polar molecules diffuse freely through the phospholipid bilayerMany other kinds of molecules diffuse through pores created by membrane proteinsThis type of transport is called facilitated diffusionSolute moleculeTransportprotein
28 Transport Across the Membrane Transport proteins can move solutes across the membrane against a concentration gradient.- This is called active transportActive transport requires ATP – cells use energy to move the molecule across the membrane.The solute is moved from low concentration to high concentration.
29 Transport Across the Membrane To move large molecules or particles across the membrane a vesicle may fuse with the membrane and expel its contents – exocytosis
30 Transport Across the Membrane Or the membrane may fold inward, trapping material from the outside, and form a vesicle that carries the material into the cell – endocytosis
31 Transport Across the Membrane There are 3 kinds of endocytosisPseudopod ofthe amoebaFood beingingestedPlasma membraneMaterial bound to receptorproteins
32 Transport Across the Membrane There are 3 kinds of endocytosis:Phagocytosis – a cell brings in macromolecules, other cells, or particlesPinocytosis – the cell takes in fluid and dissolved solutesReceptor-mediated endocytosis – specific molecules bind to receptors on the membrane that signal to the cell to take the molecule in
33 Harmful levels of cholesterol can accumulate in the blood if membranes lack cholesterol receptors