Presentation on theme: "Homeostasis and Transport"— Presentation transcript:
1 Homeostasis and Transport Chapter 5Homeostasis and Transport
2 HomeostasisThe property of a system that regulates its internal environment and tends to maintain a stable, constant conditionCell membranes help organisms maintain homeostasis by controlling what substances enter and leave cells
3 Passive TransportSubstances crossing the cell membrane without any input of energy by the cell – move down their concentration gradientTypes:DiffusionOsmosisFacilitated DiffusionIon Channels
4 Concentration Gradient Concentration - how many of a substance’s molecules are sitting in a specific volume of a solutionGradient - a measurement of how much something changes as you move from one region to anotherConcentration Gradient - the difference in the concentration of molecules across a space
8 Diffusion Add a sugar cube to a beaker of water It sinks to the bottom making the concentrationof sugar higher there
9 Diffusion As the cube dissolves sugar molecules break away and move from the bottom tothe top of the beaker
10 Diffusion Because of their kinetic energy, the molecules of sugar are in constant motionThey keep moving untilthey hit something and thenthey rebound
11 Diffusion If no object blocks their movement, molecules continue on their pathThey move down theirconcentration gradient fromareas of high concentrationto low concentration untilThey reach equilibrium
12 Do Now What is homeostasis? Do forms of Passive Transport require cell energy?What is diffusion?
13 EquilibriumDiffusion will eventually cause the concentration of molecules to be the same throughoutEquilibrium – when the concentration of the molecules of a substance is the same throughout a spaceThe molecules are still moving, but they are just as likely to move in one direction as the other – they balance each other
15 Diffusion Through Cell Boundaries Cell membrane regulates movement of dissolved molecules from the liquid on one side of the membrane to the otherCell membrane - selectively permeable - some substances can pass across it and some cannotNonpolar molecules can diffuse through the lipid bilayer as well as small molecules
16 Diffusion Through Cell Boundaries If a molecule can pass through a cell membrane, it will diffuse from an area of high concentration on one side to an area of low concentration on the otherThe cell is not required to use energy for diffusion.
19 Osmosis Both solute and solvent molecules can diffuse In cells: the solutes are organic and inorganic compoundsthe solvent is water
20 OsmosisOsmosis - diffusion of water through a selectively permeable membrane (cell membrane)Water moves down its concentration gradientIt moves from areas of high concentration of water to low concentration of waterOsmosis does not require energy
22 OsmosisWhen water is more concentrated on one side of the membrane, water will move to an area of lower concentration in order to re-establish equilibrium.Question??If there is more salt outside of the cell, will water move into the cell or out of the cell??
23 OsmosisThe net direction of osmosis depends on the concentration of solutes on the two sides of the semi-permeable membraneIn a cell, this can have important consequences
24 Types of SolutionsSolutions can be:IsotonicHypotonicHypertonic
25 Isotonic SolutionThe concentration of solutes is the same inside and outside cellWater will diffuse into and out of the cell at equal rateNo net movement of water
26 Hypotonic SolutionThe solution has a lower solute concentration than the cellWater diffuses into the cell until equilibrium is establishedNet movement of water – into the cell
27 Hypertonic SolutionThe solution has a higher solute concentration than the cellWater diffuses out of the cell until equilibrium is establishedNet movement of water is out of the cell
29 Osmotic PressureOsmosis exerts a pressure (osmotic pressure) on the hypertonic side of a selectively permeable membrane. (This could cause water to rush into cells and cells could bust)This does not happen in animal cells because they are usually in isotonic fluidsexample: blood
30 Animal Blood Cells in Different Solutions IsotonicHypertonicHypotonic
32 Osmotic PressurePlant and Bacteria cells are usually in hypotonic environments (water wants to diffuse into the cell:exposed to tremendous osmotic pressureRigid cell wall keeps plant and bacteria cells from bursting.
33 Plant Cells in Different Solutions HypotonicIsotonicHypertonic
35 Facilitated Diffusion Some molecules easily pass through the cell membrane because they dissolve in lipids (alcohols) - others can not (glucose)Specific carrier proteins allow these other molecules to pass through the cell membrane easilyThis does not require energy (type of diffusion) - only occurs when concentration is higher on one side of the membrane than the other.
36 Facilitated Diffusion Carrier protein binds to molecule and changes shapeCarrier protein shields molecule from hydrophobic lipid bilayerCarrier protein releases molecule inside cellCarrier protein returns to its original shape
38 Ion ChannelsSome ions are important for cell functions (Na+, K+, Ca2+ and Cl-)Since they are charged and hydrophilic, they can’t get across the lipid bilayerIon channels – specific membrane proteins that help ions get across cell membrane
39 Active Transport Requires cell’s energy Cells must move substances up their concentration gradientSubstances go from areas of lower concentration to areas of higher concentration
40 Types of Active Transport Cell Membrane PumpsEndocytosisExocytosis
41 Cell Membrane PumpsCarrier proteins also help out in active transport and work against the concentration gradient: Low HighSimilar to facilitated diffusion, but cell’s energy is required
42 Sodium (Na+) - Potassium (K+) Pump Many types of animal cells need to have:a high concentration of Na+ outside the cella high concentration of K+ inside the cellThe sodium-potassium pump uses cell energy to maintain this concentration difference
43 Sodium (Na+) - Potassium (K+) Pump Three Na in the cytoplasm bind to the protein pumpAt the same time, the protein splits a phosphate from an ATP molecule (energy)Protein carries the three Na across the lipid bilayer and releases them out of cell
44 Sodium (Na+) - Potassium (K+) Pump Next the protein binds two K from outside of cellAs K bind, the phosphate is released and the protein changes shape againFinally the protein releases the K into the cytoplasm of the cellThis creates an electrical gradient across cell membrane (nerve and muscle cells)
47 Endocytosis and Exocytosis Some substances (macromolecules and food particles) are too large to enter cell through membrane proteinsEndocytosis and exocytosis can move these substances across cell membraneRequires cell energy – active transport
48 EndocytosisTaking material into the cell by means of infoldings, or pouches in the cell membranePouches pinch off and form vesicles (organelles) in cytoplasm.
49 Two Types of Endocytosis Phagocytosis: cell membrane engulfs food or whole cells (bacteria and viruses)Pinocytosis: cell membrane engulfs liquids
50 ExocytosisMembrane of vesicle surrounding material fuses with cell membrane, forcing contents out of the cellReverse of endocytosisRelease of proteins