Diffusion and osmosis

Describing Solutions –Solution: One or more substances distributed uniformly in another substance. –Solute: The substance dissolved in a solution. –Solvent: The substance in which the solute is dissolved. Concentration: the measurement of the solute in a fixed amount of solvent.Concentration: the measurement of the solute in a fixed amount of solvent. –Ex: 2% sugar solution = 2 grams sugar ml water. Sucrose Solution

Passive Transport Molecules moving across the plasma membrane without use of cell’s energy.Molecules moving across the plasma membrane without use of cell’s energy.

concentration gradient –Molecules are always moving. –From area of high concentration to area of low concentration. –Equilibrium is reached when concentrations are equal. (No concentration gradient)

Diffusion The movement of any molecule in solution from high concentration to low concentrationThe movement of any molecule in solution from high concentration to low concentration –Membranes allow some molecules to pass others not to pass. Ability to pass depends on:Ability to pass depends on: –Size –Lipid soluble. –Appropriate pore

Passive Transport:Osmosis OsmosisOsmosis –Movement of water molecules through a membrane from high concentration area to low concentration.

Terms relating to osmosis. –Hypertonic; high solutes - low water. –Hypotonic; low solutes - high water. –Isotonic; equal solutes - equal water.

How Cells Deal With Osmosis Freshwater single cell organisms:Freshwater single cell organisms: Water moves in due to osmosis.Water moves in due to osmosis. Excess water collected by contractile vacuole.Excess water collected by contractile vacuole. Water is expelled from organism.Water is expelled from organism. Contractile vacuole collecting water in a paramecium.

How Plant Cells Deal With Osmosis Plant cells have turgor pressure due to water wanting to move into the cell.Plant cells have turgor pressure due to water wanting to move into the cell. Central water vacuole fills.Central water vacuole fills. Pressure against the cell wall is turgor pressure.Pressure against the cell wall is turgor pressure. Filled water vacuole due to hypotonic environment.

How Cells Deal With hypertonic solution Plasmolysis is loss of turgor pressure.Plasmolysis is loss of turgor pressure. Water leaves cell due to hypertonic solution.Water leaves cell due to hypertonic solution. Cytoplasm and organelles move to center of cell.Cytoplasm and organelles move to center of cell. Elodea cell in hypertonic solution.

How Animal Cells Deal With Osmosis Animal cells must be in isotonic solution.Animal cells must be in isotonic solution. Animal cells in a hypotonic solution gain water.Animal cells in a hypotonic solution gain water. –Cytolysis results. Animal cells in hypertonic solution lose water.Animal cells in hypertonic solution lose water. RBC’s cell in Isotonic solution. RBC’s cell in hypotonic solution. RBC’s cell in hypertonic solution.