Diffusion and osmosis

Describing Solutions Sucrose Solution 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. Ex: 2% sugar solution = 2 grams sugar + 100 ml water.

Passive Transport Molecules moving across the plasma membrane without use of cell’s energy. Think: Why do you think this is called “passive” transport?

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) Hint: Nature loves balance. To remember which way molecules think of a rock rolling down a hill – it does not take as much energy as pushing it up a hill.

Diffusion The 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: Size Lipid soluble. Appropriate pore Hint: molecules that pass the lipid bilayer of the cell (plasma) membrane are hydrophobic, i.e. nonpolar. Everything else must go through a protein channel.

Passive Transport:Osmosis Movement of water molecules through a membrane from high concentration area to low concentration. Think: what is the difference between osmosis & diffusion?

Terms relating to osmosis. These terms always describe the surrounding solution COMPARED to the cell. Hypertonic: high solutes - low water. Hypotonic: low solutes - high water. Isotonic: equal solutes - equal water. Most cells do not explode when filled with water, they would from the excess water first.

How Cells Deal With Osmosis Freshwater single cell organisms: Water moves in due to osmosis. Excess water collected by contractile vacuole. Water is expelled from organism. Contractile vacuole collecting water in a paramecium and squirt it out if too much enters the cell.

How Plant Cells Deal With Osmosis Plant cells have turgor pressure due to water wanting to move into the cell. (keep their shape) Central water vacuole fills. Pressure against the cell wall is turgor pressure. Filled water vacuole due to hypotonic environment. Look: what happened to the shape of the cell wall?

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

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

Summarize the lecture in a paragraph with a diagram that shows the following: How water moves when a cell has more water inside than out and visa versa. What the following terms mean: solute, solvent, solution. The diffusion of an drop of ink in a glass of water over time. Explain this cartoon in terms of how osmosis works.