Osmosis Chapter 5

 REVIEW: An important function of cell membrane is to regulate the movement of dissolved molecules from the liquid on one side of the membrane….. to the liquid on the other side.

 The space outside the cell,……. and in between cells if called the ECF (Extracellular fluid)  The space inside the cells….. is the cytoplasm  Cells don’t have legs, ……so in most multicellular organisms they float around in the ECF.

 Cell membranes- are semi- permeable  Although many substances can diffuse across biological membranes, some are too large or too strongly charged to cross the lipid bilayer.  Water passes quite easily across most membranes

 …the diffusion of water through a selectively permeable membrane.  Water will tend to move across the membrane until equilibrium is reached.

 What is the difference between  distilled water?  tap water?  fresh water?  salt water?

 Isotonic: same strength, equal concentrations on both sides

 Hypotonic: Less concentrated, less solute (ex. Pure water)

 Hypertonic: More concentrated, more solute

 Cells are filled with salts, sugars, proteins, and other molecules  In fact no where in your body is there “fresh water”, all of your bodily fluid contain some combo of the above-

 Stranded at sea…what do you drink?

 Drink salt-water?  ECF has salt  Cells will expel water and shrink  Body will sense this and brain will send signals that you are thirsty…  So you will drink more saltwater and ultimately expire sooner  Wait, and hope it rains, or that you get rescued?  You can go 3 days without water…..

 Is it a danger to certain plants and their cells?

 plant cells and bacteria, do come into contact with fresh water  But… they are surrounded by tough cell walls.  The cell walls prevent the cells from expanding, even under tremendous osmotic pressure, but there can still be some damage done.

 Some plants and fish are adapted to live in salt water.  Fish- expel water and salt through gills  Plants ….have a higher internal cell salt content?

 What do you think will happen to the carrot? (bigger/ smaller)  How will you know if the size changed?  Do you think it will feel any different?

 1. What happened?  Size (bigger/ smaller)  Turgidity ( flacid, or crisp)  2. Which beaker had a hypertonic solution?  Hypotonic?  Isotonic? 3. Explain how the concept of this lab relates to osmosis:

 The concentration of a solution is the mass of solute in a given volume of solution, or mass/volume.  In this lab you will have to make 3 concentrations of the solution, in which the potato will rest overnight