Osmosis

TONICITY & OUR CELLS When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell. A 0.9% solution of NaCl (saline) is isotonic to animal cells.

Way Cells Transport Molecules Passive transport (no energy required) 2. Active transport (needs energy) 3. Endocytosis / Exocytosis (larger molecules) Factors that Influence Movement Across a Membrane: concentration gradient molecular size surface area of the cell

Effects of Osmosis on Living Tissue Celery Lab *You must include the definitions for the introduction in your lab report (1 per person) *Follow Directions CAREFULLY *Complete all of the Analysis. Remember what Concentration Gradient means: In passive transport substances move from a high concentration to a low concentration – this is the natural flow of the gradient

Scalpel Safety Hold a scalpel as you would a pencil. Cut with a downward motion but never push down very hard to make a cut. (If extreme pressure is required, you have a dull scalpel or require a different instrument.) Watch the placement of your specimen-holding hand. Do not cut toward your holding hand.

Comparing Diffusion & Osmosis What is it? Diffusion is a spontaneous movement of particles from an area of high concentration to an area of low concentration. Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a more concentrated solution, up a concentration gradient. This equalizes concentrations on both sides of the membrane. Process Diffusion mainly occurs in gaseous state or within gas molecules and liquid molecules with solutes. It occurs when the medium surrounding the cell has a higher water concentration than the cell. The cell gains water along with important molecules and particles for growth. It also occurs when water and particles move from one cell to another.

Comparing Diffusion & Osmosis Importance To create energy; Helps in exchange of gases In animals, osmosis influences the distribution of nutrients and the release of metabolic waste products. In plants, osmosis is partially responsible for the absorption of soil water and for the movement of the liquid to the leaves of the plant.   Concentration Gradient Goes from a high concentration gradient to a low concentration gradient Moves down concentration gradient (from high to low) H2O concentration Water Doesn’t need water for movement Needs water for movement Examples Perfume or Air Freshener where the gas molecules diffuse into the air spreading the aroma. Movement of water into root hair cells.

Exit Slip Answer the following questions on a separate piece of paper. When you answer, think about the fact that cells have water in them, and how would they respond in hypertonic or hypotonic situations. 1) Why are you thirsty after eating a bag of potato chips? 2) After swimming in the ocean, your lips will be very dry. Explain why. 3) Describe the similarities and differences between osmosis and diffusion. 4) Compare and contrast passive and active transport (how are they the same, and how are they different?)

Egg in Salt and Water What Happened to the Egg? Place some eggs in vinegar and soak overnight to dissolve their shell. Give two eggs to each group of students. Have them place one egg in distilled water and one egg in a salt solution. Ask students to compare the eggs at the end of the class as well as the following day and explain any differences they observe. Students should see the egg in the distilled water will be enlarged while the egg in the salt solution is shrunken. Lead a class discussion to encourage students to link the explanation for why this happened to what they remember about osmosis and diffusion.