NYSED Part D Lab Review Thanks to: Michael Comet South Lewis High School Turin, NY 13473

Diffusion and Osmosis This lab is designed to help you understand the concepts of diffusion and osmosis and how these cell processes effect the cell This lab is designed to help you understand the concepts of diffusion and osmosis and how these cell processes effect the cell You should be able to define: diffusion, osmosis, hypertonic, isotonic, hypotonic, saline, selectively permeable, and understand the importance of molecular size You should be able to define: diffusion, osmosis, hypertonic, isotonic, hypotonic, saline, selectively permeable, and understand the importance of molecular size

Diffusion Diffusion: the net movement of molecules from an area of high concentration to an area of low concentration along the concentration gradient. Example is when you put your Lugol’s solution into the water and the water began to turn the “rust/tea” color. Before diffusion occurs…After diffusion occurs…

Part 1: Diffusion Through the Membrane of a “Cell” Soak 20cm of dialysis tubing Tie knot in one end Put 20mL of glucose solution in and 20mL of starch solution in Pinch/clamp closed and put into cellular environment (Lugol’s iodine and water) for 15 minutes Observe the changes and infer what happened Insert into “cellular environment” Wait about 15 minutes and observe. with glucose Water and

After 15 minutes, observe… What happened to the glucose in the “cell”? …the starch in the “cell”? …the Lugol’s iodine outside the “cell”? Why? Starch solution (S) Iodine solution (I) Glucose solution (G) G S I I G S I I G G G G S S At the beginning… After 15 minutes… I I I I

Part 2 – Diffusion of Water Across a Membrane (Osmosis) Prepare a wet mount slide of the inner epidermis of a red onion section; Observe the red onion and draw what you see; Add a couple of drops of saline (salt) solution to the epidermis. Wait 5 minutes; Observe under microscope again, note any changes; Add freshwater to the slide, wait 5 minutes, observe changes again.

Red Onion Plasmolysis Observation Before and after observations of red onion epidermis under the microscope (400X) Red onion under in isotonic (normal) solution. Note cell membrane and cytoplasm almost completely “fill” the boundary of the cell wall. Red onion under in hypertonic (salt) solution. Note cell membrane has “withdrawn” and the cytoplasm has lost water to the salty environment, making it appear smaller and darker.