NYSED Part D NYSED Part D Lab ReviewLab Review

Thanks to:Michael CometSouth Lewis High SchoolTurin, NY 13473

Diffusion and OsmosisDiffusion and Osmosis

This lab is designed to help you This lab is designed to help you understand the concepts of understand the concepts of diffusiondiffusion and and osmosisosmosis and how these cell processes and how these cell processes effect the celleffect the cell

You should be able to define: You should be able to define: diffusiondiffusion, , osmosisosmosis, , hypertonichypertonic, , isotonicisotonic, , hypotonichypotonic, , salinesaline, , selectively selectively permeablepermeable, and understand the , and understand the importance of molecular sizeimportance of molecular size

DiffusionDiffusion 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 Part 1: Diffusion Through the Membrane of a “Cell”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…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

SI

IG

S

I

I

G

G

GG

S

S

At the beginning… After 15 minutes…

II

I

I

Part 2 – Diffusion of Water Across a Part 2 – Diffusion of Water Across a Membrane (Osmosis)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 Red Onion Plasmolysis ObservationObservation

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.