1. NYSED Part D Lab Review

2. Diffusion and Osmosis
Designed to help you understand the concepts of Diffusion and Osmosis and how these cell processes effect the cell;
Define: diffusion, osmosis, hypertonic, isotonic, hypotonic, saline, selectively permeable, molecule size;

3. Part 1: Diffusion Through a Membrane
Diffusion: 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.
After diffusion occurs…
Before diffusion occurs…

4. Initial State: Create a cell
The bag is tied off
Lugols iodine solution is placed in the beaker
A starch and glucose solution is placed in a plastic bag I S G
Iodine solution (I)
Glucose solution (G)
The bag is placed in the beaker
Starch solution (S)
Lugols iodine solution is naturally a golden brown color. It turns a bluish black color when starch is added.

5. Final State: After sitting for 20 minutes…
What happened to the glucose in the “cell”? …the starch in the “cell”? …the Lugol’s iodine outside the “cell”? Why? I G I S G I S S I I I S G I S I S
Note the color changes in the bag and the beaker from the initial state

6. Part 2: Diffusion of Water Across a Membrane (Osmosis)
Prepare a wet mount slide of the inner epidermis (skin) of a red onion section;
Observe the red onion and draw/label 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.

7. Red Onion Plasmolysis Observation
Before and after observations of red onion epidermis under the microscope (400X)
Cell membrane
Second drawing
First drawing
Cell wall
cytoplasm
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. Water flows out from the cytoplasm, which reduces the volume of the cytoplasm. Like a balloon deflating inside a box, the plasma membrane pulls back from the cell wall in a process called plasmolysis.

8. Look what happens to a cell when you add distilled water
Third
drawing
These are cells from a red onion.
They are suspended in distilled (pure) water, which is greater in concentration on the outside than the inside of the onion cell.
The nuclei are prominent in the bottom cells, and the nucleoli are visible as dark areas inside the nucleus.
In the cells of the right picture, the red pigment fills the cytoplasm, and internal structures aren't as visible.

9. Concepts You Must Know
The baggie is the "cell“ and the plastic represents the cell membrane
Diffusion moves material from high to low concentration, spending no energy
Only small molecules will go through the membrane...(starch can not). Starch WILL NOT diffuse out of the cell because it is too big and not permeable
Iodine (starch indicator) is in water in beaker (outside the cell)
Benedict's solution tests for sugar...heat it and it turns red (positive for glucose)
Water is used as a control for the indicators
Iodine or Lugol’s solution tests for starch...turns blue / black in starch
The "cell" should turn blue/black indicating that the iodine diffused into the "cell" and detected the presence of starch inside the "cell'
Test the water outside the "cell" for glucose...Benedict's will turn red after heating if it detects the presence of glucose outside the "cell'.
The diffusion of water is osmosis

10. Diffusion Lab Practice questions:
1) C 2) C 3) B 4) A 5) B
BLUE-BLACK 7) C 8) B 9) A D
Homework:
Transfer your complete answers and drawings from the rough version of the NYS lab to the “FINAL” copy.
All answers should be NEATLY transferred and diagrams colored (red) and labelled.

11. RB answers: pgs 7-10 #’s
20) ) receptors 22) 2 23) ) ) 2 26) 3 27) ) 1
29) 2 30) ) 2
32) 3 33) ) 3
35) 1

12. Transport Test Monday (after the break)
NYS Diffusion lab
Transport notes & regents practice questions
Review book pgs 7-10
Castle Cell membrane review assignment
The “FINAL” version of the NYS Lab is also due. All answers should be NEATLY transferred and diagrams colored (red) and labelled.