NYSED Part D
Lab Review
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;
Part 1: Diffusion
• 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.
Before diffusion occurs…
After diffusion occurs…
Part 2: Create a “cell”
•
•
•
•
•
Soak 10 inches of dialysis tubing;
Tie knot in one end;
Put 10mL of glucose solution in and 20mL of starch solution in;
Pinch/clamp closed and put into cellular environment (Lugol’s and
water) for 15 minutes;
Observe the changes and infer what happened
Insert into
“cellular
environment”
Wait
about 15
minutes
and
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?
S
G G
GS
I
I
I
G
I
I
At the beginning…
S
G I
IS
G
I
After 15 minutes…
Iodine solution (I)
Glucose solution (G)
Starch solution (S)
And now, the part that makes you cry (ok, not
really, but the “Red Onion” part of the lab)…
• 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“withdrawn” and the cytoplasm has lost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.