LAB: OSMOSIS IN A RED ONION CELL-DO NOT PRINT THIS PAGE
Cytoplasm = very
thin white area
between vacuole and
cell well
Large Central
Vacuole = pink area
inside cell
Cytoplasm = clear
area around vacuole
Cell Wall = grayish
edges around cell
Red onion cell in distilled water
400X
Red onion cell in salt water
400X
DO NOT PRINT THIS PAGE—USE IT AS A REFERENCE TO DRAW THE
PICTURES AND ANSWER THE QUESTIONS
For your lab, pretend this is what you see under the microscope.
Step 1. After you label the magnification as 400x,
 DRAW the image of the red onion cell in distilled water (use the circles
on your data page)—don’t forget your title! It needs to look exactly like
image—fill your circle!!
 LABEL the Large Central Vacuole and Cell wall!
Step 2: After you label the magnification as 400x,
 DRAW the image of the red onion cell in salt water (use the circles on
your data page)—don’t forget your title! It needs to look exactly like
image—fill your circle!!
 LABEL the Large Central Vacuole and Cell wall!
 What happened? …..
Step 3: Complete the lab by answering the questions on the student data
page. You will need your textbook and your 7-3 notes.
DRAWINGS NEED TO BE NEAT, DETAILED, AND IN COLOR!
LAB: OSMOSIS IN AN ONION CELL Student Data Page
RESULTS
*Use pencil or colored pencil. NO DETAIL; NO CREDIT!
Figure 1: _________________________
Magnification: ___________________
Figure 2: _________________________
Magnification: ___________________
LAB QUESTIONS
1. What is the difference between osmosis and diffusion?
2. Why aren’t your cells constantly bursting (lysing) if there is a build up of
pressure inside the cell (osmotic pressure) due to the solute concentration?
3. DRAW and EXPLAIN what happens in a hypertonic solution? (look at your
poster)
4. In this lab, are we creating a hypotonic or hypertonic environment when we
add the
salt water to the onion cells (explain your answer in detail)?
5. What is the function of the central vacuole in plants?
6. Why doesn’t the cell membrane dissolve when it is in the presence of water
(think about the function of the cell membrane and what it is made
of………..look at your notes)
7. Describe what happened to the onion cells when you soaked them in salt
water. (Describe the movement of water and what happened to the vacuole.)
8. Which caused greater osmotic pressure inside the cell, the distilled water
solution or the saltwater solution? (See page 187 for extra information on osmotic
pressure.)
9.
In the plant cell, what prevents the cell from bursting (lysing)?
10. If we watered whole onion plants growing in the field with salt water, how
would the plants respond? (Explain what would happen to the onion cells and the
overall effect on the plant—look in your notes for help.)