Name: ________________________________________ Hour: ______________
Biology Unit 6 – Plant Cell & Photosynthesis Lab
Part 1: Background
Waterweed (Elodea sp.) is a submersed aquatic plant that is native to
North American and is also widely used as aquarium vegetation (top
picture). Elodea lives entirely underwater with exception of small white
flowers that bloom at the surface and are attached to the plant by long,
delicate stalks. Elodea is ideal for examining plant cell structure due to
its relatively thin leaves, which can be only a single layer of cells thick!
This allows us to see the inner cell structure, including the rigid cell
walls and the chloroplasts (bottom picture).
This highly magnified view of an Elodea leaf (bottom picture)
shows a living photosynthetic cell. Because most of the cell is
occupied by a large, water-filled central vacuole, the
chloroplasts are typically pushed to the periphery (outer edges)
of the cell, just inside the cell wall and membrane.
In addition to looking at the cells of Elodea leaves, we will be
examining the structure of onion cells. These cells are large
enough to provide us with a clear view of the some of the inner
organelles of the cell, particularly the nucleus.
Checkpoint Questions:
1. Why do we use Elodea to look at the structure of plant cells?
2. When looking at the Elodea cells under the microscope, where do you expect to find the
chloroplasts?
3. Given what you know about photosynthesis and the role of chloroplasts in this process,
do you expect to see chloroplasts in the onion cells? Why or why not?
Part 2: Slide Preparation
Using the slide kit provided, you will prepare a wet-mount slide of a layer of onion cells and a
single Elodea leaf in order to examine the structure of a plant cell. Follow the procedures
outlined below to make your slide. Though you can work with a partner, YOU ARE
REPONSIBLE FOR MAKING YOUR OWN SLIDE.
Onion Cell:
 Remove a rectangular glass slide and plastic over slip from your kit and set them on a
sheet of paper towel.
 Remove the piece of onion and set it on the sheet of paper towel.
 Using the forceps (tweezers) at your table, carefully peel away a SINGLE LAYER of
onion cells. This is not the same as the easily separated rings of an onion. The layer
should be paper-thin and nearly translucent (see-through). See the image on the overhead
for clarification!
 Once you have obtained a single layer of cells (about 1 cm in length/width), carefully
transfer it to your clean slide. The onion skin should be placed in the center of the slide.
Be sure to lay it smoothly, with no wrinkles/tears/bubbles.
 When your slide is prepared to this point, call Mrs. Gentile to your desk to place a drop of
iodine water over the layer; this will help us to view the nucleus!
 After the water drop is in place, carefully place your cover slip over the specimen (water
+ onion). FOLLOW THIS PROCEDURE: Start by placing one side of the cover slip
perpendicular to the edge of the water drop. Slowly lower the cover slip over the drop
until it is flush with the slide. Make sure there are no air bubbles!
 Set your prepared onion slide on the paper towel and proceed with the Elodea leaf
procedures.
Elodea Leaf:
 Remove a rectangular glass slide and plastic over slip from your kit and set them on a
sheet of paper towel.
 Remove the sprig of Elodea leaves and set it on the paper towel.
 Using the forceps (tweezers) at your table, carefully remove one leaf from the spring.
 Transfer the leaf to the center of the slide.
 When your slide is prepared to this point, call Mrs. Gentile to your desk to place a drop of
water over the leaf; this will help to keep it in place.
 Carefully place your cover slip over the specimen (water + leaf). FOLLOW THIS
PROCEDURE: Start by placing one side of the cover slip perpendicular to the edge of
the water drop. Slowly lower the cover slip over the drop until it is flush with the slide.
Make sure there are no air bubbles!
 Set your prepared Elodea slide on the paper towel.
Part 3: Viewing with the Microscope!
 With your partner (or on your own), carefully bring your slides to an available
microscope.
 Using proper microscope procedures, begin by examining the onion slide. SEE
MICROSCOPE PRE-LAB TO REVIEW PROCEDURES!
 Remember: Always start on LOW POWER (red objective) and move up to
MEDIUM or HIGH.
 ONCE YOU ARE ON HIGH POWER, YOU CANNOT USE THE COARSE
OBJECTIVE (big knob).
 Using the field of view circles below, draw the onion cell on both LOW and
MEDIUM/HIGH power. Be sure to label each drawing with the structures you see (e.g.
nucleus).
 Once you have completed the onion cell, repeat the procedures with the Elodea leaf.
Part 4: Recording Data
Onion Skin:
Low Power View
High Power View
Elodea leaf:
Low Power View
High Power View
Part 5: Post-Lab Analysis
1. Describe the size comparison between the onion and Elodea cells. Which were bigger?
Smaller?
2. Where did you find the nucleus in the onion cell?
3. How many chloroplasts did you find in each Elodea cell (you can estimate)? Why do you
think you think you observed that number?
4. Would you expect to find chloroplasts in a cell sample of a carrot root? WHY/WHY NOT?
5. Would you expect to find chloroplasts in a cell sample from a pine tree needle? WHY/WHY
NOT?