NAME___________________________________
HONORS BIO
Lab—Carbon Dioxide, Leaf Structure and Stomates
Chapter 4
Leaves have structural adaptations that enable them to perform their specific functions
efficiently. In this investigation, you will examine those structures and try to identify the
functions for which they are adapted.
PROCEDURE:
PART A: DETECTING CARBON DIOXIDE
1.
Add 30 mL of water to 2 flask. Add 1 mL of Bromthymol blue solution to each
flask. The solution should be light blue. Using a clean straw, gently bubble your
breath through one flask until you see a color change. Compare the one you
bubbled your breath through with the negative control flask. Complete the data
chart.
2. In another flask, add 30 mL of water. Add 1 mL of Bromthymol blue solution.
Add 1 mL of carbonated soda to the flask. Record the number of mL needed to
reach the same color as the flask you bubbled your breath through.
Before
After
pH
Negative control
Breath bubbled
mL of Carbonated
Soda
3. Measure the pH of each solution at the end of the experiment.
4. Write a few sentences on what you can conclude about the presence of carbon
dioxide.
5. Design an experiment or experiments that would show that plant used carbon
dioxide for their respiration and used up carbon dioxide in photosynthesis based
on the information above.
PART B: Examining a leaf
1. Examine the plant on display. Observe the leaf texture, size and arrangement.
Complete the chart.
Plant
LEAF TEXTURETOP & BOTTOM
LEAF
SIZE/SHAPE
ARRANGEMENT
ALONG STEM
A
B
C
What is the advantage of a flat, thin leaf blade to the process of photosynthesis?
How does the arrangement of leaves on the stem maximize photosynthesis?
2. Make a cross section of a leaf. Take a leaf. Put it between two staggered slide.
A___________________________ top slide
_____________________leaf
_____________________________bottom slide
At point A cut off the leaf with a razor blade. Move the top slide a smidgeon back and
make the narrowest cut possible. Observe under 100X (400x if you made a really
thin slice) Diagram below. Label as many parts as possible.
How is the location of chloroplasts in these cells advantageous for light absorption?
3. Examine the cuticle area. Describe what you see.
How does the cuticle affect the efficiency of photosynthesis?
4. Locate the lower epidermis, the guard cells and the stomata. Describe the spaces
above the guard cells.
How is the spongy tissue different from the palisade layer?
6. Make a new slide to observe the lower epidermis. Get a new leaf. Starting at the
top of the leaf, use a razor blade to scrape down the layers until you get to the clear
lower epidermis. Cut out a section and place on a slide. Add water and a cover slip.
Observe and diagram a pair of guard cells with their surrounding cells under 400X.
7. Count the number of guard cells under 400X in 3 fields of view.
Field 1
Field 2
Field 3
average
Number of
guard cells
How did the number of guard cells in the three areas compare to each other? Explain
why they were similar or different?
All plants do not have the same number of guard cells. Give a reason to explain this
observation.
How would you test this?
8. Make a new slide of the upper epidermis. How many guard cell pairs do you see?
Make a diagram of the upper epidermis at 400x.
9. Explain why the top and bottom of the leaf is different and how this would help the
plant survive.