Download The rate of photosynthesis is affected by many factors. In this

Name: ______________________________________
What factors affect the rate of photosynthesis in living
Date: ___________________
leaves?
Background: The rate of photosynthesis is affected by many factors. In this experiment you will
use disks of spinach leaves to look at the rate of photosynthesis for your chosen variable. Since
oxygen is a product of photosynthesis, measuring how much oxygen is produced in a given amount
of time will help us to measure the rate of photosynthesis. Leaf tissue has pockets of empty space
that hold gas, so disks cut from a leaf will float. If we remove the air from those empty spaces and
replace it with liquid, the disks will sink. As photosynthesis occurs, the oxygen that is produced will
travel into those empty spaces and once enough gas has built up in that space the disks will once
again float. Photosynthesis will be measured in this lab by counting the number of leaf disks
that float, which shows how much oxygen the plant has produced.
A sodium bicarbonate/detergent solution is used to help this process. Baking soda (sodium bicarbonate) is
added to provide a source of carbon dioxide. Detergent is used as a “wetting agent” to wet the hydrophobic
surface of the leaf, allowing the solution to be taken into the leaf and helping the disks to sink in the fluid.
Materials:
Spinach (or ivy) leaves
Sodium bicarbonate/detergent solution
Wide-mouth culture dish
4 small cups
50 ml syringe
forceps
straws/hole punch
lamp
Procedures:
1. Punch out 40 leaf disks using the hole puncher. Do not punch central vein or
stem.
2. Pull the plunger out of a syringe. Put all 20 leaf disks in the syringe.
3. Groups at numbered tables will begin with the CO2 experiment. Groups at
lettered tables will begin with the control experiment.
4. Bring the correctly marked cup to the already prepared and labeled solutions.
Pour 100 mL into the graduated cylinder and then into the cup.
5. Repeat for your other cup!
6. Bring your cup back to your station. Place your cut leaf disks into the syringe.
7. Place the plunger into the syringe and draw in 5 mL of liquid from your cup.
8. Push out excess air as gently as possible without crushing the leaves. Use the
syringe to slowly obtain about 5-6 mL of the correct solution
9. As demonstrated by Mrs. McNally, create a vacuum seal with your
syringe and leaves. Remember to gently push out excess air. Repeat 3
times.
10. Remove plunger and place all liquid and leaves back into the correct cup.
11. Record how many leaves are floating initially (it is up to your group to
determine what is and is not considered floating).
12. Record how many leaves are floating after every 5 minutes for 30 minutes.
13. Repeat the experiment using a different variable of your choice. See Mrs.
McNally for options.
Name: ______________________________________
Date: ___________________
Your assignment is to write a 2 paragraph discussion section of a lab report for the Spinach
Photosynthesis lab. This section must include:
·A data chart clearly showing the results of your experiment
Your interpretation of your results. How would you explain what you observed?
· Were the results expected or not expected? Why or why not?
What went wrong in the experiment and why?
How could you improve your experiment?
· What types of experiments should be performed in the future to enhance your results? (example:
you see bacteria, but do you know what type of bacteria?)
· Should include a brief one to two sentence conclusion at the very end.
Relevant background information:
The rate of photosynthesis is affected by many factors. In this experiment you will use disks of
spinach leaves to look at the rate of photosynthesis for your chosen variable. Since oxygen is a
product of photosynthesis, measuring how much oxygen is produced in a given amount of time will
help us to measure the rate of photosynthesis. Leaf tissue has pockets of empty space that hold gas,
so disks cut from a leaf will float. If we remove the air from those empty spaces and replace it with
liquid, the disks will sink. As photosynthesis occurs, the oxygen that is produced will travel into
those empty spaces and once enough gas has built up in that space the disks will once again float.
Photosynthesis will be measured in this lab by counting the number of leaf disks that float,
which shows how much oxygen the plant has produced.
Baking soda (sodium bicarbonate) is added to provide a source of carbon dioxide. Detergent is used
as a “wetting agent” to wet the hydrophobic surface of the leaf, allowing the solution to be taken into
the leaf and helping the disks to sink in the fluid.