Lesson 19. Inquiry on Variables that can affect the Rate of Photosynthesis
Objective: to determine the effect of different environmental conditions on the rate of
photosynthesis.
EQ: What environmental conditions can affect the rate of photosynthesis?
Bridge: Re-write the chemical formula you decided on yesterday for photosynthesis.
Mini Lesson
Share out of the bridge. Might again be worth having one student share out and then have others
make corrections/changes as needed, bringing them back to reactants on the left of the arrow,
products on the right of the arrow.
So if this is autotrophic nutrition, how is it related to heterotrophic nutrition? Where does the
original source of all energy on Earth come from then?
So how can we determine if photosynthesis really does need CO2?
With the students, perform the following procedure. This can be a tough one for them so it
might be best to do it together (takes about 10 minutes) and you will definitely want to perform it
prior to the class to make sure you are doing it and showing it to them properly…..
**I would have them do this as partners or groups, where each student is going to be responsible
for preparing one of the cups so they are ready at the same time. It should take about 10 minutes
for all the disks to come up in the baking soda container…. The soap solution should not come
up at all. By creating the vacuum, you have pulled all the gas out of the spongy layer and air
spaces and adding the baking soda creates the CO2 the disks need to do photosynthesis. The
soap is added to cut through the waxy layer of the leaf. To make the solutions, take about 500
mL water and add a DROP (put enough soap to cover a fingertip) of soap into the solution…..
any more than this and the bubbles will start to get in the way of the experiment. For the baking
soda solution, do the same but then add 1 tsp of baking soda to the soap and water.**
Materials: spinach leaves, soap solution, 10cc syringe, baking soda/soap solution, 2 clear cups,
hole punch, light source with at least a 10W light bulb (make sure the cups are sturdy so they
don’t melt)
Procedure:
1. Take the spinach leaves and punch out 20 pieces, trying to miss the veins
2. Place 10 of the disks into an empty syringe and 10 disks into a second empty syringe,
tapping them to the bottom.
3. Put the plunger back into the syringes, pushing down as far as you can without touching
the leaves
4. In the first syringe, suck up the baking soda/soap solution until about half full
5. In the second syringe, suck up the soap solution until about half full
6. Tip the syringe up so the point is up and press out all of the air (a little water should come
out the tip but don’t crush the leaves)
7. Put your finger over the syringe tip to seal then gently pull back the plunger to create a
vacuum
8. While still holding the plunger back and covering the hole, shake for about 10 seconds or
until the plant disks sink
9. CAREFULLY pull the plunger out of the syringe, putting the solution and the disk into
the cup
10. Put the prepared cup in a dark place and repeat with the second syringe having the
different solution (make sure they are labeled)
11. Add additional solution to each cup until half full, making sure to match the solutions to
the right cup (do NOT at the baking soda solution to the solution that was just soap)
12. Place the cups under the light source, making sure they are getting equal amount of light
(both cups need to go under at the same time so your times are accurate)
13. Record how many disks come up each minute until all 10 disks come up.
Expectations for the Work Period: Have students create their own investigation using the same
technique for determining if photosynthesis is occurring in plants or not. The rest of this day
should be used to figure out the question and supply you with a list of materials for carrying out
their procedure the next day. They should work either alone or in pairs so that there are many
different questions to be tested.
Work Period: Design and Run your Experiment
Use the lab template, but since they are reporting out, they can use just the headings for the
sections and create the actual lab as a poster for the gallery walk.
Day 1: figure out your variable/question, list your materials, and determine your
prediction/hypothesis.
Teacher Note: I encourage that everyone do a different variable….. there are a TON that
they can test in this experiment, and it only takes 10-15 minutes to collect data instead of
DAYS like with growing plants. Since there should be about 10-15 different experiments
going on you may want to let some students look into things like different kinds of leaves
from different plants or variegated leaves vs green leaves even though they are not
environmental conditions, but have them relate it back to evolution and the environment if
they do and make sure they have an appropriate question to answer.
Day 2. Run your experiment and complete your write up, ready to report out
Day 3. Present your findings, record other people’s findings
Summary: Answer your EQ.
Closing: Experimental Design Regents question (either marigolds or tomato plant one)
SPED and ELL Modifications:
1. Review and demonstrate (modeling) each step of the lab for visual learners
2. Prerecord directions so students can listen to them multiple times
3. Pick topics for lower functioning students and pair them with responsible students
Apps and Internet Activities:
1. I highly recommended video recording this lab
 Video Editor App:
 Video App:
2. There are several apps that offer flashcards and videos on photosynthetic processes and
plants
 Botany app:
 101 concepts biology app:
 VCell app:
 Principles of Life Flashcards app – chapter 6:
3. A virtual lab about the preferred light color for photosynthesis: http://highered.mcgrawhill.com/sites/007877800x/student_view0/unit2/chapter11/virtual_lab.html
4. A virtual lab depicting the actual molecular level – at the thylakoid membrane:
a. http://www.mhhe.com/biosci/genbio/biolink/j_explorations/ch09expl.htm
5. A virtual lab measuring Waterweed photosynthetic rate:
http://www.saddleworth.oldham.sch.uk/science/simulations/waterweed.htm
6. Another virtual lab for measuring the rate of photosynthesis:
http://www.phschool.com/science/biology_place/labbench/lab4/intro.html
7. A great tutorial with not only text but audio as well for students to review the process of
photosynthesis as needed:
http://www.harcourtschool.com/activity/science_up_close/512/deploy/interface.html
Independent Practice: Regents Questions