SBI 4U
Petrany
Lab – What Do Plants Require for Photosynthesis?
Adapted from Nelson Biology 12, 2012 and Course Content for SBI 4U from KPR eLearning
The process of photosynthesis uses light energy, carbon dioxide (CO2) and water (H2O) to form
simple sugars called glucose. The reaction for photosynthesis is:
CO2(g) + H2O(l) + light energy → [CH2O] + O2(g)
A colour pigment, chlorophyll, traps the light energy to help convert it to chemical energy in the
form of glucose. Excess glucose is stored in the leaves, stems and roots of plants as starch. In this
investigation, you will be investigating what happens to the ability of a geranium plant to produce
glucose and starch through photosynthesis when CO2, light and chlorophyll are removed.
Pre-Lab Activity - Testing for Starch in the Leaves of Plants
1. Read page 175 from the link “Requirements for Photosynthesis” (on D2L-under Unit 2)
2. Read p. 141 – 144 and p. 147 – 153 of Nelson Biology 12
3. Complete the “Testing for Biological Molecules” tutorial (you must click on the
Photosynthesis Lab on D2L-under unit 2) – DO NOT COMPLETE PART 1 – PRODUCTS OF
PHOTOSYNTHESIS...THIS IS PART OF THE LAB ACTIVITY.
4. Answer the following pre-lab questions and have them checked by your teacher before you
begin the lab.
a. What are the reactants required for photosynthesis to occur?
b. What do you think would happen if one of those reactants were removed from the
process? Explain your answer. (HINT: This is the development of your prediction and
hypothesis)
c. If a leaf has been boiled briefly in water, then boiled in alcohol, what is the expected
result of treating that leaf with 5 drops of iodine?
d. What are the control, independent and dependent variables in this lab?
5. Once you have had your Pre-Lab approved by your teacher, you may proceed with the
remainder of the on-line lab activity. Use the observation chart included in this handout for
the lab – DO NOT DOWNLOAD ANYTHING THE ON-LINE LAB ASKS YOU TO.
SBI 4U
Petrany
Observations for Photosynthesis Lab
Lab Part
Description of Experiment
1 – Control
Experiment
– Testing for
The
Presence of
Starch
A leaf from a geranium plant
will be heated in water
briefly, then heated in alcohol
for a set period of time. The
leaf will then be treated with
iodine to test for the presence
of starch.
2 – Absence
of Light
A cardboard cut-out of the
letter “A” will be placed on
top of a geranium leaf in a
petri dish. The leaf will be
exposed to a light source for
“24 hours”. It will then be
tested for the presence of
starch using the control
experiment.
3 - Absence
of CO2 - Two
geranium
plants will
be used.
One will be exposed to sodalime and placed in a sealed
bag. The other will be
exposed to sodium hydrogen
carbonate and placed n a
sealed bag. Both plants will be
exposed to a light source for
“24 hours”. A leaf from each
plant will then be tested for
the presence of starch using
the control experiment.
4 – Absence
of
Chlorophyll
A plant with variegated leaves
will be placed under a light
source for 24 hrs. A leaf from
the plant will then be tested
for the presence of starch
using the control experiment.
Observations of Leaf
Before Treatment
Observations of Leaf
After Treatment
SBI 4U
Petrany
Discussion Questions – DO NOT ANSWER THE DISCUSSION QUESTIONS AT THE END OF THE ON-LINE
LAB SLIDE SHOW!!!
1. What is the purpose of keeping the plants in the dark before using them in the experiment? (4
marks) T/I
2. What is a variegated leaf? What effect does variegation of leaves have on photosynthesis? (4
marks) A;T/I
3. What purpose do the soda lime and the sodium hydrogen carbonate serve in this investigation?
Why were the plants placed in a sealed bag? (4 marks) K;T/I