Photosynthesis
Investigating Photosynthesis
Objectives
• Controls and experimental Set-ups
• Destarching Plants
Experiments for Photosynthesis
Destarch the plants
Investigation
Testing for Starch
Conclusion
Destarching the Plants
• Before carrying out investigation, we have
to ensure that the leaves of the plants do
not contain any starch.
• This can be done by destarching the
plants.
Destarching the Plants
•
•
•
This can be done by placing the plants in
the dark for at least 48hrs.
In this way, any starch will be converted
to glucose for growth and energy
production (respiration).
The plants will not contain any starch
and are ready for investigation.
Any starch that is detected in the leaves during
the investigation shows that photosynthesis has
taken place.
Experiments for Photosynthesis
Destarch the plants
Investigation
Testing for Starch
Conclusion
Control and Experimental Setups
• To investigate photosynthesis, we need to
have to have control and experimental setups.
• Control: Everything is given to the setup.
• Experimental: Everything is given except
for the condition that is to be tested.
Is light necessary for
photosynthesis?
1.Take a destarched potted
plant as shown in the
diagram.
2.Leave in strong sunlight
for a few hours.
3.Pluck out leaf X and test
for starch.
Leaf X
(From: http://faculty.ntcc.edu/mhearron/photosynthesis.htm)
Observation
Yellowish-brown on
part not exposed to
light  showing
absence of starch
(Diagram from: http://faculty.ntcc.edu/mhearron/photosynthesis.htm)
Blue-black colour
on parts of leaf
exposed to light 
showing presence
of starch
Is carbon dioxide necessary for
photosynthesis?
Is chlorophyll necessary for
photosynthesis?
(From: http://faculty.ntcc.edu/mhearron/photosynthesis.htm)
Experiments for Photosynthesis
Destarch the plants
Investigation
Testing for Starch
Conclusion
Testing for Starch
• After carrying out investigation, we need to
test the leaves for starch in order for us to
observe the results.
Name: _______________________ (
)
Date: _____________
Class: __________
Testing for Starch
1.
2.
3.
4.
5.
6.
Place leaf in boiling water
Purpose : ___________________________________
___________________________________________
Put the leaf in a boiling tube and cover with ethanol
Purpose: ____________________________________
___________________________________________
Dip leaf into warm water to remove the alcohol so the
iodine stain can penetrate the leaf.
Cover leaf with iodine solution to test for the presence
of starch.
Those parts of the leaf that stain _______________
contain starch.
Those parts that are ________________ (the colour of
the iodine stain) do not have starch.
Testing for Starch
1. Place leaf in boiling water
Purpose : to kill the cell and tear open the cell
membranes, break the open cells and make it soft .
2. Put the leaf in a boiling tube and cover with ethanol
Purpose: to remove the green chlorophyll so the final
results can be clearly seen.
3. Dip leaf into warm water to remove the alcohol so
the iodine stain can penetrate the leaf.
4. Cover leaf with iodine solution to test for the
presence of starch.
5. Those parts of the leaf that stain blue-black contain
starch.
6. Those parts that are yellowish-brown (the colour of
the iodine stain) do not have starch.
Yellowish-brown;
this part does
not contain any
starch
(From: faculty.ntcc.edu/mhearron/photosynthesis.htm)
Blue-black; this
part contains
starch
Test leaf for starch
(From: http://www.macleans.school.nz/students/science/F4/plants/photosynthesisExptgif.gif)