Name: Raevon Roopchan Class: 4 West Teacher: Miss Mohammed-Khan Line:4L4 Subject: Biology
2021-2023 Date Given: 28/03/2022 Page Number: Lab #5
Title: Photosynthesis
Aim: To test for the presence of starch in a green leaf
Apparatus and Materials:
• Beaker
• Tripod stand
• Wire gauze
• Bunsen burner
• Forceps
• Boiling tube
• White tile
• A small green leaf
• Ethanol alcohol
• Iodine
• Stop watch
Procedure:
1. A small leaf was obtained from a plant which was exposed to strong sunlight for a few hours.
2. The leaf was then placed in a beaker of boiling water.
3. The beaker of boiling water, which was being heated over a Bunsen burner, was left to heat for
about 5 minutes to kill the leaf cells.
4. The Bunsen burner was then turned off.
5. Using a pair of forceps, the leaf was removed from the beaker and placed into a boiling tube
which was half way filled with ethanol alcohol.
6. The boiling tube was placed into the beaker of boiling water for 10 minutes.
7. The leaf was then removed from the boiling tube of alcohol and it was then dipped into the
beaker of hot water to soften the leaf.
8. The leaf was placed on a white tile then a few drops of iodine solution were added to cover the
surface of the leaf.
9. The change in the colour of the iodine solution on the leaf was then recorded.
Drawing of experimental setup:
Trends: the natural yellow-brown colour of the iodine will change to blue/black indicating starch is
present.
Discussion: Photosynthesis is the process by which plants use sunlight, water and carbon dioxide to
create oxygen and energy in the form of sugar. The Bunsen burner was turned off before heating as a
safety precaution, because alcohol is flammable. The purpose of the alcohol was to dehydrate the leaf
and also to remove the chlorophyll (green pigment). It was necessary that the leaf be placed in water a
second time so it would be rehydrated and it would lay flat as a result. Iodine was the chemical reagent
used to test the leaf for starch. After placing Iodine on the leaf, the Iodine appeared blue/black in colour
which indicated that starch was present. If a variegated leaf, having two colours, white and green was
tested, the results would be different because the iodine would only turn blue/black on the green parts
of the leaf and not the white parts.
Limitations:
• Health of the leaf
• Darkness of leaf
Precautions:
• Using forceps
• The Bunsen burner was turned off before heating alcohol
Sources of error:
• Over boiling a smaller leaf/under boiling bigger leaf
• Leaf may not have been in alcohol long enough
Reflection: This experiment taught me how to test for starch in a leaf, using iodine. This experiment was
very fun and I did enjoy getting to see everything happen before my eyes. This information could be
valuable to society since starch contains glucose and glucose is used to give plants, humans and animals
energy. So being able to test a leaf for starch can be very useful for people who work with plants/in
agriculture.
Conclusion: When iodine was placed on the leaf, it turned the colour from yellow-brown to blue/black,
indicating that starch was present in the leaf.
Mark Scheme:
