This document contains information on photosynthesis including the: raw materials needed, conditions and products. The steps needed by science students to carry out a starch test may also be found in this document. Lastly, you will find a critical thinking question involving a variegated leaf.

1. Photosynthesis
and the leaf
• Starch test

2. • The process by which green plants use Carbon dioxide and
water in the presence of sunlight energy and chlorophyll to
make food (glucose) and oxygen.
• Plants undergo photosynthesis to produce their own foods.

3. • Carbon dioxide and water are the Raw materials
• In the presence of sunlight and chlorophyll are the Conditions
necessary for photosynthesis to take place
• Glucose and oxygen are the Products of the process.

4. Testing a leaf for starch
� Investigating photosynthesis – starch and
chlorophyll
� During photosynthesis a plant absorbs
light energy using the pigment
chlorophyll.

5. This allows it to convert carbon dioxide and
water into glucose. This glucose is:
1. transported to the growing parts of the
plant for use in respiration
2. transformed into cellulose, proteins and
oils
3. turned into starch for storage

6. � After photosynthesis has taken
place, the end product is
glucose.
� Starch is made up of long
chains of glucose.
� Therefore, to prove that
photosynthesis has taken place,
you can test the leaf to see if
starch is present.

7. Starch testing
Iodine solution is used to test leaves for the
presence of starch. You need to:
1. heat a plant leaf in boiling water for 30
seconds (this kills the leaf, stopping any
chemical reactions)
1. add the leaf to boiling ethanol in a
water bath for a few minutes (the boiling
ethanol dissolves the chlorophyll and
removes the green colour from the leaf -
it turns white so it is easy to see the
change in colour)

8. 3. wash with water to re=hydrate and
soften the leaf and spread onto a white
tile
3. add iodine solution from a dropping
pipette
After a few minutes, the parts of the leaf
that contain starch turn the iodine from
brown to blue/black

9. Have you ever seen these
leaves?
� Variegated
leaves have green
parts (where the cells
contain chlorophyll)
and white parts
(where there is no
chlorophyll).

10. Since chlorophyll is necessary for
photosynthesis to take place, which parts of
this leaf:
1. will not become blue/black with iodine
solution(no presence of starch)
2. will become blue/black with iodine
solution(starch is present)
NOTE:
A CHANGE TO BLUE/BLACK
WITH IODINE SOLUTION
MEANS THAT STARCH IS
PRESENT AND PHTOSYNTHESIS
HAS TAKEN PLACE.

11. Questions
1. The starch test is done to test for which
substance?
2. If presence of
chlorophyll=>photosynthesis=>starch(glucose)
then No chlorophyll => no ___________=> no
________ _.
3. Glucose is stored in plants as S _ _ r _ h.
4. What solution is used to test leaves for the
presence of starch?