Activity Book

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Activity Book
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Practical 7.1 Detection of starch produced from
photosynthesis (the starch test) Practical
7.2 Detection of oxygen produced from
photosynthesis Practical 7.3 Investigation of
the need for chlorophyll in photosynthesis Practi
cal 7.4 Investigation of the need for carbon
dioxide in photosynthesis
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Practical 7.5 Design an investigation of the need
for light in photosynthesis Practical
7.6 Investigation of the effect of light
intensity on the rate of photosynthesis Practical
7.7 Design an investigation of the effect of
carbon dioxide concentration on the rate of
photosynthesis Practical 7.8 Test for the
different types of food in plants
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Practical 7.9 Examination of the structure of
leaves STS connection 7.1 Enhanced plant growth
in a greenhouse Exercise 7
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7.1
Detection of starch produced from photosynthesis
(the starch test)
Questions
1 What is the purpose of boiling the leaf in
water?

• This destroys the differentially permeable nature
  of the cell membrane
• and thus allows the iodine solution to pass into
  the cells.
• This also kills the leaf cells and
• stops chemical reactions like photosynthesis.

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7.1
Detection of starch produced from photosynthesis
(the starch test)
2 What is the purpose of boiling the leaf in
absolute alcohol?
Absolute alcohol dissolves and removes
chlorophyll from the leaf, so that any colour
changes can be observed clearly on this
decolourized leaf. Besides, boiling alcohol
speeds up the diffusion of chlorophyll out of the
cells.
ANS ?
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7.1
Detection of starch produced from photosynthesis
(the starch test)
3 What is the purpose of dipping the leaf into
hot water again after boiling in absolute alcohol?
This softens the leaf because alcohol makes the
leaf hard.
ANS ?
4 What do the results show? Has photosynthesis
taken place?
ANS ?
Starch is present in the green leaf.
Photosynthesis has taken place.
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7.2
Detection of oxygen produced from photosynthesis
Questions
1 Why is dilute sodium hydrogencarbonate solution
but not water used?
To supply enough carbon dioxide for
photosynthesis.
ANS ?
2 Why is the filter funnel raised by the stoppers?
ANS ?
To allow free circulation of solution.
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7.2
Detection of oxygen produced from photosynthesis
3 What do the results show? Has photosynthesis
taken place?
The gas released from the Hydrilla plants is
oxygen. Photosynthesis has taken place.
ANS ?
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7.3
Investigation of the need for chlorophyll in
photosynthesis
Questions
1 Why do we need to destarch the plant first?
To remove starch in the leaves. This ensures that
any starch found at the end of this experiment is
newly made.
ANS ?
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7.3
Investigation of the need for chlorophyll in
photosynthesis
2 Why do we need to test a leaf from the
destarched plant for starch?
To confirm that starch is absent in the leaves
before the experiment starts.
ANS ?
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7.3
Investigation of the need for chlorophyll in
photosynthesis
3 What is the control in this practical? Explain.
The yellow part serves as the control. This is
because the yellow part does not contain
chlorophyll.
ANS ?
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7.3
Investigation of the need for chlorophyll in
photosynthesis
4 Compare the colour pattern of the leaf with the
result of the starch test. Which part of the leaf
produces starch?
The green part turns blue-black upon the addition
of iodine solution. This shows that it produces
starch.
ANS ?
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7.3
Investigation of the need for chlorophyll in
photosynthesis
Conclusion
What conclusion can you draw from this practical?
Starch is made only in the presence of
chlorophyll. Chlorophyll is needed for
photosynthesis.
ANS ?
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7.4
Investigation of the need for carbon dioxide in
photosynthesis
Questions
1 What is the control in this practical? Explain.
Leaf B is the control because of the absence of
carbon dioxide in the flask.
ANS ?
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7.4
Investigation of the need for carbon dioxide in
photosynthesis
2 If conical flasks are not available, can you
think of another way to do the practical? What
modifications will be needed?
Use a plastic bag to enclose leaves A and B. Put
potassium hydroxide pellets into the bag of leaf
B. Seal the mouth of each bag by tying it around
the leaf stalk.
ANS ?
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7.4
Investigation of the need for carbon dioxide in
photosynthesis
Conclusion
What conclusion can you draw from this practical?
Starch is made only in the presence of carbon
dioxide. Carbon dioxide is needed for
photosynthesis.
ANS ?
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7.5
Design an investigation of the need for light in
photosynthesis
Design and perform an experiment
1 How to prevent light from reaching the leaf?
By masking the leaf with black paper.
ANS ?
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7.5
Design an investigation of the need for light in
photosynthesis
2 What are the controlled variables in this
experiment?
Carbon dioxide concentration in the surrounding,
temperature, water supply, etc.
ANS ?
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7.5
Design an investigation of the need for light in
photosynthesis
3 What is the independent variable in this
experiment?
The presence of light.
ANS ?
4 What is the dependent variable in this
experiment?
ANS ?
The presence of starch in the leaf.
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7.5
Design an investigation of the need for light in
photosynthesis
5 What is the control in this experiment?
The masked part of the leaf, i.e. the part that
does not receive any light.
ANS ?
6 How are you going to record and present the
results?
ANS ?
(Answer varies with Ss.)
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7.5
Design an investigation of the need for light in
photosynthesis
7 How can you obtain faster results?
Provide a higher light intensity to the plant.
ANS ?
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7.5
Design an investigation of the need for light in
photosynthesis
8 How can you make sure that the results are
reliable?
ANS ?
Mask several leaves with black paper, rather than
masking only one leaf. Test those leaves for
starch. Repeat the experiment with different
green plants.
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7.5
Design an investigation of the need for light in
photosynthesis
9 What precautions should be taken?
ANS ?
Before the experiment, destarch the plant and
test a leaf for starch.
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7.5
Design an investigation of the need for light in
photosynthesis
Write an experiment report
Objective
To find out if light is needed for photosynthesis.
ANS ?
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7.5
Design an investigation of the need for light in
photosynthesis
Write an experiment report
Procedure

• Destarch a plant by putting it in the dark for at
  least 24 hours. Pick a leaf and test it for
  starch (see Practical 7.1).

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7.5
Design an investigation of the need for light in
photosynthesis
Write an experiment report
Procedure
2. Cut out several identical black paper masks
and punch a hole at the centre.
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7.5
Design an investigation of the need for light in
photosynthesis
Write an experiment report
Procedure
3. Attach a paper mask to both sides of some of
the leaves with paper clips.
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7.5
Design an investigation of the need for light in
photosynthesis
Write an experiment report
Procedure
4. Expose the whole plant to bright light for
about 5 hours. 5. Remover the paper masks and
test the leaves for starch (see Practical 7.1).
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7.5
Design an investigation of the need for light in
photosynthesis
Write an experiment report
Results
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7.5
Design an investigation of the need for light in
photosynthesis
Analysis and discussion
1 Which parts of the leaf produce starch?
The unmasked parts.
ANS ?
2 What are the possible sources of errors in this
experiment? Suggest ways for improvement.
(Answer varies with the design.)
ANS ?
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7.5
Design an investigation of the need for light in
photosynthesis
Conclusion
Starch is made only in the presence of light.
Light is needed for photosynthesis.
ANS ?
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