Stage 6 Biology: Patterns in Nature
Student: __________________ Date: ___________
First Hand Investigation: Investigating requirements for photosynthesis
Purpose: To demonstrate the need for chlorophyll and light in photosynthesis
DOT POINT: plan, choose equipment or resources and perform first hand investigations to gather
information and use available evidence to demonstrate the need for chlorophyll and light in
photosynthesis.
Introduction
To find out what plants need in order to photosynthesise, we can test what factors allow the plant
to produce starch—starch is one of the common end products of photosynthesis (glucose is stored
as starch). It has been suggested that plants need light, carbon dioxide, chlorophyll and water to
produce starch by the process of photosynthesis. Factors such as these affect the ability of a plant
to photosynthesise and so are termed the limiting factors of photosynthesis. The syllabus requires
you to test whether light and chlorophyll are necessary for photosynthesis. You can do
experiments to find out if chlorophyll and light are factors needed for starch production. You will
need to do a separate experiment for each factor, since only one factor at a time can be varied in
any experiment to make it scientifically valid.
Part A: Light and Photosynthesis
Aim
To determine whether light is necessary for starch formation.
Materials:
 Plant left in dark for several days
 Plant in light
 Geranium plant
 250mL beaker
 Forceps
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Scalpel
Petri dish
Iodine solution
Methylated spirits
Method
Using a leaf from a plant that has been placed in the dark and a plant which is exposed to the sun, (or an alternative
is to place foil over some leaves on the plant for several days),
Stage 6 Biology: Patterns in Nature
Student: __________________ Date: ___________
Results:
Leaf Tested
Colour of leaf after boiling in methylated spirits and immersing in iodine
Geranium leaf exposed to light
Geranium leaf left in the dark
Discussion:
1. What is the control in this experiment?
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2. How do the leaves stained with iodine relate to the conditions under which the plant was kept?
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3. Explain why a leaf that has been left in the dark is ‘destarched’. Propose a suggestion as to what may have
happened to the starch that was originally present in the leaf.
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4.
Discuss why it is safer to use a hot water bath to heat ethanol, rather than using a Bunsen burner.
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5. Explain why, if a destarched leaf is covered with foil and the remainder of the plant is left exposed to sunlight
for three or four days, the results of your experiment may show that starch is present in the covered leaf.
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Conclusion:
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Stage 6 Biology: Patterns in Nature
Student: __________________ Date: ___________
Part B: Chlorophyll and Photosynthesis
A variegated leaf is a leaf which contains green and non-green parts. As the green parts contain chlorophyll they can
photosynthesise, but the non-green parts do not contain chlorophyll so they cannot photosynthesise.
Aim
To determine whether chlorophyll is necessary for starch formation.
Method
Results:
Diagram of leaf before experiment
Diagram of leaf after experiment showing areas where
starch is present
Stage 6 Biology: Patterns in Nature
Student: __________________ Date: ___________
Discussion:
1. Discuss why the students chose a variegated plant for their experiment.
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2. What is the control in this experiment?
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3. Is chlorophyll soluble in ethanol? Justify your answer using evidence from your experiment.
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4. Identify which part of a variegated leaf contains starch.
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Conclusion:
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Overall Discussion:
From your investigations, are chlorophyll and light necessary for starch formation?
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