Introduction:

Photosynthesis is the process of changing light energy into chemical energy (food or fuel). Organisms that can do this are called "autotrophic." These organisms generally appear green in color and include most true plants and some protists. Other organisms get their food by eating other organisms. Is there a relationship between color and the ability to make food? Furthermore, what evidence do we have that light is actually used in making food? After stating the two problems below, read the experimental design, identify the variables, and write a hypothesis for each problem.

State the Problem:

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Using just a single normal uncovered leaf of Coleus or some other variegated leaf plant, you can determine the relationship between photosynthesis and chlorophyll. Since the leaves are variegated, only some of the leaf is green while other parts are pink or have no color at all. Testing for the distribution of starch in the leaf will indicate photosynthesis. If starch tests out positive, we can see where food making has taken place.

What is the independent variable?__________________________________

What is the dependent variable?____________________________________

Hypothesis #1: ________________________________________________

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Experimental Design #2:

Cover a leaf from a potted plant with aluminum foil to cut off its sunlight. Place the plant in the greenhouse or under a grow light. After four days, remove the covered leaf and a normal leaf from the plant. Place both leaves in boiling water to destroy their cell membranes (heat denatures the protein). Boil the leaves in alcohol to remove their pigments. Finally, test the leaves for starch using Iodine. Presence of starch indicates food making while lack of starch would indicate that food has been used up by cellular respiration.

What is the independent variable? _________________________________

What is the dependent variable?____________________________________

Hypothesis #2: ________________________________________________

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The above procedure should provide us with observations we need to confirm or deny our hypotheses provided that the following assumptions are true: Starch is an indicator of glucose which implies that photosynthesis is going on. It is a known fact that starch is a polymer of glucose.

Since the leaf wrap in foil can not make food in darkness, then it is reasonable to think that the leaf tissues must be using stored food therefore the starch stored previously will be reduced or eliminated entirely.

It is also assumed that boiling the leaf will not remove starch from the leaves.

The colored sketch below represents the leaves as they appeared before removing their pigments and as they appeared after the Iodine was added.

Which leaf contained the most starch?____________________________

In what part of the leaves did starch appear?____________________

Write a conclusion about the relationship between chlorophyll and photosynthesis? Describe the relationship. Tell what data supports your conclusion.

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Write a conclusion about the relationship between light and photosynthesis? Describe the relationship. Tell what data supports your conclusion?

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