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Photosynthesis Science Fair Project

Carbon Dioxide and Starch in Leaves

Hard
Carbon Dioxide and Starch in Leaves | Science Fair Projects | STEM Projects
Does a plant make more starch when it gets extra carbon dioxide? Photosynthesis uses carbon dioxide and sunlight to build sugar and starch inside leaves. Changing the amount of available carbon dioxide should change how much starch a leaf produces. You seal three identical geranium plants in separate bags. Plant A gets Alka-Seltzer in water to increase carbon dioxide. Plant B gets soda lime to absorb carbon dioxide. Plant C stays sealed with normal air as the control. After one day in sunlight, you remove a leaf from each plant. You boil each leaf in alcohol to remove the green color. Then you add potassium iodide drops. The darker the purple color, the more starch the leaf contains.

Hypothesis

The hypothesis is that increased photosynthesis increases the starch in the green plant.

Method & Materials

You will mark three geranium plants, put them in bags with different materials, and place them in the sun for one day. After one day, you will break off one leaf from each plant and put it in a Petri dish. You will then put the leaf in a beaker with hot alcohol and observe the color change of the three leaves.
You will need three geranium plants, three 2 gallon plastic bags with twist to close, two 250ml Beakers, one 500ml Beaker, one Hot Plate, one Pair of Plastic Tongues, four Petri Dishes, one 1pt. 91% Isopropyl Alcohol, one Package of Alka-Seltzer, one 50mL of Soda Lime, one Bottle of Potassium Iodide, three Pieces of Cardboard, one Pitcher of Water.

Results

The results of the experiment showed that the amount of starch in the leaf of the geranium plant was affected by the amount of carbon dioxide present. The leaf with increased carbon dioxide had the most starch, while the leaf with lower carbon dioxide had the least starch.

Why do this project?

This science project is interesting and unique because it explores how carbon dioxide affects the amount of starch in a leaf of a geranium plant.

Also Consider

Variations to consider include testing different plants and shielding parts of the leaf from the sun.

Full project details

Additional information and source material for this project are available below.

Related video

These videos explain the science behind this project and demonstrate key concepts used in the experiment.
This video provides a clear demonstration how to detect the presence of starch in a leaf.
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