Photosynthesis experiments using Geranium plants

Updated April 17, 2017

Photosynthesis is the process by which plants convert carbon dioxide and water into carbohydrates using sunlight for energy. Geraniums are well suited for experiments and science fair projects involving photosynthesis because they are easy to grow from seeds or cuttings. Geraniums are annuals that can live about one and a half years. Insects and other pests are seldom a problem with Geraniums.

How fast do Geraniums use starch reserves?

During dark hours, a plant may breakdown starch, a byproduct of photosynthesis which is stored in the leaves, in order to release energy needed to carry out life processes. Test a geranium leaf for starch. A starch test can be performed by creating a hot water bath and heating a beaker of ethanol until boiling. The leaf is dipped in the boiling water for 10 seconds, then immersed in the ethanol for one minute and returned to the boiling water for 10 seconds. The leaf should be pale and whitish. Lay the leaf on a white surface, and add an iodine solution. A black colour indicates the presence of starch. Store the same geranium plant in a dark closet for two days or longer. Test a leaf each day for starch until no starch is present, and analyse your results.

What spectrum of light is best for photosynthesis in Geraniums?

In this experiment, you will block a specific spectrum of light from reaching a leaf to determine the effect on the chlorophyll content. Create coloured plastic sleeves -- using transparency film and markers -- that are red, yellow, blue, green, black and uncoloured. The sleeves can be sealed on three sides using clear tape. Slide the sleeves over individual leaves on your plant, and place your plant in direct sunlight. Remember that the colour of the sleeve is the colour that is being blocked from reaching the leaf. Note the appearance of each leaf every day for a week. The greener the leaf, the more chlorophyll present.

Which side of the leaf exchanges gasses?

Stomata are structures that plants use to exchange gases during photosynthesis. Do you know which side of the leaf the stomata are on? Geraniums either exchange gases from the top of their leaves, the bottom of their leaves or both. Coat the topside of five leaves and the underside of five different leaves with petroleum jelly. Monitor the health of these ten leaves over the next few days. The leaves that survived did not have their stomata covered with petroleum jelly.

What is the effect of the absence of light?

Plants require sunlight or artificial light in order to carry out the process of photosynthesis. You will determine the effect of light on the distribution of starch reserves within a single leaf. Using squares of aluminium foil and paper clips cover part of a geranium leaf to prevent light from reaching the chlorophyll. After a week of exposing the plant to sunlight, remove the leaf and test for starch. Do you notice a difference in the amount of starch in the area of the leaf that was blocked from light?

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About the Author

Based in San Diego, Wesley Davis has been writing and editing since receiving a grant from the National Geographic Foundation in 2005 to publish a children's science book. He now writes for Limelight Education. Davis holds a Bachelor of Science in biology from California State University-Chico.