Thursday, September 6, 2012

Examining Stomates Science Project

Stomates are tiny openings (or pores) in plants that are used for gas exchange. Plants require both water and carbon dioxide for photosynthesis. The challenge for a plant is to conserve water while permitting carbon dioxide to enter the leaf where photosynthesis will occur. Stomates are the adaptation that permits carbon dioxide to enter the leaf while allowing most of the leaf to be covered with a waxy cuticle that will conserve water.

For this project you will need to use a stereo microscope and/or a compound microscope along with a Zebrina plant. A Zebrina plant can be obtained from an garden store and the great part is - once you use it for the science project the plant should live all year in a classroom or home.

Zebrina plant photo courtesy of Ruestz.
Take a single leaf from a Zebrina plant (these plants work well because they have purple pigment in the leaves) and place it under your stereo dissecting microscope. Older leaves will have the best stomates on them. Place the leaf so the bottom side faces up. What do you see under the microscope? The stomates should be visible in green patches. They stand out against the purple background of the leaf. As you slowly increase magnification notice the details in the stomates. Why do you suppose the stomates are located on the underneath of the leaf?

Stoma captured under a high power microscope by Peter Halasz.
Next use the compound high power microscope to examine the Zebrina leaf. Start at the lowest magnification and make sure the underside of the leaf is facing the objective lenses. Do you notice that each stomate is surrounded by two long, thin guard cells? These guard cells can either open or close the stomate, depending on the availability of water.

Draw a diagram of the stomates you view and label both the stomates and the guard cells. Once you have seen stomates in the Zebrina plant, try locating them on the underside of other plants. It can be more difficult to view stomates in plants that do not have a purple background, but with a bit of practice you will be able to locate them.

Teachers and parents - if you would like a copy of this Examining Stomates lesson plan you can download it for free here.