From Seed to Seed:
Activity 7: Leaves: A Slice of Life
Associated Lesson Topics:
Planting the Seed...
How can we investigate what is going on inside a leaf? What do you think the best procedure is for doing this? What do we expect to see inside the leaf? Encourage students to experiment with their procedural suggestions. Although we include instructions below for doing so, it is very difficult to make clear hand slides. Have professional leaf cross-section slides available for them to use if their procedures fail. Are there any differences between the cells located near the upper epidermis and those near the lower epidermis? This question should guide them toward the discovery of chloroplasts. Why are the tiny green circles in that location and what function might they serve?
In this activity, students develop microscope skills while looking at the cross-section of a leaf under the microscope. The tiny green spheres, as you may infer, are chloroplasts. Chloroplasts are the site of photosynthesis and are green because of the presence of chlorophyll pigments. These pigments are responsible for the capturing of light necessary for photosynthesis to take place. They are also easy to spot! After students have made their observations, you can launch into a discussion on photosynthesis and the role that chloroplasts play in this important plant process.
Harvesting the Crop...
By looking at the cross-section of the leaf under the microscope, students will also be able to see the stomata and guard cells. These are the openings in the epidermis where oxygen and carbon dioxide are exchanged between the plant and the atmosphere. Most plants have the highest concentration of stomata on the lower surfaces of the epidermis. This allows for the maximum uptake of carbon dioxide for photosynthesis while minimizing the loss of water by protecting the stomata from direct heat from the sun. Grasses, however, have stomata evenly divided between the upper and lower surfaces of the epidermis. Why? Because as grasses get blown around in the wind, they do not know which way is up! Structure is intimately related to function.
Please click the BACK button on your browser to return to the course.
Made possible by a grant from Oracle Corp.
Copyright 2001, National Gardening
For questions regarding this web site, contact Webmaster