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ACTIVITY 4. THE PLANT LEAF: AN ORGAN DESIGNED FOR PHOTOSYNTHESIS Now that our study of light, pigments, and photosynthesis is complete, it is time to take a brief look at the place where the majority of photosynthesis occurs in a plant. While stems and some flower parts are green, the plant organ designed for optimal photosynthesis is the leaf. In a typical flowering plant, the leaf is broad to provide surface area for light absorption, but very thin since light cannot penetrate deeply into living tissue. A diagram of a typical leaf is shown below. It is cut in both longitudinal and cross section to show the cellular structure within. Note the different cell types which carry out different functions in the leaf.
Now it is time to study the cross section of a real leaf. View this stained leaf section which is displayed as if using a "virtual light microscope". Magnify the image and move to a region that contains the clearest view of internal structure, including a stoma. Perform a screen capture of the magnified leaf section, then label a stoma, mesophyll, epidermis, and a vein. Submit your labeled image to WebAssign for question 15. The openings within the epidermis are called stomata (singular is stoma). On either side of a stoma lies a guard cell, a unique cell type that can change shape to open or close the stoma. Water vapor escapes from the leaf through open stomata on a hot day. If there is insufficient water in the soil under these conditions, the stomata will close to prevent water loss. The image below shows both an open and a closed stoma on the surface of a real leaf.
When you have studied the stomata images and caption, answer question 16. |