Today students will make horizontal thin sections of a leaf to determine its 3-D structure. After viewing the horizontal sections and making sketches of them, students will predict the structure and function of each layer in the cell process of photosynthesis. Tomorrow they will construct a 3-D model using the slides they make. Here is an overview of what students will learn today.
Show students several different types of leaves. Using the plant structure assessment probe, determine students prior knowledge. Have students record their thoughts in their lab notebook.
In their lab notebooks, students should respond to the question
(Note: Most students will not think a plant leaf is an organ. Their responses will indicate this belief.)
Students are going to make thin sections of a leaf using clear nail polish and tape. First, students will collect two leaves from the class coleus plant. Using clear nail polish, students will paint a thin layer on the bottom of the leaf. Once the nail polish is tacky, they will apply clear tape to it. They should gently remove the tape from the leaf. The tape should be placed onto a clean microscope slide. The slide should be labeled bottom. Students should reapply nail polish to the bottom of the leaf, let the nail polish get tacky, apply tape, gently remove it, and place it sticky side down onto a clean microscope slide. Label the microscope slide, bottom 2. Repeat this step three to four more times, each time labeling the slide.
Students should now repeat the same procedure to the top of a new coleus leaf. They should paint the top of the leaf with clear nail polish. Once the nail polish is tacky, they should apply clear tape to it and gently remove the clear tape. The tape should be placed onto a clean microscope slide. Students should repeat this process four more times. It is important that they label each layer so as not to confuse them.
After making the thin section of the leaf, students should view each slide under the microscope. They should make sketches of leaf tissue from each section from at least two places on the slide.
Students should look at a prepared cross section of a leaf. From it, they should determine the number of tissue layers in the leaf. Using their drawings from the horizontal leaf sections and a prepared cross section of a leaf, students will begin to make a 3-D model of the leaf. They should make a sketch of a predicted leaf model in their lab notebook. (Note: Tomorrow students will use that information to build a 3-D model using paper bags and clear contact paper.)