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Elementary Science Education

Introduction. Leaves and Photosynthesis

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      Bernard Nebel


      The objective of this lesson is to gain a general understanding and appreciation for how a plant functions. Plants are the bottom of all food chains. With their ability for PHOTOSYNTHESIS, plants (unwittingly) become the food source for every other living thing on earth, humans included.

      Review photosynthesis:

                                                               light energy

                  6CO2     +     6H2O             ————→              C6H12O6     +       6O2.

      carbon dioxide.    water          absorbed by      glucose sugar         oxygen

                                                  chlorophyl in chloroplasts

      How is the plant constructed to facilitate photosynthesis? How does water get to the site of photosynthesis? What does it do with the glucose it makes? (Note that plants are interested in their own survival, not in feeding animals!) 

      Leaves and Photosynthesis

           The following video is an edgewise view of a leaf section. Have kids note that, despite the thinness of a leaf, there is considerable cellular structure between upper and lower surfaces. You may omit technical names of parts but have kids note: 

      1. The leaf is broad and flat to maximize absorption of light energy.
      2. The veins of a leaf (shown in blue in the video diagram) are continuous all the way to the roots. Some cells of the vein (xylem) carry water from the soil up to the leaves; other cells of the vein (phloem) carry glucose from the leaf cells where it is made to wherever in the plant it is needed/used or to be stored.
      3. There are pores (stomas) is the lower surface to facilitate the entry of carbon dioxide and the exit of oxygen from/to the surrounding air. 



      The following link will take you to  a photomicrograph of an actual leaf.

      From such photographs artists make the diagrams as seen in the preceding video. Kids may attempt making their own leaf cross sections for examine under their microscope. It’s a bit tricky. Use  a very sharp scalpel to make a very thin cross section, then turn it on edge in a drop of water to view it from the side.


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