Light Reactions of Photosynthesis
This activity has undergone a peer review process.
This activity has undergone a peer review process by which submitted activities are compared to a set of criteria. Activities meeting or revised to meet these criteria have been added to the collection. To learn more about the review criteria, see [http://taste.merlot.org/evaluationcriteria.html]. More information about the peer review process can be found at [http://taste.merlot.org/peerreviewprocess.html].
This page first made public: Aug 11, 2010
This material is replicated on a number of sites as part of the SERC Pedagogic Service Project
- Locate where the light reactions of photosynthesis take place within the leaf.
- Learn about the pathway through which light energy flows as it is converted into biochemical energy.
- List the basic steps for the light reactions of photosynthesis and highlight those steps that enable production of ATP, NADPH, and oxygen.
- Understand the difference between non-cyclic and cyclic photophosphorylation.
Context for Use
Description and Teaching Materials
- Use an actual dicot leaf or draw a representation of this leaf on a piece of paper and cut it in half. Explain that the light and dark reactions of photosynthesis take place inside specialized cells that are found within the edge of the leaf and traverse the inside portion.
- Draw a picture of the edge of the leaf, showing the several layers of cells within, including top epidermis, palisade parenchyma, spongy parenchyma, midvein with vascular tissue, and bottom epidermis see http://www.merlot.org/merlot/viewMaterial.htm?id=281356.
- Point out the location for photosynthetic reactions within the palisade and spongy parenchyma, and draw one cell, depicting several chloroplasts in the cytoplasm of that cell. Explain that the reactions of photosynthesis take place in the chloroplasts.
- Draw a chloroplast, showing the stroma and thylakoid membrane system and explain that the light reactions of photosynthesis take place within the thylakoid membrane.
- Explain that specific wavelengths of light (usually blue and red, but not green) have to pass through the leaf surface, enter the parenchyma cells, and excite chlorophyll molecules within the thylakoid membrane.
- Use a ball, piece of chalk, a pen, or similar item to represent a unit of light being emitted upon the reaction center (photosystem II in non-cyclic photophosphorylation) that starts a cascade of events through which excitation energy is passed from one molecule to another through inductive resonance tranasfer see http://www.merlot.org/merlot/viewMaterial.htm?id=80033. This can be done by passing the "photon energy" item from one participant to another, asking them to be less excited during each transfer of the item. The last participant can stand up and shout, "photosynthesis!" to indicate the point at which the right amount and wavelength of light has been received to begin the steps of non-cyclic photophosphorylation.
- Draw the steps of non-cyclic photophosphorylation and make note of the reaction centers for photosystem II and photosystem I. Show animations of these steps using references and resources such as http://www.merlot.org/merlot/viewMaterial.htm?id=79743 – also see References and Resources below.
- Point out three key products from the light reactions of photosynthesis, including ATP, NADPH, and oxygen.
- Show how cyclic photophosphorylation differs from non-cyclic photophosphorylation and discuss the evolutionary impact of these different processes http://www.merlot.org/merlot/viewMaterial.htm?id=79744.
- Explain that the energy from the light reactions of photosynthesis will be used in the dark reactions of photosynthesis to fix carbon and build molecules needed for energy storage.
Teaching Notes and Tips
References and Resources
MERLOT description and link to "Cyclic and Noncyclic Photophosphorylation," which is a site that provides animations and tutorials for photosynthesis. See http://www.merlot.org/merlot/viewMaterial.htm?id=79744
MERLOT description and link to "Photosynthesis Animation," which includes a simple, straightforward flash animation of the light reactions. See http://www.merlot.org/merlot/viewMaterial.htm?id=79743
MERLOT description and link to "Photosynthesis Interactive Animated Tutorial," which is a site designed to accompany a textbook on Interactive Concepts in Biochemistry. This link provides a good overview of photosynthesis. See http://www.merlot.org/merlot/viewMaterial.htm?id=80033
MERLOT description and link to "Photosynthesis Video," which provides an excellent overview and guide to where photosynthesis occurs in a leaf. See http://www.merlot.org/merlot/viewMaterial.htm?id=281356
MERLOT description and link to "The Photosynthetic Process," which includes a comprehensive paper on photosynthesis and links to all figures from the original paper. See http://www.merlot.org/merlot/viewMaterial.htm?id=85664