Mark McGinley is an Associate Professor in the Honors College and Department of Biological Sciences at Texas Tech University. He has conducted research in the evolutionary, behavioral, and community ecology of animals and plants. Dr. McGinley’s recent scholarly interests focus on educating the general public about scientific (particularly environmental) issues.
Debbie J. Swarthout is an Assistant Professor of Biology at Hope College. Her research focuses on the physiology involved in the regulation of water-use efficiency in plants under different environmental conditions, from whole plant to protein levels of organization.
- Chemistry Team Seeks to Use Artificial Photosynthesis and Nanotubes to Generate Hydrogen Fuel with Sunlight
- Light, photosynthesis help bacteria invade fresh produce
- NASA satellite detects red glow to map global ocean plant health
- Discovering the secret code behind photosynthesis
- Corralling the carbon cycle: calculating how much carbon dioxide is absorbed and released by plants
- Agriculture holds key to solving global warming
This image was taken by Luc Viatour: more can be found at www.lucnix.be
Introduction
Photosynthesis is a process in plants, algae, and some prokaryotes, that coverts light energy from the sun into chemical energy stored in glucose or other organic compounds. Photosynthesis occurs in slightly different ways in higher plants relative to photosynthetic bacteria.
Photosynthesis in Higher Plants
In higher plants, photosynthesis involves chemical reactions in which the sun’s energy is transferred along a series of oxidation and reduction events until it is stabilized in the chemical bonds of glucose. In the broadest sense, light energy converts carbon dioxide (CO2) into chemical energy while water is split to release oxygen.
photosynthesis occurs in the leaves of plants, although there may be photosynthetic stems, flowers, and fruits. At the cellular level, photosynthesis occurs inside organelles known as chloroplasts. Plants use photosynthetic pigments (e.g., chlorophyll) to capture the light energy which is ultimately converted into chemical energy in the form of sugars. Photosynthesis involves two stages, the light reactions and calvin cycle reactions.
Light Reactions
Light energy from the sun is captured by photosynthetic pigments and is transferred along a series of proteins and iron-sulfur containing compounds along the thylakoid membranes of the chloroplast; the net result being the formation of high-energy compounds such as ATP and NADPH. Water molecules are split during the transfer of light energy along the membranes. Oxgyen is produced as a result of this water-splitting event.
Calvin Cycle Reactions
In the reactions of the Calvin Cycle, chemical energy held within ATP and NADPH are used to convert carbon dioxide into sugars through a series of enzymatic reactions. In the initial step of the Calvin Cycle, carbon dioxide (from the atmosphere) reacts with a five-carbon compound, ribulose bisphosphate (RuBP), in a reaction that is catalyzed by the enzyme RuBP carboxylase/oxygenase (”RuBisco”). The first stable product of this reaction is a three-carbon compound known as phosphoglycerate (PGA). Energy captured in the light reactions in form of ATP and NADPH is used to convert PGA into glyceraldehyde 3-phosphate (G3P) which can be converted to other organic compounds, or using energy from ATP, some is converted into RuBP to continue the cycle. The Calvin cycle reactions occur in the stroma of the chloroplasts.