Chapter Outline

8.1Overview of Photosynthesis
8.2The Light-Dependent Reaction of Photosynthesis
8.3Using Light to Make Organic Molecules
The image shows a map of the world, colored by the levels of chlorophyll a on land and in the ocean.
Figure 8.1This world map shows Earth’s distribution of photosynthesis as seen via chlorophyll concentrations. On land, this is evident via terrestrial plants, and in oceanic zones, via phytoplankton. (credit: modification of work by SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE)

All biological processes require energy. To get this energy, many organisms access stored energy by eating, that is, by ingesting other organisms. But where does the stored energy in food originate? Almost all of this energy can be traced back to photosynthesis.

Photosynthetic organisms are the basis for almost all of the food webs on the planet. For example, the Indian River Lagoon, a 156 mile mixture of fresh and salt water along the eastern coast of Florida, depends on its sea grass for the survival of its marine life. Unfortunately, when certain algal phytoplankton species grow in overabundance, it destroys the sea grass. Scientists conducted a 16 year study of algal blooms and found that extreme climate conditions, such as cold weather and low rainfall, change which particular species of phytoplankton is more likely to bloom, resulting in a die-off of sea grass, decrease in other marine life, and changes in salinity. The research study can be found here.