Photosynthesis
Plants play a fundamental role in supporting all life on earth. Plants are the basis of nearly all terrestrial food chains for humans and other heterotrophic organisms. Through the process of photosynthesis, they serve as the entry point of sun energy that is essential for maintaining ordered life on earth. They capture the power of the sun (radiant energy), convert it to chemical energy, and use that energy to fix carbon dioxide into useable sugars. During the conversion of sun energy to chemical energy, a handy byproduct (oxygen) is produced. Without this byproduct, there would be next to no oxygen in the atmosphere and no aerobic life on earth. You will learn more about photosynthesis later, but for now it is important to realize that the sugars and oxygen produced through photosynthesis make life on earth as we know it possible.
The Three Domain or Superkingdom System
Plants support a tremendous diversity of life on earth. Until recently, systematists subdivided this diversity into five major groups of organisms or Kingdoms. The area of organismal systematics is rapidly changing. The "Five Kingdom" system is giving way to a three domain or superkingdom system of the Archaea (ancient bacteria), the Eubacteria (true bacteria) and the Eukaryotes (organisms with nuclei). True plants as well as other eukaryotic photosynthetic organisms are found within this last domain.
For this course we will focus on Viridaeplantae (the green plants) as well as touch on members of other life lineages including the Fungi.? Within the green plant lineage, the majority of plants with which humans have contact are angiosperms (seed bearing, flowering plants). Seeds, fruits and other organs of angiosperms make up the bulk of the world's food.
Other seed bearing plants that do not produce fruits are commonly referred to as gymnosperms. "Gymno" is from the Greek word for "naked" (the original gymnasiums were populated by naked men exercising) so this term literally means "naked seed". The conifers, the largest group of gymnosperms, are also important as sources of wood, medicines, and even food. The most abundant and economically important plants, however, are the angiosperms. Not surprisingly, this is also the most diverse and arguably successful group of plants on earth.
The other major lineage of organisms with significance to this course is the fungi. This much maligned group of yeasts, mushrooms, molds and other filamentous decomposers and parasites were historically grouped with plants and thus will be touched on by this course. The fungi do not always deserve their low status. Without fungi, there would be no yeast-leavened bread, beer, or wine, nor would there be other important products like the antibiotic penicillin. Fungi have their darker side as well. They are responsible for diseases of both plants and humans, producing toxins that can kill and spoil food in storage.