Energy for Life
Ellen S. Hood
Introduction to Biology – SCI115
The cell is the basic unit of life. Plant cells and solar cells are very important to humans and other living thing on Earth. Plants to harness solar energy use photosynthesis. A semi-conductor based solar cell harnesses solar energy to convert it to electriality.
Photosynthesis changes solar energy into chemical energy of a carbohydrate. Sunlight plays a big role in our nourishment than we may expect all the food we eat, and all the fossil fuel we use is a product of photosynthesis. Many different organisms, ranging from plants to bacteria, carry out photosynthesis. All these organisms convert CO2 (carbon dioxide) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions. Electrons for this reduction reaction come from water, which is then converted to oxygen and protons. Energy for this process is provided by light, which is absorbed by pigments primarily chlorophylls and carotenoids. Chlorophylls absorb blue and red light and carotenoids absorb blue-green light, but green and yellow light are not effectively absorbed by photosynthetic pigments in plants; therefore, light of these colors is either reflected by leaves or passes through the leaves.
The initial electron transfer reaction in the photosynthetic reaction center sets into motion a long series of redox reactions, passing the electron along a chain of cofactors and filling up the "electron hole" on the chlorophyll, much like in a bucket brigade. All photosynthetic organisms that produce oxygen have two types of reaction centers, named photosystem II and photosystem I (PS II and PS I, for short), both of which are pigment/protein complexes that are located in specialized membranes called thylakoids. In plants and algae, these thylakoids are located in chloroplasts (organelles in plant cells) and often are found in membrane stacks. Prokaryotes do not have chloroplasts or...