Bioenergetics – Growing in a Diverse World
... abundance of soil nutrients. There would be a great deal of imbalance between the two systems if they were independent of each other. Light reactions play a very important role in the surviving of all plant species. With out light reactions, plants would not be able to produce the ATP it needed to survive and continue to grow. Inside the plant, there are cells called chlorophyll that are the main producers of the ATP. Non-photophosphorylation consists of two sets of pigments to excite: PS1 (photosystem 1), and PS2 (photosystem 2). PS1 is better excited by light at about 700 nm and is thus sometimes called P-700. PS2 cannot use photons of wavelength longer than 680 nm and is sometimes called P-680. Energy enters the system when PS2 becomes excited by light. Electrons are shed by the excited PS2 (oxidation), which grabs electrons from water, producing a molecule of oxygen gas for every two waters split. PS2 thus returns it to its unexcited state (reduction). The electrons are passed through a chain of oxidation-reduction reactions. Each element in the pathway is reduced by the electrons, and turns right around to reduce its neighbor in the pathway by giving it the electrons, thus becoming reoxidized and ready for the next electrons to pass through the photsystem. PS2 passes on the energy to move the electron through the redox chain, thus pumping protons through the membrane to generate ATP. PS1, on the other hand, passes on the energy required to reduce NADPH. The Calvin Cycle is another way for energy to be produced and stored. It is stored as glucose, which can now serve as a building block to make polysaccharides, other monosaccharides, fats, amino acids, nucleotides, and all the molecules living things require. The energy required for the Calvin Cycle, in the form of ATP and NADPH, comes from the light reactions. It makes sense that the plant or photosynthesizing bacterium would want to tightly regulate the Calvin Cycle with photosynthesis. It would be detrimental and wasteful to try to run this process using ATP generated for other plant metaboli...