Nutrition
Like most plants, Linum marginale gets its nutrients through photosynthesis. Photosynthesis is two processes known as the light reactions and the Calvin cycle. The thylakoids of chloroplasts transform light energy into chemical energy which the plant can then use as a food source. A photosystem within the thylakoid membrane is made of a protein complex known as the reaction center complex. Surrounding this complex are light harvesting complexes. Pigment molecules within these complexes absorb photons of light which are then passed from one pigment molecule to the next. It is then passed to the reaction center complex. This complex includes special chlorophyll a molecules which can use the light energy to boost one of their electrons to a higher energy state and transfer it to another molecule known as the primary electron acceptor. An enzyme catalyzes the splitting of a water molecule into two electrons- which are supplied to the chlorophyll a molecules in the reaction center complex, two hydrogen ions, and an oxygen atom which is a byproduct of the light reactions. The excited electron is then passed from photosystem II to photosystem I through an electron transport chain. The drop of electrons to a lower energy level provides energy to produce ATP. In the meantime, more photons of light are absorbed by photosystem I through other light harvesting complex pigment molecules and are sent to the reaction center complex. Again, the excited electron within the chlorophyll a molecules is then transferred to the primary electron acceptor of photosystem I. The empty hole of the chlorophyll molecules can now accept electrons reaching the bottom of the electron transport chain from photosystem II. The electron at the primary electron acceptor of photosystem I is then passed through another electron transport chain. However, this chain does not produce a proton gradient and therefore it does not produce any ATP. But, the enzyme NADP reductase catalyzes the reduction of NADP to NADPH. Both the ATP and NADPH are used within the Calvin cycle (Campbell et al, 2008).
The Calvin cycle is anabolic, meaning it creates carbohydrates and consumes energy. CO2 enters the cycle and leaves in the form of sugar; however, it takes 3 CO2 molecules to produce one molecule of G3P. Phase one: carbon fixation, the CO2 molecule attaches to a five carbon sugar. This six carbon molecule is so unstable it instantly splits into two molecules of 3-phosphoglycerate. Phase two: the reduction phase uses ATP providing an additional phosphate to the 3-phosphoglycerate. Also, a pair of electrons is donated from NADPH producing G3P, which is a sugar. One sugar molecule is released for the plant to use, and the other five molecules are recycled to generate three molecules of RuBP. Phase three: the regeneration phase takes the five individual molecules of G3P and reorganizes them into three molecules of RuBP. This requires more ATP. The RuBP is now ready to accept more CO2 and start the cycle over again. The plant is able to use these sugars and starches as their food (Campbell et al, 2008).
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