HESI A2 Exam: Photosynthesis
•What is the primary function of photosynthesis?
•Light independent reactions produce _________
•What colors does chlorophyll absorb?
•What is the Calvin Cycle?
•What is the difference between photosystem I and photosystem II?
Photosynthesis is the process by which plants convert energy from the sun into stored energy. Photosynthesis brings together carbon dioxide and water, in addition to sunlight, in order to make sugar molecules.
The primary function of photosynthesis is to convert the energy from the sun (light energy) into chemical energy for food.
One round of photosynthesis requires six molecules of carbon dioxide and six molecules of water that when assembled, creates food molecules.
Six molecules of carbon dioxide (6CO2) plus six molecules of water (6H2 O), with assistance from the sun's light, is turned into one molecule of sugar (C6 H12 O6), along with six molecules of oxygen (6O2) as a by-product.
Light-dependent reactions use light to produce ATP, which then fuels the light-independent reactions.
Although the overall outcome of photosynthesis is to produce oxygen, the light-independent reactions produce sugar in order for the plant to keep functioning the proper way it is supposed to.
Light dependent reactions take place on the thylakoid membranes. There are four major protein complexes in the thylakoid membrane: photosystem I, photosystem II, ATP synthase, and cytochrome b6f complex. Together these four complexes create ATP and NADPH.
A pigment absorbs all colors it does not reflect. For example, chlorophyll reflects green, while it absorbs red, blue, violet, and so on.
Carbon dioxide is one of the reactants needed for photosynthesis. It is not one of the products because it has to bind with RuBP in order for the Calvin Cycle to function and to create sugar and oxygen.
Light intensity, carbon dioxide concentration, and temperature all affect the rate at which photosynthesis occurs. Light is needed because that is the basis of photosynthesis. Without enough carbon dioxide, RuBP would be unable to combine with anything to work the Calvin Cycle. In extreme cold or hot temperatures, photosynthesis may not function because there needs to be an optimal temperature for plant cells to be able to function.
Photosynthesis uses light energy in order to make energy-rich organics, or glucose. Cell respiration breaks down the glucose in order to synthesize ATP.
The Calvin Cycle is the process in which carbon fixation (conversion of inorganic carbon to organic compounds) occurs in the light-independent reactions. It occurs in the stroma and overall produces a 3-carbon sugar.
The photosystem I was named "I" since it was discovered before photosystem II, but this does not represent the order of the electron flow. When photosystem II absorbs light, electrons in the reaction-center chlorophyll are excited to a higher energy level and are trapped by the primary electron acceptors.
Light, temperature, and carbon dioxide are known as limiting factors. These limiting factors have the greatest impact on the rate of photosynthesis. Water (and chlorophyll concentration) are also important, but are not considered a limiting factor.
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