Energy Efficiency of Photosynthesis

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Photosynthesis is the process in which plants use the energy from the sunlight to make glucose (a type of sugar), which they then use as food. The equation for photosynthesis is: 6CO2 (carbon dioxide) +6H2O (water) –(Sunlight) C6H12O6 (glucose) +6O2 (oxygen). Plants, algae, and cyanobacteria are photosynthetic organisms. In plants and algae, light is absorbed by chlorophyll—a molecule present in the cytoplasmic organelle called the chloroplast. Chlorophyll has a porphyrin ring with a magnesium cofactor at its center.

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Plants have two forms of chlorophyll—”a” and “b”—which have slight differences in their functional groups. Chloroplasts multiply through a cycle called the Calvin cycle, which represents the light-dependent stage of photosynthesis. Cyclic electron flow occurs in photosynthetic species that possess both photosystems, including cyanobacteria and plants. Chlorophyll “b,” with a slightly different structure than chlorophyll “a,” has a different absorption spectrum and funnels the energy from these wavelengths to chlorophyll “a.” Carotenoids can funnel the energy from other wavelengths to chlorophyll “a” and also participate in photoprotection against excessive light. Chlorophyll molecules are found in the thylakoid membrane.

They are organized, along with other small molecules and proteins, into complexes called photosystems. ATP—an abbreviation for adenosine triphosphate—is a molecule made of adenosine bound to three inorganic phosphates. Similarly, ADP (adenosine diphosphate) is made up of two molecules of phosphate bound to adenosine. ATP is a molecule that stores energy for the cell. When ATP hydrolyzes and becomes ADP, energy is liberated and then consumed by various metabolic reactions within the organism. ADP phosphorylation involves the attachment of a phosphate group to ADP. Photophosphorylation is the process in which the light reactions generate ATP, using chemiosmosis to power the addition of a phosphate group to ADP. By combining electrons at the ends of the chains, the electrons are combined with molecular oxygen and hydrogen to form water. The energy released at each step of this chain is stored in a form that the mitochondrion can use to make ATP. This specific form of ATP synthesis is called oxidative phosphorylation. There are two parts to photosynthesis: the light (photo) reactions and the Calvin cycle. The light reactions convert energy into chemical energy, while the Calvin cycle uses the energy from the light reactions to incorporate CO2 from the atmosphere to make sugar. The electron acceptor from the light reaction, NADP+, is closely related to NAD+.

They both function as an electron carrier in cellular respiration. The two molecules differ only in that the NADP+ molecule has a phosphate present while the NAD+ does not. The breaking down of water through light is a basis of photosynthesis, but it is not the entirety of it. Through photosynthesis, NADP+ becomes NADPH+ by the breaking down of H2O (Water). Oxygen is released when light energy is absorbed by the chlorophyll and is used to regenerate ATP, split water, and the hydrogen released from the water is split for the NADPH+. In sulfur photosynthetic bacteria, the substance that donates hydrogen is hydrogen sulfide (H2S) and not water. Therefore, there is no liberation of molecular oxygen but there is production of molecular sulfur. People say that the carbon dioxide is being enriched by the hydrogen because the water molecule and the carbon dioxide molecule are reacting to create glucose for the plant to have food and to give off oxygen as a waste. The color divisions of the electromagnetic spectrum in decreasing order of frequency are: red, orange, yellow, green, blue, anil, and violet. When mixed together, these colors generate white. The colors blue and red appear to be the most efficient for photosynthesis, even though the reflections seem to be some shade of green. Nicotinamide adenine dinucleotide phosphate (NADP) is an acceptor that temporarily stores energized electrons produced during the light reactions. Nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) is the same thing as NADP, just adding a hydrogen atom during the process of photosynthesis. The oxygen that is the plant’s waste comes from the water (H2O).

It could also be suspected that another oxygen atom comes from another animal’s waste from when they are breathing out their CO2. The Calvin cycle takes place in the stroma of eukaryotic chloroplasts. This is the final stage in the process of photosynthesis in which the ATP and the NADPH produced during the previous photochemical reactions are used. During the light reactions phase of photosynthesis, light is absorbed and the energy is used to drive electrons from water to generate NADPH+ and to drive protons across a membrane. These protons return through ATP synthase to make ATP. “Dark reactions” is not a correct name for the chemical stage of photosynthesis since the reactions of the chemical stage also occur in the presence of light. This is the general equation for photosynthesis: CO2+H2O+Light Energy—C6H12O6+O2. This equation does not clearly show the real amount of molecular oxygen being released because this formula is not balanced. The three main limiting factors are temperature, light intensity, and carbon dioxide concentration. If the temperature fluctuates too much, the enzymes become affected by it, which can, in turn, affect the photosynthesis processes because the enzymes are what run the photosynthesis.

If the temperature increases, the kinetic energy will also increase, causing more collisions with the enzymes. The temperature will also cause the photosynthesis rate to decrease if the essential enzymes begin to denature. Light intensity is important because it is absorbed by the chlorophyll, which is converted into ATP. Light intensity can cause an increase as more chlorophyll begins to be photo-activated. At a certain point, the light intensity photosynthetic rate will plateau, as all available chlorophyll is saturated with light. The compensation point of a plant is when the amount of carbon dioxide released in respiration equals the amount used in photosynthesis, and the amount of oxygen used in respiration equals the amount released in photosynthesis. This varies in different species of plants and in response to changes in temperature and other environmental factors.

Just because the concentration of carbon dioxide increases indefinitely does not mean that photosynthesis will also increase indefinitely. Leaves lose their green color in the autumn because their chlorophyll begins to break down, and the red, yellow, and orange colors become visible. Evergreen trees are shaped differently from other trees so that they can retain water throughout the winter, allowing photosynthesis to continue. Without photosynthesis, the world as we know it would disappear. Everything would die within a short amount of time. The larger trees could last a few years, but everything else would die out rather quickly. With all the herbivores dead, the omnivores would be the next to go. Soon, with all the plants dying, there would be no oxygen for the animals to breathe, and they would eventually begin to suffocate, if they made it that far.

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Energy Efficiency of Photosynthesis. (2019, Jan 16). Retrieved from