What type of metabolic pathway is photosynthesis

Consider the metabolism of sugar. This is a classic example of one of the many cellular processes that use and produce energy. Living things consume sugars as a major energy source, because sugar molecules have a great deal of energy stored within their bonds. For the most part, photosynthesizing organisms like plants produce these sugars. During photosynthesis, plants use energy originally from sunlight to convert carbon dioxide gas CO 2 into sugar molecules like glucose: C 6 H 12 O 6.

They consume carbon dioxide and produce oxygen as a waste product. This reaction is summarized as:. Because this process involves synthesizing an energy-storing molecule, it requires energy input to proceed. When we eat foods that contain starch, we must digest that starch down into single sugars glucose in order for the glucose to be absorbed into the intestinal cells, where it will enter the bloodstream to be carried to all cells of the body to use as an energy source.

The basic process of digestion of these foods will be covered in the next section. All living things require energy to survive. For humans, and many other organisms, that energy is generated by the complex interaction of photosynthesis and cellular respiration. Cellular respiration is a key pathway in energy metabolism the process of converting food into energy of all aerobic organisms.

Respiration refers to breathing: taking in oxygen and removing carbon dioxide. But ultimately, the reason we need to breathe is to provide the oxygen needed to carry out cellular respiration in our cells and to remove the carbon dioxide that is produced as a byproduct.

During cellular respiration, glucose is broken down to carbon dioxide and water; in the process, ATP is released. Cellular respiration occurs in the mitochondria of cells and is an aerobic process, which means that oxygen is required. It is a series of reactions that can be summarized as follows:. Even though glucose is the starting substance used in cellular respiration, we do not consume only glucose as an energy source. Instead, many different kinds of food molecules are broken down into smaller molecules, metabolized, and then enter the cellular respiration pathway.

For example, complex carbohydrates like starch are readily converted to glucose. Fats and proteins can also be used in cellular respiration, but they must be modified before they can feed into the process. Nutrients fuel cellular respiration. Other carbohydrates, like starch and sugars, are converted to glucose before entering cellular respiration.

If you compare the summary reactions of photosynthesis and cellular respiration, you can see that cellular respiration is the opposite of photosynthesis. Because each process starts where the other ends, they form a cycle. In higher plant, leaf structure especially the upper site, is more suitable to receive much sunlight. However, the lower site reflects and scatters light. Cell arrangement in side leaf is also more important beside leaf morphology. Leaves in dicotyledonous plants have two epidermises: upper and lower covered by cuticle.

Mesophyll tissues, which contain the photosynthetic tissues, are found between the two epidermal layers. Generally, there are 1—3 palisade mesophyll cells in upper photosynthetic tissue. Palisade cells are special cells in shape. In lower site, there are spongy mesophyll cells, which have isodiametric shape. Leaf in monocotyledonous is similar to leaf in dicotyledonous, but there are no special mesophyll cells.

Generally, there is more number of chloroplasts in palisade cells, which have high concentration of chlorophyll than spongy mesophyll cells. The presence of more chloroplast does not mean having higher photosynthesis rate, which occurs in the upper part of the leaf. Dicotyledonous leaves have more chloroplasts in their palisade; however, a little cell volume can have more chloroplasts. Much light will pass through the first cell layer without being absorbed because the pigments get combined to the chloroplast.

Light absorption efficiency may be affected by factors that change the light direction. The surface of leaf cell may reflect off the light. If a pigment absorbs light energy, one of three things will occur: first, energy is dissipated as heat.

Second, the energy may be emitted immediately as a longer wavelength, a phenomenon known as fluorescence. Third, energy may trigger a chemical reaction, as in photosynthesis. Grana and mitochondria structure in chloroplasts have dimensions parallel to active wavelength in photosynthesis.

Light is scattered by grana and mitochondria. Deflection, reflection and scattering increase the effect of light on leaf. Longer light wave increases the number of photons absorbed by leaves [ 3 ].

The light absorbed by palisade cell is not much as projected as it is thought and has lower light reduction efficiency. This may be due to the palisade that acts as a light guide. Some of the incident light goes through the intercellular spaces between the palisade cells in much the same way as the light is transmitted by an optical fiber.

It is likely that photosynthesis in the highest layer of palisade is light saturated. Any excess of light would be wasteful and lead to photoinhibition. Thus, the increased diffusion of light to the lower cell layers resulting in both scattering light and the light-guide impact would no doubt be advantageous by contributing to a more efficient allocation of photosynthetic energy throughout the leaf. Different plants have different leaves. Due to environmental situations, leaves may make some changes for adaptation.

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