In all autotrophic eukaryotes, photosynthesis takes place inside an organelle called a chloroplast. Each stoma is flanked by guard cells that regulate the opening and closing of the stomata by swelling or shrinking in response to osmotic changes. The stomata are typically located on the underside of the leaf, which helps to minimize water loss. The gas exchange of carbon dioxide and oxygen occurs through small, regulated openings called stomata (singular: stoma), which also play roles in the regulation of gas exchange and water balance. The process of photosynthesis occurs in a middle layer called the mesophyll. In plants, photosynthesis generally takes place in leaves, which consist of several layers of cells. Before learning the details of how photoautotrophs turn sunlight into food, it is important to become familiar with the structures involved. Glucose, the primary energy source in cells, is made from two three-carbon GA3Ps.Īlthough the equation looks simple, the many steps that take place during photosynthesis are actually quite complex. In reality, the process takes place in many steps involving intermediate reactants and products. The basic equation for photosynthesis is deceptively simple. When a top predator, such as a wolf, preys on a deer (Figure 2), the wolf is at the end of an energy path that went from nuclear reactions on the surface of the sun, to light, to photosynthesis, to vegetation, to deer, and finally to wolf.įigure 4. Therefore, photosynthesis powers 99 percent of Earth’s ecosystems. Those carbohydrates are the energy source that heterotrophs use to power the synthesis of ATP via respiration. Photosynthesis is vital because it evolved as a way to store the energy in solar radiation (the “photo” part) as high-energy electrons in the carbon-carbon bonds of carbohydrate molecules (the “synthesis” part). A lizard sunning itself on a cold day can use the sun’s energy to warm up. The importance of photosynthesis is not just that it can capture sunlight’s energy. A third very interesting group of bacteria synthesize sugars, not by using sunlight’s energy, but by extracting energy from inorganic chemical compounds hence, they are referred to as chemoautotrophs. Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs (“other feeders”), because they must rely on the sugars produced by photosynthetic organisms for their energy needs. Because they use light to manufacture their own food, they are called photoautotrophs (literally, “self-feeders using light”). Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis (Figure 1). (credit: modification of work by Steve VanRiper, U.S. The predator that eats these deer receives a portion of the energy that originated in the photosynthetic vegetation that the deer consumed. The energy stored in carbohydrate molecules from photosynthesis passes through the food chain.
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