How Do Photosynthesis & Respiration Differ?
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Respiration represents the reverse of photosynthesis. In photosynthesis, light energy is harvested from the sun and used to build food. In respiration, food is broken down to release stored energy so it can be used to fuel an organism's activities.
Photosynthesis
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Energy from the sun is what feeds all living things. Plants harvest this energy through the process of photosynthesis, and all other organisms live off the energy originally captured this way. For instance, animals obtain energy either by eating plants or by eating something that eats plants. For this reason, plants are called the producers of the ecosystem. Photosynthesis takes place in green organelles called chloroplasts, and a green pigment called chlorophyll is what captures the energy from photons. The two main stages of photosynthesis are the light reactions and the Calvin cycle, but there are many intermediate steps in the process. The general equation that represents the overall process of photosynthesis is: 6CO2 + 6H2O + Light energy = C6H12O6 + 6O2. Or: plants use carbon dioxide from the air, water from the soil, and sunlight to produce sugar and oxygen.
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Respiration
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Living cells require energy to perform work. In respiration, organisms break down food molecules, releasing energy and converting it into adenosine triphosphate (ATP). ATP is then used to power any cellular processes that require an input of energy. All living cells, including both plants and animals, undergo the process of respiration to fuel their activities. Respiration occurs in organelles called mitochondria, and is a complex process that involves a series of different enzymes and reactions. There are three key biochemical pathways: glycolysis, the citric acid cycle, and oxidative phosphorylation. The general equation for respiration (C6H12O6 + 6O2 = 6CO2 + 6H2O + ATP + heat) is the opposite of the one for photosynthesis, except that the energy from sunlight is converted into energy in the form of ATP and heat.
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