Privacy Policy. Skip to main content. Microbial Metabolism. Search for:. Types of Metabolism. Photoautotrophs and Photoheterotrophs Photoautotrophs and photoheterotrophs are organisms that rely on light as their source of energy to carry out cellular processes. Learning Objectives Differentiate photoautotrophs from photoheterotrophs. Key Takeaways Key Points Phototrophs are organisms that carry out photon capture to acquire energy. Photoautotrophs convert inorganic materials into organic materials for use in cellular functions such as biosynthesis and respiration and provide nutrition for many other forms of life.
Photoheterotrophs depend on light for their source of energy and mostly organic compounds from the environment for their source of carbon. Key Terms ATP synthase : an important enzyme that catalyzes the conversion of adenosine diphosphate into adenosine triphosphate. Chemoautotrophs and Chemoheterotrophs Chemoautotrophs and chemoheterotrophs make their food using chemical energy rather than solar energy. Learning Objectives Compare chemoautotrophs and chemoheterotrophs.
Key Takeaways Key Points Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environment. Chemoautotrophs use inorganic energy sources to synthesize organic compounds from carbon dioxide. Chemoheterotrophs are unable to utilize carbon dioxide to form their own organic compounds.
Their carbon source is rather derived from sulfur, carbohydrates, lipids, and proteins. Key Terms inorganic molecule : lacks carbon and hydrogen atoms. Heterotrophs degrade some of the organic molecules they take in catabolism to make the ATP that they need to synthesize the others into the macromolecules of which they are made anabolism. Within cells, these molecules are further degraded into still simpler molecules containing two to four carbon atoms.
These fragments acetyl-CoA for example face one of two alternatives:. This phase of catabolism releases large amounts of energy in the form of ATP. The producers , as autotrophs are also known, begin food chains which feed all life.
Food chains will be discussed in the " Food Chains and Food Webs " concept. Heterotrophs cannot make their own food, so they must eat or absorb it. For this reason, heterotrophs are also known as consumers. Consumers include all animals and fungi and many protists and bacteria. They may consume autotrophs or other heterotrophs or organic molecules from other organisms. Heterotrophs show great diversity and may appear far more fascinating than producers. But heterotrophs are limited by our utter dependence on those autotrophs that originally made our food.
If plants, algae, and autotrophic bacteria vanished from earth, animals, fungi, and other heterotrophs would soon disappear as well. All life requires a constant input of energy. Only autotrophs can transform that ultimate, solar source into the chemical energy in food that powers life, as shown in Figure below.
Photosynthetic autotrophs, which make food using the energy in sunlight, include a plants, b algae, and c certain bacteria. Photosynthesis provides over 99 percent of the energy for life on earth. A much smaller group of autotrophs - mostly bacteria in dark or low-oxygen environments - produce food using the chemical energy stored in inorganic molecules such as hydrogen sulfide, ammonia, or methane. While photosynthesis transforms light energy to chemical energy, this alternate method of making food transfers chemical energy from inorganic to organic molecules.
It is therefore called chemosynthesis , and is characteristic of the tubeworms shown in Figure below. Some scientists think that chemosynthesis may support life below the surface of Mars, Jupiter's moon, Europa, and other planets as well. Ecosystems based on chemosynthesis may seem rare and exotic, but they too illustrate the absolute dependence of heterotrophs on autotrophs for food. A food chain shows how energy and matter flow from producers to consumers.
Matter is recycled, but energy must keep flowing into the system. Where does this energy come from? Though this food chains "ends" with decomposers, do decomposers, in fact, digest matter from each level of the food chain?
Tubeworms deep in the Galapagos Rift get their energy from chemosynthetic bacteria living within their tissues. No digestive systems needed! The flow of energy through living organisms begins with photosynthesis.
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