GC: n

CT: Autotrophs vs. Heterotrophs. Living organisms obtain chemical energy in one of two ways.
Autotrophs, shown in Figure below, store chemical energy in carbohydrate food molecules they build themselves. Food is chemical energy stored in organic molecules. Food provides both the energy to do work and the carbon to build bodies. Because most autotrophs transform sunlight to make food, we call the process they use photosynthesis. Only three groups of organisms – plants, algae, and some bacteria – are capable of this life-giving energy transformation. Autotrophs make food for their own use, but they make enough to support other life as well. Almost all other organisms depend absolutely on these three groups for the food they produce. 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 But heterotrophs are limited by our utter dependence on those autotrophs that originally made our food.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.

S: CK12 – https://www.ck12.org/book/CK-12-Biology-Concepts/section/2.18/ (last access: 26 November 2017)

N: 1. German, from autotroph, adjective. First Known Use: 1938. An autotrophic organism.
Adjective: autotrophic.
2. An organism that utilizes carbon dioxide as its major source of carbon and obtain energy from the sun through photosynthesis (photoautotroph) or from organic or inorganic reduced chemicals (chemoautotroph).
3. Autotrophs are the producers in a food chain, such as plants on land or algae in water. They are also referred to as the producers of the food chain. They are capable of manufacturing their own food by photosynthesis or by chemosynthesis. Thus, autotrophs may be photoautotrophs or chemoautotrophs.

• Photoautotrophs are autotrophs that produce complex organic compounds such as carbohydrates, fats, and proteins with the absorption of light. This process mediated by light is called photosynthesis. Photosynthesis is a process wherein plants absorb light from a light source (e.g. sunlight) and use carbon dioxide, inorganic salts, and water to produce an energy-rich carbohydrate like glucose (C6H12O6) and to produce oxygen (O2) as a by-product. Photoautotrophs are land plants and photosynthetic algae. These organisms have light-capturing pigments such as chlorophyll.
• Chemoautotrophs are those that make their own food by chemosynthesis. Chemosynthesis is a process by which some organisms, such as certain bacteria, use chemical energy to produce carbohydrates. They utilize inorganic compounds such as hydrogen sulfide, sulfur, ammonium, and ferrous iron as reducing agents.

S: 1. MW – https://www.merriam-webster.com/dictionary/autotroph (last access: 26 November 2017). 2. TERMIUM PLUS – http://www.goo.gl/e4BHDb (last access: 26 November 2017). 3. BO – https://goo.gl/yudt8C (last access: 22 November 2017).

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CR: alternative energy sources, biomass energy, clean energy, energy, green energy, primary energy, renewable energy.