This meal you ate? Any idea what it

This lesson introduces the concept of chemosynthesis.

It explains that energy is necessary for all life and provides a description of the chemosynthetic process. The lesson also includes examples of where chemosynthesis occurs in nature along with a brief quiz.

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Energy for Life

What was the last meal you ate? Any idea what it did for your body? Chances are that meal provided your body with the energy necessary for life. All living things on Earth need energy in order to survive.

However, how life forms obtain their energy various. People obtain this energy by consuming other organisms, such as with your last meal. On the other hand, plants are capable of obtaining energy directly from the sun through the process of photosynthesis.These two energy-obtaining pathways are probably somewhat familiar to you. However, there is another, less familiar method for obtaining energy. This method is known as chemosynthesis and, as known biological processes go, it’s relatively new, at least when compared to photosynthesis and consuming food. Chemosynthesis is characterized by using inorganic molecules to aid in the conversion of carbon molecules into organic matter.

Sound confusing? Let’s try to clarify the concept with an example.

Chemosynthesis in Nature

Found deep within the ocean are structures known as hydrothermal vents. These vents produce a seemingly toxic compound, known as hydrogen sulfide. I say ‘seemingly’ because hydrogen sulfide is toxic to humans, but not to all life. In fact, living amidst the hydrothermal vents are organisms called giant tube worms.These tube worms rely on chemosynthesis in order to survive. You see, within the gut of tube worms live chemosynthetic bacteria.

Chemosynthetic organisms all tend to be bacteria, even if larger organisms incorporate these bacteria into themselves. These bacteria use the hydrogen sulfide, an inorganic molecule, to produce sugar, a carbon-based organic molecule. That sugar then serves as a usable energy source for the tube worm, much like table sugar functions as a usable energy source for people. In fact, it might even be the same type of sugar, with the only difference being how it was produced. The sugar on your kitchen table was likely produced by plants using photosynthesis, while the sugar in tube worms was produced by bacteria using chemosynthesis.


In this case, hydrogen sulfide plus carbon dioxide becomes sugar, water and sulfur gas. The chemical equation is:12H2S + 6CO2 ——> C6H12O6 + 6H2O + 12SThis reaction is only slightly different than the equation for photosynthesis, where sunlight combines with carbon dioxide and water to make sugar and oxygen gas. Notice how the distinguishing characteristic of chemosynthesis is the utilization of hydrogen sulfide, not sunlight, which acts as a driver for the reaction.Scientists hypothesize that chemosynthesis could be responsible for life below the surface of Mars or on Jupiter’s moon, Europa, which is thought to be liquid water underneath a frozen surface.

If true, the first life discovered beyond Earth would most likely be simple bacteria, such as those living inside the gut of tube worms.

Lesson Summary

Living organisms obtain energy in different ways. Some things, such as people, obtain energy by consuming their food.

Other organisms produce food by either photosynthesis or chemosynthesis, the process of using inorganic molecules to aid in the conversion of carbon molecules into organic matter. This process most often occurs in bacteria that are found living near hydrothermal vents on the ocean floor. Some of these bacteria live in the gut of tube worms, where they use toxic hydrogen sulfide to create sugar for the tube worms to use as an energy source.


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