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5.2: Bacteria Nutrition

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Can bacteria make their own food from sunlight?

Plants aren't the only organisms that use the energy of the sun to make food. Some bacteria can also perform photosynthesis. In fact, the first photosynthetic organisms on earth were bacteria. Photosynthesis is just one of many ways that bacteria can obtain energy.

Bacteria Nutrition

Like all organisms, bacteria need energy, and they can acquire this energy through a number of different ways.


Photosynthetic bacteria use the energy of the sun to make their own food. In the presence of sunlight, carbon dioxide and water are turned into glucose and oxygen. The glucose is then turned into usable energy. Glucose is like the "food" for the bacteria. An example of photosynthetic bacteria is cyanobacteria, as seen in the opening image.


Bacteria known as decomposers break down wastes and dead organisms into smaller molecules. These bacteria use the organic substrates they break down to get their energy, carbon, and nutrients they need for survival.


Bacteria can also be chemotrophs. Chemotrophs obtain energy by breaking down chemical compounds in their environment. An example of one of these chemicals broken down by bacteria is nitrogen-containing ammonia. These bacteria are important because they help cycle nitrogen through the environment for other living things to use. Nitrogen cannot be made by living organisms, so it must be continually recycled. Organisms need nitrogen to make organic compounds, such as DNA.


Some bacteria depend on other organisms for survival. For example, some bacteria live in the roots of legumes, such as pea plants ( Figure below ). The bacteria turn nitrogen-containing molecules into nitrogen that the plant can use. Meanwhile, the root provides nutrients to the bacteria. In this relationship, both the bacteria and the plant benefit, so it is known as a mutualism .

These bacteria-containing nodules on a soybean root help provide the plant with nitrogen.


Other bacteria are parasitic and can cause illness. In parasitism , the bacteria benefit, and the other organism is harmed. Harmful bacteria will be discussed in another concept.


  • chemotroph : Organism that obtains energy by breaking down chemical compounds in the environment.
  • mutualism : Close relationship between organisms that is beneficial to both.
  • parasitism : Relationship between two organisms in which one benefits and the other is harmed.


  • Bacteria can obtain energy and nutrients by performing photosynthesis, decomposing dead organisms and wastes, or breaking down chemical compounds.
  • Bacteria can obtain energy and nutrients by establishing close relationships with other organisms, including mutualistic and parasitic relationships.


Use the resources below to answer the questions that follow.

  1. What are the three nutritional types of bacteria?
  2. What is the base energy source for these three types?
  3. How does the base energy source limit where specific types of bacteria can live?
  1. What is the difference between a heterotroph and an autotroph?
  2. What is the difference between aerobic, anaerobic, and facultative anaerobic bacteria?
  3. What are two ways bacteria play important roles in the ecosystem?


  1. What are some ways that bacteria can obtain nutrients and energy?
  2. What is an example of a mutualism with a bacteria?

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Difficulty Level:

At Grade


7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Dec 01, 2014
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