Question

5. Define the following terms, and identify which of these four nutritional groups most of the medically important microbes would belong to.
   

   a. photoautotroph
   b. photoheterotroph c. chemoautotroph d. chemoheterotroph

Answer 1

a.

Photoautotroph

Photoautotrophs are organisms which use light to make their own food and perform cellular functions. Light is used as the source of energy here. They make food for themselves and also for other heterotrophic organisms. Photoautotrophs are seen at the base of the foodchain as producers. They take up carbondioxide formed as a result of respiration and give out oxygen as part of photosynthesis. They are considered as the inevitable part of ecosystem.

Examples

* Green plants

* Algae

* Cyanobacteria /Blue green algae

* Green sulphur bacteria

b.

Photoheterotroph

Photoheterotroph can be defined as organisms which use light as the source of energy but they can't use carbondioxide as the source of carbon. So they depend on organic compounds in the environment for carbon source. Photoheterotrophs produce ATP in two ways- One is by the use of bacteriorhodopsin , a cholorophyll based mechanism. This results in the electron flow through electron transport chain and pumping of H+ ions across membrane. Second method is by the use of purple rhodopsin based proton pumps.

Examples

* Purple non sulphur bacteria

* Green non sulphur bacteria

* Heliobacteria

c.

Chemoautotrophs

Chemoautotrophs are organisms which can make their own food by fixation of carbondioxide. The energy required for the process is obtained by oxidation of inorganic molecules such as iron or sulphur. Most of the chemoautotrophs are extremophiles, which live in harsh habitats.

examples

* Sulphur oxidizing bacteria

* Iron oxidizing bacteria

* Methanogens

d.

Chemoheterotroph

Chemoheterotrophs are organisms which obtain energy by oxidation of inorganic molecules. But they cannot utilize carbondioxide to form torganic compounds.They donot live in harsh conditions instead live in areas where other forms of life exists.

examples

* Fungi

* Protists

Chemoheterotroph Is the nutritional group  where most of the medically important microbes belong. it includes fungi, protists and other organisms.