Nutrition: Heterotrophy
Heterotrophy is the use of previously formed organic compounds to provide energy for maintenance, growth and replication by organisms. That is, the organic compounds are digested in a controlled process and the energy made available is used by the organism for growth and respiration.
Digestion can be one of two forms:
- Extracellular
- Phagocytotic
Extracellular Digestion
Extracellular digestion can be found in all fungi, some bacteria and some protists. Enzymes are released into the environment surrounding the cell. Digestion takes place outside the cell and the breakdown products are absorbed by the cell.
View
animation of extracellular digestion (10 Kb).
Consequences of Extracellular Digestion:
Digestion takes place outside the cell and as a result, the products of digestion are available to all in the immediate vicinity. Microbes are usually in close proximity to each other, thus the need to "make the most" of their digestion leads to competition/specialisation/cooperation (See later section on competition).
Question
2Phagocytosis
Phagocytosis is found in some protists and a few bacteria. All these microbes lack a cell wall. It is not found in the fungi, algae and all bacteria with a cell wall. Food particles are enveloped by the cell and enclosed in to a food vacuole, digested there and the energy released used. Note that waste can be expelled from the cell following digestion.
