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Up to date as of January 23, 2010

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Life processes of microorganisms

A common guide to defining life is MRS GREN.


Bacteria and fungi have all of the above life processes thus are considered to be alive. Viruses are thought by most scientists to be alive but some disagree because they do not feed, respire (breath) and excrete (expel waste).




Enzymes in extracellur digestion

Bacteria is a consumer in the food chain thus it needs to gets its glucose from plant or animal matter. Unlike humans, a bacterium is an individual cell. This means that it must feed by extracellular digestion.

Extracellular digestion involves enzymes being allowed out through the cell membrane and being secreted onto food molecules. The enzymes catalyse (break down) the food into molecules small enough to be absorbed into the bacterium. Since the digestion is done outside of the cell, it is said to be extracellular.

Saprophytic bacteria feed off dead matter. Bacteria which are parasitic feed off living matter.


Bacteria grow bigger by using nutrients gained through digestion of food and energy released through respiration. When cells reach about optimum size, they split into two.


All living things respire (breath) in order to convert glucose into energy.

Aerobic bacteria use oxygen in their respiration process. Their reaction is:

C6H12O6 (glucose) + O2 (oxygen)→ 4H2O (Water) + 2CO2 (Carbon dioxide) + 118kJ of Energy

Anaerobic bacteria do not use oxygen in respiration thus are less efficient and produce alcohol as a product.

C6H12O6 (glucose)→ 2CH3CH2OH (Alcohol) + 2CO2 (Carbon dioxide) + 118kJ of Energy

They by-product of anaerobic bacteria can be useful. Yeast, an anaerobic bacteria is useful in baking and fermentation (making wine).

Most bacteria do not require oxygen but will use it if it is available. Some bacteria require it, but most bacteria will use oxygen if it is available, but they can also undergo anaerobic respiration.


Binary fission anim.gif

The process in which bacteria reproduces is called binary fission (split into two). The process for binary fission is as followed:

1. The DNA duplicates itself and splits
2. Cell membranes pinch together
3. A second bacterium is formed that is exactly like its parent cell

Bacteria can reproduce once every 20 minutes if under ideal conditions. The ideal temperature for human bacterial diseases is between 30-40°C. Their growth is initially exponential ie 1,2,4,8,etc.

Stages of bacterial growth
Exponential Growth of Bacteria
Time (minutes) Number of Bacteria
0 1
40 4
80 16
120 64
160 256
200 1 024
240 4 096
280 16 384
320 65 536
360 262 144
400 1 048 576
440 2 097 152
480 4 194 304
Growing colony of E. coli.jpg

The first phase is the lag phase where reproduction does not increase very much. The exponential phase follows where a plentiful supply of nutrient and space allow an ever-increasing rate of growth, and bacterial production outstrips bacterial death.

Once the carrying capacity (the maximum population the environment can support), is reached, the population enters the stationary phase where no net change in population occurs. The environment is changed by the bacteria as metabolic waste builds up and the conditions become increasingly difficult. Eventually, this leads to the death phase where more cells die than are produced, as a result of waste toxicity, starvation and oxygen shortage; and the population declines.


Humans excrete by producing faeces, carbon dioxide and water. Aerobic bacteria release carbon dioxide and water. Anaerobic bacteria release alcohol and carbon dioxide.

Most saprophytic bacteria excrete usable nutrients. Pathogenic bacteria excrete toxins (strong poisons).


Fungus spore ejection.ogg
Video of spores being released.


Fungi also practise extracellular digestion in order to respire. The hyphae release enzymes onto the food source. The enzymes break down the food into food molecules which are then absorbed by the hyphae. The glucose from this is used in respiration.


Fungi grow bigger through the nutrients absorbed by extracellular digestion. As they get taller, sporangia appear appear and eventually, the sporangia will become so large that it bursts.


Aerobic fungi use oxygen in their respiration process. Their reaction is:

C6H12O6 (glucose) + 6O2 (oxygen)→ 6H2O (Water) + 6CO2 (Carbon dioxide) + 2830kJ of Energy

Anaerobic fungi do not use oxygen in respiration thus are less efficient and produce alcohol as a product.

C6H12O6 (glucose)→ 2CH3CH2OH (Alcohol) + 2CO2 (Carbon dioxide) + 118kJ of Energy

An example of anaerobic fungi is yeast which is useful in baking.


Fungi Reproduction.png

Reproduction follow the above process. A mature sporangia bursts releasing a huge number of spores. These spores land on a food source and grow hyphae. Within 3-5 days, sporangia appears and soon, they become mature releasing spores. The cycle repeats.


Saprophytic fungi digest dead plant and animal matter and release nutrients.


Phage viruses breaking into a cell

The main function viruses perform is reproduction. They do not grow, feed, respire or excrete.


Phage viruses reproduce in the lytic cyle. They follow the following stages:

Phage viruses reproduce through the lytic cycle.
  • Penetration
To infect the cell, the virus must enter through the cell membrane and (if present) cell wall. It attaches its tail fibre onto the surface and injects its genetic material (DNA and RNA). In doing this, the cell is infected with the virus.
  • Biosynthesis
A host cell cannot differentiate between the proteins of itself and a virus. This is exploited by DNA viruses which uses this to destroy the host's cell DNA and replaces it with its own DNA. Then biosysnthesis or the manufacturing of virus parts occur. First enzymes are produced to trick the cell into manufacturing viral parts. Genetic material (DNA) is first manufactured and in the later stages, the protein coat (head and tail).
  • Maturation and lysis
Once many copies of the viral components have been made, they are assembled into complete viruses. The phage then produces an enzyme that breaks down the bacteria cell wall and allows fluid to enter. The cell eventually becomes filled with viruses (typically 100-200) and liquid, and bursts. The new viruses are then free to infect other cells.

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