The Growth Curve

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The Standard Growth Curve

A small number of organisms places in a fresh 'closed culture' environment will undergo population growth in a very predictable, standard way. Plotting the growth in a population over time, gives the standard growth curve. A closed culture refers to the growth of microogransisms in an environment where all conditions are fixed and contained. No new materials are added and no waste products or organisms removed.
first stage=the LAG stage- Organisms are adjusting to the surrounding conditions. This may mean taking in water, cell expansion, activating specific genes and synthesising specific enzymes. The cells are active but not reproducing so population remains fairly constant. The length of this period depends on the growing conditions.

second stage=the LOG stage-The population size doubles each generation as every individual has enough space and nutrients to reproduce. In some bacteria, the population can double every 20-30 minutes in these conditions. The length of this phase depends on how quickly to organisms reproduce and take up the available nutrients and space.

the third stage=Stationary Phase-Nutrient levels decrease and waste products like CO2 and other metabolites build up. Individual organisms die at the same rate at which new individuals are being produced. In an open system, this would be the CARRYING CAPACITY of the environment

The last stage-Decline/death stage-Nutrient exhaustion and increased levels of toxic waste products and metabolites lead to the death rate increasing above the reproduction rate. Eventually, all organisms will die in a closed system

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Fermentation and Fermentors

Term was originally applied only to the yse of anaerobic respiration to produce a substance. E.g the production of ethanol through the anaerobic respiration of yeast.

These naturally produced fermentation products are by-products of anaerobic respiration pathways.

It now also refers to the culturing of mircroorganisms both aerobically and anaerobically in fermentation tanks.

The substances generated by growth of the mircroorganism culture are separated and treated to produce the final useful product.

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Metabolism and Metabolites

Metabolism=the sum total of all the chemical reactions that go on in an organism.

These processes produced;

  • new cells and  cellular components.
  • chemicals such as hormones and enzymes.
  • waste products. The waste products produced vary depending on the type of organism and metabolic process involved, ranging from gases such as CO2 and O2 to soluble molecules like urea, ammonia and nitrates.

The waste products of some organisms' metabolic processes are the  vital nutrients required by other organisms.

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Primary and Secondary metabolites

Primary metabolite=substances produced by an organism as part of its normal growth. They include amino acis, proteins, enzymes, nucleic acids, ethanol and lactate. The production of primary metabolites matches the growthh in population of the organism.

Secondary metabolites=substances produced by an organism that are not of its normal growth. THe antibiotic chemicals produced by a number of microorganisms are almost all secondary metabolites. The production of secondary metabolites usuallly begins after the main growth period of the organisms and so does not match the growth in population of the organism.

It is important to remember that whilst all mircroorganisms produce primary metabolites, they need in order to grow, only a relatively small number of microorganisms produce secondary metabolites.

All organisms use this growth curve not just microorganisms. If they can grow and reproduce. They will also be subkect to similar constraints.

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