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Requirements for Growth
Key terms
Macronutrients- required in relatively large amounts, includes carbon, hydrogen, oxygen, nitrogen,
sulphur, magnesium and iron. All nutrients have to be provided in a suitable form in the culture media
in which the microorganisms are grown.
Micronutrients- required in small amounts, may also be known as trace elements. Micronutrients
include copper, manganese, vanadium and zinc.…read more

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Environmental Influences on the Growth of Microorganisms
As temperature increases enzyme activity within the cells also increases and growth becomes faster
until a certain temperature when proteins and ENZYMES will become denatured. Then growth will fall
rapidly until it reaches zero.…read more

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Growth of Cultures
The Important Bits…read more

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Phases of Growth
1. Lag phase- Growth does not happen immediately when the medium is inoculated with a
culture of a microorganism, there is a period where the cells must synthesise the enzymes
required for metabolism of nutrients present in the medium and become adjusted to the
culture conditions.
2. Exponential phase- period of constant growth in size of population, both in cell numbers and
cell mass.…read more

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Diauxic Growth
This is characterised by two distinct phases
of exponential growth separated by a brief lag phase. It occurs when there are two different carbon
sources to grow on and so once one is used up new enzymes must be synthesised for the
metabolism of the other. For example, glucose and lactose; glucose inhibits the synthesis of lactase
so glucose must be used up before lactose can be metabolised. This is called catabolite repression.…read more

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Viable cell count- only considers living cells
Cell counts using a Haemocytometer
The number of cells in a suspension can be determined by counting the number of cells present in an
accurately determined, very small volume of culture medium. This is usually carried out using special
microscope slides called Haemocytometers (counting chambers). It provides a TOTAL CELL COUNT.
Plate Counts
The number of cells can also be determined using the pour plate dilution method.…read more

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The transfer of the sample should be done as quickly as possible to minimise contamination from
organisms present in the air and surroundings.
Streak Plating
Streak plates are used to isolate pure cultures as individual colonies will have grown from a single
cell. These can then be used to subculture another agar plate and obtain a pure isolate.
The loop should be flamed and allowed to cool between each set of four streaks and then again
after streaking is complete.…read more

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Use of Biotechnology
Food and Drink
Mycoprotein (Quorn)
Single celled Protein (SCP)- made by a microbe rather than an animal
Quorn is a meat substitute for vegetarians designed to provide them with protein.
Fungi used are called Fusarium graminareum.
The whole fungi is harvested and consumed- it is the hyphae that gives the texture of meat.
Culture Technique
A continuous culture in a bioreactor at around 30oc.…read more



This a very detailed set of notes that includes growth requirements,fermenters, growth phases, aseptic technique and uses of biotechnology. There are  clear annotated flow diagrams included which help illustrate the key points. Team these up with a set of flashcards that include definitions of the biological terms included in this topic for a complete set of resources.

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