- Biology notes that will help international a level students prepare for their unit 4 exam.
- Consist of Chapter 5B: Ecology.
- 95% typed notes with the other 5% being hand written usually in tables.
- Useful tools to help learn and memorise them like emojis, diagrams, tables and shortcuts
,1) Culturing Microorganism
• It is necessary to culture microorganisms for microbe investigations
this grows enough microorganisms to make measurements during investigations
• Microorganisms need proper conditions to grow:
nutrients
oxygen ( for anaerobic bacteria)
optimum pH
favourable temperature
• They need to be cultured with great care as
Risk that a mutation could lead to the formation of pathogenic strains
Pathogenic bacteria form the environment could contaminate the bacteria being
investigated
· follow health and safety precaution (aseptic techniques)
· sterilise equipment
· keep culture in
· seal culture in plastic bag and sterilise at high temps
Culturing steps
1. Obtain supply of type of microorganism
2. Provide correct type of nutrients (nutrient growth medium with C, N and minerals,
could be a liquid culture or a solid nutrient agar)
3. Keep nutrient medium in sterile conditions.
4. Selective medium = adjusting the type of nutrients in the medium to promote
growth of specific microorganism while inhibiting the growth others
Used to identify mutant strains, resistance to antibiotics and identifying genetically
modified microorganisms
5. Microorganisms are introduced to a growth medium using inoculation (can be
used to transfer microorganisms between media)
6. New medium should be sealed or covered to avoid contamination (not airtight
seal for aerobic bacteria)
7. Label the medium and incubate at around 20° to prevent the growth of
pathogenic organisms (which tends to grow at surround 37°)
, • To grow a single type of microorganism (pure
culture) = microorganism must be isolated. This is
useful in the diagnosis and treatment of diseases.
Examples include:
• Growing under aerobic or anaerobic conditions to reduce the variety
• Using selective medium
• Indicator media (provides colour change to distinguish desired colonies from the
rest)
2) Measuring the growth of microorganisms
• Many methods are used to count microorganisms
• Haemocytometer is a microscope slide with a rectangular chamber marked with
grid lines. Can hold a volume of 0.1mm^3
1. Nutrient broth is diluted with an equal volume of trypan blue (stains dead cells
blue so allows just to count the live cells)
2. Chamber of haemocytometer filled with the stained broth
3. Cells are counted to find the mean number of cells from the four corner squares
4. Haemocytometer is calibrated to calculate the number of cells in known columns
broth
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