6.1.1Unit 6: Practical Skills in Biology II
Culturing Microorganisms — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 5 parts Lesson 2 of 48 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Why and What to Provide
Reason for culture
- Reason for culture Microorganisms are too small to see, so they are grown until colonies are large enough to observe and measure.
Colonies
- Colonies Bacteria divide to produce clones, so a single cell on agar forms a visible colony of identical cells.
Needs
- Needs Cultures need nutrients, a suitable pH, a favourable temperature and oxygen unless the organism is anaerobic.
Growth medium
- Growth medium A medium contains carbon, nitrogen and minerals, and can be a liquid broth or solid nutrient agar.
Part 2 of 5Aseptic Technique
1
Wipe the work area with disinfectant, and work near a Bunsen flame so that air currents carry microorganisms away from the culture.
2
Sterilise equipment and media beforehand by heating, or with chemicals, to kill any microorganisms.
3
Pass the inoculating loop through the flame and let it cool before taking or transferring microorganisms.
4
Cover the dish or plug the flask with cotton wool, so that air can enter but contaminants cannot.
5
Label the dish, tape the lid lightly, and incubate it inverted so condensation does not fall onto the agar.
Part 3 of 5Incubation and Safety
Incubation and Safety
Temperature
- Temperature School cultures are kept at about 20–25 °C, because pathogens that harm humans grow best at about 37 °C.
Airflow
- Airflow Do not seal dishes fully, because aerobic organisms need oxygen and anaerobic growth could favour pathogens.
Disposal
- Disposal Sterilise cultures at high temperature and pressure before disposal, and never open dishes after growth.
Why take care
- Why take care Contamination or mutation could produce pathogenic strains.
Keeping cultures in
- Keeping cultures in Cultures stay in the laboratory, and hands and benches are disinfected at the end of the work.
Part 4 of 5Selective Media and Pure Cultures
Selective medium
- Selective medium The nutrients are chosen so that only the wanted microorganism grows well.
Uses
- Uses Selective media can identify antibiotic-resistant or mutant strains and genetically modified microorganisms.
Indicator media
- Indicator media A colour change helps distinguish the wanted colonies from the rest.
Controlling growth conditions
- Controlling growth conditions Growing under aerobic or anaerobic conditions also reduces the variety of organisms that can grow in the culture.
Importance
- Importance Isolating a pathogen helps with diagnosis and treatment of disease.
Part 5 of 5Exam Checklist & Tips
6.1.1 – Key Points for the Exam
- Aseptic technique Working methods that prevent unwanted microorganisms from contaminating cultures or the environment.
- Nutrient agar A solid growth medium made from a gel extracted from seaweed, with added nutrients.
- Inoculation Introducing microorganisms to a growth medium.
- Selective medium A medium that allows only particular microorganisms to grow.
Common Mistakes
- Sealing the lid of the dish completely, which could allow anaerobic pathogens to grow.
- Incubating school cultures at 37 °C, the temperature at which human pathogens grow best.
- Saying sterile means clean; it means free from all living microorganisms.
- Opening the dish to look at colonies, which risks releasing microorganisms.
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