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Edexcel GCSE Biology · 1BI0
Edexcel 1BI0 · 5.17B Check the specification (PDF) (opens in a new tab)
A culture is a population of microorganisms grown in a laboratory. Microorganisms from the air, hands or equipment could get into it and grow alongside the organism being studied. That would make the culture unreliable. Cultured microorganisms could also escape and contaminate people or the work area. means working in ways that reduce both risks.
Microorganisms need nutrients to grow, so a Petri dish may contain agar jelly as a growth medium. Before a culture is set up, an autoclave uses hot, pressurised steam to sterilise the growth medium and suitable Petri dishes. Sterilising kills microorganisms already present. It gives the intended microorganism a clean starting place; it does not keep the dish sterile if it is left open afterwards.
An autoclave prepares materials before growth. An incubator has a different job: it provides conditions in which an established culture can grow.
A sterile inoculating loop transfers a small sample from a culture vial to fresh growth medium. A reusable loop can be sterilised in a flame and allowed to cool before it touches the sample; a hot loop could kill the microorganisms being transferred. Open the culture vial only for the transfer, then replace its cap promptly. Likewise, lift the Petri-dish lid only enough to use the loop on the agar, then replace it promptly. Keeping culture vials and Petri dishes covered limits microorganisms entering from the surroundings and those in the culture escaping.
Sterile materials and a sterile loop help prevent unwanted microorganisms entering a culture; covers are replaced promptly after transfer.
The key idea is a sequence: start with sterile materials, use a sterile tool to make the transfer, and keep each container covered whenever access is not needed.
Aseptic technique reduces contamination of the culture and its surroundings.
Autoclave the growth medium and suitable Petri dishes before use. Transfer microorganisms with a sterile inoculating loop; let a flame-sterilised loop cool first. Open culture vials and Petri dishes only briefly, then cover them again. An incubator grows a culture; it does not sterilise it.
Explain the purpose of each technique: it reduces contamination of the culture, the surroundings or both.
Do not confuse an autoclave with an incubator: the autoclave sterilises materials before use; an incubator provides conditions for growth.
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Aseptic technique
A method of handling microorganisms that reduces contamination of a culture and its surroundings.
Contamination
The presence of unwanted microorganisms in a culture, on equipment or in the surroundings.
Growth medium
A nutrient material, such as agar jelly, on or in which microorganisms can grow.
Autoclave
A machine that uses hot, pressurised steam to sterilise suitable equipment and growth media.
Inoculating loop
A small tool used to pick up and transfer microorganisms between cultures.
Put your knowledge into practice — try past paper questions for Biology
Aseptic technique
A method of handling microorganisms that reduces contamination of a culture and its surroundings.
Contamination
The presence of unwanted microorganisms in a culture, on equipment or in the surroundings.
Growth medium
A nutrient material, such as agar jelly, on or in which microorganisms can grow.
Autoclave
A machine that uses hot, pressurised steam to sterilise suitable equipment and growth media.
Inoculating loop
A small tool used to pick up and transfer microorganisms between cultures.