Practise Culturing microorganisms. 19 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Required practical:Microbiology (method, variables and exam tips)
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At what temperature should cultures of bacteria generally be incubated in a school laboratory?
25 °C
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Bacteria can be grown in the laboratory.
(a) Bacteria multiply by simple cell division. What is the name of this type of cell division? Tick (✓) one box.[1]
Binary fission
Differentiation
Fertilisation
Meiosis
(b) Give two ways that bacteria can be grown in the laboratory.[2]
(c) Give the reason why an inoculating loop is passed through a flame before it is used.[1]
(d) At what temperature should cultures of bacteria generally be incubated in a school laboratory?[1]
Show the answer and mark scheme
(a)Answer: Binary fission
(b)
in a nutrient broth (solution)
as colonies on an agar gel plate
(c)
to kill microorganisms on the loop / to sterilise it
(d)Answer: 25 °C
25 (°C)
Question 2Medium5 marks
A student prepared an uncontaminated culture of bacteria on an agar plate using aseptic technique.
(a) Explain why the Petri dish and the agar must be sterilised before use.[1]
(b) The student secured the lid of the Petri dish with adhesive tape. Explain why.[1]
(c) The student stored the Petri dish upside down. Explain why.[1]
(d) The student incubated the culture at 25 °C and not at 37 °C. Explain why.[2]
Show the answer and mark scheme
(a)
to kill any microorganisms already present (so that only the bacteria being studied grow)
(b)
to stop microorganisms from the air getting in and contaminating the culture
(c)
so that condensation does not drip onto the agar / colonies
(d)
harmful bacteria / pathogens are less likely to grow at 25 °C
pathogens grow best at body temperature / 37 °C
Question 3Hard7 marks
Under ideal conditions, one type of bacterium divides by binary fission once every 20 minutes. A single bacterium of this type is placed in a flask of nutrient broth.
(a) Calculate the number of bacteria in the flask after 4 hours. Give your answer in standard form.[3]
(b) A second flask started with 500 bacteria of a different type. The mean division time of this type is 30 minutes. Calculate the number of bacteria in the second flask after 3 hours. Give your answer in standard form.[2]
(c) After 24 hours, the number of bacteria in the first flask was much lower than the number predicted by calculation. Suggest two reasons why.[2]