Edexcel A-level biology Topic 6 - Microbiology and
Pathogens Questions With Answers
What are the four different types of microorganisms?
bacteria, fungi, viruses and protozoa
What are pathogens?
microorganisms that cause disease
What does culturing microoganisms involve?
microoganisms are provided with the temperature, level of oxygen, pH and nutrients
that they require to grow
What is the use of culturing microorganisms?
to grow large numbers so they can be observed and measured
Why is it important to be careful when culturing microorganisms?
- safe organisms may mutate to dangerous forms in the culture
- contamination by unwanted organisms
- risk of contamination of the culture by pathogenic microorganisms from the
environment which leads to disease
What is meant by the term sterile?
completely free of all living organisms, including spores and viruses.
What is a nutrient medium?
a substance used for the culture of microorganisms, which can be in liquid form
(nutrient broth) or solid form (nutrient agar)
What is nutrient broth?
liquid nutrient for culturing microorganisms
What is nutrient agar?
a jelly extracted from seaweed and used as a solid nutrient for culturing
microorganisms
What is a selective medium?
a growth medium for a specific type of microorganism containing a specific mixture
of nutrients
What is the importance of selective media?
- identifying particular mutant strains of microorganisms and antibiotic resistance
- identifying microorganisms that have been genetically modified
What is inoculation?
, The process by which microorganisms are transferred into a culture medium under
sterile conditions.
The majority of microorganisms grow on or in a medium enriched with...
good protein sources such as blood, yeast or meat extract
What does aseptic culture technique include?
- sterilising all equipment, including agar and Petri dishes, using an autoclave and
UV light
- sterilising the inoculating loop by passing it through a blue Bunsen burner flame
until it glows red hot
- keeping Petri dish lid closed as much as possible
- passing open lids through Bunsen flame
Describe the steps in aseptic culture technique
1. Decide which microorganisms you want to culture and obtain a culture of them.
2. Provide microorganisms with appropriate nutrients in sterile nutrient medium:
either broth (liquid) or agar (solid).
3. Inoculate the culture. If using broth, either use an inoculating loop and swirl it in
the culture or mix
inoculating broth with sterile medium in a flask.
If using agar, either make a streak plate or a spread plate (drop some on and use a
sterile spreader to distribute it).
When using nutrient broth in a flask to culture bacteria, why is the flask
stoppered with cotton wool and then shaken later on?
- stoppered with cotton wool to prevent contamination with pathogenic
microorganisms from the air
- shaken to allow oxygen to the growing bacteria
- Shaken to prevent bacteria settling at the bottom of the flask
How do you make a streak plate (inoculating solid agar)?
1. Sterilise the inoculating loop by holding it in a blue Bunsen burner flame until it
glows red hot.
2. Dip the sterilised loop in the suspension of bacteria.
3. Streak the loop across the surface of the agar, avoiding digging into the agar.
4. Replace the Petri dish lid, tape closed and label. Turn dish upside down.
Growing a pure culture
What are the different ways of growing a single bacterium or fungus?
Pathogens Questions With Answers
What are the four different types of microorganisms?
bacteria, fungi, viruses and protozoa
What are pathogens?
microorganisms that cause disease
What does culturing microoganisms involve?
microoganisms are provided with the temperature, level of oxygen, pH and nutrients
that they require to grow
What is the use of culturing microorganisms?
to grow large numbers so they can be observed and measured
Why is it important to be careful when culturing microorganisms?
- safe organisms may mutate to dangerous forms in the culture
- contamination by unwanted organisms
- risk of contamination of the culture by pathogenic microorganisms from the
environment which leads to disease
What is meant by the term sterile?
completely free of all living organisms, including spores and viruses.
What is a nutrient medium?
a substance used for the culture of microorganisms, which can be in liquid form
(nutrient broth) or solid form (nutrient agar)
What is nutrient broth?
liquid nutrient for culturing microorganisms
What is nutrient agar?
a jelly extracted from seaweed and used as a solid nutrient for culturing
microorganisms
What is a selective medium?
a growth medium for a specific type of microorganism containing a specific mixture
of nutrients
What is the importance of selective media?
- identifying particular mutant strains of microorganisms and antibiotic resistance
- identifying microorganisms that have been genetically modified
What is inoculation?
, The process by which microorganisms are transferred into a culture medium under
sterile conditions.
The majority of microorganisms grow on or in a medium enriched with...
good protein sources such as blood, yeast or meat extract
What does aseptic culture technique include?
- sterilising all equipment, including agar and Petri dishes, using an autoclave and
UV light
- sterilising the inoculating loop by passing it through a blue Bunsen burner flame
until it glows red hot
- keeping Petri dish lid closed as much as possible
- passing open lids through Bunsen flame
Describe the steps in aseptic culture technique
1. Decide which microorganisms you want to culture and obtain a culture of them.
2. Provide microorganisms with appropriate nutrients in sterile nutrient medium:
either broth (liquid) or agar (solid).
3. Inoculate the culture. If using broth, either use an inoculating loop and swirl it in
the culture or mix
inoculating broth with sterile medium in a flask.
If using agar, either make a streak plate or a spread plate (drop some on and use a
sterile spreader to distribute it).
When using nutrient broth in a flask to culture bacteria, why is the flask
stoppered with cotton wool and then shaken later on?
- stoppered with cotton wool to prevent contamination with pathogenic
microorganisms from the air
- shaken to allow oxygen to the growing bacteria
- Shaken to prevent bacteria settling at the bottom of the flask
How do you make a streak plate (inoculating solid agar)?
1. Sterilise the inoculating loop by holding it in a blue Bunsen burner flame until it
glows red hot.
2. Dip the sterilised loop in the suspension of bacteria.
3. Streak the loop across the surface of the agar, avoiding digging into the agar.
4. Replace the Petri dish lid, tape closed and label. Turn dish upside down.
Growing a pure culture
What are the different ways of growing a single bacterium or fungus?
