1. Cell Biology (required practical 2 - culturing micro-organisms)

Question 1

What are micro-organisms?

Answer 1

Microorganisms are bacterial cells (prokaryotes)

Question 2

How are micro-organisms cultured?

Answer 2

• Micro-organisms are grown (cultured) on a “culture medium”.
• This is usually agar jelly containing everything micro-organisms need to grow, like nutrients

Question 3

What do micro-organisms need to grow?

Answer 3

Carbohydrates, proteins, minerals, vitamins

Question 4

What is a mutation?

Answer 4

A random change in DNA

Question 5

What equipment is required for the practical?

Answer 5

Agar jelly, petri dish, inoculating loop, paper discs, substance you want to test on bacterial growth (ie: antibiotic)

Question 6

What are the steps for the experiment? (7)

Answer 6

1. Agar jelly is heated to kill unwanted micro-organisms and then is poured into a petri dish
2. Inoculating loop passed through a flame. Transfer microorganisms to the agar jelly once it has cooled down
3. Paper discs are soaked in different types of antibiotics and placed in the jelly.
4. A paper disk not soaked in anything is added as a control
5. Sellotape the lid onto the petri dish
6. Turn the petri dish upside down so that the microorganism’s vapour will not drop into the experiment
7. Incubate for sometime at 25 degrees celsius

Question 7

What incubation temperatures are culture of micro-organisms kept at in a lab/industrial conditions?

Answer 7

• Much higher temerpatures than in a school setting so micro-organisms can grow faster

Question 8

What incubation temperature do cultures grow at in school and why?

Answer 8

25 degrees celcius, because any higher could mean harmful pathogens are more likely to grow

Question 9

How can you avoid contamination/ what are some aseptic techniques?

Answer 9

• The agar jelly is heated up
• The petri dishes, inoculating loops, and culture medium(is the same as agar jelly) must be sterilised.
• Wipe down work area with disinfectant
• Petri dish must have lid to prevent microorganisms in the air contaminating the culture
• Ensuring that the lid is opened as little as possible and only when necessary

Question 10

What could be a consequence if the equipment is not sterilised?

Answer 10

Unwanted microorganisms in the culture medium will grow + affect the results

Question 11

What is the control in the experiment?

Answer 11

The control variable is what is done to make the experiment fair and accurate, which is the paper disc that is not soaked.

Question 12

Why do doctors not give antibiotics every time someone is sick?

Answer 12

• Because it may promote antibiotic resistant bacteria
• which will survive and reproduce passing on the resistant gene
• so there is a whole colony of bacteria, that the antibiotic can no longer kill

Question 13

What is IV, DV and CV

Answer 13

• Independent variable - variable that you are changing
• Dependant variable - variable that you are measuring in the experiment
• Control variable - the different factors that you keep the same

Question 14

How do I measure the area of bacteria killed in the experiment around the paper disc?

Answer 14

• Area = Pi x (Radius)^2

Question 15

Why do petri dishes and culture media must be sterilized before use?

Answer 15

Because if not sterilized unwanted micro-organisms in the culture medium will grow and affect the results

Question 16

Why does the lid of the petri dish have to be secured with adhesive tape and stored upside down?

Answer 16

• to ensure that no unwanted micro-organisms can enter
• to ensure the water vapour on the lid, produced from the bacteria respiring, will not fall onto the experiment and will instead condense on the lid

Question 17

Why is an inoculating loop passed through a flame?

Answer 17

To sterilize it by killing any unwanted micro-organisms

Question 18

What does incubate mean?

Answer 18

letting the bacteria grow and develop in a warm environment

Question 19

Why are cultures not incubated at 37 degrees celcius?

Answer 19

37 degrees is the average body temperature for humans, so we could get ill if the microorganisms are in contact with us.

Question 20

When do you use the mean division time?

Answer 20

When you want to estimate the number of bacteria in a population

Question 21

How do you calculate the number of bacteria in a population after a certain time if the mean division time is given?

Answer 21

1. Make sure both times are in the same units
2. Divide the toal time that the bacteria are producing by the mean division time. This gives you the number of divisions
3. Multiply two to the power of the number of divisions to find the number of cells

Question 22

What is the mean division time?

Answer 22

The average amount of time it takes for 1 bacterial cell to divide into 2