# Worksheet: Culturing Microorgansims

In this worksheet we will practice describing the best methods to culture microorganisms, and using the process of binary fission to estimate population sizes of bacteria.

**Q1: **

A *Streptococcus* bacteria cell divides, on average, once every 30 minutes. How many
bacteria cells will there be after 3.5 hours?

**Q2: **

A scientist timed how long it took a bacterial cell to replicate in hours. They would like to convert this to minutes. How can they convert a value from hours to minutes?

- A
- B
- C
- D

**Q3: **

A *Staphylococcus* bacteria cell divides, on average, once every 180 minutes.

How many bacteria cells will there be after 24 hours?

**Q4: **

When microorganisms are cultured, they are often grown on a culture medium (e.g., agar gel). Choose the correct words to complete the description of a culture medium:

A culture medium is a liquid or gel that contains appropriate to encourage the cells to .

- Anutrients, die off
- Borganisms, reproduce
- Cnutrients, grow
- Dtemperatures, replicate

**Q5: **

A *Salmonella* bacteria cell divides, on average, once every 45 minutes.
How many bacteria cells will there be after 12 hours?
Use the following formula: number of cells = .

**Q6: **

What scientific term is given to the most common process by which bacteria cells replicate?

- AMitosis
- BSynthesis
- CBinary fusion
- DBinary fission
- EMeiosis

**Q7: **

An *E. coli* bacteria cell divides, on average, once every
20 minutes.
How many bacteria cells will there be after 3 hours?

**Q8: **

The diagram provided shows colonies of bacteria grown on an agar plate. Four different disks of antibiotics, A, B, C, and D, have been added.

What do the clear areas around the antibiotic disks indicate?

- AThey show where the agar plate is contaminated.
- BThey show where the bacteria have killed off the antibiotics.
- CThey show where more than one antibiotic is growing.
- DThey show where the antibiotics have killed off the bacteria.

Looking at the agar plate, which antibiotic is the most effective?

- AB
- BA
- CD
- DC

**Q9: **

When an antibiotic is placed on an agar plate of bacteria, the circular area around the antibiotic that is clear of bacterial growth is called the zone of inhibition.

For the following questions, take the area of a circle to be .

Antibiotic A gives a clear area with a diameter of 3 cm. What is the area of the zone of inhibition in square centimeters? Give your answer to one decimal place.

Antibiotic B gives a clear area with a diameter of 5.5 cm. What is the area of the zone of inhibition in square centimeters? Give your answer to the nearest whole number.

Antibiotic C gives a clear area with a diameter of 6 cm. What is the area of the zone of inhibition in square centimeters? Give your answer to one decimal place.