Micro-organisms

Question 1

How do scientists study microorganisms?

Answer 1

Scientists grow them into large numbers. This is often done on agar which has nutrients added to feed the microorganisms in a petri dish. Bacteria grows very quickly and each bacterium that lands on the agar will soon grow into a circular patch called a colony which can be seen with the naked eye.

Question 2

How can you work out the number of bacteria originally put onto the plate?

Answer 2

By counting the colonies

Question 3

What may affect the counting of colonies?

Answer 3

Clumping of cells which can lead to misleading estimates.

Question 4

What does bacterial population growth depend on and why?

Answer 4

Temperature - At low temperatures the rate of growth is slower and at a very high temperatures the bacteria are killed.

Question 5

Why is food refrigerated?

Answer 5

To slow the growth of microorganisms to keep it longer before becoming spoilt. Freezing food completely stops growth.

Question 6

What are aseptic techniques used for?

Answer 6

Aseptic techniques reduce contamination from other microorganisms.

Question 7

Order of aseptic techniques?

Answer 7

1. Sterilise all equipment and surfaces before and after experiment
2. Inoculating loop held in bunsen burner flame to kill any bacteria
3. Flame the rim of the bacterial culture tube
4. Loop is dipped into the culture to pick up bacteria
5. Mouth of the tube is flamed again and stopper replaced
6. Lid of petri dish is slightly raised and loop is drawn across agar surface.
7. Inoculating loop is sterilised again which kills any bacteria left

Question 8

How do you know when you’ve killed the bacteria on the inoculating loop?

Answer 8

Glows red

Question 9

Why must you flame the mouth of the tube again?

Answer 9

Kills bacteria that may be drifting into the culture tube to stop it getting contaminated

Question 10

Why is the plate not completely uncovered when the loop is drawn across agar surface?

Answer 10

So bacteria from the air will not be able to fall onto it.

Question 11

What is penicillin?

Answer 11

An antibiotic commonly used to treat bacterial diseases. It has no effect on viruses.

Question 12

What is penicillin produced from?

Answer 12

The penicillium fungus

Question 13

What is the fungus grown in?

Answer 13

Industrially in a tank called a fermenter.

Question 14

What is the temperature kept at in a fermenter?

Answer 14

The optimum temperature for growth is 23-28°C

Question 15

What is the pH kept at in a fermenter?

Answer 15

Around 6.5

Question 16

What are the oxygen levels kept at in a fermenter?

Answer 16

Penicillium is an aerobic fungus so it needs oxygen for respiration and growth.

Question 17

When are nutrients added to the fermenter?

Answer 17

Although penicillium needs nutrients, these are not added once the growth has started as the fungus only produces penicillin when the nutrient levels are low.

Question 18

What happens after 200 hours in the fermenter?

Answer 18

The liquid is drained from the fermenter, filtered to remove fungal cells and then treated chemically to extract the penicillin drug.

Question 19

What does the air intake in a fermenter allow?

Answer 19

Sterile air to get in

Question 20

What does the stirrer in a fermenter allow?

Answer 20

The stirrer mixes the nutrients throughout the fermenter otherwise they would collect near the bottom.

Question 21

What does the water jacked in a fermenter allow?

Answer 21

Water jacket to control temperature