Micro-organisms Flashcards
(21 cards)
How do scientists study microorganisms?
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.
How can you work out the number of bacteria originally put onto the plate?
By counting the colonies
What may affect the counting of colonies?
Clumping of cells which can lead to misleading estimates.
What does bacterial population growth depend on and why?
Temperature - At low temperatures the rate of growth is slower and at a very high temperatures the bacteria are killed.
Why is food refrigerated?
To slow the growth of microorganisms to keep it longer before becoming spoilt. Freezing food completely stops growth.
What are aseptic techniques used for?
Aseptic techniques reduce contamination from other microorganisms.
Order of aseptic techniques?
- Sterilise all equipment and surfaces before and after experiment
- Inoculating loop held in bunsen burner flame to kill any bacteria
- Flame the rim of the bacterial culture tube
- Loop is dipped into the culture to pick up bacteria
- Mouth of the tube is flamed again and stopper replaced
- Lid of petri dish is slightly raised and loop is drawn across agar surface.
- Inoculating loop is sterilised again which kills any bacteria left
How do you know when you’ve killed the bacteria on the inoculating loop?
Glows red
Why must you flame the mouth of the tube again?
Kills bacteria that may be drifting into the culture tube to stop it getting contaminated
Why is the plate not completely uncovered when the loop is drawn across agar surface?
So bacteria from the air will not be able to fall onto it.
What is penicillin?
An antibiotic commonly used to treat bacterial diseases. It has no effect on viruses.
What is penicillin produced from?
The penicillium fungus
What is the fungus grown in?
Industrially in a tank called a fermenter.
What is the temperature kept at in a fermenter?
The optimum temperature for growth is 23-28°C
What is the pH kept at in a fermenter?
Around 6.5
What are the oxygen levels kept at in a fermenter?
Penicillium is an aerobic fungus so it needs oxygen for respiration and growth.
When are nutrients added to the fermenter?
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.
What happens after 200 hours in the fermenter?
The liquid is drained from the fermenter, filtered to remove fungal cells and then treated chemically to extract the penicillin drug.
What does the air intake in a fermenter allow?
Sterile air to get in
What does the stirrer in a fermenter allow?
The stirrer mixes the nutrients throughout the fermenter otherwise they would collect near the bottom.
What does the water jacked in a fermenter allow?
Water jacket to control temperature
