Aerobic respiration

food (glucose)oxygen

carbon dioxide

water

energy

+

+

+

Growing Microbes

In today’s lesson we will be growing microbes and

evaluating our practical skills

Learning Outcomes:By the end of the lesson you should:

•learn how to inoculate an agar plate to grow micro-organisms.

•evaluate the competency of their practical skills in terms of controlling risks to themselves and others

•be able to explain the significance of steps in the process

•know micro-organisms can cause infections and can be passed from one person to another.

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MovementRespirationSensitivityGrowthReproductionExcretionNutrition

Note: A living organism must be able to demonstrate that it can perform ALL the 7 life processes.

Microbe can be put into a number of categories. The three types which you need to know about are listed below:

Reminder:Microbe uses

BACTERIAVIRUS

FUNGI

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Microbes

Microbes multiply very rapidly. Two can, very quickly, become four then eight and so on.

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Microbe uses

Microbes have many uses. This is mainly because we can ‘grow’ microbes if we wish to.

Another type of microbe (fungi) are used to make Quorn (mycoprotein) which is a commonly used meat substitute.

Microbes (in this case bacteria) will grow in milk to make it ‘go off’. This is used in the yoghurt making process. Cheese is also another product made due to the use of microbes in industry.

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Yeast is a microbe which RESPIRES to give off carbon dioxide. This is used in baking bread and in winemaking.

Microbe uses

We can use the AEROBIC respiration of yeast to make bread rise. Yeast uses the sugar in bread dough to respire. The reaction is:

Glucose + oxygen + water + energycarbon dioxide

The carbon dioxide given off causes the bread to rise.

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Microbe uses

We can use the ANAEROBIC respiration of yeast to make beer and wine. This means that the yeast respires WITHOUT oxygen. This process produces alcohol (ethanol) and is known as FERMENTATION.

Glucose + ethanol + energycarbon dioxide

Yeast converts the sugar into alcohol:

Introduction to practicalIn this practical you will grow the micro-organism Bacillus subtilus (bacteria found on teeth) on agar jelly. At certain steps in the practical (designated by an *) you will either explain the reasons for the steps and/or evaluate your practical skills.

Getting prepared (working individually)1. No eating or drinking. *2. Cover any cuts or broken skin with a waterproof plaster. *3. Clear and clean your work surface with a disinfectant.* QuestionsQ1. Explain the reasons for steps 1 to 3

4. Collect the following equipment: Bunsen burner, safety goggles, agar plate, OHT pen and wire loop..

Labelling the agar plate5. Using the OHT pen write your initials, date and B.subtilus at the outer edge on the bottom dish of the agar plate.

6. Light the Bunsen burner and ensure there is a safety flame. *7. Wash your hands with warm soapy water. *QuestionsQ2. Explain the reasons for steps 6 and 7.

Your teacher will demonstrate the next 3 steps first. You will then carry them out followed by answering the questions.Sterilising a wire loop The wire loop should be sterilised before and after use. To do this:

8. The wire loop is held almost vertically in the hot part of a Bunsen flame until it glows red. Then remove the loop from the flame and allow it to cool for about 10 seconds before use. Do not allow it to touch any surface whilst it is cooling. *QuestionsQ3. Explain the reason for step 8.

Flaming a bottle neckWhen using any glass bottle or test tube, the neck should be flamed when opening or closing. To do this: 9. Loosen the top (lid, cap or cotton wool).

10. Do not put the top down on the bench, but hold it using the small finger of your other hand.11. Pass the open neck through the Bunsen flame for 2-3 seconds before taking a sample from the bottle.12. Flame the neck again before replacing the top. *QuestionsQ4. Explain the reasons for steps 9 to 12.

Inoculating agar plates – streaking a plateThe wire loop can be used to introduce B.subtilus onto the surface of the plate.13. After flaming the loop and the bottle neck containing B.subtilus, dip the loop into the sample. Lift the lid of the agar plate and lightly spread the sample across the surface of the agar in streaks as shown below.

Inoculating agar plates – streaking a plate (continued)14. Close the agar plate and secure with sticky tape, go over the top and bottom of the plate.Do not go round the edge as air must be able to get in.*15. The plates will be placed in a warm oven, base up, until next lesson.*Clearing up16. After completing the practical work and putting all the equipment away, make sure you wipe your work area with disinfectant, and wash your hands with warm water and soap.*

Questions Q5. Explain the reasons for steps 14 and 15.Q6. Explain the reason for step 16.

Dough = flour + water + yeast + sugar + salt

Questions for your group1. What is the gas which makes the dough rise?2. What process produces this gas?3. Why is the dough kept somewhere warm to rise?4. How might the amount of sugar affect how high

the dough rises?5. Yeast is alive. What happens to it when the bread

is baked at 200oC?

Making Bread

bakingproving

dough kept in warm place

at 200oC