Aerobic respiration
+
food (glucose)
oxygen
energy
carbon dioxide
+
+
water
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 microorganisms.
•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.
Reminder:Microbe uses
Microbe can be put into a number of categories. The three
types which you need to know about are listed below:
BACTERIA
VIRUS
FUNGI
Note: A living organism must be able to
demonstrate that it can perform ALL the 7
life processes.
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
© Boardworks Ltd 2003
Microbes
Microbes multiply very
rapidly. Two can, very
quickly, become four then
eight and so on.
© Boardworks Ltd 2003
Microbe uses
Microbes have many uses. This is mainly because we
can ‘grow’ microbes if we wish to.
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.
Another type of microbe (fungi) are used to make Quorn
(mycoprotein) which is a commonly used meat substitute.
© Boardworks Ltd 2003
Microbe uses
Yeast is a microbe which RESPIRES to give off carbon
dioxide. This is used in baking bread and in winemaking.
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
carbon + water + energy
dioxide
The carbon dioxide given off causes the bread to rise.
© Boardworks Ltd 2003
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.
Yeast converts the sugar into alcohol:
Glucose
carbon + ethanol + energy
dioxide
© Boardworks Ltd 2003
Introduction to practical
In 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.*
Questions
Q1. 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 plate
5. 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. *
Questions
Q2. 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. *
Questions
Q3. Explain the reason for step 8.
Flaming a bottle neck
When 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. *
Questions
Q4. Explain the reasons for steps 9 to 12.
Inoculating agar plates – streaking a plate
The 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 up
16. 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.
Making Bread
Dough = flour + water + yeast + sugar + salt
proving
baking
dough kept in
warm place
at 200oC
Questions for your group
1. 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?