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National 4 and 5 Biology
Unit 1
Name______________________
Class___________
 I am confident that I understand this and I can apply this to problems
? I have some understanding but I need to revise this some more
 I don’t understand this and I need help with it
National 4 outcomes are in lighter font.
National 5 outcomes are in bold
1.6 Properties of micro-organisms and their use in
Industry
1. Can I name the raw materials yeast need to grow?
Covered
()
How well can you
do this?
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?

2. Can I name the products yeast make?
?
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3. Can I describe the conditions yeast need to make these
products?
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?
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4. Can I describe the role of yeast in the baking industry?
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?
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5. Can I describe how to investigate the activity of yeast in
making dough rise?
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?
6. Can I give the relationship between temperature and yeast
activity?
?
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7. Can I describe the role of yeast in the brewing industry?
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?
8. Can I describe the properties of bacteria that allow them to
be used in industry?
?
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National 4 and 5 Biology
Unit 1
Covered
()
How well can you
do this?
9. Can I give examples of food sources bacteria can use?
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?

10. Can I give examples of products that comes form different
bacteria?
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?
11. Can I describe the process and precautions involved in
making yoghurt?
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?
12. Can I describe the change from milk to yoghurt in terms of
consistency and composition?
?
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13. Can I give the name of the process bacteria use to make
yoghurt?
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?
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14. Can I describe what a biofuel is?
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?
15. Can I describe why biofuels are important to us in today’s
society?
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?
16. Can I give examples of at least two different biofuels and
the micro organism involved in their production?
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?
17. Can I state what all materials that can be converted into
biofuels have in common?
?
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18. Can I describe the problems associated with sewage being
released into the environment?
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?
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19. Can I state in general terms what we do to sewage to
make it safe?
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
?
Covered
()
How well can you
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National 4 and 5 Biology
Unit 1
do this?
21. Can I state why a range of micro organisms is necessary in
the breakdown of sewage?
?
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22. Can I describe what is meant by the term bioremediation?
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?
23. Can I give examples of substances which can be removed
from the environment by micro organisms naturally?
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?
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24. Can I give examples of substances which can be removed
from the environment by us using micro organisms?
?
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Yeast
Yeast are single-celled fungi which need an organic material to grow on.
Their preferred food source would be sugar, for example sucrose. They can respire aerobically (in
the presence of oxygen) or anaerobically (in the absence of oxygen).
In industry we use yeast in anaerobic conditions as they give the most useful products.
sugar
raw material
carbon dioxide + ethanol
products
Baking
In the baking industry, yeast is added to dough with some sugar to make the dough rise.
It does this by making carbon dioxide in the dough. This collects as small bubbles, making the
dough bigger in volume and the bread lighter in texture.
Bubbles of carbon dioxide
At start
After 2 hours
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National 4 and 5 Biology
Unit 1
Like all living things, yeast has a range of temperatures that it is active in.
If the temperature is too low the yeast won’t respire and make carbon dioxide. However, if the
temperature is too high, the yeast will die and will no longer be able to respire.
This is important for industry to know, especially in brewing.
Brewing
Brewing is where the yeast is grown on sugar to produce alcohol (ethanol).
Hops
added for
flavour
malting
Filtration
Fermentation
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National 4 and 5 Biology
Unit 1
Bacteria
Bacteria such as E. coli can complete a life cycle and make another E. coli within 20 minutes in a
laboratory. This quick growth means you don’t need to wait long for a small number to become a
very large number. The more bacteria you have, the more products you can make.
In industry, this means you spend less money growing the bacteria.
There are several types of bacteria which give us different products.
Lactic acid bacteria
This group of bacteria produce lactic acid as a product when grown on a carbohydrate such as a
basic sugar. The sugar is called lactose (some people are lactose intolerant).
The lactic acid can be used to turn milk into yoghurt as it causes the milk proteins to clump
together making the milk thicken.
The steps of making yoghurt are designed to make sure only the bacteria we want to grow in the
milk can.
1. Use fresh pasteurised milk to ensure there is as few bacteria there as possible.
2. Heat the milk up to 73oC to kill any remaining bacteria.
3. Cool the milk to 44oC and add lactic acid bacteria. This could be from a packet or using live
yoghurt in natural yoghurt from the supermarket.
4. Leave at 44oC for four hours to let the bacteria grow on the lactose to make lactic acid
5. Store at 4oC to slow growth of the bacteria.
Lactic acid bacteria are also used in the first stage of making cheese.
Again the lactic acid starts clumping the proteins together before a special enzyme called rennet is
added. This makes the solids collect together, becoming curds. This leaves a liquid behind called
whey.
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National 4 and 5 Biology
Unit 1
Biofuels
A biofuel is produced by living cells and will burn to give energy. These are produced so
successfully some cars are designed to be run on them.
They are important to society as they can replace the fossil fuels, coal, oil and gas which are
running out as they are finite.
Biofuels can be produced from many waste products from industry so they also help find a use for
material that would otherwise be rubbish.
The waste material could be sugar cane, which is a rich source of sugar for yeast to grow on,
producing ethanol.
This gets mixed with normal petrol and used in cars.
The waste can also include oils produced from sunflower, rapeseed and soya. This undergoes a
process where it is made suitable to go into a diesel engine for a car to use. This called biodiesel.
Filtered vegetable oil can also be used to make biodiesel, instead of being put out with food waste.
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National 4 and 5 Biology
Unit 1
Biogas
Biogas is another type of biofuel, but is produced by micro-organisms breaking down organic
waste in anaerobic conditions (no oxygen). The gas produced is methane which burns well and
can be used for heating, cooking etc.
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National 4 and 5 Biology
Unit 1
Sewage Treatment
Sewage needs to be treated before it can be released into rivers and streams. This prevents
disease-causing bacteria growing on it in our water ways, carrying disease throughout the local
community.
A wide range of specific bacteria are used for this as they use the organic waste in sewage as a
food source and none are the type to cause disease. They all need oxygen to break down sewage
into harmless products.
The wide range of bacteria allows all the different substances to be broken down at the same time.
Bacteria
Bioremediation
Bioremediation is when bacteria are used to help us remove harmful substances which are
released into our environment. They can break them down (biodegrade) into safer products.
Examples can include breaking down oil in oil spills, or in biodegrading things like polystyrene
which was through to be non-biodegradable.
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National 4 and 5 Biology
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1. Uses of microbes
Read the following passage and answer the questions based on it.
Fight for your Life!
Adapted from Biological Sciences Review, September 2005
Every day there is a battle inside our bodies between invading micro-organisms and our immune system.
Bacteria are present inside and out. Most are harmless but others are pathogens which cause disease.
Infectious diseases are a major killer in developing countries. Vaccination programmes, public health
improvements and increasing the availability of antibiotics are required to overcome them. However,
there is a growing problem of resistance to antibiotics demonstrated by the “super bug” MRSA. The first
thing a micro-organism does is to find its way into a cell in the body. Cells of the immune system have to
recognise that this has happened and make the appropriate response. The first cells on the scene are
neutrophils. They engulf bacteria and kill them with enzymes. The next cells to arrive are macrophages
which have a variety of specialised killing mechanisms. Dendritic cells are also involved. They are able to
recognise pathogens and stimulate other immune cells to react. Fortunately, our immune system has a
memory. This means that when we encounter a micro-organism for the second time, a much faster
response is triggered that rapidly wipes out the pathogen. Our immune system is very powerful, giving us
the best chance to win the battle with these invaders. Sometimes this system breaks down and immune
cells wrongly target and destroy our own body cells. This causes conditions such as rheumatoid arthritis
and multiple sclerosis.
(a) What name is given to micro-organisms such as bacteria which cause disease?
__________________________
1
(b) Give three actions which are needed by developing countries to overcome infectious diseases.
1 __________________________________________________________________
2 __________________________________________________________________
3 __________________________________________________________________
3
(c) Why is MRSA a growing problem?
___________________________________________________________________
1
(d) Name three types of immune cells involved in a response to an attack by invading micro-organisms.
1_______________________________________
2_______________________________________
3_______________________________________
1
(e) Why is the response of the immune system faster the second time a type of micro-organism invades?
___________________________________________________________________
1
(f) What causes conditions such as rheumatoid arthritis?
___________________________________________________________________
___________________________________________________________________
1
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National 4 and 5 Biology
Unit 1
2. a) During an investigation into the activity of yeast in bread making, a pupil divided a batch of dough into two equal
portions. He added yeast to each portion before placing the dough into identical beakers as shown in the diagrams.
The volume of dough in each beaker was measured at the start and end of the investigation. The results are
shown in the table below.
Beaker
Volume of dough
(cm3)
At start
At end
A
100
250
B
100
100
(i) How many times greater was the volume of dough in beaker A at the end compared to the start?
___________ times greater
1
(ii) The production of which substance caused the increase in the volume of the dough?
________________________
1
(iii) Give two factors, not already mentioned, which would need to be kept constant during this investigation.
1 ____________________________________________________________
2 ____________________________________________________________
2
(iv) What was the purpose of setting up control beaker B?
______________________________________________________________
1
3. What type of micro-organism is yeast?
__________________________________________
1
4. Give one use of yeast in a manufacturing process, other than the raising of dough.
___________________________________________________________________
1
5. Bacteria are used to sour milk in the manufacturing of yoghurt.
Name the process carried out by the bacteria which causes the milk to sour.
__________________________________________
1
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National 4 and 5 Biology
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3a) During the brewing of beer, ingredients including yeast and malted barley are added to a fermentation vessel.
(i) What does the malted barley provide for fermentation which ungerminated barley does not?
________________________________________________
1
(ii) How does sterilising the fermentation vessel before the raw materials are added help to provide optimum
conditions for the yeast?
________________________________________________________________
1
b) The concentrations of lactic acid and lactose in a milk sample were measured every two hours for 100 hours.
The results are shown in the graph below.
(i) What evidence from the graph suggests that lactose is converted into lactic acid?
________________________________________________________________________________
________________________________________________________________________________
1
(ii) What evidence from the graph supports the theory that lactose is being converted into compounds other than
lactic acid?
________________________________________________________________________________
________________________________________________________________________________
1
c) Calculate the average hourly rate of lactose breakdown over the 100 hours of this investigation.
Space for calculation
______________ g / l /hour
1
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National 4 and 5 Biology
Unit 1
4. Five groups of pupils carried out an investigation into flour types. Dough was made by mixing flour, sugar,
water and yeast. It was then rolled into a ball which was put into a glass container and its height measured. After
24 hours the height of the dough was remeasured.
The table below shows the average results for the five groups.
Type of flour
stone ground
self raising
wholemeal
plain
organic
Average increase in
height of dough (%)
34
76
68
42
56
(a) Use the results to complete the bar chart by:
(i) labelling the vertical axis;
(ii) adding a suitable scale to the vertical axis;
(iii) plotting the remaining bars.
1
1
1
(b) (i) What was the advantage of expressing the increase in height as a percentage, rather than in millimetres?
_________________________________________________________________________________
_________________________________________________________________________________
1
(iii) One pupil recorded the initial height of his dough as 30 mm and the final height as 42 mm. What was the
percentage increase in height of his sample?
Space for calculation
_____________ %
1
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National 4 and 5 Biology
Unit 1
(c) (i) Name two factors which would have to be kept the same for each dough mixture to make the investigation
valid.
1 _________________________________________________________
2 _________________________________________________________
1
(iii) Which ingredient of the dough mixture would provide most of the yeast’s energy?
_____________________________________
1
(iv) Name the gas released by the yeast which made the dough rise.
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1
(d) (i) Name one product, other than bread, which is made using yeast.
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1
(ii) Give an example of a food which is made using bacteria.
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1
5. The diagram below shows some stages in the industrial process for making ethanol from a substance extracted
from maize seeds.
(a) Name the substance extracted from maize seeds which is broken down by the enzyme into sugar.
___________________________________________________
1
(b) Explain why it is important that conditions in the fermentation vessels are anaerobic, rather than aerobic.
_____________________________________________________________________________________
_____________________________________________________________________________________
1
(c) Suggest one use for the ethanol made by this industrial process.
_____________________________________________________________________________________
1
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National 4 and 5 Biology
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(d) The table below shows the increase in the concentration of ethanol during fermentation.
Time
(hours)
Ethanol
concentration (%)
5
0.7
10
2.2
15
3.8
20
7.6
25
8.8
30
9.2
(i) During which 5 hour period did the concentration of ethanol increase the most?
Space for calculation
from __________ hours to ___________ hours
1
(ii) Calculate the percentage increase in ethanol concentration between 10 hours and 25 hours.
Space for calculation
_________%
1
6. The flow chart below shows steps in the production of biofuel (ethanol) from plant biomass (wood).
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National 4 and 5 Biology
Unit 1
(a) How many different types of organisms are involved in the production of this biofuel?
___________________________________________________________________________
1
(b) Name the process involved in the fixation of energy into plant biomass.
___________________________________________________________________________
1
(c) Name the simple substances that yeast converts into ethanol.
___________________________________________________________________________
(d) State two benefits of biofuels.
1
1
_________________________________________________________________________
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2
1
__________________________________________________________________________
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1
7. Complete the following sentences about landfills by underlining one of the options in each pair.
The reduction in methane emissions from landfills has been due to less organic material being placed into
more
the landfills.
The production of methane in landfills is the result of
aerobic
anaerobic
respiration by micro-organisms.
1
8.a) Small-scale digesters are used to produce methane in developing countries with an agricultural economy.
(i) What source of materials could be used in these anaerobic digesters?
______________________________________________________________________________
1
(ii) State one use of the methane produced.
______________________________________________________________________________
1
b) Bioremediation is an important part of removing unwanted chemicals from land or water.
Give an example of an unwanted substance which needs to be removed from the environment, and name the type
of micro-organism which does it.
Unwanted substance____________________________________________________________
1
Type of micro-organism _________________________________________________________
1
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