Bacteria and viruses are among the smallest organisms. Bacteria are classified as prokaryotes and have different shapes. They lack membrane-bound organelles and a nucleus. Bacteria reproduce through binary fission and can form spores. They are useful in food production and decay of organic matter but some cause diseases. Viruses are not living cells and are much smaller than bacteria. They contain genetic material surrounded by a protein coat and reproduce by infecting host cells.

1. BACTERIA
&
VIRUSES

2. Bacteria
belong to
the
Kingdom:
MONERA
Plant
Animal
Fungi
Protist
or
PROKARYOTA
Monera

3. BACTERIA
 are among the smallest
organisms
 about 1/1000 mm
 occur in the:
 soil
 air
 water
 inside
organisms

4. Bacteria have different shapes
Staphilococcus
(cluster)

5. Flagella are used for locomotion

6. Structure of a bacterium
[learn to draw]
Slime capsule
Cell wall
Cell membrane
Chromosome /DNA
Food store/glycogen
granule
Cytoplasm
Flagella

7. Two types
of cells:
Plant
Animal
Fungi
EUKARYOTIC
all other cells
Protist
PROKARYOTIC
bacterial cells
Monera

8. Differences between prokaryotic and
eukaryotic cells
PROKARYOTES
EUKARYOTES
1. No proper nucleus is
1. Have a proper nucleus,
present, that is their
that is their genetic
DNA is NOT enclosed in
material is enclosed
a nuclear membrane
within a nuclear
but lies free in the
membrane
cytoplasm

9. PROKARYOTES
2. Smaller cells
EUKARYOTES
2. Larger cells
3. Their organelles are
3. Their organelles are
NOT membrane-bound
membrane-bound
A eukaryotic cell
is generally
10x greater.

10. SPORE FORMATION
 bacteria produce a thick
protective wall around them in
adverse conditions e.g.
 heat
 drought
 presence of poisons
 they are now known as SPORES: can
survive for many years [anthrax spores,
1,300 years old can cause disease]
 the wall breaks when favourable
conditions return

11. ASEXUAL
REPRODUCTION
 bacteria reproduce
by BINARY FISSION

12. A single bacterial cell inside the human
body can reproduce every 20 minutes.
Mention three conditions inside the human body
that provide bacteria with the ideal environment.

13. 1.Temperature is warm
2.Food
3.Water
4.pH is ideal

14. Question: SEP, 2009
Why are bacteria classified as prokaryotic
organisms? (2)
Lack a proper nucleus i.e. chromosomes are nor
enclosed in a nuclear membrane. There are no
membrane-bound organelles.
Name the type of reproduction that takes place
in bacteria. (2)
Asexual reproduction by binary fission.

15. A group of bacteria is called a
colony

16. How can bacteria respire?
 AEROBICALLY
 use oxygen
 e.g. nitrogen fixing bacteria
 ANAEROBICALLY
 do not use oxygen
 e.g. denitrifying bacteria

17. FEEDING
1) PHOTOSYNTHETIC
 build up their food by a chemical like
chlorophyll
2) SAPROTROPHIC
 decay dead material
3) PARASITIC
 get food from living organisms, causing
them harm

18. Bacteria and other organisms
which cause disease are called:
PATHOGENIC

20. 1) Decay bacteria
(in soil)
 saprophytic bacteria
break down dead
organisms to return
essential nutrients
to the soil

21. 2) Decay bacteria (in sewage)
 bacteria decompose sewage before it is
thrown into the sea

22. 3) Genetic engineering
 bacteria can be used to produce useful
chemicals such as insulin

23. Question: MAY, 2009
Give the biological explanation of each of the
following statements.
Most bacteria are saprophytes but some are
mutualistic bacteria. (3)
Saprophytes feed on dead and decaying
material and live freely. Some live in a close
association with another organism where both
benefit. E.g. bacteria in rumen of cow.

24. Most bacteria feed on dead and decaying matter
and so are saprophytes. Help in recycling
nutrients.
Mutualistic bacteria:
 Some bacteria form a relationship within
intestines of mammals where both help each
other. Digest cellulose in herbivores. Produce
vitamins B and K in humans.
 Nitrogen-fixing bacteria in root nodules of
leguminous plants get food and shelter from
plant and give the plant ammonium
compounds.

25. 4) Vinegar production
 bacteria are used to
convert:
ethanol to ethanoic acid
Acetobacter aceti

26. 5) Making silage
silage is:
 undecayed grass
 used for feeding livestock in winter

27. the newly cut grass:
 is allowed to wilt (to remove water and so
concentrate the sugar in grass)
 but is not dried before conversion to silage
newly cut grass

28.  the grass:
 is prevented from decaying by lactic acid produced
by anaerobic bacteria
 is covered by plastic sheeting to exclude oxygen and
rain
A silo in which silage is
made and then stored.

29. 6) Biogas formation
Biogas is produced
when anaerobic
bacteria breakdown:
Biogas is a mixture of:
 methane
 carbon dioxide
 sewage
 manure
 plant material
Anaerobic
bacteria
Effluent

30. A biogas plant is built underground:
 to keep a constantly cool temperature –
overheats if above ground
A biogas plant as
used by a family in
China.

32. What can biogas be used for?
When biogas is burnt, it
can be used for:
 heating the home
 cooking
 to generate electricity

33. Question: SEP, 2003
A major concern for most people these days is the use
and availability of energy. Fossil fuels are nonrenewable forms of energy. One excellent source of
energy is Biogas. This is a mixture of methane (CH4) and
carbon dioxide (CO2). This can be produced in a
laboratory using the simple set-up shown below.

34. a) Name:
i) One suitable material which can be placed in
the flask to generate Biogas;
Plant material/animal manure
ii) The organisms that must be present in the
flask together with this material to produce
Biogas;
Bacteria
iii) The process occurring within the flask
Anaerobic respiration

35. 7) Cheese, butter & yoghurt
making all require:
lactic
acid
bacteria
Bacteria convert
LACTOSE
[sugar in milk]
LACTIC ACID

36. Lactic acid is:
 made by the process called lactic acid
fermentation : lactose  lactic acid

37. The manufacture of cheese, butter & yoghurt
depend on the curdling (coagulation) of milk.
 lactic acid is needed to make the milk curdle

38. 4
Cheese making
1 Milk pasteurised at 73C for 15
sec to kill most microbes
2
Curds cut into blocks
and piled up
Huge vat
Special strain of cheese-making
bacteria added to convert sugar
in milk to lactic acid
5 Blocks chopped and mixed
with salt to slow down
bacterial growth
6 Cheese packed into
3 Enzyme (rennin) added to
moulds and left to ripen
separate into curds & whey
6 Flavour gradually develops and
bacterial action makes cheese
more digestible

39. Rennet for cheese
making can be made by:
animals
Huge vat
bacteria

40. Whey poured
off
Curds cut into blocks
Ripening

42. Moulds in
press
[seen better in this
picture]

43. Yoghurt production

44. Yoghurt production
Lactic acid is produced during fermentation by
special strains of bacteria added to the milk
Spherical
Streptococcus
Rod-shaped
Lactobacillus

45. The following list gives five of the steps involved
in the commercial production of a well known
brand of yoghurt.
A)Milk heated to 73C for at least 30 seconds to make it
virtually sterile.
B)‘Sterilised’ milk is cooled to 44C.
C) Special ‘yoghurt’ bacteria added to ‘sterilised’ milk.
D)Milk kept at 44C for four hours to allow bacteria to
convert it to yoghurt by making lactic acid.
E) Yoghurt stored in cartons at 4C to slow down further
bacterial action.

46. Question: MAY, 2012
Humans use different micro-organisms including
bacteria to produce useful substances and food
stuffs. Bacteria are added to pasteurised milk to
produce yoghurt.
Explain why milk is pasteurised before producing
yoghurt. (2)
To kill living microbes
so that yoghurt can
have a longer shelf-life.

47. Butter making
Fermentation
Churning

48. Butter-making machine

49. Bacteria are added to cream
This culture has 4 bacteria — 2 which seem to primarily drive the
acidification and 2 which drive the flavour.

50. The cream is beaten/churned
Churning the milk
Butter can be made at home.
What forms after 5 minutes beating
the cream?

51. Soft butter and a
liquid called
buttermilk form.

52. The buttermilk is
strained out.
The butter is
squeezed to
remove the
remaining liquid.

53. Question: SEP, 2008
Milk is used in the production of butter and
cheese. Below is a simplified flow diagram
which describes the production of butter:
Fermentation
Churning

54. i) Why is bacteria added to the cream? (2)
Bacteria produce lactic acid which makes
milk curdle. Also to add flavour.
ii) Write a word equation to show the
fermentation process in which cream is
converted to sour cream. (3)
Lactose
Lactic acid

55. Question: [MAY, 2010]
Give a biological explanation for each of the
following statements:
In cheese making when the enzyme rennin is
added to milk, the temperature of the curding
(clotting) milk is kept in the region of 40C. (3)
Enzymes must be kept at their optimum
temperature to work fast.
Increasing the temperature above the optimum
denatures the enzyme and the reaction slows
down or even stops.

56. Question: [SEP, 2009]
A group of biology students investigated a type
of yoghurt. Some yoghurt samples were taken.
The pH of yoghurt samples was tested. Would
you expect the pH to be acidic, neutral or
alkaline? Give a reason for your answer. (3)
Acidic.
Bacteria change the sugar in milk called lactose
into lactic acid.

57. Question: [MAY, 2010]
Give a biological explanation for the following
statement:
Bacteria are involved in making yoghurt. (5)
Certain types of bacteria are needed to make
yoghurt.
Bacteria change lactose into lactic acid by
fermentation.
The lactic acid makes the milk curdle.
Flavour , colouring & fruit may be added.

58. 1) Cause diseases in animals and plants, e.g.
Tuberculosis in man, cause tooth decay
2) Spoil food
3) Denitrifying bacteria reduce the nitrate
content in the soil

59. Question: MAY, 2004
a) i) Name one organism that has a mutually
beneficial symbiotic relationship with a
bacterium.
ii) Explain what each organism benefits from
the symbiotic relationship. (1, 2)
e) Describe one saprophytic activity of bacteria
that is:
i) useful to humans;
ii) harmful to humans. (2)

60. Question: MAY, 2007
Explain how bacteria inside the body may have
both beneficial and harmful effects. (4)
Beneficial effects:
 digest cellulose in herbivores as they produce
cellulase
 produce vitamins B and K in intestines of
humans
Harmful effects:
 cause disease

61. RESISTANCE TO DISEASE
1) The skin forms a barrier
to bacteria.
2) Chemicals e.g.
 hydrochloric acid in the
stomach
 lysozyme in tear fluid
destroy bacteria

62. 3) Body fluids such
as saliva, contain
antibodies.
4) White blood cells can:
i) engulf bacteria
ii) produce antibodies
to kill bacteria

63. FOOD PRESERVATION
[this section acts as background knowledge
about bacteria].
1) COLD TREATMENT
 freezing does not kill
microbes, but stops
them multiplying and
slows their action

64. 2) DRYING
 microbes need moisture and if the food is
dried, they become dormant
 dried food lasts indefinitely
 food is dried by blowing air over it
Grapes soon go bad BUT
raisons can be stored
for a long time.

65. 3) HEAT TREATMENT
 heat:
 kills many of the microbes
 can STERILISE food

66. Question: MAY, 2012
Explain the following statement:
In food preparation, a clean sterile surface is
necessary. (2)
To avoid contamination of food with harmful
microbes.

67. Method used to find out which is the
most effective antibiotic to kill
microbes

69. Viruses consist of:
 a strand of DNA or RNA surrounded by
a protein coat (capsid)
Protein coat
(made of capsomeres)
Genetic material
(DNA or RNA)
Viruses are NOT cells as they lack the usual
cell components

70. Different shapes of viruses
AIDS virus
Tobacco mosaic virus
which causes
tobacco mosaic disease
in tomato plants.

71. Different shapes of viruses
Virus that attacks
bacteria.
Influenza virus
Bacterium attacked by
viruses.

72. Viruses:
 are smaller than bacteria (measured in nm,
1nm = 1/1000 000 mm)
 reproduce only when inside living organisms
virus
bacterium

73. Viruses are borderline between
living & non-living things
Living
Carry out all 7
vital functions
Made of cells
Non-living
Can be
crystallised
Viruses: REPRODUCE and CAN BE
CRYSTALLISED

74. Question: MAY, 2007
Explain why viruses are always
considered parasitic. (2)
Always cause harm to the cell in
which they have reproduced.
Cell bursts and dies.

75. Question: SEP, 2008
a) The diagram below shows the generalized
structure of a virus.
Label the parts A and B. (2)

76. Question: SEP, 2008
a) The diagram below shows the generalized
structure of a virus.
Label the parts A and B. (2)
Protein coat / capsid
DNA or RNA /
genetic material

77. Question: SEP, 2008
b)Viruses are not usually considered to be
living organisms. Why? (2)
Are not composed of cells.
Do not carry out all of the seven vital
functions.

78. Question: SEP, 2008
The diagram below shows the reproductive stages of a
virus in an incorrect order. Fill in the table to indicate
the correct order in which these events take place. (3)
Step
Letter
1
2
3
4
5
6

79. Step
1
2
3
4
5
6
Letter
B
F
D
E
A
C

80. Question: June, 1998
Explain clearly, how viruses differ from bacteria
in their structure and in their mode of life.
(Present your answer in the form of a table.)
(8)

81. Viruses
1. No cell membrane
2. No organelles
3. Never present
4. Never present
5. No food stores
6. Do not respire
7. Do not excrete
8. Do not grow
Bacteria
1. Cell membrane
present
2. Organelles present
3. May have flagella
4. May have a slime
capsule
5. Store food granules
6. Respire
7. Excrete
8. Grow

82. THE END