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
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.
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.
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
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
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.
31.
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 73C 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
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 73C for at least 30 seconds to make it
virtually sterile.
B)‘Sterilised’ milk is cooled to 44C.
C) Special ‘yoghurt’ bacteria added to ‘sterilised’ milk.
D)Milk kept at 44C for four hours to allow bacteria to
convert it to yoghurt by making lactic acid.
E) Yoghurt stored in cartons at 4C 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.
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 40C. (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.
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
68.
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
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
