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Biology
Revision
B6 Beyond the
Microscope
6a Understanding Bacteria
 Bacteria
– smaller than animal or plant
cells, typically a few microns long (1000 of
a mm)
Flagellum – for movement
 Cell wall – for maintaining
shape & stop it bursting
 Bacterial DNA – for
cell replication & control of cell
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1.
2.
3.
4.
Bacteria lack:
A ‘true’ nucleus
Mitochondria
Chloroplasts
A vacuole
Main shapes:
Spherical
Rod
Spiral
Curved rods
6a Understanding Bacteria
 Food
sources – some consume organic
nutrients like carbohydrates & proteins,
some make their own using sunlight
 Survival – extreme habitats e.g. hot
springs, inside humans
 Reproduction – by binary fission
Rapid reproduction
causes fast spread of
disease & food
spoilage, but can be
useful

6a Understanding Bacteria
 Making
Yoghurt
 In large steel fermenters
1. Equipment sterilised
2. Raw milk pasteurised – heated to 80°C,
then cooled rapildy
3. Heated to 40°C
4. Live bacterial culture added & incubated
5. Bacteria feed on lactose & make lactic
acid
6. Manufacturer samples yoghurt
7. Flavours & colours added
6b Harmful Microorganisms
 Pathogens
Pathogen
Bacteria
Protozoa
Viruses
Fungi
– microbes that cause disease
Illness caused
Transmission method
Cholera (Vibrio)
Contaminated water
TB
Airborne droplets
Food poisoning (salmonella & Contaminated food
E. coli)
Septic wound
Contact with wound
Dysentery (Entamoeba)
Contaminated food/water
Malaria
Mosquito bite
‘Flu
Airborne droplets
Chickenpox/smallpox
Direct contact or airborne
droplets
Athlete’s foot
Direct contact
6b Harmful Microorganisms
 Natural
Disasters
Rapid spread of disease because:
 Sewage systems & water supplies damaged
 Electrical supplies damaged -> food decay
 Disrupted health services
 Dysentery,
common
cholera & food poisoning
6b Harmful Microorganisms
 History
of Disease Treatment
 Pasteur
– 1860’s – Germ Theory – microbes
in the air cause food decay & passed
from person to person causing disease
 Lister
– 1865 – development of antiseptics
– use of carbolic acid during surgery
 Fleming
– 1928 – Penicillin – discovered
accidentally that this mould killed
bacteria
6c Microorganisms – factories
for the future?
 Yeast
– single celled fungus
 Asexual reproduction – budding
 Conditions for reproduction:
1. Lots of sugar
2. Optimum temperature (rate doubles for
every 10°C rise, above 40°C?) & pH
3. Removal of waste products e.g. alcohol
6c Microorganisms – factories
for the future?
 Fermentation
– anaerobic respiration in
yeast
 Sugar -> Alcohol + Carbon Dioxide
 Uses:
 Cleaning
sugar in water from food
processing factories
 Making alcohol e.g. beer from barley,
wine from grapes, cider from apples
6c Microorganisms – factories
for the future?
 Brewing
Beer
1. Mashing – extraction of sugar from source
material
2. Hops added for flavour
3. Yeast added to ferment (keep warm)
4. Tank sealed to cause anaerobic
respiration & prevent unwanted microbes
entering
5. Clarifying/clearing to leave a clear liquid
6. Pasteurising to kill harmful microbes
7. Bottling or casking
6c Microorganisms – factories
for the future?
 Distilling
spirits
 Rum from cane sugar
 Whisky form malted barley
 Vodka from potatoes
 Process:
1. Liquid heated to evaporate alcohol
2. Concentrated alcohol trapped and
condensed into a liquid
 Fermentation is limited by increasing levels
of alcohol that eventually kill yeast
6d Biofuels
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Biogas – contains mainly methane (50% burns
easily 10% is explosive), some carbon dioxide,
traces of hydrogen, nitrogen & hydrogen
sulphide
Biogas produced by decomposer bacteria in
marshes, septic tanks, animal’s digestive
systems
Uses:
Burned to generate electricity
Burned to produce hot water & steam for
central heating
Fuel for buses (cleaner than diesel & petrol,
but doesn’t produce as much energy)
6d Biofuels

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1.
2.
3.
4.
5.
Large scale production of methane
Continuous flow method in a digester –
organic material added daily & gas siphoned
off
Optimum temperature – too low, little gas
produced; above 45°c enzymes denatured,
no gas produced
Advantages of biofuels:
Alternative source to fossil fuels – reduce
greenhouse effect
No particulates produced
Cheap
Renewable/sustainable
Conservation of resources
6e Life in Soil
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1.
2.
3.
4.
Composition of soil:
Rock particles
Humus (dead organic matter)
Water
Living organisms e.g. fungi, microscopic
protozoans, nematode works, earthworms,
bacteria
Importance of worms:
Burying organic material for decomposition
Mixing soil layers
Aerating & draining soil
Neutralising acid soil
6e Life in Soil
 Soil
Food Webs
Detritivores e.g.
earthworms
Decomposers
e.g. fungi
6e Life in Soil
 Nitrogen
Cycle
Nitrogen fixing e.g.
Azobacter, Rhizobium
& Clostridium
Nitryfying e.g.
Nitrosomonas &
Nitrobacter convert
ammonia to nitrates
Saprophytic
bacteria start
decomposition &
make ammonia
6f Microscopic life in water
Advantages of living in
water
Disadvantages of living in
water
No problem of water shortage
or dehydration
Water is dense so resists
movement
Less variation in temperature
Difficult to control the
absorption & release of water
from living cells
Water gives more support so
organisms grow bigger without
increases in skeleton size
Waste is easily disposed
Amoeba use active transport
to pump water into small
vacuoles which join into one
contractile vacuole which
empties out of the cell
Salmon move from salt to fresh
water – they alter their urine
concentration to counteract
osmosis in or out of cells
6f Microscopic life in water
 Plankton

Phytoplankton – microscopic plants capable of
photosynthesis
Zooplankton – microscopic animals

Have limited movement/rely on currents

Seasonal variation in population due to changes
in:
Light
Temperature
Nitrates
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Can cause algal blooms
6f Microscopic life in water
 Water
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Pollution
Sewage - cause eutrophication
Oil
Fertilisers – cause eutrophication
Pesticides e.g. DDT - bioaccumulate
Detergents
Acid rain
PCBs (chemical used to insulate electrical
equipment) – bioaccumulate
Biological Indicators – of pollution/cleanliness
6g Enzymes in action
 Uses:
 Biological
washing powders – enzymes
digest food stains
 Cheese making – separate curds & whey
 Fruit juice extraction
 Alter food flavour
 Reagent sticks e.g. glucose/urine test stick