Transcript Humans and micro

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Humans and micro-organisms
24.1
What are micro-organisms?
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24.2 How are micro-organisms useful
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to us?
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24.3 How are micro-organisms harmful
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to us?
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24.4 The importance of antibiotics
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24.5 Food preservation
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Humans and micro-organisms
24.1 What are micro-organisms?
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Micro-organisms (or microbes)
• very
small organisms that can
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only be seen with a microscope
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• can be useful or harmful to us
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there is an
organism
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Humans and micro-organisms
24.2 How are micro-organisms useful to us?
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• some micro-organisms are useful in
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Recycling of
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materials
Producing
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useful
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nitrogen
Wine and
compounds
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bread making
for legumes
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Humans and micro-organisms
Wine and bread making
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Yeast
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anaerobic
alcoholic
CO2
alcohol
fermentation
respiration
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for bread-making
for wine-making
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• fruit juices are
• CO2 bubbles form
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converted into wines
holes in the dough
through the process
 make the dough
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rise and spongy
of fermentation
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Humans and micro-organisms
Recycling of materials
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• important in maintaining the balance in ecosystems
• example:
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saprophytic
nitrite &
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bacteria &
nitrate
inorganic
bacteria
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organic
nitrogen
matter
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compounds
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nitrate
ions
absorbed by plants &
recycled in ecosystem
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Humans and micro-organisms
Producing useful nitrogen compounds for
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legumes
• legumes have nitrogen-fixing bacteria in the
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swollen
parts of their roots (root nodules)
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•nitrogen
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in the air
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nitrogen-fixing
bacteria
nitrogen
compounds
nutrients
for plants
Farmers take advantage of the plant/bacteria relationship by
growing legumes in poor soil. Other plants grown in the field,
after the legumes, will grow well, because excess nutrients
are left in the soil when the legumes are harvested.
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Humans and micro-organisms
24.3 How are micro-organisms harmful to us?
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Micro-organisms
are harmful because they may be
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parasitic
saprophytic
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 cause diseases
 spoil our food
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and other useful
materials
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Humans and micro-organisms
Micro-organisms which cause diseases
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1 live in and obtain nutrients from host cells
2 • may
destroy host cells later
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3 release toxins
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Micro-organisms
which may cause diseases
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fungi
• viruses
第五層 bacteria protozoa
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Humans and micro-organisms
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viruses
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bacteria
protozoa
fungi
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live
inside living cells
第三層on the proteins of the cells,
relying
reproduce
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release new viruses
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e.g. influenza, rabies, measles and AIDS
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Humans and micro-organisms
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viruses
bacteria
protozoa
fungi
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• live
inside cells  intracellular
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•• live
outside cells  extracellular
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• cause harm by
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1 destroying body tissues
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e.g. tuberculosis
2 releasing toxins which affect normal
functioning of body
e.g. food poisoning
Humans and micro-organisms
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viruses
bacteria
protozoa
fungi
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•• feed
on body tissues and produce harmful
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effects
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e.g. amoebic dysentery, malaria and
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sleeping sickness
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viruses
bacteria
protozoa
fungi
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•• infectious
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•• cause
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inflammation and itching
•e.g.
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skin infections (ringworm & athlete’s foot),
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mouth infections and vaginal infections in
women
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Humans and micro-organisms
Spoilage of food and other useful materials
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• some micro-organisms are saprophytic because
they grow and feed on organic matter
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change and spoil our food and other useful
materials
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e.g.
fruit, bread,
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leather, wood
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and camera lens
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Some people put their lenses in a
special air-tight box with silica
gel to prevent fungal growth
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Humans and micro-organisms
24.4 The importance of antibiotics
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Antibiotics
• chemicals produced by micro-organisms, usually
fungi
or bacteria
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• can
kill other micro-organisms or inhibit their
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growth
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• important for curing diseases caused by bacteria
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• example:
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Remember: Do not stop taking
antibiotics until the period given
by the doctor ends !!
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Humans and micro-organisms
Demonstrating
the effect of penicillin
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Demonstrating the effect
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of penicillin
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24.5 Food preservation
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• micro-organisms spoil our food
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food preservation is needed
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• basic
principles include :
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killing the micro第五層
organisms
inhibiting the
growth of the
microorganisms
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Humans and micro-organisms
Methods of food preservation
1 Removing
water
2 Killing bacteria with high
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temperature/chemicals
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3 Preventing bacterial growth with low temperature
refrigeration
freezing
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Humans and micro-organisms
Natural drying
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• dehydration prevents micro-organisms from growing
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Dried food
• the food may taste different from when it is fresh
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Freeze-drying
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• the food is frozen very quickly at -196°C and
then water inside is removed under low pressure
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• the food is very light in weight
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• the food substances are not changed
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• when water is added, the food returns to a
•form
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similar to the original
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Humans and micro-organisms
Smoking
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• smoke from the fire dries the food and coats
it with substances which stop the growth of
•bacteria
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Smoked trout fillet
• the flavour of food is changed
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Humans and micro-organisms
Osmotic preservation
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• the food is covered with salt or sugar
• •water
will be drawn out due to osmosis
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• •micro-organisms
are either killed or inactivated
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Food preserved by
osmotic effects
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Humans and micro-organisms
Pickling
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• the food is salted first and then stored in vinegar
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As a weak acid,
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vinegar can prevent the
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growth of bacteria.
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Pickled food
• citric acid and alcohol are also used in pickling
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Humans and micro-organisms
Canning and bottling
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• the food is first heated to a high temperature
under high pressure to kill the bacteria and
•destroy
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their toxins
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The process of killing bacteria is
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food is then sealed into sterilized tin cans
jars while the food is still hot
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prevents bacteria from getting into the
food as it cools at lower pressure
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Humans and micro-organisms
Pasteurization
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• invented by Louis Pasteur
• suitable for preservation of milk
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• 2 methods:
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The holding method
The flash method
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Heat milk to 75°C for Heat milk to 63-66 °C
• 15
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seconds.
for 30 minutes.
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Cool it down quickly to about
10°C in sterilized bottles.
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Humans and micro-organisms
UHT treatment
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• UHT = ultra high temperature
• •another
method for killing
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bacteria in milk
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• milk is heated to 132°C for 1
•second,
第三層then sealed into plastic•lined
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cardboard boxes
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• •milk
can be stored at room
temperature for a longer time
than pasteurized milk
UHT milk
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Humans and micro-organisms
Refrigeration
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• the food is kept at a low temperature (2-7°C)
to slow down bacterial and fungal growth
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Fish preserved by ice
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Humans and micro-organisms
Freezing
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• the food is frozen below -18°C to inhibit
bacterial growth
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• once the food
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begins to thaw,
•the
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bacteria
will start
•inside
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to grow again
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Humans and micro-organisms
Food is preserved inside
the food freezer
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Adding preservatives
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• chemicals to kill bacteria
• •examples:
SO2 in fruit juices & E211 in cakes
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• •may
be harmful to health
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Soft drink with
preservatives
Soy sauce with
preservatives
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Humans and micro-organisms
Concept diagram
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Micro-organisms
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include
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第二層 bacteria
viruses
protozoa
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can be
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第五層
useful
fungi
harmful
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Humans and micro-organisms
Concept diagram
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useful
harmful
in
in
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wineand
recycling of
causing
spoilage
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bread-making
materials
diseases
of food
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can be
producing nitrogen
prevented by
•compounds
第四層 in legumes
food
preservation
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works by
dehydration
killing microorganisms
preventing growth
of micro-organisms
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Humans and micro-organisms
Concept diagram
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dehydration
by means of
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•natural
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freeze-drying
drying
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osmotic
pickling
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preservation
smoking
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Humans and micro-organisms
Concept diagram
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killing microorganisms
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with high
temperature by
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sterilization
UHT
pasteurization
(e.g.•in第四層
canning
treatment
and bottling)
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with
chemicals
by
adding
preservatives
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Humans and micro-organisms
Concept diagram
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preventing growth
of micro-organisms
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by
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第二層
第三層
refrigeration
freezing
第四層
第五層
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