Transcript Microbes Revisionx

12 / 04 Friday
Learning objective:
Discuss how and why we use bacteria
and fungi to make food such as
yoghurt and beer.
Starter
1) Describe the optimum condition
for most bacteria and fungi
2) Describe the difference between
bacterial respiration and fungal
respiration
Optimum conditions
 Warmth (temperature ~ 37oC)
 Nutrient
 Moisture (Water)
 Acidity (pH level)
 Oxygen level (aerobic ones only)
Anaerobic respiration (Fermentation)
 Homolactic fermentation – common
in animals and bacteria
Glucose → Lactic acid + water + energy
 Heterolatic fermentation – common
in fungi
Glucose → Alcohol + CO2 + water + energy
Assessment Overview
• Week 12 Mon & Tue → Making yoghurt
• Week 12 Thu & Fri → Research Project
• Week 1 Mon → Revision Work
• Week 1 Tue & Thu → Report
Assessment Overview
Use observations, findings & biological
ideas to describe and explain:
1) how and why humans use bacteria and
fungi
2) how humans are affected by bacteria
and fungi
3) Also describe how this knowledge
impacts your personal actions or
everyday life
 Achieved – Describe biological ideas and
how humans use / or are affected by two
micro-organisms.
 Merit – Explain biological ideas and how
humans use / or are affected by two
micro-organisms.
 Excellence – Explain with significant links
between biological ideas and how
humans use / or are affected by two
micro-organisms.
Example – Achieved
The results from our experiment
showed that the yoghurt mixture
incubated at 40 oC was the thickest. It
became thick because of the lactic acid
made by the bacteria.
Example – Merit
The results from our experiment showed
that the yoghurt mixture incubated at 40
oC was the thickest.
The yoghurt mixture incubated at 60 oC did
not thicken at all and the yoghurt mixture
incubated at 30 oC thickened very little.
Example – Merit (contd.)
This would be because 40 oC is the
optimum temperature for bacteria to
reproduce by binary fission.
Having a greater number of bacteria
present means they produce lots of lactic
acid by homolactic fermentation
(anaerobic respiration in bacteria).
Example – Merit (contd..)
At 60 oC, the temperature would be too
high for bacteria to survive, so there was
no bacteria to produce lactic acid which is
why the yoghurt was not thickened at all.
At 30 oC, although bacteria can survive and
reproduce, their reproduction and
respiration rate would be slower so smaller
amount of lactic acid was produced which
is why the yoghurt was less thick.
Example – Excellence (Merit +)
Bacteria in the mixture feed on lactose in
the milk by performing extra-cellular
digestion and they change the lactose into
lactic acid through homolactic fermentation
(anaerobic respiration in bacteria).
The lactic acid makes the sour taste in the
yoghurt and also makes it thicken by
coagulating milk protein.
Example – Excellence (Beer)
Usually using a greater amount of sugar in
the process would make more alcoholic
beer as the yeasts will keep producing
alcohol by heterolactic fermentation
(anaerobic respiration in fungi) process
until the point is reached where the yeasts
are unable to tolerate the level of alcohol.
If the yeasts have low tolerance for alcohol,
they will die earlier and the remaining
sugar makes the beer sweeter.
Revision List
 Extracellular digestion
 Reproduction (binary fission, spores)
 Anaerobic respiration /
Fermentation (homolactic,
heterolactic)
 Optimum conditions
 Process of making yoghurt & beer
Ginger Beer – Making Links
(examples)
 heterolactic fermentation
 CO2 -> carbonic acid -> pH ->
bacteria control
 Glucose level -> Alcohol level &
Sweet taste
 Temperature control
 Pressure control
Alcohol & CO2 = ???