12 / 04 Friday

Learning objective:Discuss how and why we use bacteria and fungi to make food such as yoghurt and beer.

Starter1) Describe the optimum condition

for most bacteria and fungi2) 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 OverviewUse observations, findings & biological ideas to describe and explain:1) how and why humans use bacteria and

fungi2) how humans are affected by bacteria

and fungi3) 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 – AchievedThe 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 – MeritThe 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 = ???