Anaerobic respiration (Fermentation) Homolactic fermentation – common in animals and bacteria Glucose → Lactic acid + water + energy Heterolatic fermentation – common in fungi Glucose → Alcohol + CO 2 + water + energy
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 o C 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 o C was the thickest. The yoghurt mixture incubated at 60 o C did not thicken at all and the yoghurt mixture incubated at 30 o C thickened very little.
Example – Merit (contd.) This would be because 40 o C 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 o C, 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 o C, 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 CO 2 -> carbonic acid -> pH -> bacteria control Glucose level -> Alcohol level & Sweet taste Temperature control Pressure control