Scheme of Work Cambridge International as & a level

Extension activity: Learners interpret how respiratory inhibitors can be used to study aerobic respiration, and to draw conclusions from graphs. Further information can be sourced online, e.g. www.biologymad.com/master.html?http://www.biologymad.com/PhotosynResp/PhotosynResp.htm

12.2.10 Outline respiration in anaerobic conditions in mammals (lactate fermentation) and in yeast cells (ethanol fermentation). 12.2.11 Explain why the energy yield from respiration in aerobic conditions is much greater than the energy yield from respiration in anaerobic conditions. 12.2.12 Explain how rice is adapted to grow with its roots submerged in water, limited to the development of aerenchyma in roots, ethanol fermentation in roots and faster growth of stems. 12.2.13 Describe and carry out investigations using redox indicators, including DCPIP and methylene blue, to determine the effects of temperature and substrate concentration on the rate of respiration of yeast. 12.2.14 Describe and carry out investigations using simple respirometers to determine the effect of temperature on the rate of respiration.

Learners brainstorm and list what they know about anaerobic respiration. After a few minutes, pairs join together into groups of four and then groups of eight to discuss this further and come up with an agreed list of points. One or two learners from each group then write the group’s ideas on the class board to form a ‘mind map.’ (F) Learners carry out a practical activity to investigate effect of glucose concentration on the respiration rate of yeast using a redox indicator. Indicators such as 2,6-dichlorophenolindophenol (DCPIP) and methylene blue are often used to detect oxidation and reduction reactions. Both these substances change from blue to colourless when they accept electrons or hydrogen (i.e. are reduced). With this knowledge, small groups can be set the task of planning an appropriate investigation to carry out.