Edexcel IGCSE Biology: Double Science 复习笔记 5.1.4 Anaerobic Respiration in Yeast

Edexcel IGCSE Biology: Double Science 复习笔记 5.1.4 Anaerobic Respiration in Yeast

Practical: Investigating Anaerobic Respiration in Yeast

 

  • Yeast can respire anaerobically (without oxygen), breaking down glucose in the absence of oxygen to produce ethanol and carbon dioxide
  • Anaerobic respiration in yeast cells is called fermentation
  • Fermentation is economically important in the manufacture of bread (where the production of carbon dioxide makes dough rise) and alcoholic drinks (as ethanol is a type of alcohol)
  • It is possible to investigate the effect of temperature on yeast fermentation, by seeing how temperature affects the rate of anaerobic respiration in yeast

 

 

Word-equation-for-anaerobic-respiration-in-yeast

 

The process of anaerobic respiration in yeast

 

 

 

Apparatus

  • Boiling tubes
  • Capillary tubes
  • Bungs
  • Yeast
  • Sugar solution
  • Oil
  • Stopwatch
  • Water bath
  • Limewater

 

 

 

Method

  • Mix yeast with sugar solution in a boiling tube
    • The sugar solution provides the yeast with glucose for anaerobic respiration

     

  • Carefully add a layer of oil on top of the solution
    • This prevents oxygen from entering the solution (prevents aerobic respiration in the yeast)

     

  • Using a capillary tube, connect this boiling tube with another boiling tube that is filled with limewater
  • Place the boiling tube with yeast and sugar solution into a water bath at a set temperature and count the number of bubbles produced in a fixed time (e.g. 2 minutes)
    • The rate that carbon dioxide is produced by yeast can be used to measure the rate of anaerobic respiration (i.e. the rate of fermentation)

     

  • Change the temperature of the water bath and repeat

 

 

 

Investigating-anaerobic-respiration-in-yeast

 

Experimental set up for investigating anaerobic respiration in yeast

 

 

 

Results and Analysis

  • Compare results at different temperatures to find out at which temperature yeast respires fastest
  • The higher the temperature, the more bubbles of carbon dioxide should be produced as higher temperatures will be closer to the optimum temperature of enzymes in yeast, increasing enzyme activity
  • As respiration is an enzyme controlled reaction, as enzyme activity increases, the rate of anaerobic respiration will increase
  • If the temperature is too high (beyond the optimum temperature), the enzymes will denature causing carbon dioxide production to slow down and eventually stop

 

 

Applying CORMS to practical work

  • When working with practical investigations, remember to consider your CORMS evaluation

 

 

CORMS-evaluation

 

CORMS evaluation

 

 

 

  • In this investigation, your evaluation should look something like this:
    • C – We are changing the temperature in each repeat
    • O – The type (species) of yeast we are using must be the same
    • R – We will repeat the investigation several times at each temperature to make sure our results are reliable
    • M1 – We will measure the number of bubbles (of carbon dioxide) produced
    • M2 – in a set time period (e.g. 2 minutes)
    • S – We will control the concentration, volume and pH of the sugar solution, as well as the mass of yeast added

    转载自savemyexams

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