In biology the term anaerobic respiration means a way for a life form to generate usable energy without involvement from oxygen. So in brief it is respiration without oxygen. Respiration is a redox reaction which processes energy in a form which is usable by a life form, mainly a process of generating ATP the universal energy currency of life. Anaerobic respiration however should not be confused with fermentation like say ethanol fermentation. The commercial applications of anaerobic respiration include anaerobic digestion and mechanical biological treatment. These applications are used for waste water treatment.
Yeasts are eukaryotic micro-organisms classified in the Fungi and have about 1500 known species. They are dominant fungi in the ocean. Yeast is a micro life form or an organism which similar to your muscles can respire in two forms. We will see some of the features of this in this simple experiment. The indicator Janus Green B will change its colour depending upon the quantity of oxygen available.
Oxygen present: Indicator is oxidised to a blue colour
Oxygen absent: The indicator is reduced to a pink colour.
The apparatus required:
2 test tubes having delivery tubes
2 collection tubes
Paraffin, bicarbonate indicator solution
Janus Green B indicator solution
20 cm glucose solution
1. Put the 20 cubic cm of glucose solution in some of the yeast added in a test tube. Add 2 drops of indicator solution to it. The colour developed will indicate the presence of oxygen in the mixture.
2. Add some quantity of liquid paraffin over the mixture to form a layer exactly over the top surface. This layer will stop additional oxygen from the surrounding to enter the mixture.
3. Immediately after the colour of the mixture indicates that there is no oxygen preset in the mixture, fix up the delivery tube causing a little amount of bicarbonate/indicator in the other test tube.
4. Prepare and install a suitable control. Remember that in this experiment you are trying to learn if the yeast will respire in the absence of oxygen.
5. Leave the apparatus as it is for ten to twenty minutes and then record your observations.
1. Record the results in the form of a table (prepare a table for this purpose).
2. Describe the control you have used briefly.
3. Complete the following questionnaire.
1. What do you conclude from the final colour of-
a. the bicarbonate indicator solution?
b. the Janus Green B indicator solution?
2. What is your conclusion from the two answers to the question above?
3. Why is a layer of liquid paraffin used during the experiment?
4. if the yeast is to be left within a sugar liquid for a few days, a typical smell is produced. This is the result of ethanol getting collected in the mixture. The process in which the yeast turns sugar into ethanol is called fermentation.
Also suggest how we evaluate if any energy was release during this process.