1. Higher Biology Anaerobic Respiration & Alternative Substrates

2. Anaerobic respiration  In animal cells:  In the absence of oxygen Glucose (6C)  This reaction is reversible since there is no loss of carbons (as CO 2 ). pyruvic acid (3C ) Lactic acid (3C) Krebs cycle O 2 debt repaid

3. Anaerobic respiration  In plant and yeast cells:  In the absence of oxygen Glucose (6C)  This reaction is irreversible since there is a loss of carbons (as CO 2 ).  This process is also called fermentation. pyruvic acid (3C ) ethanol (2C) + CO 2

4. Anaerobic respiration  In the absence of oxygen there is only partial breakdown of glucose and less energy produced.  For 1 molecule of glucose only 2 ATP are released (compared to 38 ATP in aerobic respiration)  Anaerobic respiration is much less efficient than aerobic respiration.  View the ANIMATION 5.5

5. Alternative Substrates  A respiratory substrate is any substrate that can be broken down to release energy.  Fatty acids are formed from the digestion of fat in food.  They can be converted into Acetyl CoA in the matrix of the mitochondria.  The Acetyl CoA then enters the Krebs cycle.  The use of fatty acids results in twice the energy compared to the same quantity of carbohydrate.

6. Alternative Substrates  Excess Amino acids (from proteins) are broken down in the liver.  The amine group is converted into urea and excreted by the kidney.  The remaining carbon skeleton can be used as a respiratory substrate.  It can be converted into pyruvic acid which is then converted into Acetyl CoA.  The Acetyl CoA then enters the Krebs cycle.  Excess protein from the diet always provides a certain amount of energy.  Only in extreme conditions, such as starvation, is tissue protein used as an energy source.

7. Alternative Substrates 1. On your Respiration Summary mark where fatty acids and amino acids would enter the process.

8. Measuring the rate of respiration  View the activity from Scholar

9. Practice Questions From the Torrance textbook: 1. TYK page 30 Q2 & 3 2. AYK page 30 Q1, 3, 5 & 6.