9.3: Anaerobic Respiration

oxygen’s role in cellular respiration

complete oxidation bc oxygen is the final electron acceptor - results in 32 ATP per glucose and waste products H2O and CO2

cellular respiration in anaerobic conditions

No oxygen = no final electron acceptor = incomplete oxidation. Instead pyruvate is metabolised by fermentation = lactic acid or ethanol, CO2 and 2 ATP per glucose = less energy than aerobic

fermentation

the metabolic process that converts sugars to acids, gases, or alcohol in the absence of oxygen and without cellular respiration, producing a small amount of energy.

what does fermentation involve

glycolysis then regeneration of NAD+ by transferring electrons from NADH to pyruvate. NAD+ reused to oxidise sugar in glycolysis = nets 2 ATP

NAD+

coenzyme that accepts electrons forming NADH (Reduced form)

different types of fermentation

alcohol (yeast and bacteria) and lactic acid (animals)

lactic acid fermentation

converts pyruvate into lactic acid by lactate dehydrogenase producing 2 ATP and regenerating NAD+

• occurs in muscle cells during intense exercise

alcoholic fermentation

Converts pyruvate into ethanol and 2 ATP in 2 steps:

1. pyruvate converted into acetaldehyde and carbon dioxide by pyruvate decarboxylase

2. acetaldehyde converted into ethanol by alcohol dehydrogenase which uses NADH = regenerates NAD+ for glycolysis

disadvantage of fermentation

yields less than cellular respiration (2 to 36) and glucose only partially oxidised meaning more energy remains in products = fermentation less efficient