Describe and explain what happens in mitochondria when oxygen is absent.
Without oxygen, only glycolysis can be used to generate ATP.
All the FAD and NAD will be reduced, so they cannot accept the protons and electrons released during the Krebs cycle and link reaction. The electron transfer chain stops and no further ATP is formed by oxidative phosphorylation without oxygen as the final electron acceptor.
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How can a cell produce ATP in anaerobic conditions?
Cells can produce a small yield of ATP through glycolysis if the reduced NAD that is produced can be oxidised again.
This can be achieved through ethanol fermentation or lactate (or lactic acid) fermentation.
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What may happen to the lactic acid and ethanol produced in anaerobic respiration?
Lactic acid can be oxidised back to pyruvate and generate ATP, or it can be converted to glycogen and stored.
Ethanol cannot be further metabolised and is a waste product that is removed from the organism.
As the oxidation of lactic acid requires oxygen, it is sometimes referred to as an oxygen debt.
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What are some of the adaptations of certain rice varieties that allows them to grow with their roots submerged in water?
- Growing taller to keep the top parts of their leaves above the water for gas exchange
- Gases like oxygen can diffuse through the loosely packed cells in aerenchyma in the stems and roots to other parts of the plant
- The submerged roots of rice plants use ethanol fermentation, can tolerate higher levels of ethanol, and produce more ethanol dehydrogenase to break down ethanol
Growing in flooded fields where most weeds cannot reduces competition for light, space, and mineral ions, which increases rice yields.
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What happens to pyruvate during anaerobic respiration in plants and some microorganisms like yeast, and what does this reaction produce?
- During anaerobic respiration in plants and yeast, pyruvate is first decarboxylated, losing a molecule of carbon dioxide, and is converted to ethanal
- Ethanal is then reduced by accepting hydrogen from reduced NAD, catalysed by the enzyme alcohol dehydrogenase
- This produces ethanol and regenerates NAD to enter glycolysis
The process is sometimes referred to as alcohol fermentation or ethanol fermentation.
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What happens to pyruvate during anaerobic respiration in animals, and what does this reaction produce?
During anaerobic respiration in animals, pyruvate accepts hydrogen from the reduced NAD produced in glycolysis, catalysed by the enzyme lactate dehydrogenase.
This forms lactic acid and regenerates NAD to enter glycolysis.
This process is sometimes referred to as lactic acid fermentation.
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