What are the differences in energy yields from anaerobic respiration and aerobic respiration?

Anaerobic respiration is less efficient than aerobic respiration and produces less ATP.

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What is the difference between obligate anaerobes, facultative anaerobes, and obligate aerobes?

  1. Obligate anaerobes - organisms that cannot survive in the presence of oxygen, and can only synthesise ATP in the absence of oxygen
  2. Facultative anaerobes - organisms that can synthesise ATP by aerobic respiration if oxygen is present, but can switch to anaerobic respiration in the absence of oxygen
  3. Obligate aerobes - organisms that can only synthesise ATP in the presence of oxygen

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What happens when too much anaerobic respiration occurs in muscle tissue?

The reduced quantity of ATP produced is insufficient to maintain vital processes for extended time periods.


Lactate (lactic acid) accumulates, causing cramp and muscle fatigue, and it also reduces the pH affecting enzymes.

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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 first loses a molecule of carbon dioxide and is converted to ethanal. Ethanal then accepts hydrogen from reduced NAD.


This produces an alcohol called 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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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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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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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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