Anaerobic respiration
Introduced| English | Meaning |
|---|---|
| fermentation/fɜːmənˈteɪʃn/ | The breakdown of sugars without oxygen, often by microorganisms, to release energy and form products such as ethanol or lactic acid. |
| lactate/ˈlækteɪt/ | The ion formed from lactic acid, produced when pyruvate is reduced in lactate fermentation. |
| anaerobic respiration/ˌæneəˈrəʊbɪk ˌrespɪˈreɪʃn/ | The release of usable energy from nutrients without using oxygen; some syllabuses use this term broadly to include fermentation. |
| aerenchyma/ˈeərəntʃɪmə/ | Plant tissue with large interconnected air spaces that help gases move to submerged or waterlogged organs. |
| indicator/ˈɪndɪkeɪtə/ | A substance that shows a change in chemical conditions through an observable change, often in colour. |
Respiring without oxygen
- With no oxygen, only glycolysis can run.
- To keep it going, the cell must regenerate its NAD.
- This is done by fermentation 发酵 — and it yields far less energy.
Fermentation
- Fermentation uses up reduced NAD so glycolysis can continue:
- in mammals, pyruvate → lactate 乳酸 (later broken down when oxygen returns).
- in yeast, pyruvate → ethanol + CO₂.
Anaerobic respiration 无氧呼吸: lactate or ethanol fermentation
Why fermentation matters
Step through it. Without oxygen, fermentation regenerates NAD so glycolysis can keep making a little ATP.
Why does fermentation matter when there is no oxygen?
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Without oxygen, NAD must be regenerated by fermentation so glycolysis can continue making ATP.
Anaerobic respiration turns pyruvate into:
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Mammals make lactate (lactate fermentation); yeast makes ethanol and CO₂ (ethanol fermentation).
In mammals anaerobic respiration produces lactate, while in yeast it produces ethanol and carbon dioxide.
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Same problem (no oxygen), two different products: lactate in mammals, ethanol + CO₂ in yeast.
Match each to the right description.
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Mammals make lactate, yeast makes ethanol; both regenerate NAD for a small ATP yield from glycolysis.
Much less energy
- Anaerobic respiration gains only the small amount of ATP from glycolysis.
- Aerobic respiration also runs the Krebs cycle and oxidative phosphorylation, releasing far more ATP.
- Rice copes with waterlogged roots: it grows aerenchyma 通气组织 (air spaces), uses ethanol fermentation, and grows stems fast to reach air.
Anaerobic respiration only gains ATP from ______ (there is no Krebs cycle or oxidative phosphorylation).
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Aerobic respiration adds the Krebs cycle and oxidative phosphorylation, which release far more ATP.
One way rice survives waterlogged, low-oxygen roots is by:
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Aerenchyma carries air to the roots; rice also uses ethanol fermentation and grows stems fast to reach air.
Measuring the rate
- A redox indicator 指示剂 like DCPIP or methylene blue loses its colour when it gains hydrogen from respiring cells.
- The faster the colour is lost, the faster respiration is — so you can test temperature or substrate effects. (A respirometer can also track oxygen uptake.)
How does DCPIP or methylene blue show the rate of respiration?
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These redox indicators decolourise when reduced (gaining hydrogen); the faster they fade, the faster respiration.
You've got it
- no oxygen → only glycolysis; fermentation regenerates NAD to keep it running
- mammals → lactate; yeast → ethanol + CO₂
- anaerobic gives far less ATP (no Krebs / oxidative phosphorylation)
- rice: aerenchyma + ethanol fermentation + fast stems; rate measured with DCPIP / methylene blue