AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
Glycolysis is the first stage of anaerobic and aerobic respiration. It…
Full specification wording
Respiration (A-level only): Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process.
Glycolysis happens in the cytoplasm of the cell, not inside the mitochondrion, and it needs no oxygen, which is what makes it the one stage common to aerobic and anaerobic respiration.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Glycolysis happens in the cytoplasm of the cell, not inside the mitochondrion, and it needs no oxygen, which is what makes it the one stage common to aerobic and anaerobic respiration. Every organism carries it out, including prokaryotes, which have no mitochondria at all, and that universality is evidence of a shared evolutionary origin. Because glycolysis is anaerobic, a cell can keep making ATP when oxygen runs short; the limit is that the reduced NAD it produces must be re-oxidised, which anaerobically requires pyruvate to be converted to lactate or to ethanol. When oxygen is available, the pyruvate from glycolysis is moved into the mitochondrial matrix and oxidised further, so glycolysis is only the opening stage, worth a net two ATP out of the far larger yield a glucose molecule gives aerobically.
What earns the marks
- Locating glycolysis in the cytoplasm.
- Stating that glycolysis does not require oxygen, so it is an anaerobic process.
- Identifying it as the first stage of both aerobic and anaerobic respiration.
- Explaining that a cell short of oxygen can still make ATP because glycolysis continues.
Common mistakes and how to put them right
Placing glycolysis in the mitochondrial matrix, which is where the link reaction and the Krebs cycle occur.
Describing glycolysis as aerobic simply because it happens when oxygen is present.
Claiming glycolysis produces no ATP because ATP is used at the start, when there is a net gain.
Forgetting that prokaryotes respire despite having no mitochondria.
Treating anaerobic respiration as a wholly different process rather than the same first stage with a different ending.
Exam tips
- Give both facts when asked where and how glycolysis occurs: in the cytoplasm, and with no oxygen needed.
- If a question describes a cell with damaged mitochondria, glycolysis is the stage that still runs.
- Use the words 'net gain' when quoting ATP from glycolysis, because ATP is spent before any is made.
Try the lesson
The start of the Respiration (A-level only): Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an anaerobic process. lesson, made from checked teaching notes for this specification point.
Have a go first
In which part of a eukaryotic cell does glycolysis take place?
Listen
Glycolysis happens in the cytoplasm of the cell, not inside the mitochondrion, and it needs no oxygen, which is what makes it the one stage common to aerobic and anaerobic respiration. Every organism carries it out, including prokaryotes, which have no mitochondria at all, and that universality is evidence of a shared evolutionary origin. Because glycolysis is anaerobic, a cell can keep making ATP when oxygen runs short; the limit is that the reduced NAD it produces must be re-oxidised, which anaerobically requires pyruvate to be converted to lactate or to ethanol. When oxygen is available, the pyruvate from glycolysis is moved into the mitochondrial matrix and oxidised further, so glycolysis is only the opening stage, worth a net two ATP out of the far larger yield a glucose molecule gives aerobically. A strong answer earns marks for these points. locating glycolysis in the cytoplasm. stating that glycolysis does not require oxygen, so it is an anaerobic process. identifying it as the first stage of both aerobic and anaerobic respiration. explaining that a cell short of oxygen can still make ATP because glycolysis continues. Exam tip: Give both facts when asked where and how glycolysis occurs: in the cytoplasm, and with no oxygen needed.
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Key words
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cytoplasm
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anaerobic stage
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common first stage
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net ATP gain
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See every definition
- cytoplasm
- The location where glycolysis occurs, outside the mitochondrion, and where the process needs no oxygen.
- anaerobic stage
- Glycolysis is described as this because it does not require oxygen, so a cell can keep making ATP when oxygen runs short.
- common first stage
- Glycolysis is the first stage of both anaerobic and aerobic respiration, the one stage common to both.
- net ATP gain
- The ATP from glycolysis is worth a net two, because ATP is spent before any is made.
Label the diagram
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1Box 1
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3Box 3
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