National 5 Biology
Unit 1
1.4 Respiration
Pupil Course Notes
Topic 8
Pupil Notes
Respiration
Respiration is a series of enzyme controlled reactions by which energy from food is
released.
The word equation below summarises aerobic respiration (breakdown of glucose in
the presence of oxygen).
Glucose + Oxygen
Carbon Dioxide + Water
ATP production
The energy released from glucose is stored in a molecule called ATP. ATP is
produced when a molecule of ADP is joined to a molecule of Pi (inorganic
phosphate). When the energy is required for a cellular process, such as muscle
contraction or protein synthesis, the ATP is broken down to for ADP and Pi releasing
the stored energy.
Glucose +
Oxygen
ADP + Pi
Cellular
Processes, e.g.
protein synthesis
Respiration
Carbon
Dioxide +
Water
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Protein
ATP
Amino Acids
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National 5 Biology
1.4 Respiration
Pupil Course Notes
Processes in cells and organisms that require energy
These are examples of processes in cells and organisms that require energy

Protein synthesis

Cell division

Active transport

Muscle contraction

Transmission of nerve impulses
Respiration reactions
The first stage of respiration occurs in the cytoplasm of the cell. It involves the
breakdown of glucose to form pyruvate (pyruvic acid).
(This stage is called glycolysis)
Glucose
Pyruvate
This stage does not require oxygen and it occurs in both aerobic respiration and
fermentation
The second stage of respiration requires oxygen. It takes place in the mitochondria
and only occurs in aerobic respiration. Carbon dioxide and water are produced from
pyruvate by these reactions
Mitochondria
The diagram shows a mitochondrion
Cells that need to use a lot of energy, like muscle cells, sperm cells
and neurones (nerve cells) have a lot of mitochondria.
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National 5 Biology
1.4 Respiration
Pupil Course Notes
Fermentation
Fermentation is the breakdown of glucose in the absence of oxygen.
Fermentation in yeast cells and plant cells produces ethanol and
carbon dioxide
The summary equation for fermentation in yeast and plant cells is:
glucose
ethanol + carbon dioxide
Fermentation in animal cells (including human muscle cells) produces lactic acid.
The summary equation for fermentation in animal cells is:
glucose
lactic acid
Production of ATP
Aerobic respiration produces 38 molecules of ATP for each glucose
molecule broken down.
Fermentation produces 2 molecules of ATP for each glucose molecule broken down.
Comparison of aerobic respiration and fermentation
Type of
Aerobic
Fermentation in
Fermentation in
Respiration
Respiration
Animals
Plants and Yeast
Cytoplasm
Cytoplasm
Location(s)
Cytoplasm and
Mitochondria
Final
Carbon Dioxide
Products
and Water
ATP Yield
38 molecules
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Lactic Acid
2 molecules
Ethanol and
Carbon Dioxide
2 molecules
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