1. National 5 Biology Course Notes
Unit 1 : Cell Biology
Part 8 : Respiration

2. Glucose + Oxygen Carbon dioxide + Water + Energy
Respiration
Respiration is a series of enzyme controlled reactions by which energy stored in glucose molecules is released.
The word equation below summarises aerobic respiration (breakdown of glucose in the presence of oxygen).
Glucose + Oxygen Carbon dioxide + Water + Energy
ATP production
The energy released from glucose is used to make ATP.
ATP is produced when a molecule of ADP is joined to a molecule of Pi (inorganic phosphate).
Energy is stored in ATP until it is needed for cell processes.
When the energy is required for a cellular processes the ATP is broken down to for ADP and Pi releasing the stored energy.
Respiration
ADP + Pi
ATP
Glucose + Oxygen
Amino Acids
Protein
Carbon Dioxide +
Water
Cellular Processes, e.g. protein synthesis

3. 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.
During this stage, glucose is broken down to form pyruvate (pyruvic acid).
(This stage is called glycolysis)
Glucose Pyruvate

4. Second stage of respiration in the mitochondria
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
Pyruvate Carbon dioxide + Water
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.

5. 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.

6. Comparison of aerobic respiration and fermentation Type of Respiration
Fermentation in Animals
Fermentation in Plants and Yeast
Location(s)
Cytoplasm and Mitochondria
Cytoplasm
Final Products
Carbon Dioxide and Water
Lactic Acid
Ethanol and Carbon Dioxide
ATP Yield
38 molecules
2 molecules