Cell respiration — IB Diploma Biology SL
IB Biology C1.2: ATP, aerobic and anaerobic respiration, and measuring the rate of cell respiration.
Revision notes
3 short notes, in the order of the specification. Each one in short:
ATP, adenosine triphosphate, is a nucleotide that distributes energy within cells. Hydrolysis of ATP to ADP and phosphate releases enough energy for many tasks, such as active transport, synthesis of macromolecules and movement of cells or chromosomes. Synthesising ATP from ADP and phosphate requires energy, which comes from cell respiration.
Cell respiration is a system for producing ATP within the cell using energy released from carbon compounds, mainly glucose and fatty acids. Aerobic respiration needs oxygen and mitochondria, gives a large ATP yield and produces carbon dioxide and water. Anaerobic respiration in humans happens in the cytoplasm without oxygen, uses only glucose, gives a small yield and produces lactate.
The rate of cell respiration can be measured as oxygen used or carbon dioxide produced per unit time, often per gram of organism. Variables that affect it include temperature, oxygen concentration and the availability of respiratory substrate. A simple respirometer with an alkali to absorb carbon dioxide measures oxygen uptake from the movement of a liquid drop.
Exam questions
4 exam-style questions (10 marks), each with its mark scheme.
Answer the questionsFlashcards
9 cards: flip them, mark what you knew, and practise the rest.
Practise the cardsMind map
The whole of molecules (interaction and interdependence) on one page, so you can see where this subtopic fits.
Open the mind mapPrint it
Free PDFs to print or save.
Quick check questions
What is the full name of ATP and what type of molecule is it?
Show answer
Adenosine triphosphate; a nucleotide.
Write the word equation for anaerobic respiration in humans.
Show answer
glucose → lactate
Why is soda lime used in a respirometer?
Show answer
It absorbs carbon dioxide, so the movement of the drop measures oxygen uptake.
Frequently asked questions
Why is ATP called the energy currency of the cell?
ATP is called the energy currency because it distributes energy within cells. It is soluble, stable without enzymes and stays inside the cell, and hydrolysis to ADP and phosphate releases enough energy for tasks such as active transport, building macromolecules and movement. It is quickly regenerated from ADP using energy from respiration.
What is the difference between cell respiration and gas exchange?
Cell respiration is a set of enzyme-catalysed reactions inside cells that produce ATP using energy from carbon compounds. Gas exchange is the diffusion of oxygen and carbon dioxide between an organism and its environment, for example in the lungs. Gas exchange supplies oxygen for aerobic respiration and removes the carbon dioxide it produces.
What are the differences between aerobic and anaerobic respiration?
Aerobic respiration needs oxygen and mitochondria, can use carbohydrates, lipids and amino acids, gives a large yield of ATP and produces carbon dioxide and water. Anaerobic respiration in humans needs no oxygen, happens only in the cytoplasm, uses only glucose, gives just 2 ATP per glucose and produces lactate.
Written and checked against the IB Biology SL specification · Updated October 2026