Metabolism, anabolism and catabolismIB MYP Biology: Revision notes
Section 1
What is metabolism?
Metabolism is the sum of all the chemical reactions that happen inside an organism. It includes reactions that build new molecules and reactions that break molecules down. Every living organism, from a bacterium to a human, has a metabolism, and most of these reactions take place inside cells.
Metabolic reactions are of two types: anabolic and catabolic.
Reactions go faster when it is warmer, so cold-blooded animals have a faster metabolism at higher temperatures.
Section 2
Anabolic reactions: building up
Anabolic reactions build up larger molecules from smaller ones. Examples:
- Photosynthesis: carbon dioxide and water are built up into glucose.
- Protein synthesis: amino acids are joined together to make proteins.
Anabolic reactions are needed for growth and for repairing the body.
Section 3
Catabolic reactions: breaking down
Catabolic reactions break down larger molecules into smaller ones. Examples:
- Respiration: glucose is broken down into carbon dioxide and water, releasing energy.
- Digestion: large food molecules, such as starch and protein, are broken down into small molecules such as glucose and amino acids.
Digestion is catabolic: it breaks molecules down. Do not mix up anabolic (build up) with catabolic (break down).
Section 4
Working together
A living organism carries out both types of reaction all the time. For example, a student who eats a meal uses catabolic reactions to digest the food and respire glucose, and anabolic reactions to build new proteins for growth and repair.
A good way to remember: anabolic = add up and build; catabolic = cut up and break down.
Must know
- Metabolism is all the chemical reactions in an organism
- Anabolic reactions build up larger molecules from smaller ones, e.g. photosynthesis and protein synthesis
- Catabolic reactions break down larger molecules into smaller ones, e.g. respiration and digestion
That's the notes covered.
Carry on to the next subtopic.
Exam questions on Metabolism, anabolism and catabolism
- After a meal of rice and lentils in Mumbai, a student's body digests the food. Later her cells use some of the glucose to release energy, and use amino acids from the lentils to build new proteins for growth and repair.State whether digestion of the lentils and building new proteins are catabolic or anabolic, giving a reason for each.2 marks
- A mango tree in Kerala, India, stands in bright sunshine. Its leaves make glucose, and all the living cells in the tree, including those in its roots, release energy from that glucose.Explain why photosynthesis is described as an anabolic reaction.2 marks
- A student investigates how temperature affects the metabolism of woodlice, which are cold-blooded animals. She seals 10 woodlice in a respirometer tube containing soda lime, which absorbs carbon dioxide, and places it in a water bath. As the woodlice use oxygen, a drop of coloured liquid in a capillary tube moves towards them, and she measures how far it moves in 10 minutes. She repeats this at 10 °C, 20 °C and 30 °C, and the liquid moves 4 mm, 9 mm and 19 mm.State a hypothesis for this investigation with a scientific reason, and name the independent and dependent variables.3 marks
Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).