Metabolism (AQA GCSE Combined Science: Trilogy) : Revision Note

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Lucy Kirkham

Updated on

Metabolism: basics

  • Metabolism can be defined as:

the sum of all the reactions in a cell or the body

  • Energy released during respiration allows enzyme-controlled reactions to occur inside cells, e.g. to produce new molecules

Synthesis & breakdown of molecules

  • Organisms gain organic molecules, either by consuming food, e.g. in animals, or carrying out photosynthesis, e.g. in plants

  • The molecules gained can then be broken down and used to produce, or synthesise, new molecules

  • Metabolic reactions include the synthesis and breakdown of:

    • carbohydrates; complex carbohydrates are built from sugars, e.g. glucose

    • lipids; these are built from fatty acids and glycerol

    • proteins; synthesised from amino acids

Flowchart of food digestion: Glucose, fatty acids, glycerol, and amino acids processed in cells for storage, energy, membranes, or protein synthesis.
The products of digestion are used to build substances, and some of these are then broken down; this is metabolism

Examiner Tips and Tricks

You should be able to explain the importance of sugars, amino acids, fatty acids and glycerol in the synthesis and breakdown of carbohydrates, proteins and lipids.

Examples of metabolic reactions

  • Carbohydrates

    • Glucose is used in the synthesis of:

      • starch; energy storage in plants

      • glycogen; energy storage in animals

      • cellulose; strengthens plant cell walls

    • Glucose is broken down during respiration to release energy

  • Lipids

    • Glycerol is combined with three fatty acids in the synthesis of lipids, which can be used in energy storage

  • Proteins

    • Glucose and nitrates are involved in the production of amino acids

    • Amino acids are used in the synthesis of proteins

    • Excess proteins are broken down to produce urea, which is excreted from the body

Examiner Tips and Tricks

All of the features of metabolism listed are covered in more detail in the relevant topics but you should be aware of how they all link together here.

You've read 0 of your 5 free revision notes this week

Sign up now. It’s free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

Lucy Kirkham

Reviewer: Lucy Kirkham

Expertise: Head of STEM

Lucy has been a passionate Maths teacher for over 12 years, teaching maths across the UK and abroad helping to engage, interest and develop confidence in the subject at all levels.Working as a Head of Department and then Director of Maths, Lucy has advised schools and academy trusts in both Scotland and the East Midlands, where her role was to support and coach teachers to improve Maths teaching for all.