5.1 Metabolism
Metabolism comprises all chemical reactions taking place within living organisms. These biochemical processes are vital for sustaining life as they allow cells to convert food into energy in the form of adenosine triphosphate (ATP) and synthesise essential cellular components including carbohydrates, proteins, lipids, and nucleic acids. In a cell, metabolism is categorised into two main types: catabolism and anabolism.
Learning Objectives
- Define metabolism in living organisms.
- State the two types of metabolism in a cell: catabolism and anabolism.
- Describe catabolism and provide relevant biological examples.
- Describe anabolism and provide relevant biological examples.
- Compare catabolic and anabolic pathways in terms of molecular breakdown, synthesis, and energy changes.
Comparison of Catabolism and Anabolism
Catabolism breaks down complex substances and releases energy, while anabolism synthesises complex molecules and absorbs energy.
Short Explanation
Definition of Metabolism
Metabolism refers to all chemical reactions that occur in a living organism. These processes involve the conversion of food into energy in the form of ATP, and the formation of carbohydrates, proteins, lipids, and nucleic acids.
Catabolism
The process of breaking down complex substances into simple substances. This reaction releases energy. Example: the breakdown of glucose during cellular respiration to generate energy.
General representation: \(\text{A (substrate)} \longrightarrow \text{B} + \text{C (products)}\)
Anabolism
The process of synthesising complex molecules from simple molecules. This reaction uses or absorbs energy. Example: the formation of glucose during photosynthesis.
General representation: \(\text{A} + \text{B (substrate)} \longrightarrow \text{C (product)}\)
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is meant by metabolism?
What is the primary difference in energy change between catabolism and anabolism?
State one example of an anabolic reaction in plants.
Common Mistakes
- Confusing catabolism and anabolism by stating that catabolism synthesises molecules and anabolism breaks them down.
- Misidentifying cellular respiration as an anabolic reaction instead of a catabolic reaction.
- Stating that catabolism absorbs energy and anabolism releases energy, which reverses their actual energy changes.
Concept Misunderstandings
Metabolism only involves digestion or breaking down food.
Metabolism includes both breakdown (catabolism) and synthesis (anabolism) of biological molecules.
All metabolic reactions release energy.
Anabolic reactions require and absorb energy to build complex molecules, while catabolic reactions release energy.
Summary
- Metabolism is the totality of chemical reactions in an organism, responsible for converting food into ATP and building vital macromolecules (carbohydrates, proteins, lipids, and nucleic acids).
- Catabolism breaks down complex substances into simpler ones, releasing energy. Example: cellular respiration.
- Anabolism synthesises complex molecules from simpler ones, absorbing energy. Example: photosynthesis.
- Catabolism and anabolism are the two main types of metabolism in a cell.
Short Activity
Objective: identify catabolism, anabolism and their energy changes.
A. Objective Quiz
Which of the following describes an anabolic reaction?
Which process is an example of catabolism?
B. Fill in the Blanks
The process of breaking down complex substances into simple substances that releases energy is known as .
In metabolism, food is converted into energy in the form of .
C. Matching / Drag and Drop
Drag each metabolic term or reaction to its correct description. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Term or Reaction to Its Description
Write the correct term or reaction next to each description.
| Description | Term / Reaction |
|---|---|
| 1. Process of breaking down complex substances into simple substances, releasing energy | |
| 2. Process of synthesising complex molecules from simple molecules, using or absorbing energy | |
| 3. Catabolic reaction involving the breakdown of glucose to generate energy | |
| 4. Anabolic reaction resulting in the formation of glucose |
Answer choices: Catabolism • Anabolism • Cellular respiration • Photosynthesis
