Lesson 1 of 7 / Biological molecules
Carbohydrates, fats and proteins
What does each group contribute to a living organism?
In this lesson: State the main elements and roles of the three molecule groups.
About 4 min
The key ideaCarbohydrates provide an immediate energy source, fats provide insulation and long-term energy storage, and proteins support cell growth and repair.
An element is a type of atom. A molecule contains atoms joined together. These groups differ in their composition and in the roles they perform.
Explore the idea
Same elements, different roles
Immediate source of energy. Glucose can be broken down in respiration, releasing energy for cellular activities.
C = carbon; H = hydrogen; O = oxygen; N = nitrogen. These symbols list elements; their spacing and number do not represent a chemical formula.
Explanation
Carbohydrates contain carbon, hydrogen and oxygen. Glucose is a carbohydrate that cells can break down in respiration to release energy. Carbohydrates are therefore an immediate source of energy for activities such as muscle contraction and active transport.
Fats also contain carbon, hydrogen and oxygen. They are useful for long-term energy storage. Fat beneath the skin helps reduce heat loss by providing insulation. A fat molecule has a different structure from a carbohydrate even though both contain the same three elements.
Proteins contain carbon, hydrogen, oxygen and nitrogen. Some proteins also contain sulfur. They are needed for the growth and repair of cells because they form many cell structures. Enzymes and haemoglobin are examples of proteins with particular functions.
These are main roles, not a claim that each group has only one possible use. For this comparison, connect carbohydrate with an immediate energy source, fat with storage and insulation, and protein with growth and repair. A meal can supply all three groups at once.
Step by step
- 1
Name the molecule group
Use carbohydrate, fat or protein, rather than a food such as rice or egg.
- 2
State its elements
All three contain carbon, hydrogen and oxygen. Protein also contains nitrogen.
- 3
Match the main role
Decide whether the context is immediate energy, longer-term storage, insulation, or growth and repair.
Worked example
A seed begins to grow
A germinating seed uses stored food for respiration and makes new cells. Explain the roles of carbohydrate and protein in these two processes.
One way to explain it
Carbohydrate can supply glucose that is broken down in respiration to release energy. Proteins are needed to build and repair the structures of the growing cells.
Why this answer works
- Link carbohydrate to respiration and energy release.
- Link protein to building cell structures.
- Do not describe energy as a substance that becomes a cell.
Is this true? "Carbohydrates and fats are the same because they contain the same elements."
The types of atoms are the same, but their proportions and arrangement differ. This produces different molecules with different properties and roles.