Lesson 1 of 8 / Biological molecules
Carbohydrates, fats and proteins
What does each group contribute to a living organism?
I can state the main elements and roles of the three molecule groups.
I can state the elements in carbohydrates, fats and proteins.Syllabus
Syllabus K325, Topic 3(a). State the elements in carbohydrates, fats and proteins.
I can state the main roles of carbohydrates, fats and proteins.Syllabus
Syllabus K325, Topic 3(b). State the main roles of carbohydrates, fats and proteins.
About 4 min
Make a guess. You are not marked.
Carbohydrates and fats are both made of carbon, hydrogen and oxygen. Which food group contains nitrogen as well?
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Proteins, which are built from amino acids.
Every amino acid contains nitrogen, so every protein does. Some proteins contain sulfur too.
The key idea
Carbohydrates 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.
Watch out for this
A student says: "Carbohydrates and fats are the same because they contain the same elements." What is wrong with this?
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The types of atoms are the same, but their proportions and arrangement differ. This produces different molecules with different properties and roles.
Check your understanding
Which statement correctly pairs a molecule group with its main role?
Show the answer
Fat provides long-term energy storage and insulation.
Fats contain carbon, hydrogen and oxygen, but differ in structure from carbohydrates.
Quick recall
What does each group contribute to a living organism?