By the end of this lesson
- Identify sources of required dietary components.
- Explain the principal function of each component.
- Link named deficiencies to biological consequences.
BIG QUESTION
How can a small shortage of one dietary component disrupt an entire organ system?
Each required component contributes particular atoms, structures or regulatory functions that another nutrient cannot always replace.
Energy-yielding and structural nutrients
carbohydrateA food molecule made of carbon, hydrogen and oxygen, such as glucose, starch and glycogen, used mainly as an energy source. include sugars and starches and are important respiratory substrates. proteinA large molecule made of chains of amino acids, used for growth and repair and to make enzymes, antibodies and some hormones. supply amino acids for enzymes, antibodies and tissue growth and repair.
lipidA fat or oil, made of fatty acids and glycerol, used for energy storage, insulation and in cell membranes. are concentrated energy stores, provide insulation and form membrane components. Essential fatty acids must be obtained through diet.
Vitamins have distinct functions
vitamin AA vitamin needed to make visual pigments in the eye and for healthy epithelial tissues; too little can cause night blindness. supports visual pigments and epithelial tissues. vitamin CA vitamin needed for collagen synthesis and healthy connective tissue; too little causes scurvy. is needed for collagen synthesis and healthy connective tissue. vitamin DA vitamin that supports calcium absorption and bone mineralisation; too little causes rickets. supports calcium absorption and bone mineralisation.
Deficiencies can cause night blindness, scurvy and rickets respectively; supplements do not substitute for an otherwise balanced diet.
Calcium and iron are required minerals
calciumA mineral needed in the diet for bones and teeth, and for muscle contraction and cell signalling. contributes to bones and teeth and also functions in muscle contraction and cell signalling. ironA mineral needed in the diet to make haemoglobin in red blood cells; too little causes anaemia. is required to make haemoglobin.
Iron deficiency can cause anaemia, reducing oxygen transport and contributing to fatigue.
Water and fibre support whole-system function
Water is the medium for reactions and transport, contributes to temperature regulation and replaces losses in urine, sweat and exhaled air.
Fibre from plant cell walls adds bulk and supports movement through the gut. Whole grains, pulses, fruit and vegetables commonly provide fibre.
Required sources and functions
Learn a defensible source and a precise function for each named component.
| Component | Example sources | Principal function |
|---|---|---|
| Carbohydrate | Bread, rice, pasta, potatoes, fruit. | Respiratory substrate and energy supply. |
| Protein | Pulses, eggs, fish, meat, dairy, nuts. | Amino acids for growth, repair and functional proteins. |
| Lipid | Oils, nuts, seeds, dairy, oily fish. | Energy store, membranes and insulation. |
| Vitamin A | Liver, dairy, eggs; carotenoids in leafy vegetables. | Visual pigments and epithelial health. |
| Vitamin C | Citrus, berries, peppers and other vegetables. | Collagen synthesis and connective tissue. |
| Vitamin D | Oily fish, eggs, fortified foods; skin synthesis in sunlight. | Calcium absorption and bone mineralisation. |
| Calcium | Dairy, fortified alternatives, leafy vegetables. | Bones/teeth, muscle and signalling. |
| Iron | Meat, pulses, fortified cereals, leafy vegetables. | Haemoglobin synthesis. |
| Water | Drinks and water-rich foods. | Solvent, transport and temperature regulation. |
| Dietary fibre | Whole grains, pulses, fruit and vegetables. | Bulk and healthy gut movement. |
Language that earns precision
- vitamin
- An organic micronutrient required in small amounts for normal function.
- mineral
- An inorganic element or ion required in the diet.
- anaemia
- A condition involving reduced oxygen-carrying capacity of blood; iron deficiency is one cause.
- scurvy
- Disease caused by severe vitamin C deficiency.
- rickets
- Poor bone mineralisation in children, often linked to vitamin D deficiency.
Common misconceptions
Claim: All carbohydrate is table sugar.
Correction: Carbohydrates include monosaccharides, disaccharides and polysaccharides such as starch.
Claim: Protein is only needed for muscle.
Correction: Proteins include enzymes, antibodies, receptors and many structural molecules.
Claim: Iron provides energy.
Correction: Iron supports haemoglobin production; food molecules supply respiratory substrates.
Claim: Sunlight is vitamin D.
Correction: UVB radiation enables vitamin D synthesis in skin; it is not itself the vitamin.
Match the answer to the command word
Give a food source, not merely another nutrient class.
Write nutrient → molecule/process → consequence.
Keep vitamin C/collagen, vitamin D/calcium and iron/haemoglobin distinct.
Recall, apply, then justify
Explain how iron deficiency can reduce exercise tolerance.
Hint
Iron → haemoglobin → oxygen.
Suggested marking points
- Iron is needed to make haemoglobin.
- Less haemoglobin reduces oxygen transport.
- Less aerobic respiration/energy release can contribute to fatigue during exercise.
Give a source and function for vitamins A, C and D.
Hint
One valid source and one specific function for each.
Suggested marking points
- Vitamin A source such as liver/dairy/eggs or carotenoid-rich vegetables.
- Vitamin A supports vision/epithelial tissue.
- Vitamin C source such as citrus/peppers.
- Vitamin C supports collagen/connective tissue.
- Vitamin D source such as oily fish/fortified food or synthesis in sunlight.
- Vitamin D supports calcium absorption/bone mineralisation.
Explain two functions of water in the body.
Hint
Name each role and its consequence.
Suggested marking points
- Water acts as a solvent/medium for reactions.
- This allows dissolved substances to react or be transported.
- Evaporation of water in sweat transfers heat.
- This helps regulate body temperature.
Evaluate the claim that a person who eats enough protein cannot be malnourished.
Planning hint
Distinguish protein sufficiency from overall nutritional adequacy.
What a strong design includes
- Protein may supply adequate amino acids.
- Energy intake could still be deficient or excessive.
- Vitamin or mineral deficiencies can occur independently.
- Water and fibre requirements may not be met.
- Absorption, illness and food bioavailability also affect nutritional status.
- The claim is false because malnutrition includes multiple forms of imbalance.