Nutrition and energy is one of the most heavily examined sections of the edexcel igcse human biology course. If you only have time to master a handful of topics deeply, this should be one of them.
The specification groups everything here under one topic, diet and digestion, but the breadth is considerable. You need to know what a balanced diet contains, how the alimentary canal breaks food down, which enzymes act where, how the products of digestion are absorbed, how teeth develop and decay, how BMI is calculated and what it means, and why food hygiene matters. A strong grasp of edexcel igcse human biology nutrition and energy equips you for some of the most predictable questions on both papers. These edexcel igcse human biology revision notes for the 4HB1 specification take you through each area in the order the exam is most likely to test them.
A balanced diet
A balanced diet provides the correct amounts of carbohydrates, fats, proteins, vitamins, mineral ions, fibre and water. Each group has specific sources and functions:
| Nutrient | Sources | Function |
|---|---|---|
| Carbohydrates | Bread, rice, pasta, potatoes | Provide energy for respiration |
| Proteins | Meat, fish, eggs, beans, lentils | Growth and repair of tissues; making enzymes and antibodies |
| Lipids (fats and oils) | Butter, oils, nuts, fatty fish | Energy reserve, insulation, protection of organs, cell membranes |
| Vitamin A | Liver, carrots, dark leafy greens | Needed for healthy skin and vision (rhodopsin production in the retina) |
| Vitamin C | Citrus fruits, peppers, tomatoes | Needed for healthy connective tissue and wound healing |
| Vitamin D | Sunlight, oily fish, eggs | Required for calcium absorption from the small intestine |
| Calcium | Dairy, green leafy vegetables | Strengthens bones and teeth; needed for muscle contraction and blood clotting |
| Iron | Red meat, spinach, fortified cereals | Component of haemoglobin in red blood cells; carries oxygen |
| Fibre | Whole grains, vegetables, fruit | Adds bulk to food, aiding peristalsis and preventing constipation |
Deficiency diseases
The specification limits these to four:
- Scurvy (lack of vitamin C): Symptoms include bleeding gums, weakness, and slow wound healing.
- Anaemia (lack of iron): Symptoms include tiredness, pallor, and breathlessness because red blood cells cannot carry enough oxygen.
- Blindness (lack of vitamin A): Vitamin A is needed for making rhodopsin, the light-sensitive pigment in the retina. Deficiency causes night blindness and can progress to total blindness.
- Kwashiorkor (lack of protein): Common in regions where diets are high in carbohydrate but low in protein. Symptoms include swollen abdomen (oedema), wasted muscles, and stunted growth.
Diet variations
The specification states that you must understand how dietary needs vary with age, pregnancy, climate and occupation. A growing child needs more protein relative to body mass for tissue growth. A pregnant woman needs extra iron (for the developing baby's blood supply), calcium (for bone development) and folic acid. People in cold climates need more energy-rich foods to maintain body temperature. Workers in physically demanding occupations need more carbohydrates and fats to fuel the higher rate of energy expenditure.
The alimentary canal
The alimentary canal is the continuous tube from the mouth to the anus. Each section has a specific role in digestion:
| Structure | Function |
|---|---|
| Mouth | Mechanical digestion (teeth break food into smaller pieces); chemical digestion begins (salivary amylase starts breaking starch into maltose) |
| Oesophagus | Moves food from the mouth to the stomach by peristalsis |
| Stomach | Churns food and mixes it with gastric juice containing hydrochloric acid (kills bacteria, provides acidic pH for pepsin) and pepsin (a protease that begins protein digestion) |
| Small intestine | Completes digestion and absorbs the products. Receives bile from the liver via the gall bladder, and pancreatic juice from the pancreas. |
| Large intestine | Absorbs water from the remaining undigested food, forming faeces |
| Pancreas | Produces pancreatic juice containing amylase, trypsin (a protease), and lipase, which are released into the small intestine |
Peristalsis and fibre
Food is moved through the gut by peristalsis: waves of muscular contraction behind the food bolus push it along the alimentary canal. Dietary fibre adds bulk to the food, giving the muscles something to grip and push against, which speeds up the movement of food through the gut and helps prevent constipation.
Digestive enzymes
This is one of the most commonly tested areas. You need to know each enzyme, where it is produced, where it acts, what it breaks down, and what the products are:
| Enzyme | Produced in | Acts in | Substrate | Products |
|---|---|---|---|---|
| Amylase | Salivary glands and pancreas | Mouth and small intestine | Starch | Maltose |
| Maltase | Small intestine wall | Small intestine | Maltose | Glucose |
| Pepsin | Stomach wall | Stomach | Proteins | Shorter polypeptides |
| Trypsin | Pancreas | Small intestine | Proteins | Amino acids |
| Lipase | Pancreas | Small intestine | Lipids | Fatty acids and glycerol |
The role of bile
Bile is produced by the liver and stored in the gall bladder. It is released into the small intestine, where it performs two functions:
- Neutralises stomach acid: Bile is alkaline. The enzymes in the small intestine (trypsin, lipase) work best at a slightly alkaline pH, so bile neutralises the acidic chyme arriving from the stomach.
- Emulsifies lipids: Bile breaks large fat droplets into smaller droplets, increasing the surface area available for lipase to act on. This speeds up lipid digestion.
Absorption in the small intestine
The small intestine is adapted for efficient absorption through its villi, tiny finger-like projections that line its inner surface. Each villus has features that maximise absorption:
- A large surface area created by the many villi and microvilli on their surface
- A thin epithelial wall (one cell thick) for a short diffusion distance
- A rich blood supply (a network of capillaries) to maintain a steep concentration gradient by carrying absorbed nutrients away
- A lacteal (lymph vessel) to absorb fatty acids and glycerol
Teeth
The specification requires you to know the types, structure and functions of teeth:
- Incisors: Sharp, chisel-shaped front teeth for cutting and biting food.
- Canines: Pointed teeth for tearing food.
- Premolars and molars: Broad, flat teeth for crushing and grinding food.
Tooth decay occurs when bacteria in the mouth feed on sugars and produce acid. The acid dissolves the enamel, eventually reaching the dentine and pulp cavity, causing pain and infection. Prevention includes regular brushing with fluoride toothpaste, reducing sugar intake, and visiting the dentist regularly. Fluoride strengthens enamel by making it more resistant to acid attack. The gums can also become inflamed (gingivitis) if plaque builds up along the gum line, and untreated gingivitis can progress to periodontal disease, which damages the tissues supporting the teeth.
BMI and obesity
Body Mass Index (BMI) is calculated as:
BMI = body mass (kg) / height2 (m2)
Worked example
A person has a mass of 80 kg and a height of 1.75 m. Calculate their BMI.
Step 1: Height2 = 1.75 x 1.75 = 3.0625
Step 2: BMI = 80 / 3.0625 = 26.1 kg/m2
A BMI above 25 is classified as overweight; above 30 is classified as obese. Obesity is a risk factor for early onset of type 2 diabetes, because excess body fat reduces the body's sensitivity to insulin. The specification also requires you to understand that high cholesterol levels contribute to atherosclerosis: fatty deposits build up inside artery walls, narrowing the lumen, reducing blood flow, and increasing the risk of heart attack and stroke.
Food hygiene
The specification requires you to explain the importance of hygienic methods of food preparation, cooking, storage and preservation:
- Preparation: Wash hands, use clean utensils, avoid cross-contamination between raw and cooked foods.
- Cooking: Heat food thoroughly to kill pathogenic bacteria. The centre of the food must reach a high enough temperature.
- Storage: Keep food at the correct temperature. Refrigeration (below 5 degrees C) slows bacterial reproduction. Freezing stops bacterial reproduction entirely.
- Preservation: Methods such as canning, salting, smoking, drying and adding preservatives remove conditions that bacteria need to grow (water, warmth, nutrients).
Self-check questions
- Name two nutrients whose deficiency causes a specific disease, and name each disease.
- State where amylase is produced and what it breaks down.
- Describe two functions of bile in the small intestine.
- Calculate the BMI of a person who weighs 65 kg and is 1.60 m tall.
- Explain how the structure of a villus aids absorption.
- Name the enzyme that breaks proteins into amino acids in the small intestine.
- Describe two ways to reduce the risk of tooth decay.
- Explain why a pregnant woman needs more iron in her diet than usual.
These edexcel igcse human biology notes on nutrition and energy cover every specification point the exam tests. Head to the Green Bridge CBT platform for nutrition and energy edexcel igcse practice questions and igcse 4hb1 nutrition and energy revision sets. For the full breadth of the course, explore the edexcel igcse human biology explained series and the full bank of edexcel igcse human biology practice questions.
Edexcel IGCSE Human Biology nutrition and energy revision notes: balanced diet, the alimentary canal, digestive enzymes, teeth, BMI and food hygiene.
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