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Cambridge IGCSE Biology · 0610

Chapter 7: Human nutrition (Part 1)

Balanced diet

Definition
A balanced diet includes all essential nutrients in the correct amounts needed for growth and repair.
Factors affecting dietary needs
Balanced diets vary between individuals based on:
  • Age and gender: Different stages of life and biological sex require different nutrient proportions.
  • Physical activity: Highly active individuals require more energy.
  • Pregnancy and breastfeeding: Women in these stages need extra nutrients to support both themselves and their babies.

Principal dietary sources and functions

Humans require the following nutrients for survival:

  1. Carbohydrates: Found in pasta, rice, and potatoes. Used as a source of energy for respiration.
  2. Fats and oils: Found in butter and cheese. Used for insulation, energy, waterproofing, and protection around organs.
  3. Proteins: Found in meat, fish, and eggs. Broken down into amino acids for protein synthesis (enzymes, hormones, and structure).
  4. Vitamin C: Found in citrus fruits. Used in the synthesis of proteins for skin and blood vessels, and for tissue repair.
  5. Vitamin D: Found in dairy and fish oil. Helps the uptake of calcium and maintenance of healthy bones.
  6. Calcium: Found in dairy and fish. Needed for healthy bones and teeth and blood clotting.
  7. Iron: Found in red meat and green vegetables. Present in haemoglobin for transporting oxygen.
  8. Fibre (roughage): Found in fruit and whole grains. Not digested; adds bulk to help food move through the intestines.
  9. Water: Acts as a solvent for chemical reactions, a metabolite, and helps maintain body temperature.

Malnutrition

A lack of a balanced diet leads to deficiency diseases:

Scurvy
Caused by a lack of vitamin C. Symptoms include bleeding gums and stunted bone growth.
Rickets
Caused by a lack of vitamin D. Leads to weak and soft bones and deformities.
Anaemia
Caused by a lack of iron, leading to tiredness due to insufficient oxygen transport.

Exam Traps

  • Avoid describing anaemia as a lack of oxygen in the air rather than insufficient haemoglobin.

Structure of the digestive system

The system is comprised of the alimentary canal and associated organs:

Alimentary canal
Mouth, oesophagus, stomach, small intestine (duodenum and ileum), and large intestine (colon, rectum, and anus).
Associated organs
Salivary glands, pancreas, liver, and gall bladder.
The human digestive system showing the alimentary canal from mouth to anus, including the liver, gall bladder, and pancreas
Diagram 1: The human digestive system. Clear labels of the alimentary canal from mouth to anus, including the liver, gall bladder, and pancreas.

Main digestive processes

  1. Ingestion: The taking of substances (food and drink) into the body through the mouth.
  2. Digestion: The breakdown of food into smaller molecules.
  3. Absorption: The movement of nutrients from the intestines into the blood.
  4. Assimilation: The uptake and use of nutrients by cells.
  5. Egestion: The removal of undigested food from the body as faeces through the anus.

Exam Traps

  • Do not use “egestion” for removal of urea or CO2 — that is excretion.
  • Avoid confusing ingestion (food into mouth) with absorption (nutrients into blood).

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