Digestive SystemCambridge IGCSE Biology: Revision notes
Section 1
What Is a Balanced Diet?
A balanced diet contains the right types and amounts of nutrients needed to stay healthy, in the correct proportions for a person's age, activity level and health.
The main dietary components and their importance:
| Nutrient | Importance |
|---|---|
| Carbohydrates | main energy source |
| Fats and oils | energy store, insulation |
| Proteins | growth and repair |
| Vitamin C | healthy skin and gums; prevents scurvy |
| Vitamin D | calcium absorption; prevents rickets |
| Calcium (mineral ion) | strong bones and teeth |
| Iron (mineral ion) | making haemoglobin in red blood cells |
| Fibre (roughage) | keeps the gut muscles working, prevents constipation |
| Water | solvent for reactions, transport, temperature control |
When asked to name a nutrient's importance, always link it to its specific role - e.g. iron for haemoglobin, not just 'good for blood'.
Section 2
What Happens When Diets Lack Key Nutrients?
A deficiency of certain nutrients causes specific diseases:
- Lack of vitamin C causes scurvy (bleeding gums, poor wound healing)
- Lack of vitamin D (or calcium) causes rickets (soft, weak bones in children)
Sailors on long voyages historically developed scurvy from a lack of fresh fruit and vegetables containing vitamin C.
Section 3
The Organs of the Digestive System
The digestive system is made up of the alimentary canal and associated organs.
Alimentary canal (the tube food passes through):
- Mouth
- Oesophagus
- Stomach
- Small intestine (duodenum and ileum)
- Large intestine (colon, rectum, anus)
Associated organs (not part of the tube, but release substances into it):
- Salivary glands
- Pancreas
- Liver
- Gall bladder
Section 4
The Five Functions of the Digestive System
The digestive system carries out five key processes:
- Ingestion - taking food into the mouth
- Digestion - breaking down large food molecules into smaller ones
- Absorption - movement of digested food molecules through the gut wall into the blood
- Assimilation - using absorbed nutrients, e.g. building them into new cell material
- Egestion - removal of undigested food (faeces) from the body via the anus
Do not confuse egestion (removing undigested waste) with excretion (removing metabolic waste like urea) - they are different processes.
Section 5
Teeth: Types and Structure
Humans have four types of teeth: incisors, canines, premolars and molars.
Structure of a tooth:
- Enamel - hard outer covering, protects the tooth
- Dentine - layer beneath enamel, supports it
- Pulp - contains nerves and blood vessels
- Nerves and blood vessels - supply and sense the tooth
- Cement - anchors the tooth root in the bone
Teeth are embedded in the jaw bone and surrounded by the gums.
Must Know
- A balanced diet supplies carbohydrates, fats, proteins, vitamins, minerals, fibre and water in the right amounts
- Lack of vitamin C causes scurvy; lack of vitamin D/calcium causes rickets
- The alimentary canal runs mouth to oesophagus to stomach to small intestine to large intestine to anus
- Associated organs: salivary glands, pancreas, liver, gall bladder
- The five functions are: ingestion, digestion, absorption, assimilation, egestion
- Teeth types: incisors, canines, premolars, molars; layers: enamel, dentine, pulp, cement
That's the notes covered.
Carry on to the next subtopic.