7.3 Physical digestion
- Syllabus
- 0610–2026–2027
- Topic
- 7.3
- Level
- —
Learning objectives
7.3.1Physical digestion as the breakdown• Describe physical digestion as the breakdown of food into smaller pieces without chemical change to the food molecules7.3.2Physical digestion increases• State that physical digestion increases the surface area of food for the action of enzymes in chemical digestion7.3.3Types of human teeth• Identify in diagrams and images the types of human teeth: incisors, canines, premolars and molars7.3.4Structure of human teeth• Describe the structure of human teeth, limited to: enamel, dentine, pulp, nerves, blood vessels and cement, and understand that teeth are embedded in bone and the gums7.3.5Functions of the types of human teeth• Describe the functions of the types of human teeth in physical digestion of food7.3.6Function of the stomach in physical• Describe the function of the stomach in physical digestion7.3.7Bile and fat emulsification• Outline the role of bile in emulsifying fats and oils to increase the surface area for chemical digestion
Define physical digestion
Physical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules.
The pieces change in size and shape, but the molecules in the food remain the same. No new substances are made.
| Physical digestion changes | Physical digestion does not change |
|---|---|
| piece size, shape and total exposed surface | molecular identity and chemical composition |
Chewing by teeth and churning by the stomach are physical digestion because they fragment or mix food mechanically.
Smaller pieces are not smaller molecules. Breaking chemical bonds and producing different molecules is chemical digestion.
Explain why smaller food pieces speed chemical digestion
Breaking one large piece into many smaller pieces increases the food's total surface area while its amount stays the same.
smaller pieces → greater total surface area → more food exposed to enzymes at once → faster chemical digestion
| Food form | Exposed surface | Enzyme access |
|---|---|---|
| one large piece | relatively low | mainly the outside |
| many small pieces | higher total area | more enzyme–food contact |
Physical digestion does not itself create soluble products. It makes chemical digestion more efficient by improving enzyme access.
Recognise incisors, canines, premolars and molars
From the centre/front of a jaw towards the back, the usual sequence is incisors → canines → premolars → molars.
| Tooth type | Position and visible shape clues |
|---|---|
| incisor | front; broad, flat, sharp edge |
| canine | beside incisors; pointed crown |
| premolar | behind canines; broader crown with ridges/cusps |
| molar | back; largest, broad multi-cusped crown, often multiple roots |
In an unfamiliar diagram, use both position and crown shape. A pointed tooth near the front is a canine; a broad cusped tooth at the back is a premolar or molar, with molars larger and farther back.
Do not identify a tooth by root number alone; diagrams vary. Position plus crown shape is the safer combination.
Describe the structure of a human tooth
A tooth has a visible crown and a root embedded in jaw bone and surrounded by gum.
| Structure | Location or role |
|---|---|
| enamel | very hard outer covering of the crown |
| dentine | layer beneath enamel; forms most of the tooth |
| pulp | central living region |
| nerves | in the pulp; detect stimuli such as pain |
| blood vessels | in the pulp; supply oxygen and nutrients and remove wastes |
| cement | covers the root and helps anchor it |
| bone and gums | bone holds the roots; gums surround and protect the tooth base |
Read a section from outside to inside: enamel on the crown (cement on the root) → dentine → pulp containing nerves and blood vessels.
Enamel does not cover the whole root, and the pulp is not an empty space: it contains living tissues, nerves and blood vessels.
Match tooth types to their functions
Different crown shapes apply different forces during physical digestion.
| Tooth type | Main action on food | Shape–function link |
|---|---|---|
| incisors | bite and cut | sharp edge slices food |
| canines | pierce and tear | pointed crown grips and tears |
| premolars | crush and grind | broad ridged surface presses food |
| molars | crush and grind thoroughly | large, broad cusped surface withstands strong forces |
Together, the teeth reduce food to smaller pieces, increasing surface area and making swallowing and enzyme action easier.
Canines tear; incisors cut. Premolars and molars both grind and crush, but molars are larger and farther back.
Explain physical digestion in the stomach
The stomach's muscular wall contracts to churn food, physically breaking it into smaller pieces and mixing it with gastric juice.
Repeated muscular contractions squeeze and turn the stomach contents. This makes a more uniform mixture and exposes more food surface.
Churning increases the surface area available for chemical digestion without changing the food molecules itself.
The stomach performs both physical and chemical digestion, but churning and mixing are the physical part; acid and enzymes belong to chemical digestion.
Explain how bile emulsifies fats and oils
Bile emulsifies fats and oils: it breaks large fat globules into many small droplets in the small intestine.
large fat globule → many small droplets → greater total surface area → more contact with lipase → faster chemical digestion of fat
Bile is made by the liver, stored in the gall bladder and released into the duodenum.
Emulsification is physical digestion: it changes droplet size but does not chemically break fat molecules. Bile is not an enzyme; lipase performs the chemical digestion.