7.1.3Human Nutrition
Physical Digestion — Cambridge IGCSE Co-ordinated Sciences 0654 - Biology Revision Notes & Topical Questions
5 min read 10 parts Lesson 4 of 8
Part 1 of 8What physical digestion is
1Physical (mechanical) digestion
- The breakdown of food into smaller pieces without chemical change to the food molecules.
2Purpose
- It increases the surface area of food for the action of enzymes during chemical digestion.
3Three processes
- Chewing by the teeth, churning by the stomach and emulsification of fats by bile in the duodenum.
Part 2 of 8Types of human teeth
| Tooth | Shape | Function |
|---|---|---|
| Incisor | Chisel-shaped | Biting and cutting |
| Canine | Pointed | Tearing, holding and biting |
| Premolar and molar | Large flat surfaces with ridges | Chewing and grinding up food |
Part 3 of 8Why chewing helps
Surface area
- Chewing increases the surface area of the food.
Exposure
- More of the food is exposed to saliva and digestive enzymes, so it is broken down more quickly.
Position
- Teeth are located in the bone of the jaws.
Part 4 of 8Structure of a tooth
| Part | Description |
|---|---|
| Enamel | Hard outer layer that protects the tooth |
| Dentine | Layer beneath the enamel that protects the nerves |
| Pulp | Soft internal tissue containing nerves and blood vessels |
| Cement | Hard layer around the root that anchors the tooth in the jaw |
Part 5 of 8The stomach
Churning
- Muscles in the stomach lining contract to squeeze and mix food with strong digestive juices.
Duration
- Food is digested in the stomach for several hours.
Tissues
- The stomach contains muscular, epithelial and glandular tissue.
Part 6 of 8Bile and emulsification (Supplement)
Emulsification
- Bile breaks large drops of fat into smaller ones.
- The larger surface area lets lipase break fats into glycerol and fatty acids faster.
Mechanical, not chemical
- Emulsification breaks no bonds and changes no molecules, so it is physical digestion.
Part 7 of 8Dental decay
Cause
- Bacteria in plaque respire sugar and produce acid.
Effect
- The acid dissolves the enamel.
Prevention
- Reducing sugary food and brushing teeth lowers decay.
Part 8 of 8More from the specification
More from the specification
Metabolic energy supply to somatic cells
- Metabolic energy supply to somatic cells dietary glucose and amino acids provide respiratory fuel and biosynthetic building blocks for all human body cells.
Mastication and mechanical breakdown in digestive organs
- Mastication and mechanical breakdown in digestive organs mechanical action across oral organs grinds food boluses, exposing cellular nutrients to enzymatic attack.
Role of Physical Digestion in the Alimentary Canal
- Chewing by teeth and peristaltic churning by muscular stomach walls pulverize solid food into chyme, optimizing subsequent pancreatic enzymatic hydrolysis in the small intestine.
Pancreatic and Intestinal Secretions
- The pancreas secretes alkaline pancreatic fluid containing amylase, protease,
- and lipase into the duodenum, neutralising gastric chyme to create the optimum pH for terminal macromolecular digestion.
Digestive System Adaptations for Absorption
- The highly folded mucosa of the small intestine, structured with villi and microvilli, maximizes the absorptive surface area for rapid uptake of digested nutrients into blood capillaries and lacteals.
Scurvy
- A deficiency disease caused by lack of vitamin C.
Adaptation
- The process by which populations become better suited to their environment.
Growth
- A permanent increase in size and dry mass.
Digestive system
- Organ system that breaks down and absorbs food.
Amino acid
- The unit from which proteins are made; the sequence decides the protein's shape and function.
Dietary fibre
- Indigestible plant material giving bulk to the intestine contents.
Vitamin
- A nutrient needed in small amounts to stay healthy.
Absorption
- Movement of small food molecules into the blood.
Starch
- An insoluble polysaccharide of glucose used by plants for energy storage.
Organ
- A structure of different tissues working together for specific functions.
Pancreas
- Gland producing insulin and glucagon.
Key terms
| Term | Meaning |
|---|---|
| Physical digestion | Breaking food into smaller pieces without chemical change. |
| Incisor | Chisel-shaped tooth for biting and cutting. |
| Canine | Pointed tooth for tearing and holding. |
| Enamel | Hard outer layer of a tooth. |
| Emulsification | Breaking large fat drops into smaller ones by bile. |
| Plaque | A film of bacteria on teeth that produces acid from sugar. |
| Churning | Contraction of the stomach muscles that mixes food with digestive juices. |
Avoid these mistakes
1
Saying emulsification is chemical digestion — it only breaks fat into smaller drops and changes no molecules.
2
Saying physical digestion breaks chemical bonds — the food molecules are unchanged.
3
Mixing up incisors and canines — incisors cut, canines tear.
4
Saying sugar itself dissolves enamel — the acid made by plaque bacteria does.
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