Physical digestion — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

Section 1 of 23What 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.

Section 2 of 23Types 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

Section 3 of 23Why 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.

Section 4 of 23Structure 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

Section 5 of 23The 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.

Section 6 of 23Bile 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.

Section 7 of 23Dental 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.

Section 8 of 23More 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.

Section 9 of 23What physical digestion does

1Physical (mechanical) digestion

Physical (mechanical) digestion breaking large pieces of food into smaller pieces without changing the chemicals in the food.

2Purpose

• Purpose it increases the surface area of food so enzymes act faster during chemical digestion.

3Sites

• Sites chewing by teeth, churning by the stomach muscles, and emulsification of fat by bile in the small intestine.

4Without it

• Without it enzymes would act only on the surface of large lumps and digestion would be far too slow.

Section 10 of 23Types of teeth

Tooth	Shape	Function
Incisor	Flat with a sharp chisel edge	Biting and cutting food
Canine	Pointed	Tearing and gripping food
Premolar	Broad with ridges	Crushing and grinding
Molar	Large, broad, with cusps	Grinding food into small pieces

Section 11 of 23Structure of a tooth

Structure of a tooth

Enamel

• Enamel the hard outer covering of the crown.

Dentine

• Dentine a bone-like layer beneath the enamel.

Pulp cavity

• Pulp cavity contains nerves and blood vessels, so decay reaching it is painful.

Cement and gum

• Cement and gum fix the root into the jaw bone; a periodontal ligament acts as a shock absorber.

Section 12 of 23Tooth decay and its prevention

1

Bacteria in plaque (a film of bacteria and food debris) feed on sugars in the mouth.

2

The bacteria release acid as a waste product.

3

The acid dissolves the enamel, forming a cavity.

4

If untreated, decay reaches the dentine and pulp, causing toothache and infection.

Section 13 of 23Gum disease

Cause

• Cause bacteria in plaque at the gum line make the gums inflamed and bleeding.

Effects

• Effects gums may recede, so teeth loosen.

Calculus

• Calculus plaque hardens into calculus if not removed;
  • the dentist can remove it and fill cavities before decay spreads.

Section 14 of 23Churning and emulsification

Stomach churning

• Stomach churning muscular contractions mix food with acid and enzymes, increasing the surface area exposed to enzymes.

Emulsification

• Emulsification bile from the liver breaks large fat droplets into many tiny droplets.
• This gives a much larger surface area for lipase, so fat digestion is faster.

Physical, not chemical

• Physical, not chemical the fat molecules themselves are not changed.

Alkaline bile

• Alkaline bile also neutralises the acidic chyme from the stomach, giving the pH needed by small intestine enzymes.

Saliva

• Saliva lubricates food into a bolus for swallowing, and the tongue pushes the bolus to the back of the mouth.

Section 15 of 23Human dentition and diet

Adults have 32 teeth

• Adults have 32 teeth eight incisors, four canines, eight premolars and twelve molars.
• Each side of each jaw has 2 incisors, 1 canine, 2 premolars and 3 molars.

Children

• Children have 20 milk teeth that are replaced by permanent teeth.

Wisdom teeth

• Wisdom teeth the last molars, which may lack space to grow and cause pain.

Herbivores

• Herbivores large flat molars and premolars for grinding plants, and no upper incisors.

Carnivores

• Carnivores large pointed canines for tearing flesh.

Humans

• Humans omnivores, with a mix of tooth types.

Section 16 of 23Why physical digestion matters

Definition

• Definition it breaks food into smaller pieces without changing its chemical nature.

Surface area

• Surface area it increases the area available to enzymes, so chemical digestion is faster.

Swallowing and movement

• Swallowing and movement smaller pieces are easier to swallow and move along the gut.

Without it

• Without it large lumps would be digested slowly and incompletely, because enzymes act only at the surface.

Section 17 of 23Teeth

Type	Shape	Function
Incisors	Flat, chisel-like edge	Biting and cutting
Canines	Pointed	Tearing food
Premolars	Broad, ridged surface	Grinding and crushing
Molars	Large, broad cusps	Grinding

Section 18 of 23Muscular churning and emulsification

Stomach

• Stomach the thick muscular wall contracts to churn food with gastric juice into a semi-liquid chyme with a larger area exposed to enzymes.

Peristalsis

• Peristalsis rhythmic contractions of circular and longitudinal muscles move food along the gut and mix it with enzymes.

Bile

• Bile emulsifies fats into tiny droplets, which greatly increases the surface area for lipase.

Physical, not chemical

• Physical, not chemical the fat molecules remain fats.

Section 19 of 23Peristalsis in detail

Behind the bolus

• Behind the bolus circular muscles contract and longitudinal muscles relax, narrowing the tube and squeezing food forward.
• Ahead of the bolus — circular muscles relax and longitudinal muscles contract, widening the tube.

Wave

• Wave this pattern passes along the gut, so food can move even upside down.

Segmentation

• Segmentation in the small intestine, contractions squeeze and release adjacent sections to mix food with juices.

Fibre

• Fibre provides bulk for the gut muscles to push against.

Section 20 of 23Surface area and enzyme action

1Surface area to volume ratio

• Surface area to volume ratio a 2 cm cube has a ratio of 3:1; cutting it into 1 cm cubes gives 6:1.
• More surface means faster reaction.

2Investigation

• Investigation compare whole and crushed antacid tablets, or whole and chopped potato in amylase, at the same temperature.

3Result

• Result the crushed or chopped sample reacts faster because more enzyme molecules contact the substrate at once.

4Control variables

• Control variables volume and concentration of enzyme, temperature, pH and mass of food.

Section 21 of 23Dental health

Tooth decay (caries)

• Tooth decay (caries) bacteria in plaque feed on sugars and produce acid, which dissolves enamel and then dentine.
• Gum disease is caused by a build-up of plaque at the gum line.

Prevention

• Prevention brush twice a day, use fluoride toothpaste, reduce sugary food and drinks, floss and visit the dentist.
  • (fluoride strengthens enamel)

Sugary drinks

• Sugary drinks bacteria produce acid for longer; drinking water after eating lets saliva neutralise it.

Wisdom teeth

• Wisdom teeth the last molars, which may lack space to grow and cause pain.

Number of teeth

• Number of teeth children have 20 milk teeth replaced by 32 permanent teeth, with 2 incisors, 1 canine, 2 premolars and 3 molars on each side of each jaw.

Section 22 of 23Key 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.

Term	Meaning
Physical digestion	Breaking food into smaller pieces without chemical change.
Enamel	Hard outer layer of the tooth crown.
Plaque	A film of bacteria and food debris on teeth.
Emulsification	Breaking fat into tiny droplets.
Dentine	Bone-like tissue beneath tooth enamel.
Chyme	Partly digested acidic food leaving the stomach.

Term	Meaning
Physical digestion	Breakdown of food into smaller pieces without chemical change.
Enamel	Hard outer layer of the tooth.
Emulsification	Splitting fats into small droplets.
Chyme	Semi-liquid mixture of food and gastric juice.
Peristalsis	Muscle contractions that push food along the gut.
Plaque	Film of bacteria on teeth.

Section 23 of 23Exam technique

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.

1

Saying bile digests fat chemically — it only emulsifies; lipase digests fat.

2

Thinking sugar itself damages enamel — the acid made by bacteria does.

3

Saying fluoride kills bacteria — it strengthens enamel.

4

Believing mechanical digestion changes food molecules — it does not.

1

Saying bile digests fat chemically — it emulsifies; lipase digests fat.

2

Saying churning breaks chemical bonds — it only breaks food into smaller pieces.

3

Mixing up the functions of incisors (cutting) and molars (grinding).

4

Saying enamel has nerves — nerves are in the pulp.

5

Stating that sugar itself damages teeth directly — acid from bacteria does.