S2 2026 science study

What is digestion?

Breaking large food molecules into small, soluble molecules.

Why do we need digestion?

To break food down so nutrients can be absorbed into the blood.

What are the four processes of digestion?

Ingestion, digestion, absorption and egestion.

What is ingestion?

Taking food into the mouth.

What is absorption?

Small nutrients pass through the small intestine into the blood.

What is egestion?

Undigested waste leaves the body as faeces.

What is the alimentary canal?

One long tube from the mouth to the anus.

What happens in the mouth?

Teeth chew food, saliva starts digestion and the tongue forms a bolus.

What is a bolus?

A ball of chewed food mixed with saliva.

What is the oesophagus?

A muscular tube that pushes food to the stomach.

What is peristalsis?

Waves of muscle contractions that push food along the gut.

What happens in the stomach?

Muscles churn food while acid and pepsin digest proteins.

What does hydrochloric acid do?

Creates acidic conditions in the stomach and helps pepsin work.

What is the small intestine's main job?

Completes most chemical digestion and absorbs nutrients.

What does the large intestine do?

Absorbs remaining water and some minerals.

What do the rectum and anus do?

The rectum stores faeces; the anus releases them.

What are accessory organs?

Organs that make or store digestive substances but food does not pass through them.

What do salivary glands produce?

Saliva containing the enzyme amylase.

What does the liver produce?

Bile, which helps break large fat globules into tiny droplets.

What does the gall bladder do?

Stores bile and releases it into the small intestine.

What does the pancreas produce?

Pancreatic juice containing amylase, protease and lipase.

Is bile an enzyme?

No. Bile emulsifies fats but does not contain enzymes.

What is an enzyme?

A protein that speeds up a chemical reaction and is not used up.

What does it mean that enzymes are specific?

Each enzyme works on only one type of molecule (substrate).

What does amylase break down?

Carbohydrates such as starch into simple sugars.

Where does amylase work?

In the mouth and small intestine.

What does protease break down?

Proteins into amino acids.

Where does protease work?

In the stomach and small intestine.

What does lipase break down?

Fats into fatty acids and glycerol.

Where does lipase work?

In the small intestine.

What are carbohydrates used for?

Providing energy. Examples include bread, pasta, rice and potatoes.

What are proteins made into during digestion?

Amino acids.

What are fats (lipids) made into during digestion?

Fatty acids and glycerol.

What is mechanical digestion?

Physical breakdown of food into smaller pieces without making new substances.

Give three examples of mechanical digestion.

Chewing, stomach churning and peristalsis.

What is chemical digestion?

Breaking large food molecules into small molecules using enzymes and chemicals.

What is the difference between mechanical and chemical digestion?

Mechanical is physical; chemical uses enzymes and changes molecules.

Why is the small intestine adapted for absorption?

It is long, has many villi, thin walls and a rich blood supply.

What are villi?

Tiny finger-like projections that increase the small intestine's surface area.

What nutrients are absorbed into the blood?

Glucose, amino acids, fatty acids and glycerol.

What temperature do most human enzymes work best at?

About 37°C.

What pH does pepsin work best in?

Acidic conditions in the stomach.

Why does amylase stop working in the stomach?

Stomach acid changes its shape.

What is the order of food through the digestive system?

Mouth → oesophagus → stomach → small intestine → large intestine → rectum → anus.

What are the levels of organisation from smallest to largest?

Cell → tissue → organ → organ system → organism.