Digestive system

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Lesson notes

Overview of the Digestive System

The **digestive system** breaks down food into small molecules that can be absorbed into the blood.
It consists of many organs, each with a specific role in digestion.
**Enzymes** are biological catalysts that speed up chemical reactions in digestion.
Some bacteria live in the **large intestine**; they protect against harmful bacteria and help digest food.

Organs Food Travels Through

**Mouth**: teeth mechanically break food; saliva contains **amylase** which breaks down starch.
**Oesophagus**: walls squeeze to move food to the stomach.
**Stomach**: muscular walls mechanically break food; contains **hydrochloric acid** to kill bacteria; **protease** breaks down proteins.
**Small intestine**: contains **villi** with a large surface area for absorbing digested food into the blood.
**Large intestine**: absorbs water from undigested food.
**Rectum**: stores faeces (waste material) before it leaves through the anus.

Accessory Organs (Food Does Not Pass Through)

**Liver**: produces **bile** to neutralise stomach acid.
**Gall bladder**: stores bile and releases it into the small intestine.
**Pancreas**: produces enzymes **protease**, **amylase**, and **lipase** (which breaks down lipids) and releases them into the small intestine.

Enzymes in Digestion

**Amylase** (in saliva and from pancreas) breaks down starch (carbohydrates).
**Protease** (in stomach and from pancreas) breaks down proteins.
**Lipase** (from pancreas) breaks down lipids (fats).
Enzymes work best at specific pH conditions; protease works best in acidic conditions in the stomach.

Absorption and Waste

Digested food is absorbed in the **small intestine** via **villi**, which increase surface area for faster absorption.
Water is absorbed in the **large intestine**.
Undigested material forms **faeces**, stored in the **rectum** until eliminated.

The human digestive system showing the main organs.

Slides

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Practice questions

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1.Which organ contains hydrochloric acid that kills bacteria?
Easy
- AStomach
- BSmall intestine
- CLarge intestine
- DLiver
2.Where are villi found and what is their main function?
Easy
- ASmall intestine; to absorb digested food
- BLarge intestine; to absorb water
- CStomach; to kill bacteria
- DOesophagus; to move food
3.In which organ is water absorbed?
Easy
- ALarge intestine
- BSmall intestine
- CStomach
- DRectum
4.Which organ stores faeces before it leaves the body?
Easy
- ARectum
- BAnus
- CLarge intestine
- DColon
5.Which enzyme breaks down starch, and where is it produced?
Medium
- AAmylase; mouth
- BProtease; stomach
- CLipase; pancreas
- DAmylase; pancreas
6.What is the role of bile in digestion?
Medium
- ANeutralise stomach acid
- BBreak down proteins
- CBreak down carbohydrates
- DAbsorb water
7.Enzymes are biological catalysts. What does this mean?
Medium
- AThey speed up chemical reactions without being used up
- BThey are used up in reactions
- CThey slow down reactions
- DThey are only found in the stomach
8.Which organ produces enzymes that are passed into the small intestine, including protease, amylase, and lipase?
Hard
- APancreas
- BLiver
- CGall bladder
- DStomach

Revision notes

## Digestive System Revision Notes - **Purpose**: Break down food into small molecules for absorption. - **Enzymes**: Biological catalysts that speed up chemical reactions. Key enzymes: - **Amylase**: Breaks down starch (carbohydrates). Found in saliva (mouth) and produced by pancreas. - **Protease**: Breaks down proteins. Works best in acidic conditions (stomach). Produced by pancreas. - **Lipase**: Breaks down lipids (fats). Produced by pancreas. ### Organs in order food passes through: 1. **Mouth**: Mechanical breakdown by teeth; saliva contains amylase. 2. **Oesophagus**: Squeezes food to stomach. 3. **Stomach**: Muscular walls mechanically break food; contains hydrochloric acid (kills bacteria) and protease. 4. **Small intestine**: Villi (large surface area) absorb digested food into blood. 5. **Large intestine**: Absorbs water. 6. **Rectum**: Stores faeces (waste) until expelled via anus. ### Accessory organs (food does not pass through): - **Liver**: Produces bile (neutralises stomach acid). - **Gall bladder**: Stores bile, releases into small intestine. - **Pancreas**: Produces enzymes (protease, amylase, lipase) and releases into small intestine. ### Key Points: - **Bile**: Neutralises stomach acid in small intestine. - **Villi**: Increase surface area for faster absorption. - **Bacteria**: Live in large intestine; protect against harmful bacteria and aid digestion.

Enzyme: Biological catalyst that increases the rate of a chemical reaction.
Amylase: Enzyme that breaks down starch (a carbohydrate).
Protease: Enzyme that breaks down proteins.
Lipase: Enzyme that breaks down lipids.
Bile: Substance produced by the liver that neutralises stomach acid.
Villi: Finger-like projections in the small intestine that increase surface area for absorption.
Faeces: Waste material stored in the rectum before leaving the body through the anus.

Flashcards

What is the role of the digestive system?

It breaks down food into small molecules that can be absorbed into the bloodstream.

What are enzymes?

Enzymes are biological catalysts that increase the rate of chemical reactions.

Where do bacteria live in the digestive system and what do they do?

They live mainly in the large intestine, protect against harmful bacteria, and help with digestion.

What is the function of the mouth in digestion?

Teeth mechanically break down food; saliva contains amylase which breaks down starch.

What enzyme is found in saliva and what does it break down?

Amylase, which breaks down starch (a carbohydrate).

How does food move through the oesophagus?

The walls of the oesophagus squeeze together to move food towards the stomach.

What does the stomach contain to kill bacteria?

Hydrochloric acid.

Which enzyme works best in acidic conditions and what does it break down?

Protease, which breaks down proteins.

What are villi and where are they found?

Villi are finger-like projections in the small intestine that increase surface area for absorption.

Why is it advantageous for villi to have a large surface area?

It allows digested food to be absorbed more quickly into the bloodstream.

What is absorbed in the large intestine?

Water.

Where is faeces stored before leaving the body?

In the rectum.

What is the role of the liver in digestion?

It produces bile, which neutralises stomach acid.

What is the function of the gall bladder?

It stores bile and releases it into the small intestine.

Which enzymes does the pancreas produce?

Protease, amylase, and lipase.

What does lipase break down?

Lipids (fats).

What is the purpose of bile?

To neutralise stomach acid in the small intestine.

Name two organs where food is mechanically broken down.

Mouth (teeth) and stomach (muscular walls).

What is faeces?

Waste material that is stored in the rectum and leaves the body through the anus.

Which organ produces bile?

The liver.

Where are the enzymes protease, amylase, and lipase released into?

They are released into the small intestine from the pancreas.

What is the role of enzymes in digestion?

They chemically break down food into smaller molecules, speeding up digestion.

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