The digestive system overview
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of the levels of biological organisation from cells to organ systems, and a basic understanding of the structure and function of the digestive system from Key Stage 3 Science.
What is a tissue?
A group of similar cells that carry out a specific function.
How is an organ different from a tissue?
An organ is made of different tissues working together to carry out a specific function.
Name two organs in the digestive system and describe their functions.
Stomach – breaks down food by churning and using enzymes.
Small intestine – absorbs nutrients into the bloodstream.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains the digestive system, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
The Digestive System Overview
Purpose of the Digestive System:
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To break down large, insoluble molecules into small, soluble molecules. Large, insoluble molecules (like starch or proteins) cannot be absorbed, so need to be broken down into smaller, soluble molecules first.
There are two types of digestion; mechanical digestion which increases the surface area of food particles and chemical digestion which is carried out by enzymes.
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To absorb nutrients like glucose and amino acids into the blood.
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To remove undigested waste through egestion.
Our diet contains 3 major types of polymers. Polymers are large molecules made of repeating subunits (monomers)
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Carbohydrates (e.g starch) - broken down into sugars (e.g glucose).
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Proteins - broken down into amino acids.
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Lipids (Fats and Oils) - broken down into glycerol and fatty acids.
Main Organs of the Digestive System
|
Organ |
Function |
|
Mouth |
Mechanical digestion (teeth) and chemical digestion (salivary amylase). |
|
Salivary Glands |
Produce salivary amylase to break down starch into sugars. |
|
Oesophagus |
Transports food to the stomach via peristalsis (muscle contractions). |
|
Stomach |
Churns food to mechanically digest it. Produces hydrochloric acid and protease enzymes. Protease enzymes break down proteins into amino acids. Stomach acid DOES NOT digest food, it helps provide the optimum pH for protease enzymes and also helps to kill pathogens in our food and drink. |
|
Liver |
Produces bile to emulsify fats and neutralise stomach acid. |
|
Gall Bladder |
Stores and releases bile into the small intestine. |
|
Pancreas |
Produces enzymes (amylase, protease and lipase) and releases them into the small intestine. |
|
Small Intestine |
Produces enzymes (amylase, protease and lipase) to complete digestion and absorbs nutrients into the bloodstream. |
|
Large Intestine |
Absorbs water and forms faeces. |
|
Rectum & Anus |
Stores and removes undigested food as faeces (egestion) |
Key Terms
- Digestion - Breakdown of large insoluble molecules into small soluble ones that can be absorbed.
- Absorption - movement of digested molecules from the small intestine into the blood.
- Emulsification - breaking up larger fat globules into smaller droplets with a larger surface area.
No answer provided.
Exam Tips
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Don't mix up digestion and absorption. Digestion is the break down, absorption is when the molecules enter the bloodstream.
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Make sure you know where all the enzymes are produced.
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Amylase is produced by the salivary glands, the pancreas and the small intestine.
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Protease is produced by the stomach, the pancreas and the small intestine.
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Lipase is produced by the pancreas and the small intestine.
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No answer provided.
Practice Question
Describe the function of the human digestive system. (2 marks)
- The digestive system breaks down large insoluble molecules into smaller, soluble molecules.
- These small molecules (nutrients) are absorbed into the bloodstream.
More Practice
Try to answer the practice question from the TikTok video on your own, then watch the video to see how well you did!