Follow one nutrient at a time from the mouth to the large intestine, and say what happens at each organ. The route is the same for everyone; the nutrient decides the story.
This lesson is part of nutrition and digestion in SPM Biology.
What happens at each organ?
| Organ | What happens |
|---|---|
| Mouth | Teeth chew food. Salivary amylase begins starch digestion. |
| Oesophagus | Muscles push food to the stomach by peristalsis. |
| Stomach | Acid and pepsin begin protein digestion. |
| Small intestine | Bile, pancreatic juice and intestinal juice complete digestion. Absorption also happens here. |
| Large intestine | Water is absorbed. |
Worked example: rice and boiled egg
An original meal. Rice supplies starch and the egg supplies protein and some fat.
Starch. In the mouth, salivary amylase breaks some starch into maltose. In the small intestine, pancreatic amylase continues the work, and maltase completes it, giving glucose.
Protein. In the stomach, pepsin begins digesting protein into polypeptides in acidic conditions. In the small intestine, trypsin and peptidases finish the job, giving amino acids.
Fat. Fat is mainly digested in the small intestine, where bile emulsifies the fat and lipase breaks it into fatty acids and glycerol.
The mistake that costs marks
A common slip is writing that “bile digests fats”. Bile is not an enzyme and it does not chemically break fat down. It emulsifies fat, making small droplets, so lipase can work faster.
Another slip is placing all digestion in the stomach. Most digestion is completed in the small intestine, where more enzymes join.
How do I write a full answer?
Use three parts for each step: the organ, the substance that acts and what it does. For example: “In the stomach, pepsin breaks down proteins into polypeptides.”
Keep substrates and products in the same sentence. A sentence that names both shows that you understand the change.
A self-check question
Trace a fatty piece of chicken through the canal. State where fat digestion begins and what the products are.
Answer
Fat is mainly digested in the small intestine. Bile from the liver emulsifies the fat into small droplets. Lipase then breaks the fat into fatty acids and glycerol.
Next, pair each enzyme with its substrate and product in relating enzymes to substrates and products. The biological data interpretation trainer adds data-based practice.
If you still list organs without the story, SPM Biology one-to-one tuition lets a teacher trace a meal with you aloud.