Locate protease and lipase secretion and action
Use stomach and pancreatic sources without confusing their destinations.
Section B7.4 · Chemical digestion
Cross-referenced to the 2028–2029 0653 section using original teaching from the related single-science courses. A 0653-specific objective-by-objective and Core/Supplement review is in progress. Written practice is self-checked and does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall large and small nutrient molecules, cell membranes and enzyme specificity.
- Use the stated diagram keys and evidence; models are not to scale.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which source supplies a protease to the stomach contents?
What you will learn
- Use stomach and pancreatic sources without confusing their destinations.
- State major secretion/action routes while keeping minor physiological roles outside the model.
Protein pathways at two major regions
The stomach secretes a protease in gastric juice, supporting protein digestion there. The pancreas supplies proteases to the small intestine. Additional intestinal enzymes help complete the overall protein pathway.
For Core, distinguish the stomach source/action region from the pancreas source → small-intestine action route. The Extended sequence names pepsin and trypsin and their different conditions.
Lipid digestion in the small intestine
The pancreas supplies lipase to the small intestine, where it acts on fats and oils. Bile enters the duodenum by a different route and helps present lipid substrate and suitable conditions.
Some enzymes have additional sources or minor roles in detailed physiology. This teaching map names the major school-level routes rather than claiming there are no other enzymes anywhere. Secreted enzyme, canal region and product must remain separate.
Sources for this lesson
Pause and explain
Which source/action pair fits the major lipase route?
Worked example
A source table lists pancreas → small intestine for protease and lipase. Explain both substrates and products.
Show the worked solution
- Pancreatic proteases contribute to protein breakdown.
- Pancreatic lipase acts on fats/oils.
- Keep amino-acid and lipid products separate.
Answer Protease pathway: protein to amino acids overall; lipase pathway: fats/oils to fatty acids and glycerol overall.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
State the major Core protease source/action pairs and lipase source/action pair.
Give me a hint
Use stomach and pancreas separately.
Compare my reasoning
- Stomach protease → stomach.
- Pancreatic proteases → small intestine.
- Pancreatic lipase → small intestine.
Stomach protease acts in stomach; pancreatic protease and lipase act in small intestine.
Look for these in your work
- Both protease routes.
- Lipase route.
An enzyme is delivered through a pancreatic duct. Does that mean the food must pass through the pancreas?
Give me a hint
Secretion and food routes differ.
Compare my reasoning
- Enzyme moves from pancreas to canal.
- Food travels through canal.
No; pancreatic secretion enters the small intestine while food stays in the alimentary canal.
Look for these in your work
- Correct direction.
- Separate routes.
A label groups bile and lipase as “two pancreatic digestive enzymes”. Correct it.
Give me a hint
Check source and substance type.
Compare my reasoning
- Lipase is an enzyme supplied mainly by pancreas.
- Bile is made by liver and stored in gallbladder.
- Bile is not an enzyme.
Lipase is a pancreatic digestive enzyme; bile is a liver-produced mixture stored in the gallbladder.
Look for these in your work
- Source corrections.
- Enzyme distinction.
Common mistakes
- Bile duct and pancreatic enzyme source are distinct.
- The map describes major routes, not every physiological enzyme.
What can you explain now?
Which source/action pair fits the major lipase route?
Compare with the explanation
Pancreas → small intestine.
The secretion reaches the lipid substrate there.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain why a pancreas-to-intestine arrow carries secretion rather than swallowed food.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.