Trace starch through maltose to glucose
Locate maltase at the small-intestine epithelial membrane.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it 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
What is the intermediate named in this pathway?
What you will learn
- Locate maltase at the small-intestine epithelial membrane.
- Distinguish surface enzyme action from absorption of its product.
Use two enzyme steps
In the required Extended sequence, amylase breaks starch down to maltose. Maltase then breaks maltose down to glucose. A two-stage pathway needs the correct enzyme for each substrate; amylase and maltase are not synonyms.
The first step can occur in the mouth and small intestine through the amylase routes. The second step is associated with maltase on the membranes of the epithelium lining the small intestine.
Locate the membrane-associated action
The epithelial lining separates the gut contents from underlying tissues. Membrane-associated maltase acts at this surface; it is not simply a pancreas-secreted enzyme acting inside the stomach.
Glucose produced becomes available for absorption. Making glucose and transporting it across the lining are distinct events. The diagram shows the required pathway, not every other starch product or transport protein.
Sources for this lesson
Pause and explain
Which location fits maltase?
Worked example
A pathway shows starch —amylase→ maltose —?→ glucose beside the epithelial membrane. Complete and locate the enzyme.
Show the worked solution
- The second substrate is maltose.
- Choose maltase.
- Place it at small-intestine epithelial membranes.
Answer Maltase on membranes of the small-intestine epithelium catalyses maltose breakdown to glucose.
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.
Write the starch → maltose → glucose pathway with both enzymes.
Give me a hint
Use one enzyme above each step.
Compare my reasoning
- Amylase: starch to maltose.
- Maltase: maltose to glucose.
Starch —amylase→ maltose —maltase→ glucose.
Look for these in your work
- Correct intermediate.
- Both enzymes correctly placed.
Correct a label that places maltase secretion by the pancreas as the required site.
Give me a hint
The syllabus specifies membrane-associated action.
Compare my reasoning
- Maltase is on small-intestine epithelial membranes.
- Pancreatic amylase has a separate route.
Place maltase at the epithelial membranes lining the small intestine.
Look for these in your work
- Correct location.
- No amylase/maltase swap.
A mixture forms maltose but no glucose is detected under the stated test conditions. Which named step needs investigation next?
Give me a hint
The second product is missing.
Compare my reasoning
- First step produced maltose.
- Investigate maltase and suitable conditions.
- Check the glucose measurement before inferring failure.
Investigate the maltase step and the glucose test, rather than assuming amylase must perform both stages.
Look for these in your work
- Second-step logic.
- Measurement control.
Common mistakes
- Amylase does not perform the named maltase step.
- Membrane enzyme action is not the same as glucose transport.
What can you explain now?
Which location fits maltase?
Compare with the explanation
Membranes of the small-intestine epithelium.
It is associated with the lining surface.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Draw both reactions and the epithelial-membrane location of the second.
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.