The diagram shows the two stages by which starch is broken down during chemical digestion in the alimentary canal. The two enzymes responsible are labelled ...
Question 1 Report
The diagram shows the two stages by which starch is broken down during chemical digestion in the alimentary canal. The two enzymes responsible are labelled enzyme 1 and enzyme 2.
(a) Name enzyme 1, which breaks starch down to maltose. [1]
(b) Name enzyme 2, which breaks maltose down to glucose. [1]
(c) State the region of the alimentary canal where enzyme 1 is first produced. [1]
(d) Define the term chemical digestion. [2]
(e) Suggest why glucose can be absorbed into the blood but starch cannot. [1]
Answer Details
This question tests the enzymes and stages that digest starch to glucose, and why size and solubility control absorption.
(a) Enzyme 1, which breaks starch down to maltose, is amylase [1].
(b) Enzyme 2, which breaks maltose down to glucose, is maltase [1].
(c) Amylase is first produced in the salivary glands (in the mouth) [1]. (It is also later made by the pancreas.)
(d) Chemical digestion is the breakdown of large, insoluble food molecules [1] into small, soluble molecules that can be absorbed [1], carried out by enzymes [2].
(e) Glucose can be absorbed because it is small and soluble, so it passes through the gut wall into the blood, whereas starch is too large and insoluble to cross the wall until it is digested [1].
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