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Question 18

From Biology SL Paper 3 (November 2024, TZ2)

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  1. Many animals have a gene that codes for L-gulonolactone oxidase (GULO), a key enzyme in the biosynthesis of ascorbic acid (vitamin C). The graphs show the presence of ascorbic acid in rats’ urine after the injection of the lactones gulono, galactono, mannono and altrono.
Four line graphs (Gulono, Galactono, Mannono, Altrono) showing ascorbic acid / mg day-1 on the y-axis and Days on the x-axis, with arrows indicating when lactone was injected and when it was no longer injected.
Four line graphs (Gulono, Galactono, Mannono, Altrono) showing ascorbic acid / mg day-1 on the y-axis and Days on the x-axis, with arrows indicating when lactone was injected and when it was no longer injected.

(a) Determine with a reason which lactone cannot be used in the synthesis of ascorbic acid in rats. [2]

(b) Explain the need in humans to include ascorbic acid in the diet. [2]

Textbook topics in this question

Review the exact course sections assessed by each question part.

Mixed-topic question
18(a)2.1 Enzymes and Metabolic PathwaysVitamin biosynthesis and metabolic pathways · legacy topic
18(b)Vitamins and human nutrition · legacy topic