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WAEC Biology 2002 Question 33

Question 33

Food Substances and Enzymes

Using, iodine solution, Biuret test, Benedict reagents and ethanol, respectively in testing for reducing sugars, which of the following trends of colour changes would be observed?

  1. A.Blue-black→blue→brown→clear
  2. B.Brown→blue→brick red→clear
  3. C.Brown→violet→blue→clear
  4. D.Brown→blue→violet→milky.
Show the answer and explanation

Answer: B (Brown→blue→brick red→clear)

Explanation

A reducing sugar gives no starch (iodine stays brown), no protein (Biuret stays blue), a brick-red Benedict's result and no fat (the ethanol test stays clear).