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CIE iGCSE Co-Ordinated Science B4 Biological molecules Exam Style Questions Paper 1

CIE iGCSE Co-Ordinated Science Paper 1 - All Chapters

Question

Which molecules make up fats and oils?

A. amino acids and glycerol
B. fatty acids and glycerol
C. glucose and amino acids
D. glucose and fatty acids

▶️ Answer/Explanation
Fats and oils (lipids) are made up of one molecule of glycerol and three molecules of fatty acids.
Amino acids make proteins, and glucose makes carbohydrates.
Therefore, fats and oils consist of fatty acids and glycerol.
✅ Answer: (B)

Question

The starch in a plant is removed. One part of a leaf of the plant is covered with black card.

The plant is then put in the light for six hours. The card is removed and the leaf is tested for starch using iodine solution.

Which row shows the colours of the iodine solution after it is added to different parts of the leaf?

▶️ Answer/Explanation
The part of the leaf not covered by card receives light, so photosynthesis occurs and starch is produced. Iodine solution turns blue-black in the presence of starch.
The covered part receives no light, so no starch is produced, and iodine remains yellow-brown. Therefore, option B is correct.
✅ Answer: (B)

Question

Which row shows the colour of copper(II) sulfate and of cobalt(II) chloride when they are added to water?

▶️ Answer/Explanation
When added to water, anhydrous copper(II) sulfate dissolves to form a blue solution. Anhydrous cobalt(II) chloride dissolves to form a pink solution. Both compounds change colour when hydrated (copper(II) sulfate turns blue, cobalt(II) chloride turns pink). Therefore, row B correctly shows these colours.
✅ Answer: (B)

Question

What is the test for the presence of protein in a food sample?

A. Benedict’s solution
B. biuret test
C. ethanol emulsion
D. iodine solution

▶️ Answer/Explanation
The biuret test is used to detect the presence of proteins in a food sample. A positive result is indicated by a colour change from blue to purple/violet. Benedict’s solution tests for reducing sugars, the ethanol emulsion test tests for fats and oils, and iodine solution tests for starch. Therefore, the biuret test is the correct test for proteins.
✅ Answer: (B)

Question

Which row represents a food that contains a reducing sugar and a fat?

▶️ Answer/Explanation
Benedict’s solution turns orange with a reducing sugar. The ethanol emulsion test gives a milky-white colour for fats.
Row D shows orange with Benedict’s (reducing sugar present) and milky-white with ethanol (fat present), while biuret (protein) and iodine (starch) are negative.
✅ Answer: (D)
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