IB Biology HL B1.1 Carbohydrates and lipids questions

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Question 1

Multiple choiceMedium1 mark

A molecule is formed by condensation reactions linking one glycerol molecule to three fatty acid molecules. It dissolves in a non-polar solvent but is only sparingly soluble in water. Which statements are correct?

I. Its solubility pattern is consistent with it being a lipid.
II. The molecule is a triglyceride.
III. The molecule is a phospholipid.

Show answer and explanation

Answer: A. Lipids dissolve in non-polar solvents and are only sparingly soluble in aqueous solvents, so the observed pattern is consistent with a lipid. A glycerol molecule linked by condensation to three fatty acids forms a triglyceride; a phospholipid has two fatty acids and a phosphate group.

B: recognizes the solubility pattern but confuses the three-fatty-acid product with a phospholipid.
C: identifies the triglyceride but mistakes it for a phospholipid and omits the matching solubility evidence.
D: accepts the correct statements but also labels the product a phospholipid, despite its specified composition.

Remember: three fatty acids form a triglyceride; two fatty acids and a phosphate group form a phospholipid.

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