Carbon & the Macromolecules of Life — Drills · Grade 10 Science

Chapter: Investigating the Chemistry of Life

What these drills covers

By the end of Carbon & the Macromolecules of Life you should be able to:

6 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: macromolecule, monomer, polymer, carbohydrate, lipid, protein, nucleic acid.

Problem 1

Joining two monomers by removing a water molecule is called
  1. hydrolysis
  2. dehydration synthesis
  3. denaturation
  4. diffusion
Answer and explanation

dehydration synthesis

Dehydration synthesis builds a polymer and releases water; hydrolysis is the reverse, using water to split the bond.

Problem 2

A polypeptide is assembled from 25 amino acids in a single chain. How many peptide bonds does it contain?
Answer and explanation

24

Each bond joins two neighbours, so n monomers in one chain give n − 1 bonds: 25 − 1 = 24.

Problem 3

Which pairing of macromolecule and monomer is correct?
  1. Protein — nucleotide
  2. Nucleic acid — amino acid
  3. Carbohydrate — monosaccharide
  4. Lipid — glucose
Answer and explanation

Carbohydrate — monosaccharide

Carbohydrates are built from monosaccharides. Proteins use amino acids, nucleic acids use nucleotides, and lipids are not true polymers of a single repeating monomer.

Problem 4

Carbohydrate and protein each release about 17 kJ per gram, while fat releases about 38 kJ per gram. How many kilojoules does 5.0 g of fat release?
Answer and explanation

190 kJ

5.0 g × 38 kJ/g = 190 kJ, roughly twice what the same mass of carbohydrate would release.

Problem 5

Boiling an egg changes the white from clear liquid to opaque solid, and cooling it does not reverse the change. Explain what happened to the protein.
Answer and explanation

Heat disrupted the weak interactions — hydrogen bonds and other side-chain attractions — that held the protein in its folded shape, so the chains unfolded and became tangled with one another. The amino-acid sequence and peptide bonds are intact, but the three-dimensional shape is lost, and because the unfolded chains have aggregated the change does not reverse on cooling.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 6

A nutrition label lists 0 g of fat but the food is high in calories. Explain how that is possible using macromolecule energy densities.
Answer and explanation

Carbohydrate and protein also supply energy, about 17 kJ per gram each. A food with no fat can still be dense in carbohydrate, so its energy content comes from sugars or starch rather than lipids. Energy content depends on how much of each macromolecule is present, not on fat alone.

Response criteria

  • State a biologically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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