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

Chapter: Investigating the Chemistry of Life

What this practice covers

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

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

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

Problem 1

Why is carbon so well suited to building the molecules of life?
  1. It cannot bond with any other element
  2. It can form four covalent bonds, letting it build long chains, branches, and rings
  3. It is the most abundant element on Earth
  4. It always forms ionic bonds
Answer and explanation

It can form four covalent bonds, letting it build long chains, branches, and rings

Each carbon atom can form four covalent bonds, so carbon can link into the large, varied skeletons that macromolecules need.

Problem 2

The monomer (building block) of a protein is a(n)
  1. monosaccharide
  2. fatty acid
  3. amino acid
  4. nucleotide
Answer and explanation

amino acid

Proteins are polymers of amino acids; there are 20 kinds that cells string together in different orders.

Problem 3

Which macromolecule family stores genetic information?
  1. Protein
  2. Lipid
  3. Carbohydrate
  4. Nucleic acid
Answer and explanation

Nucleic acid

Nucleic acids — DNA and RNA — store and carry the genetic instructions for building proteins.

Problem 4

A polymer is built by linking 12 monomers into a single chain. How many bonds connect them?
Answer and explanation

11 bonds

In a single chain, the number of bonds is one less than the number of monomers: 12 − 1 = 11 bonds.

Problem 5

Explain the phrase 'a protein's shape determines its function,' and connect it to why proteins can act as enzymes.
Answer and explanation

A protein's chain of amino acids folds into a specific 3-D shape, and that shape decides which molecules it can fit and interact with. Enzymes depend on this because their folded shape forms an active site that fits one specific substrate — change the shape and the enzyme can no longer do its job.

Problem 6

A growing plant gains dry mass while soil mass changes little. Explain a major source of its carbon. Explain the reasoning in your own words.
Answer and explanation

Atmospheric carbon dioxide is a major carbon source; water and mineral nutrients are also required.

Photosynthesis incorporates carbon from atmospheric CO₂.

That carbon can be rearranged into carbohydrates and other organic molecules.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 7

Identify the building units of DNA and explain why their order matters. Show the reasoning, not just the conclusion.
Hints

Do not infer that every carbon-containing molecule has the same biological role.

Answer and explanation

DNA contains nucleotides; base sequence carries information affecting RNA and proteins.

Problem 8

Why cannot equal food mass establish equal available energy or nutrient function?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Composition, digestibility and molecule types differ; mass alone does not identify chemical stores or biological roles.

Problem 9

Protein function depends on sequence, folding and contextProtein function depends on sequence, folding and contextSequenceFolded structureInteractions depend on conditionsSequence → interactions / folding → possible function
Original symbolic amino-acid sequence and folded-chain model. It illustrates an explanatory relationship, not a solved structure of a named protein.
Interpret the supplied visual. Does an unfolded protein necessarily have a newly rewritten amino-acid sequence?
Answer and explanation

No. Its interactions and folding may change while much of the covalent chain sequence remains; hydrolysis and denaturation are different processes.

A protein consists of one or more folded polypeptides, chains of amino acids joined by peptide bonds. Each amino acid has a side group whose interactions influence folding. A different sequence can change a binding site, stability or location, but some sequence changes have little detectable effect. Denaturation disrupts an important folded arrangement; it is not the same as cutting every peptide bond. Enzymes, structural components, receptors and transporters are protein roles. A correct explanation connects a particular structural change to a tested function rather than saying all proteins behave alike.

No. Its interactions and folding may change while much of the covalent chain sequence remains; hydrolysis and denaturation are different processes.

Response criteria

  • Read the structures, axes, directions and units correctly.
  • Connect the evidence with the biological mechanism.
  • Respect stated model assumptions and distinguish an observation from a further inference.

Problem 10

A treatment unfolds an enzyme but leaves its amino-acid chain largely intact. Explain what may change, what need not change, and what evidence would test retained function.
Answer and explanation

Folding and active-site arrangement may change while amino-acid sequence remains largely intact. Compare catalytic rates under matched conditions and examine whether the fold/function can recover; unfolding is not automatically complete peptide hydrolysis.

Folding and active-site arrangement may change while amino-acid sequence remains largely intact. Compare catalytic rates under matched conditions and examine whether the fold/function can recover; unfolding is not automatically complete peptide hydrolysis.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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