AP Biology Unit 1: Chemistry of Life

Unit 1 covers the chemistry that biology runs on: water’s properties, the four macromolecule classes, and how structure determines function. Almost everything later in the course — enzymes, membranes, DNA — assumes this unit, which is why it is tested through application rather than recall.

Practise this unit free All Biology units

160 questions8 CED topics50% with a figure

How this unit behaves

What 160 questions on it look like

It spans 8 CED topics, which is wide enough that "I've studied this unit" is not a meaningful statement. Track your accuracy by topic, not by unit.

50% of the questions come with a figure — a graph, diagram or data display. Reading the figure correctly is most of the work before any content knowledge applies.

Properties of Biological Macromolecules43

Proteins28

Nucleic Acids27

Structure and Function of Biological Macromolecules23

Structure of Water and Hydrogen Bonding16

Elements of Life11

Introduction to Biological Macromolecules10

Carbohydrates2

Questions per CED topic.

From the bank

Three real chemistry of life questions

Drawn from the practice pool, not from the mock papers.

Nucleic Acids · Concept Explanation

Which statement correctly compares DNA and RNA?

AThe sugar differs between DNA and RNAcorrect
BDNA contains amino acids, while RNA contains fatty acids.
CDNA is made only of glucose monomers.
DRNA cannot contain nitrogenous bases.

Why A is correct

DNA nucleotides contain deoxyribose sugar, while RNA nucleotides contain ribose sugar.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Which statement correctly compares DNA and RNA". The correct choice is supported by DNA nucleotides contain deoxyribose sugar, while RNA nucleotides contain ribose sugar. The tempting alternatives such as DNA contains amino acids, while RNA contains fatty acids or DNA is made only of glucose monomers fail because they do not produce the same outcome described in the stem.

Common mistakes. Do not stop at a nearby term such as DNA contains amino acids, while RNA contains fatty acids or DNA is made only of glucose monomers. The explanation has to make "DNA usually contains deoxyribose, while RNA contains ribose" fit this stem clue: "Which statement correctly compares DNA and RNA".

Structure of Water and Hydrogen Bonding · Concept Explanation

Which property of water best explains why water forms droplets on a waxy leaf surface?

ALow specific heat prevents water interactions
BHydrogen bonding creates cohesion among water moleculescorrect
CIonic bonding between water molecules and nonpolar wax molecules
DHydrolysis of water molecules into hydrogen gas and oxygen gas

Why B is correct

Water molecules are polar and form hydrogen bonds with one another. Cohesion among water molecules helps droplets hold together, especially on hydrophobic surfaces.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Which property of water best explains why water forms droplets on a waxy leaf surface". The correct choice is supported by Water molecules are polar and form hydrogen bonds with one another. The tempting alternatives such as low specific heat that prevents water molecules from interacting or Ionic bonding between water molecules and nonpolar wax molecules fail because they do not produce the same outcome described in the stem.

Common mistakes. Do not stop at a nearby term such as low specific heat that prevents water molecules from interacting or Ionic bonding between water molecules and nonpolar wax molecules. The explanation has to make "Cohesion among polar water molecules caused by hydrogen bonding" fit this stem clue: "Which property of water best explains why water forms droplets on a waxy leaf surface".

Proteins · Concept Explanation · with figure

A protein contains a charged amino acid at position 82. A mutation replaces it with a nonpolar amino acid. Which outcome is most likely if position 82 normally forms an ionic interaction with another side chain?

AThe tertiary structure is less stable because a side-chain interaction is lost.correct
BThe mutation creates a new phospholipid bilayer around the protein.
CThe peptide backbone is completely hydrolyzed at position 82.
DThe DNA sequence remains unchanged because proteins cannot be affected by mutations.

Why A is correct

Tertiary structure depends partly on interactions among amino acid side chains. Replacing a charged side chain with a nonpolar one can remove an ionic interaction and reduce stability.

The evidence in the prompt matters before the topic label: "A protein contains a charged amino acid at position 82. A mutation replaces it with a nonpolar amino acid. Which...". The supported answer is "tertiary structure is less stable because a side-chain interaction is lost" because Tertiary structure depends partly on interactions among amino acid side chains. Distractors such as mutation creates a new phospholipid bilayer around the protein or peptide backbone is completely hydrolyzed at position 82 either ignore the stated pattern or name a related concept without matching the evidence.

Common mistakes. Do not stop at a nearby term such as mutation creates a new phospholipid bilayer around the protein or peptide backbone is completely hydrolyzed at position 82. The explanation has to make "tertiary structure is less stable because a side-chain interaction is lost" fit this stem clue: "A protein contains a charged amino acid at position 82. A mutation replaces it with a...".

160 questions on this unit, free to start.

Ten a day at no cost. One account covers SAT, ACT and AP.

Start free

FAQ

Chemistry of Life questions

How much of the AP Biology exam is Unit 1?

The College Board weights Chemistry of Life at roughly 8–11% of the multiple-choice section, but its content underpins units that carry far more.

What is most tested in Unit 1?

Structure-to-function reasoning: why a protein’s shape follows from its sequence, and why water’s polarity produces the properties it does.

Last reviewed 2026-08-28. Unit and topic names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.

Topic by topic

Worked questions by topic

3 of this unit’s topics have enough practice questions for a page of their own.

Same course

Practise chemistry of life until the reasoning is automatic.

Real AP questions with a full explanation on every answer, and a mistake bank that only clears when you get it right.

Start free See pricing