---
title: "AP Bio Unit 1 Review: Chemistry of Life | Fiveable"
description: "AP Biology Unit 1 covers Structure of Water and Hydrogen Bonding and Elements of Life. Study guides, practice questions, and key terms for every topic."
canonical: "https://fiveable.me/ap-bio/unit-1"
type: "unit"
subject: "AP Biology"
unit: "Unit 1 – Chemistry of Life"
---

# AP Bio Unit 1 Review: Chemistry of Life | Fiveable

## Overview

Unit 1 covers the chemistry that makes life possible: water's unique properties, the six key elements of life, the reactions that build and break macromolecules, and the structure and function of carbohydrates, lipids, nucleic acids, and proteins.

## AP CED Alignment

This unit hub is organized around AP Course and Exam Description topics, skills, and exam task types when they are available in the source data.
- Topic 1.1: Structure of Water and Hydrogen Bonding
- Topic 1.2: Elements of Life
- Topic 1.3: Introduction to Macromolecules
- Topic 1.4: Carbohydrates
- Topic 1.5: Lipids
- Topic 1.6: Nucleic Acids
- Topic 1.7: Proteins
- Topic 1.1: Water Properties and Hydrogen Bonding
- Topic 1.3: Dehydration Synthesis and Hydrolysis
- Science Practice 4 - Representing and Describing Data
- Science Practice 2 - Visual Representations
- FRQ 4 – Conceptual Analysis (Short)
- FRQ 6 – Analyze Data (Short)
- FRQ 2 – Interpreting and Evaluating Experimental Results with Graphing (Long)

## Topics

- [Topic 1.1: Structure of Water and Hydrogen Bonding](/ap-bio/unit-1/structure-water-hydrogen-bonding/study-guide/bMEKm5Pi5y3Y3XRln0Bj): Water's polarity and hydrogen bonding produce cohesion, adhesion, surface tension, high specific heat, and high heat of vaporization, all of which support life at the molecular and organismal level.
- [Topic 1.2: Elements of Life](/ap-bio/unit-1/elements-life/study-guide/kLZ8GN081XmAmZpivYFN): Carbon, hydrogen, and oxygen build all four macromolecule classes. Nitrogen is in nucleic acids and proteins; phosphorus is in nucleic acids and phospholipids; sulfur is in proteins.
- [Topic 1.3: Introduction to Macromolecules](/ap-bio/unit-1/intro-biological-macromolecules/study-guide/GbUEgZQ9FSaSLCMi5Emo): Dehydration synthesis builds polymers from monomers by releasing water; hydrolysis breaks them apart by adding water. These two reactions apply to carbohydrates, proteins, and nucleic acids.
- [Topic 1.4: Carbohydrates](/ap-bio/unit-1/properties-biological-macromolecules/study-guide/aAm3FBn4yaR06XhOtFLI): Monosaccharides join via glycosidic bonds to form polysaccharides. Starch and glycogen store energy using alpha-glucose; cellulose provides structural support using beta-glucose.
- [Topic 1.5: Lipids](/ap-bio/unit-1/structure-function-biological-macromolecules/study-guide/2Wz7ufs9Bp8zVuceCdg3): Lipids are hydrophobic molecules. Triglycerides store energy; phospholipids form membranes; steroids like cholesterol regulate membrane fluidity and act as hormone precursors. Saturation level controls fluidity.
- [Topic 1.6: Nucleic Acids](/ap-bio/unit-1/nucleic-acids/study-guide/RKOM4rhL6iJsAMdbDOWU): DNA and RNA are built from nucleotide monomers. DNA is an antiparallel double helix with A-T and G-C base pairing that stores hereditary information. RNA is usually single-stranded and carries out information transfer.
- [Topic 1.7: Proteins](/ap-bio/unit-1/proteins/study-guide/UyJypYtavwuCLFlWa8wo): Amino acids link via peptide bonds to form polypeptides. Primary sequence drives folding into secondary, tertiary, and quaternary structures. R group chemistry and denaturation connect structure directly to function.

## Hardest Topics And Analytics

Snapshot: practice snapshot
This snapshot uses Fiveable practice activity to show where students tend to miss questions and which review moves are worth prioritizing first.
- **67% average MCQ accuracy** (Across 69k multiple-choice practice attempts for this unit.)
- **69k MCQ attempts** (Practice activity included in this snapshot.)
- **65% average FRQ score** (Across 419 scored free-response attempts for this unit.)
- **Topic 1.7: Proteins**: 45% MCQ miss rate across 3123 attempts. Review Proteins with attention to how the concept appears in AP-style source and evidence questions.
- **Topic 1.4: Carbohydrates**: 40% MCQ miss rate across 9818 attempts. Review Carbohydrates with attention to how the concept appears in AP-style source and evidence questions.
- **Topic 1.5: Lipids**: 38% MCQ miss rate across 8400 attempts. Review Lipids with attention to how the concept appears in AP-style source and evidence questions.
- **Topic 1.6: Nucleic Acids**: 30% MCQ miss rate across 12136 attempts. Review Nucleic Acids with attention to how the concept appears in AP-style source and evidence questions.

## Review Notes

### Topic 1.1: Water Properties and Hydrogen Bonding

Water is polar because oxygen is more electronegative than hydrogen, creating partial negative charge on oxygen and partial positive charges on the two hydrogens. This polarity allows water molecules to form hydrogen bonds with each other and with other polar molecules. Those hydrogen bonds produce four biologically critical properties.

- **Cohesion and adhesion**: Hydrogen bonds between water molecules create cohesion; attraction to other polar surfaces creates adhesion. Together they drive capillary action and water transport in plants.
- **Surface tension**: Cohesive forces at the water surface resist breaking, allowing small organisms like water striders to move across it.
- **High specific heat capacity**: Water absorbs a large amount of heat before its temperature rises, buffering organisms and aquatic environments against rapid temperature swings.
- **High heat of vaporization**: Breaking hydrogen bonds during evaporation requires substantial energy, so evaporating sweat or transpired water carries away significant heat and cools the organism.
- **Ice density anomaly**: Hydrogen bonds in ice form a lattice that is less dense than liquid water, so ice floats and insulates aquatic environments in winter.

**Checkpoint:** Can you explain why sweating cools the body using water's heat of vaporization, and why cohesion matters for water moving up a plant stem?

Property | Molecular cause | Biological example
--- | --- | ---
Cohesion | H-bonds between water molecules | Water column in plant xylem
Adhesion | H-bonds to polar surfaces | Capillary action in narrow tubes
High specific heat | Energy absorbed breaking H-bonds | Stable ocean and body temperatures
High heat of vaporization | Energy needed to vaporize water | Evaporative cooling via sweating
Ice floats | Lattice structure less dense than liquid | Aquatic life survives under ice

### Topic 1.2: Elements of Life

Six elements make up the vast majority of biological molecules: carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), and sulfur (S). Carbon, hydrogen, and oxygen appear in all four macromolecule classes. The other three have more specific roles.

- **Carbon, hydrogen, oxygen**: Found in carbohydrates, lipids, proteins, and nucleic acids. Carbon's four bonding sites allow the branched and ring structures that define macromolecules.
- **Nitrogen**: Present in the nitrogenous bases of nucleic acids and in the amino groups of amino acids, making it essential for both DNA/RNA and proteins.
- **Phosphorus**: Forms the phosphate groups in the sugar-phosphate backbone of nucleic acids and in the phosphate head of phospholipids.
- **Sulfur**: Found in the R groups of cysteine and methionine amino acids; cysteine residues can form disulfide bridges that stabilize protein tertiary structure.

**Checkpoint:** Given a macromolecule type, can you name which elements it contains and explain why each element is there?

Element | Macromolecule(s) | Specific role
--- | --- | ---
C, H, O | All four classes | Carbon backbone; H and O in functional groups
Nitrogen (N) | Nucleic acids, proteins | Nitrogenous bases; amino groups
Phosphorus (P) | Nucleic acids, lipids | Sugar-phosphate backbone; phospholipid head
Sulfur (S) | Proteins | Disulfide bridges in cysteine residues

### Topic 1.3: Dehydration Synthesis and Hydrolysis

Macromolecules are built from monomers through dehydration synthesis and broken down through hydrolysis. These two reactions are opposites and apply to carbohydrates, proteins, and nucleic acids. Lipids use related chemistry but are not true polymers built from identical repeating monomers.

- **Dehydration synthesis**: A hydrogen is removed from one monomer and a hydroxyl group from another; the two monomers join by a new covalent bond and one water molecule is released.
- **Hydrolysis**: Water is added across a covalent bond between monomers, breaking the bond and regenerating the original functional groups on each monomer.
- **Polymerization**: Repeated dehydration synthesis links many monomers into a polymer such as a polysaccharide, polypeptide, or nucleic acid strand.
- **Lipids and these reactions**: Triglycerides form when fatty acids join glycerol via ester bonds through dehydration, but lipids are not polymers because they lack a repeating monomer unit.

**Checkpoint:** Can you draw or describe what happens chemically when two amino acids join, and what happens when a disaccharide is digested?

Reaction | What happens to water | Result
--- | --- | ---
Dehydration synthesis | Water is released | Monomers join; polymer grows
Hydrolysis | Water is added | Bond breaks; monomers released

### Topic 1.4: Carbohydrates

Carbohydrates are built from monosaccharide monomers joined by glycosidic bonds through dehydration synthesis. The resulting polysaccharides can be linear or branched, and that structural difference determines whether the carbohydrate stores energy or provides structural support.

- **Monosaccharides**: Simple sugars like glucose (C6H12O6) that serve as the monomer unit for all polysaccharides and as the primary fuel for cellular respiration.
- **Starch**: Plant energy storage polysaccharide made of alpha-glucose; amylose is linear and amylopectin is branched, allowing rapid glucose release.
- **Glycogen**: Animal energy storage polysaccharide; highly branched chains of alpha-glucose stored in liver and muscle for quick glucose mobilization.
- **Cellulose**: Structural polysaccharide in plant cell walls made of beta-glucose; the beta linkage creates straight chains that hydrogen-bond into strong fibers most animals cannot digest.

**Checkpoint:** Why can animals digest starch but not cellulose, even though both are made of glucose? What structural difference explains this?

Polysaccharide | Monomer linkage | Structure | Function
--- | --- | --- | ---
Starch | Alpha-glucose | Linear/branched | Energy storage in plants
Glycogen | Alpha-glucose | Highly branched | Energy storage in animals
Cellulose | Beta-glucose | Linear, H-bonded fibers | Structural support in plant walls

### Topic 1.5: Lipids

Lipids are nonpolar, hydrophobic molecules. Their structure is not based on a repeating monomer but on the arrangement of glycerol, fatty acid tails, phosphate groups, or steroid ring systems. The degree of saturation in fatty acids directly controls lipid fluidity and function.

- **Saturated vs. unsaturated fatty acids**: Saturated fatty acids have only single C-C bonds, pack tightly, and are solid at room temperature. Unsaturated fatty acids have one or more double bonds that kink the chain, preventing tight packing and keeping the lipid fluid.
- **Triglycerides**: Three fatty acids joined to a glycerol backbone by ester bonds; primary long-term energy storage molecule in animals.
- **Phospholipids**: Two fatty acid tails and a phosphate head group attached to glycerol; the amphipathic structure drives spontaneous bilayer formation in aqueous environments, forming cell membranes.
- **Steroids**: Four fused carbon rings; cholesterol stabilizes membrane fluidity and is the precursor for steroid hormones like testosterone and estrogen.

**Checkpoint:** How does the number of double bonds in a fatty acid affect membrane fluidity, and why does that matter for cells in cold environments?

Lipid type | Key structural feature | Primary function
--- | --- | ---
Triglyceride | 3 fatty acids + glycerol, ester bonds | Long-term energy storage
Phospholipid | 2 fatty acids + phosphate head, amphipathic | Cell membrane bilayer
Steroid (cholesterol) | 4 fused carbon rings | Membrane fluidity; hormone precursor

### Topic 1.6: Nucleic Acids

DNA and RNA store and transmit genetic information using nucleotide monomers. Each nucleotide has three parts: a five-carbon sugar, a phosphate group, and a nitrogenous base. The sequence of bases encodes biological information.

- **Nucleotide structure**: Sugar (deoxyribose in DNA, ribose in RNA) + phosphate group + nitrogenous base (A, T, G, C in DNA; A, U, G, C in RNA). Nucleotides link via phosphodiester bonds to form the sugar-phosphate backbone.
- **Antiparallel double helix**: DNA consists of two strands running in opposite 5' to 3' directions, held together by hydrogen bonds between complementary base pairs: A-T (2 H-bonds) and G-C (3 H-bonds).
- **Base pairing rules**: In DNA: A pairs with T, G pairs with C. In RNA: A pairs with U, G pairs with C. These rules allow accurate replication and transcription.
- **DNA vs. RNA**: DNA uses deoxyribose and thymine, is double-stranded, and stores hereditary information. RNA uses ribose and uracil, is usually single-stranded, and carries out information transfer (mRNA) and translation (tRNA, rRNA).

**Checkpoint:** If one DNA strand reads 5'-ATCGGA-3', what is the sequence and direction of the complementary strand?

Feature | DNA | RNA
--- | --- | ---
Sugar | Deoxyribose | Ribose
Bases | A, T, G, C | A, U, G, C
Strands | Double-stranded | Usually single-stranded
Function | Hereditary information storage | Information transfer and translation

### Topic 1.7: Proteins

Proteins are polymers of amino acids linked by peptide bonds. The specific sequence of amino acids determines how the protein folds, and the final shape determines its function. This structure-function relationship is the central theme of Topic 1.7.

- **Amino acid structure**: Each amino acid has a central carbon bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen, and a variable R group. The R group determines whether the amino acid is nonpolar, polar, or ionic.
- **Primary structure**: The linear sequence of amino acids in a polypeptide, held together by peptide bonds formed through dehydration synthesis between the carboxyl group of one amino acid and the amino group of the next.
- **Secondary structure**: Local folding patterns stabilized by hydrogen bonds along the polypeptide backbone: alpha helices (coiled) and beta-pleated sheets (zigzag).
- **Tertiary and quaternary structure**: Tertiary structure is the overall 3D shape of a single polypeptide, driven by R group interactions including hydrophobic clustering, ionic bonds, and disulfide bridges. Quaternary structure involves two or more polypeptide subunits, as in hemoglobin.
- **Denaturation**: Heat, extreme pH, or chemical agents disrupt the bonds maintaining secondary, tertiary, and quaternary structure, unfolding the protein and destroying its function without breaking peptide bonds.

**Checkpoint:** Which bonds are broken during denaturation, and which are not? Why does denaturation destroy protein function?

Level | Structural feature | Bonds involved
--- | --- | ---
Primary | Amino acid sequence | Peptide bonds (covalent)
Secondary | Alpha helix or beta sheet | Hydrogen bonds (backbone)
Tertiary | Overall 3D shape | H-bonds, ionic, hydrophobic, disulfide bridges
Quaternary | Multiple subunits | Same as tertiary, between subunits

## Study Guides

- [1.5 Lipids](/ap-bio/unit-1/structure-function-biological-macromolecules/study-guide/2Wz7ufs9Bp8zVuceCdg3)
- [1.3 Introduction to Biological Macromolecules](/ap-bio/unit-1/intro-biological-macromolecules/study-guide/GbUEgZQ9FSaSLCMi5Emo)
- [1.4 Properties of Biological Macromolecules](/ap-bio/unit-1/properties-biological-macromolecules/study-guide/aAm3FBn4yaR06XhOtFLI)
- [1.6 Nucleic Acids](/ap-bio/unit-1/nucleic-acids/study-guide/RKOM4rhL6iJsAMdbDOWU)
- [1.1 Structure of Water and Hydrogen Bonding](/ap-bio/unit-1/structure-water-hydrogen-bonding/study-guide/bMEKm5Pi5y3Y3XRln0Bj)
- [1.2 Elements of Life](/ap-bio/unit-1/elements-life/study-guide/kLZ8GN081XmAmZpivYFN)
- [1.7 Proteins](/ap-bio/unit-1/proteins/study-guide/UyJypYtavwuCLFlWa8wo)

## Practice Preview

### Multiple-choice practice

- **Stimulus-based practice question**: Science Practice 4 - Representing and Describing Data | Why is a scatter plot with a trend line most appropriate?
- **Stimulus-based practice question**: Science Practice 4 - Representing and Describing Data | Based on the gel data, which conclusion is best supported?
- **Stimulus-based practice question**: Science Practice 4 - Representing and Describing Data | Based on the data, which relationship is best supported?
- **Stimulus-based practice question**: Science Practice 4 - Representing and Describing Data | Based on the data, which of the following best describes the relationship between pH and alpha-helix formation?
- **Stimulus-based practice question**: Science Practice 4 - Representing and Describing Data | Based on the data, which best describes the relationship between the variables?
- **Stimulus-based practice question**: Science Practice 2 - Visual Representations | Which revision correctly represents phospholipids?

### FRQ practice

- **Protein folding and hydrophobic interactions in aqueous environments**: FRQ 4 – Conceptual Analysis (Short) | Protein folding and hydrophobic interactions in aqueous environments
- **Protein stability through amino acid substitution mutations**: FRQ 6 – Analyze Data (Short) | Protein stability through amino acid substitution mutations
- **Enzyme activity across pH conditions; protein structure stabilization**: FRQ 2 – Interpreting and Evaluating Experimental Results with Graphing (Long) | Enzyme activity across pH conditions; protein structure stabilization

## Key Terms

- **Hydrogen Bonds**: Weak attractive forces between a slightly positive hydrogen atom and a slightly negative atom (usually oxygen or nitrogen). In water, hydrogen bonds between molecules produce cohesion, surface tension, high specific heat, and high heat of vaporization.
- **Polarity**: Uneven distribution of electrons in a molecule creating partial positive and negative regions. Water is polar because oxygen pulls shared electrons more strongly than hydrogen, enabling hydrogen bonding.
- **Evaporative Cooling**: Heat loss that occurs when water evaporates from a surface; water's high heat of vaporization means evaporation carries away substantial thermal energy, cooling organisms through sweating or transpiration.
- **Dehydration Synthesis**: Reaction that joins two monomers by removing a water molecule and forming a new covalent bond; the mechanism for building polysaccharides, polypeptides, and nucleic acids.
- **Hydrolysis**: Reaction that breaks a covalent bond between monomers by adding water; the mechanism for digesting and recycling macromolecules.
- **Monosaccharides**: Simple sugar monomers such as glucose (C6H12O6) that join via glycosidic bonds to form polysaccharides like starch, glycogen, and cellulose.
- **Polysaccharides**: Large carbohydrate polymers formed by linking monosaccharides; starch and glycogen store energy using alpha-glucose linkages, while cellulose provides structural support using beta-glucose linkages.
- **Fatty Acids**: Long hydrocarbon chains with a carboxyl group at one end; saturated fatty acids have only single bonds and pack tightly, while unsaturated fatty acids have double bonds that kink the chain and increase fluidity.
- **Phospholipids**: Amphipathic lipid molecules with two fatty acid tails and a phosphate head group; their hydrophilic heads and hydrophobic tails drive spontaneous bilayer formation, creating cell membranes.
- **Nucleotide**: Monomer of nucleic acids consisting of a five-carbon sugar, a phosphate group, and a nitrogenous base; nucleotides link via phosphodiester bonds to form DNA and RNA strands.
- **Base pairing**: Complementary hydrogen bonding between nitrogenous bases: A-T and G-C in DNA, A-U and G-C in RNA. Base pairing holds the two strands of the DNA double helix together and enables accurate replication and transcription.
- **antiparallel**: The orientation of the two DNA strands, where one runs 5' to 3' and the other runs 3' to 5' in the opposite direction; required for complementary base pairing across the double helix.
- **Amino Acid**: Monomer of proteins; each has a central carbon bonded to an amino group, a carboxyl group, a hydrogen, and a variable R group that determines the amino acid's chemical properties and role in protein folding.
- **Primary Structure**: The specific linear sequence of amino acids in a polypeptide, held together by peptide bonds; this sequence determines all higher levels of protein structure and ultimately protein function.
- **Denaturation**: Loss of a protein's three-dimensional structure caused by heat, extreme pH, or chemical agents; disrupts hydrogen bonds, ionic interactions, and hydrophobic interactions without breaking peptide bonds, destroying protein function.

## Common Mistakes

- **Confusing hydrogen bonds with covalent bonds in water**: Hydrogen bonds form between water molecules; the O-H bonds within a single water molecule are polar covalent bonds. Cohesion, adhesion, and specific heat all depend on intermolecular hydrogen bonds, not the intramolecular covalent bonds.
- **Treating lipids as polymers**: Lipids are not polymers. Triglycerides and phospholipids are assembled through dehydration-like reactions, but they do not have a repeating monomer unit. Do not apply the monomer-polymer framework to lipids the same way you do to carbohydrates, proteins, or nucleic acids.
- **Mixing up starch and cellulose functions**: Both are glucose polysaccharides, but the alpha linkage in starch allows enzymes to break it down for energy, while the beta linkage in cellulose creates rigid fibers most organisms cannot digest. The linkage type, not just the monomer, determines function.
- **Saying denaturation breaks peptide bonds**: Denaturation disrupts hydrogen bonds, ionic interactions, hydrophobic interactions, and disulfide bridges that maintain secondary, tertiary, and quaternary structure. Peptide bonds in the primary structure remain intact. The protein unfolds but the amino acid sequence does not change.
- **Forgetting that DNA strands are antiparallel**: When writing the complementary strand, the direction matters. If the template strand runs 3' to 5', the new strand runs 5' to 3'. Writing both strands in the same direction is a common error that also affects base-pairing answers.

## Exam Connections

- **Structure-to-function reasoning**: AP Bio questions frequently present an unfamiliar molecule or a mutation and ask you to predict the effect on function. Unit 1 trains this skill directly: explain why a change in fatty acid saturation alters membrane fluidity, why a single amino acid substitution can denature a protein, or why the beta linkage in cellulose prevents digestion. Practice moving from structural detail to functional consequence in every macromolecule.
- **Experimental design and data interpretation**: Free-response questions in AP Bio often ask you to design an experiment or interpret data involving macromolecules. Unit 1 concepts appear in scenarios such as testing enzyme activity on starch hydrolysis, comparing membrane fluidity across temperatures, or analyzing the effect of pH on protein structure. Be ready to connect experimental observations back to hydrogen bonding, R group chemistry, or lipid saturation.
- **Cross-unit application of Unit 1 chemistry**: The chemistry from Unit 1 reappears throughout the course. Phospholipid bilayer structure connects to membrane transport in Unit 2; ATP as a nucleotide connects to cellular energetics in Unit 3; DNA structure connects to replication and gene expression in Units 5 and 6. Exam questions may ask you to apply macromolecule structure or water properties in a context drawn from a later unit, so understanding Unit 1 deeply pays off all year.

## Final Review Checklist

- **Final Unit 1 review checklist**: Use this list to confirm you can handle every major concept before the exam.
- **Explain water's properties from its structure**: Connect polarity and hydrogen bonding to each property: cohesion, adhesion, surface tension, specific heat, heat of vaporization, and ice density. Be ready to give a biological example for each.
- **Match elements to macromolecules**: Know which elements appear in each macromolecule class and why. Phosphorus in nucleic acids and phospholipids; sulfur in proteins; nitrogen in nucleic acids and proteins.
- **Describe dehydration synthesis and hydrolysis**: Explain what happens to water in each reaction, which bond forms or breaks, and give one example for each macromolecule class.
- **Compare carbohydrate polysaccharides by structure and function**: Distinguish starch, glycogen, and cellulose by their glucose linkage type, branching pattern, and biological role. Explain why the beta linkage in cellulose makes it indigestible for most animals.
- **Connect lipid structure to function**: Explain how saturated vs. unsaturated fatty acids affect fluidity, how phospholipid amphipathic structure drives bilayer formation, and what role cholesterol plays in membranes.
- **Apply base-pairing rules and explain DNA vs. RNA differences**: Write the complementary strand for a given DNA sequence, identify 5' and 3' ends, and list the structural and functional differences between DNA and RNA.
- **Trace protein structure from primary to quaternary**: Identify which bonds stabilize each level of protein structure, explain how R group properties drive folding, and describe what denaturation does and does not break.

## Study Plan

- **Step 1: Water and elements (Topics 1.1-1.2)**: Read the Topic 1.1 and 1.2 guides. For each water property, write the molecular cause and one biological example. Then make a table matching each element (N, P, S) to the macromolecule it appears in and the specific structure it forms.
- **Step 2: Reactions that build and break macromolecules (Topic 1.3)**: Review the Topic 1.3 guide on dehydration synthesis and hydrolysis. Practice drawing or describing both reactions for at least two macromolecule types. Note why lipids are handled separately.
- **Step 3: Carbohydrates and lipids (Topics 1.4-1.5)**: Use the Topic 1.4 and 1.5 guides to compare starch, glycogen, and cellulose in a table. Then do the same for triglycerides, phospholipids, and steroids. For each, connect the structural feature to the function.
- **Step 4: Nucleic acids (Topic 1.6)**: Review the Topic 1.6 guide. Practice writing complementary DNA strands with correct 5' to 3' orientation. Make a side-by-side comparison of DNA and RNA covering sugar, bases, strand number, and function.
- **Step 5: Proteins and full-unit review (Topic 1.7)**: Work through the Topic 1.7 guide on amino acids and the four levels of protein structure. Then use the key terms list and the AP score calculator to estimate your readiness. Review any macromolecule comparison where you hesitated.

## More Ways To Review

- [Topic study guides](/ap-bio/unit-1#topics)
- [FRQ practice](/ap-bio/frq-practice)
- [Cram archive videos](/cram-archives?subject=ap-biology&unit=unit-1)
- [Cheatsheets](/ap-bio/cheatsheets/unit-1)
- [Key terms](/ap-bio/key-terms)

## FAQs

### What topics are covered in AP Bio Unit 1?

AP Bio Unit 1 covers 7 topics built around the chemistry of life: the properties of water and hydrogen bonding (1.1), elements of life (1.2), introduction to macromolecules (1.3), carbohydrates (1.4), lipids (1.5), nucleic acids (1.6), and proteins (1.7). Together these topics explain how biological molecules are built and how they function in living systems. See all 7 topics with practice on the [AP Bio Unit 1 page](/ap-bio/unit-1).

### How much of the AP Bio exam is Unit 1?

AP Bio Unit 1 makes up 8-11% of the AP exam. That weight covers everything in the Chemistry of Life unit, including carbohydrates, lipids, nucleic acids, proteins, and the properties of water. It's a smaller unit by exam weight, but the macromolecule concepts it introduces show up again in nearly every later unit, so a strong foundation here pays off throughout the course.

### What's on the AP Bio Unit 1 progress check (MCQ and FRQ)?

The AP Bio Unit 1 progress check includes both MCQ and FRQ parts drawn from all 7 topics in the Chemistry of Life unit. MCQ questions typically test your ability to identify macromolecule structures, compare monomers and polymers, and apply properties of water to biological scenarios. The FRQ portion asks you to explain or analyze concepts like how carbohydrates, lipids, nucleic acids, or proteins relate to biological function. For matched practice questions that mirror the progress check format, visit the [AP Bio Unit 1 page](/ap-bio/unit-1).

### How do I practice AP Bio Unit 1 FRQs?

AP Bio Unit 1 FRQs most often pull from the macromolecule topics: carbohydrates, lipids, nucleic acids, and proteins. Questions typically ask you to describe the relationship between structure and function, explain how monomers and polymers are formed or broken down, or connect a molecule's properties to a biological process. To practice, write out full responses using specific vocabulary, then check that every claim is supported with evidence from the topic. Find Unit 1 FRQ practice on the [AP Bio Unit 1 page](/ap-bio/unit-1).

### Where can I find AP Bio Unit 1 practice questions?

The best place to find AP Bio Unit 1 practice questions, including multiple-choice and practice test sets, is the [AP Bio Unit 1 page](/ap-bio/unit-1). It has MCQ and FRQ practice covering all 7 topics, from properties of water and macromolecules to carbohydrates, lipids, nucleic acids, and proteins. Working through topic-by-topic MCQs before attempting a full practice test helps you spot which concepts need more review.

### How should I study AP Bio Unit 1?

Start AP Bio Unit 1 by locking in the properties of water, since concepts like cohesion, adhesion, and hydrogen bonding reappear throughout the course. Then work through each macromolecule group in order: carbohydrates, lipids, nucleic acids, and proteins. For each one, learn the monomer, the polymer, how they're linked, and what biological role they serve. Drawing out the structures by hand and explaining them out loud helps more than re-reading notes. A practical study sequence: read the topic, do a short MCQ set to check understanding, then try an FRQ response before moving to the next topic. You can find topic-by-topic practice on the [AP Bio Unit 1 page](/ap-bio/unit-1).

## Structured Data

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{"@context":"https://schema.org","@type":"FAQPage","inLanguage":"en","mainEntity":[{"@type":"Question","@id":"https://fiveable.me/ap-bio/unit-1#what-topics-are-covered-in-ap-bio-unit-1","name":"What topics are covered in AP Bio Unit 1?","acceptedAnswer":{"@type":"Answer","text":"AP Bio Unit 1 covers 7 topics built around the chemistry of life: the properties of water and hydrogen bonding (1.1), elements of life (1.2), introduction to macromolecules (1.3), carbohydrates (1.4), lipids (1.5), nucleic acids (1.6), and proteins (1.7). Together these topics explain how biological molecules are built and how they function in living systems. See all 7 topics with practice on the <a href=\"/ap-bio/unit-1\">AP Bio Unit 1 page</a>."}},{"@type":"Question","@id":"https://fiveable.me/ap-bio/unit-1#how-much-of-the-ap-bio-exam-is-unit-1","name":"How much of the AP Bio exam is Unit 1?","acceptedAnswer":{"@type":"Answer","text":"AP Bio Unit 1 makes up 8-11% of the AP exam. That weight covers everything in the Chemistry of Life unit, including carbohydrates, lipids, nucleic acids, proteins, and the properties of water. It's a smaller unit by exam weight, but the macromolecule concepts it introduces show up again in nearly every later unit, so a strong foundation here pays off throughout the course."}},{"@type":"Question","@id":"https://fiveable.me/ap-bio/unit-1#whats-on-the-ap-bio-unit-1-progress-check-mcq-and-frq","name":"What's on the AP Bio Unit 1 progress check (MCQ and FRQ)?","acceptedAnswer":{"@type":"Answer","text":"The AP Bio Unit 1 progress check includes both MCQ and FRQ parts drawn from all 7 topics in the Chemistry of Life unit. MCQ questions typically test your ability to identify macromolecule structures, compare monomers and polymers, and apply properties of water to biological scenarios. The FRQ portion asks you to explain or analyze concepts like how carbohydrates, lipids, nucleic acids, or proteins relate to biological function. For matched practice questions that mirror the progress check format, visit the <a href=\"/ap-bio/unit-1\">AP Bio Unit 1 page</a>."}},{"@type":"Question","@id":"https://fiveable.me/ap-bio/unit-1#how-do-i-practice-ap-bio-unit-1-frqs","name":"How do I practice AP Bio Unit 1 FRQs?","acceptedAnswer":{"@type":"Answer","text":"AP Bio Unit 1 FRQs most often pull from the macromolecule topics: carbohydrates, lipids, nucleic acids, and proteins. Questions typically ask you to describe the relationship between structure and function, explain how monomers and polymers are formed or broken down, or connect a molecule's properties to a biological process. To practice, write out full responses using specific vocabulary, then check that every claim is supported with evidence from the topic. Find Unit 1 FRQ practice on the <a href=\"/ap-bio/unit-1\">AP Bio Unit 1 page</a>."}},{"@type":"Question","@id":"https://fiveable.me/ap-bio/unit-1#where-can-i-find-ap-bio-unit-1-practice-questions","name":"Where can I find AP Bio Unit 1 practice questions?","acceptedAnswer":{"@type":"Answer","text":"The best place to find AP Bio Unit 1 practice questions, including multiple-choice and practice test sets, is the <a href=\"/ap-bio/unit-1\">AP Bio Unit 1 page</a>. It has MCQ and FRQ practice covering all 7 topics, from properties of water and macromolecules to carbohydrates, lipids, nucleic acids, and proteins. Working through topic-by-topic MCQs before attempting a full practice test helps you spot which concepts need more review."}},{"@type":"Question","@id":"https://fiveable.me/ap-bio/unit-1#how-should-i-study-ap-bio-unit-1","name":"How should I study AP Bio Unit 1?","acceptedAnswer":{"@type":"Answer","text":"Start AP Bio Unit 1 by locking in the properties of water, since concepts like cohesion, adhesion, and hydrogen bonding reappear throughout the course. Then work through each macromolecule group in order: carbohydrates, lipids, nucleic acids, and proteins. For each one, learn the monomer, the polymer, how they're linked, and what biological role they serve. Drawing out the structures by hand and explaining them out loud helps more than re-reading notes. A practical study sequence: read the topic, do a short MCQ set to check understanding, then try an FRQ response before moving to the next topic. You can find topic-by-topic practice on the <a href=\"/ap-bio/unit-1\">AP Bio Unit 1 page</a>."}}]}
```