AP Biology - Big Ideas from Unit #1: The Chemistry of Life

Comprehensive Quizlet for AP Biology Unit #1: Chemistry of Life, primarily aligned to the 2020 CED (for the May 2025 exam) and also fully compatible with the 2025 CED (May 2026+ exams). 🎯 This set is designed as a review resource, not a replacement for instruction—it emphasizes core content, corrects common misconceptions, and integrates scenario-based practice aligned to AP Biology Science Practices (e.g., 1.C, 2.A, 6.E). ✅ Includes both fact recall and application-level flashcards to help build the thinking needed for a 4 or 5 on the exam. 🔁 Topics Covered: Water’s properties (Topic 1.1) Elements of life (1.2) Macromolecules: Carbs, Lipids, Nucleic Acids, Proteins (2020 1.3-1.6, 2025 1.3–1.7) Structure-function relationships Visual interpretation & predictive reasoning Ideal for daily review leading up to the AP exam.

Water Properties

1) Cohesion

2) Adhesion

3) High Surface Tension

4) High Specific Heat (High Heat Capacity)

5) Great solvent for life! (Closest thing we have to a universal solvent)

6) Less dense as a solid

Hydrogen Bond

An intermolecular bond between 1 Hydrogen Atom (on one molecule) and a slightly electronegative atom (on the other molecule).

Hydrogen atoms usually bond with one of the FON.

F - Fluorine

O - Oxygen

N - Nitrogen

Hydrogen Bonds in Water

They are located between the slightly electropositive Hydrogen atom of one molecule and another molecule's slightly electronegative oxygen atom.

Hydrogen Bonds in DNA

They are located between nitrogenous bases. The DNA double-helix structure is held together by a phosphodiester covalent bond, but the nitrogenous bases are held together by hydrogen bonds.

Polar molecule

Uneven distribution of electric charge (+/-)

T/F: Water is a polar molecule.

True! Water is a polar molecule due to the uneven distribution of charge between the electronegative oxygen atom and the electropositive hydrogen atom.

What do the properties of water result from?

They result from the polarity of the water molecule and hydrogen bonding between water molecules.

Cohesion

Property of water - Attraction between water molecules - Water sticks together!

Adhesion

Property of water - Attraction between water molecules and polar substances. Water sticks to other polar substances!

Why can water move up a xylem (capillary action)?

Water can move up a xylem, from the roots to the leaves in a plant, due to its properties of cohesion and adhesion, as cohesion keeps the water molecules together and adhesion keeps water attached to the xylem of the plant (polar!).

Water is held together by a ___________________________________.

Water is held together by a polar covalent bond!

High Surface Tension

Property of water - Difficulty in breaking through the liquid surface of water due to Hydrogen bonds above and below.

*Connected to Cohesion

High Specific Heat & Ability to Moderate Temperature

Water property - Water is an effective heat bank due to hydrogen bonding as when hydrogen bonds are broken, thermal energy (heat) is absorbed and when bonds are formed, thermal energy is released. Since water's able to absorbe thermal energy w/o having a drastic change in its own temperature, it has an ability to moderate temperature.

Ex. Temperatues in Bozeman, MT vs Seattle, WA.

Evaporative Cooling

Water property - As water (liquid) evaporates, the surfaceof the liquid that remains cools down.

Think: Sweat.

Good Solvent for Life - Closest thing to a universal solvent

Water property - Water is the closest thing we have to a universal solvent since it can dissolve all polar molecules.

"Like disolves like"

Hydrophillic

Affinity/Attraction for Water - Water-LOVING!

All polar molecules are hydrophilic.

Hydrophobic

NO affinity/attraction for Water - Water-HATING!

All nonpolar molecules are hydrophobic.

Less Dense as a Solid

Water property - Water is less dense as a solid! ICE FLOATS! Water forms crystal-like bonds when it freezes, putting the molecules at fixed distances from each other.

Why it matters: Floating ice allows for life to exist overwinter in places like lakes. As it is, the floating ice insulates the water below so life can continue until spring thaw. Living systems depend on the properties of water that result from its polarity and hydrogen bonding.

Elements of Life

Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur

CHONPS!

Elements found in Carbohydrates

CHO

Note: Carbohydrates always have a CHO ratio of 1:2:1.

Ex: C₆H₁₂O₆ (Glucose!)

Elements found in Lipids

CHO

Note: Phospholipids have CHO + P!

Elements found in Proteins

CHON + S*

Note: Sulfur is sometimes found in proteins. Most of the time, it's just CHON.

Elements found in Nucleic Acids

CHONP

Biological Macromolecules

Carbohydrates, Lipids, Proteins, Nucleic acids

CHO - Carbs

CHO - Lipids

CHON + S* - Proteins

CHONP - Nucleic Acids

Functions of Carbohydrates in Living Organisms

1) Provide Energy

2) Store Energy

3) Build Macromolecules

Functions of Lipids in Living Organisms

1) Important constituent for cell membranes

2) Building blocks of many hormones

3) Cells store energy for long-term usage in the form of lipids (fats)

Functions of Proteins in Living Organisms

1) Catalyze reactions (enzymes)

2) Provide structural support

3) Provide defenses

Functions of Nucleic Acids

1) Store genetic information

2) Guide protein synthesis

3) Facilitate appropriate linkage of polypeptides

Glycosidic Bond

covalent bond between two monosaccharides

Peptide Bond

covalent bond formed between amino acids

Phosphodiester Bond

covalent bond that is responsible for the polymerization of nucleic acids by linking sugars and phosphates of adjacent nucleotides

Dehydration Synthesis

To build polymers from monomers while losing water.

Hydrolysis

To split a polymer into monomers while gaining water.

Describe the properties of the monomers and the type of bonds that connect the monomers in biological macromolecules.

Hydrolysis and dehydration synthesis are used to cleave and form covalent bonds between monomers.

How does the R group affect protein folding?

It affects tertiary and quarternary structure(s), altering the 3D shape.

Why does structure determine function in macromolecules?

The 3D structure of macromolecules (especially proteins) determines how they interact with other molecules and carry out their functions in cells.

Changes in structure = changes in function.

These theme is common in AP Biology and the general study of Biology.

pH

Measure of Acidic/Alkaline (Basic) a solution is.

pH and H+ ion concentration have a _______ relatonship

pH and H+ ion concentration have an INVERSE relatonship.

⬆️ H+ Concentration = ⬇️ pH (more acidic)

Acidic pH

pH less than 7 is ACIDIC!

Alkaline (Basic) pH

pH greater than 7 is ALKALINE (BASIC)!

Neutral pH

pH = 7

Saturated Lipid

Structure: Contain only single bonds between carbon atoms in the fatty acid chains.

Kinks?: No kinks - the hydrocarbon chains are straight.

Packing: Because of their straight structure, they pack tightly together.

State at Room Temp: Typically solid (e.g., butter).

Sources: Commonly found in animal fats.

Saturated with Hydrogen Atoms! NO DOUBLE BONDS

Unsaturated Lipid

Structure: Contain one or more double bonds between carbon atoms.

Kinks?: Yes, the double bonds create kinks or bends in the fatty acid chains.

Packing: These kinks prevent tight packing, so they are less dense.

State at Room Temp: Typically liquid (e.g., olive oil).

Sources: Commonly found in plant oils and fish.

DOUBLE BONDS PRESENT!

Monomer of Carbohydrate

monosaccharide

Monomer of Protein

Amino Acid

Components of Amino Acid: (Amine Group on left, ⍺-carbon in center, R group in center top, Hydrogen atom in center bottom, Carboxyl group on right)

Monomer of Nucleic Acid

Nucleotide

Components of Nucleotide: (Pentose Sugar, Charged Phosphate Group, Nitrogenous Base)

Components of a Phospholipid

hydrophilic head and hydrophobic tail

Which can be broken down by animals: Starch or Cellulose?

Starch

Protein Structure

a) Primary Structure = Poly-peptide chain, peptide covalent bonds involved

b) Secondary Structure = Hydrogen bonds between amino acids, no R-group action, proteins folded into the a-helix or b-pleated sheet. No R-group action.

c) Tertiary Structure = Bonds between R-groups such as hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges. The protein forms its 3D shape.

d) Quarternary Structure = Tertiary Structure but with Multiple Polypeptide Chains

Primary Structure

Poly-peptide chain, peptide covalent bonds involved

Secondary Structure

Hydrogen bonds between amino acids, no R-group action, proteins folded into the α-helix or β-pleated sheet. No R-group action.

Tertiary Structure

Bonds between R-groups such as hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges. The protein forms its 3D shape.

Quarternary Structure

Tertiary Structure but with Multiple Polypeptide Chains

Why is the specific order of amino acids in a polypeptide (primary structure) so important?

In proteins, the specific order of amino acids in a polypeptide (primary structure) determines the overall shape of the protein. Order of amino acids in a polypeptide determined by DNA.

R groups

Groups that give different amino acids different properties. Variable groups. Interactions between R groups are very important regarding Tertiary and Quaternary Structure!

Are lipids polar or nonpolar?

Lipids are nonpolar molecules that do not follow the standard "monomer-polymer" rule.

Hydroxyl Group (-OH)

A polar functional group is found in alcohols and carbohydrates. Increases solubility in water by forming hydrogen bonds.

Carboxyl Group (-COOH)

Acts as an acid by donating an H⁺ ion. Found in amino acids and fatty acids. Contributes to acidic properties in molecules.

Amino Group (-NH₂)

Acts as a base by accepting an H⁺ ion. Found in amino acids. Plays a role in peptide bond formation during protein synthesis.

It is part of the AMINO ACID STRUCTURE!

Phosphate Group (-PO₄²⁻)

Adds a negative charge to molecules and is involved in energy transfer (like in ATP). Found in nucleic acids and phospholipids. Highly polar and reactive.

*DNA is slightly electronegative due to the charge in the phosphate group. This is important to know for 6.8 Biotechnology, such as DNA Gel Electrophoresis (Unit #6).

Sulfhydryl Group (-SH)

Found in the amino acid cysteine. Forms disulfide bridges that help stabilize the tertiary structure of proteins.

Methyl Group (-CH₃)

A nonpolar and hydrophobic functional group. Often involved in gene regulation, such as DNA methylation, which can silence gene expression. Common in lipids and epigenetic modifications.

*This ties into Unit #6 when we discuss Epigenetics, specifically DNA methylation.

Skill/Scenario Practice: What happens to a protein if a hydrophobic R-group is replaced with a hydrophilic one?

It could misfold because the hydrophilic R-group may interact with water instead of staying in the protein’s hydrophobic core, disrupting the tertiary structure and function. The structure would be altered, meaning there would be a change in function.

Science Practice: 6.E - Argumentation & Prediction

Why It Matters: This kind of mutation-based reasoning appears in FRQs and MCQs, testing how changes in structure affect function.

Skill/Scenario Practice: A mutation causes a polar amino acid to be replaced by a nonpolar one. Predict the effect on protein folding.

This may cause misfolding, especially if the region is normally exposed to water, disrupting tertiary or quaternary structure. Once again, there would be a change in the protein folding and function as the structure has been altered.

Science Practice: 6.E - Argumentation & Prediction

Why It Matters: You’ll often need to justify the impact of chemical changes on protein function, especially in system-focused questions.

Skill/Scenario Practice: Why do phospholipids form bilayers in water?

Their hydrophilic heads interact with water, while hydrophobic tails cluster inward, forming a bilayer.

Science Practice: 1.C – Concept Explanation

Why It Matters: This concept shows up frequently in early FRQs, membrane-based questions, and MCQs.

Skill/Scenario Practice: How does the sequence of amino acids in a protein (primary structure) determine its final 3D shape?

The sequence determines how R-groups interact (hydrophobic, ionic, disulfide bonds), which drives tertiary and quaternary structure.

Science Practice: 1.C – Concept Explanation

Why It Matters: College Board loves asking you to connect sequence → structure → function.

Skill/Scenario Practice: In a diagram of three water molecules, where are the hydrogen bonds located?

Between the partially negative oxygen of one molecule and the partially positive hydrogen of another.

Science Practice: 2.A - Visual Representations

Why It Matters: These diagrams appear in MCQs and lab FRQs. You must identify molecular interactions quickly.

Skill/Scenario Practice: A structural diagram shows a fatty acid with kinks. What type of fat is it?

An unsaturated fat; the kinks are caused by double bonds in the hydrocarbon chains. Recall that fats are lipids!

Science Practice: 2.A - Visual Representations

Why It Matters: You’ll need to distinguish saturated vs. unsaturated fats visually and understand how this affects fluidity.

Skill/Scenario Practice: A macromolecule contains nitrogenous bases, phosphate groups, and a sugar. What is it?

A nucleic acid (either DNA or RNA) as only nucleic acids contain CHONP.

Science Practice: 1.A – Concept Identification

Why It Matters: You’re expected to ID macromolecules from structure and function. This shows up in experimental setups and basic MCQs.

Skill/Scenario Practice: A molecule has long hydrocarbon chains, no nitrogen, and is nonpolar. What macromolecule is it?

A lipid.

Science Practice: 1.A – Concept Identification (focusing on Macromolecule Identification - 2020 CED Topics 1.3-1.6, 2025 CED Topics 1.3-1.7)

Why It Matters: Lipids are structurally unique; you’ll be asked to recognize them and understand their hydrophobic behavior

Skill/Scenario Practice: In an experiment, a student finds that water rises up a thin capillary tube. Which property of water explains this?

Adhesion and cohesion via hydrogen bonding.

Science Practice: 4.B – Data Interpretation

Why It Matters: You must interpret phenomena like transpiration using water’s properties.

Skill/Scenario Practice: A graph shows protein denaturation above 60°C. Why?

Heat disrupts hydrogen bonds and other interactions that stabilize protein structure.

Science Practice: 4.B - Data Interpretation

Why It Matters: Experimental data questions often ask you to explain a graph using molecular reasoning.

Skill/Scenario Practice: T/F - Lipids are made of repeating monomers.

FALSE! Lipids are not true polymers as they don’t have repeating monomer units.

Science Practice: 1.A – Concept Identification

Why It Matters: Commonly tested trick question—avoid the trap!

Skill/Scenario Practice: T/F - Proteins are made of nucleotides.

FALSE! Proteins are made of amino acids; nucleotides are monomers of nucleic acids (DNA/RNA).

Science Practice: 1.A – Concept Identification

Why It Matters: This misconception appears often in MCQs

Skill/Scenario Practice: T/F - A phospholipid is entirely hydrophobic.

FALSE! It has a hydrophilic phosphate head and hydrophobic fatty acid tails.

Science Practice: 1.C - Concept Explanation

Why It Matters: Amphipathic nature of phospholipids is crucial for understanding the cell membrane. *Connects to Unit #2.

Skill/Scenario Practice: If an enzyme's active site becomes nonpolar instead of polar, how will substrate binding be affected?

Polar substrates will not bind well, reducing enzyme activity. Due to the change in structure of the enzyme, there will be a change in function of the enzyme. Thus, polar substrates will not be able to bind well to the enzyme as it has a nonpolar active site, meaning only nonpolar substrates will be able to bind well to the active site.

Science Practice: 6.E - Argumentation & Prediction & 1.C - Concept Explanation

*This connects to Unit #3, when we're discussing Enzymes and Changes in Enzyme Structure & Function.

Why It Matters: This bridges Unit 1 & 3. AP loves testing structure-function through real molecular examples.

Skill/Scenario Practice: Differentiate between a protein and a proton.

A protein is a large, complex molecule made up of amino acids that perform various functions in many organisms, while a proton is a subatomic particle with a positive charge found in the nucleus of an atom.

Protein = Biological Macromolecule that plays crucial functions such as catalyzing reactions (enzymes!), providing structural support, and defense.

Proton = Subatomic particle with a positive charge found in an atom’s nucleus.

Science Practice: 1.A - Concept Explanation

Why It Matters: Popular misconception previous students have made during the AP Biology EXAM.