AP BIO UNIT ONE TEST

1.1 Structure of Water & Hydrogen Bonding — AP Bio Notes

Water Structure

• Water (H₂O) has 2 hydrogen atoms + 1 oxygen atom.

• Oxygen is more electronegative than hydrogen, so it pulls electrons closer.

• This creates polarity:

  • Oxygen = slightly negative (δ−)

  • Hydrogen = slightly positive (δ+)

• The bonds inside a water molecule are polar covalent bonds.

Hydrogen Bonds

• A hydrogen bond forms between the slightly positive H of one water molecule and the slightly negative O of another.

• Hydrogen bonds are weaker than covalent bonds but are extremely important because many occur together.

Properties of Water

1. Cohesion

• Water molecules stick to other water molecules.

• Caused by hydrogen bonding.

• Example: Water droplets sticking together.

2. Adhesion

• Water sticks to other substances.

• Example: Water sticking to the walls of a plant's xylem.

3. Surface Tension

• Water's surface resists being broken because water molecules strongly attract each other.

• Allows some organisms, like the basilisk lizard, to move across water.

4. Capillary Action

• Movement of water through a narrow space due to cohesion + adhesion.

• Important for moving water upward through plants.

5. High Specific Heat Capacity

• Water requires a lot of energy to change its temperature.

• Helps organisms maintain a stable body temperature.

• Helps aquatic environments resist rapid temperature changes.

6. High Heat of Vaporization

• A lot of energy is needed to turn liquid water into gas.

• When water evaporates, it takes heat with it.

• This produces evaporative cooling, such as sweating.

7. High Solvency

• Because water is polar, it can dissolve many ionic and polar substances.

• This makes water an excellent solvent for biological reactions and transport.

8. Density

• Ice is less dense than liquid water, so it floats.

• Floating ice can insulate the liquid water underneath, allowing aquatic life to survive.

Key Terms

AP Bio Cause → Effect

Water's polarity → hydrogen bonding → water's unique properties → supports life

Know these especially well:

Polarity → Hydrogen bonding → Cohesion/adhesion → Capillary action

Hydrogen bonding → High specific heat → Temperature stability

Hydrogen bonding → High heat of vaporization → Evaporative cooling

Polarity → High solvency → Dissolves substances needed for life

Elements of Life

1. Energy in Living Systems

• The Law of Conservation of Energy states that energy cannot be created or destroyed; it can only be transformed.

• Living systems follow the laws of energy.

• Living organisms need a constant input of energy to:

  • Grow

  • Reproduce

  • Maintain organization

• Much of the energy used by living systems is stored in chemical bonds.

2. Matter in Living Systems

Living systems require a constant exchange of matter with their environment.

Atoms and molecules from the environment are needed to build new molecules.

Important elements include:

3. Why Carbon Is So Important

Carbon is the backbone of biological molecules.

• Carbon can bond with other carbon atoms to create carbon skeletons.

• Carbon skeletons can form large and complex molecules.

• Carbon-containing molecules can:

  • Store energy

  • Build cellular structures

  • Form biological macromolecules

The four major biological macromolecules are:

1. Carbohydrates

2. Lipids

3. Proteins

4. Nucleic acids

Key Vocab

• Law of Conservation of Energy — Energy cannot be created or destroyed, only transformed.

• Living systems — Organized systems that require energy and matter to maintain themselves.

• Biological macromolecules — Large molecules essential for life.

• Chemical bonds — Attractions between atoms that can store chemical energy.

• Carbon skeleton — The carbon framework that forms the backbone of many biological molecules.

• Exchange of matter — The movement of atoms and molecules between an organism and its environment.

AP Bio Big Picture

ENERGY + MATTER → LIFE

Living things need energy to maintain organization and perform life processes, and they need matter—especially C, N, and P—to build the molecules and structures required for life.

Quick memory trick:
C = Carbon → macromolecules
N = Nitrogen → proteins + nucleic acids
P = Phosphorus → nucleic acids + some lipids

1.3 — Macromolecules: What to Know

Macromolecules = large biological molecules made from smaller units called monomers.

The four major biological macromolecules:

• Carbohydrates

• Lipids

• Proteins

• Nucleic acids

Dehydration Synthesis

Builds larger molecules.

• Joins monomers

• Forms a covalent bond

• Removes H₂O

• H comes from one monomer

• OH comes from the other

• Repeated joining of monomers = polymerization

Think:
Dehydration = remove water → build

Hydrolysis

Breaks larger molecules apart.

• Adds H₂O

• Breaks a covalent bond

• H goes to one monomer

• OH goes to the other

• Polymer → smaller molecules/monomers

Think:
Hydrolysis = water → break

The AP Bio Connection

The visual question you should be ready for

If you see:

Monomer + Monomer → Polymer + H₂O

That's dehydration synthesis.

If you see:

Polymer + H₂O → Monomer + Monomer

That's hydrolysis.

Most important distinction

Don't just memorize "dehydration = build, hydrolysis = break."

Understand why:

Dehydration synthesis forms a covalent bond by removing the components of water. Hydrolysis breaks a covalent bond by adding water.

1.4 Carbohydrates — Notes

Carbohydrates

• Biological molecules made mainly of carbon, hydrogen, and oxygen

• Used for energy storage and structural support

• Structure determines function

Monosaccharides

• Monomer of carbohydrates

• Also called simple sugars

• Examples: glucose, fructose

• Small molecules that can be linked together

Polysaccharides

• Polymers made of many monosaccharides

• Monomers are connected by covalent bonds

• Can be:

  • Linear → straight chains

  • Branched → chains with branches

Structure → Function

• The arrangement of monosaccharides affects the carbohydrate's shape and function

• Linear vs. branched structure can give carbohydrates different functions

Important Examples

• Starch → energy storage in plants

• Glycogen → energy storage in animals

• Cellulose → structural support in plant cell walls

Key Relationship

Monosaccharide → covalent bonds → polysaccharide

Structure → Function

1.5 Lipids — AP Bio Notes

Key Vocabulary

• Lipid — Nonpolar, hydrophobic molecule.

• Hydrophobic — Repels water; does not dissolve well in water.

• Fatty acid — Hydrocarbon chain with a carboxyl group; found in some lipids.

• Saturated fatty acid — Has only single bonds between carbon atoms.

• Unsaturated fatty acid — Has at least one C=C double bond.

• Triglyceride — Lipid made of glycerol + 3 fatty acids; used mainly for energy storage.

• Phospholipid — Lipid with a phosphate-containing head and fatty acid tails; forms cell membranes.

• Steroid — Lipid with four fused carbon rings; many function as hormones.

• Cholesterol — Steroid that helps maintain stability and fluidity of animal cell membranes.

• Lipid bilayer — Two layers of phospholipids forming the basic structure of cell membranes.

• Kink — Bend in an unsaturated fatty acid caused by a double bond.

• Insulation — Lipid storage that helps reduce heat loss in mammals.

Must-Know Concepts

Saturated vs. unsaturated

• Saturated → no double bonds → straight tails → pack tightly → more solid

• Unsaturated → ≥1 double bond → kinked tails → pack loosely → more liquid

• More double bonds = more unsaturated = more liquid at room temperature

Types & Functions

AP Bio Cause → Effect

If a lipid has more double bonds:

More double bonds → more kinks → weaker packing → greater membrane/lipid fluidity

If phospholipids are placed in water:

Hydrophilic heads face water + hydrophobic tails avoid water → phospholipids spontaneously form a bilayer.

One-Sentence Summary

Lipids are mostly hydrophobic molecules used for energy storage, hormones, insulation, and membranes, with their structure—especially fatty-acid saturation—determining their properties and functions.

1.6 Nucleic Acids

Figure 1. A typical chromatogram of DNA sequence data. Notice the 4 nucleotides, A, C, G, and T.

Video 1

Figure 1. Main objectives of this subunit.

Figure 2. Similarities between DNA and RNA.

Figure 3. Differences between DNA and RNA.

Figure 4. Practice MCQ. Answer below at bottom of page.

Figure 10. Key takeaways.

Video 2

Figure 1. Main objectives of this subunit.

Figure 2. Directionality of the subcomponents influences structure of the amino acid polymers.

Figure 3. Directionality influences the synthesis of nucleic acids.

Figure 4. Practice MCQ. Answer below at bottom of page.

Figure 5. Key takeaways.

Lesson Skill Focus

Describe characteristics of visual representations of biological concepts and processes.

Big Idea:

Information Storage and Transmission: Living systems store, retrieve, transmit, and respond to information essential to life processes.

Learning Objective:

Describe the structure and function of DNA and RNA.

Essential Knowledge:

In nucleic acids (DNA and RNA), biological information is encoded in sequences of nucleotide monomers. Each nucleotide has the following structural components: a five-carbon sugar (deoxyribose or ribose), a phosphate, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil).

Nucleic acids have a linear sequence of nucleotides that have ends, defined by the 3’ (three prime) hydroxyl and 5’ (five prime) phosphates of the sugar in the nucleotide. During nucleic acid synthesis, nucleotides are added to the 3’ end of the growing strand, resulting in the formation of covalent bonds between nucleotides.

DNA is structured as an antiparallel double helix, with two strands of nucleotides running in opposite 5’ to 3’ orientation. In DNA, adenine
nucleotides pair with thymine nucleotides via hydrogen bonds (A-T), and cytosine nucleotides pair with guanine nucleotides via hydrogen bonds (C-G). In RNA, adenine pairs with uracil (A-U).

Structural differences between DNA and RNA include:
i. DNA contains the sugar deoxyribose, and RNA contains the sugar ribose.
ii. DNA contains the nitrogenous base thymine, and RNA contains the nitrogenous base uracil.
iii. DNA is typically double stranded, while RNA is typically single stranded.

Assignment/Homework:

AP Classroom

Links to an external site.

. Answer the 3 Topic Questions.

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Click the Next button at the bottom of the page to go to the next Topic Overview.

 Absolutely — here are clean AP Bio notes for 1.7 Proteins, focused on what you actually need to know.

1.7 Proteins — AP Bio Notes

🧬 Proteins

• Proteins are polymers made of amino acids.

• Amino acids are connected by peptide bonds.

• Protein structure determines function.

Amino Acid Structure

Every amino acid has:

• Central carbon

• Hydrogen (H)

• Amino group (NH₂)

• Carboxyl group (COOH)

• R group → determines the amino acid's properties

R Groups

🔗 Peptide Bonds

• Form between the carboxyl group of one amino acid and the amino group of another.

• This creates a polypeptide chain.

• Formation occurs through dehydration synthesis.

Amino acids → peptide bonds → polypeptide → functional protein

4 Levels of Protein Structure

1. Primary Structure

• Sequence of amino acids

• Held together by peptide bonds

• Determines how the protein will fold.

Think: amino acid order

2. Secondary Structure

Local folding of the polypeptide backbone.

Main shapes:

• Alpha helix (α-helix)

• Beta-pleated sheet (β-sheet)

Held together by hydrogen bonds.

3. Tertiary Structure

• Overall 3D shape of one polypeptide

• Caused by interactions between R groups.

Important interactions:

• Hydrogen bonds

• Hydrophobic interactions

• Ionic interactions

• Disulfide bridges

4. Quaternary Structure

• Occurs when multiple polypeptide chains interact.

• Not every protein has quaternary structure.

⭐ Most Important AP Bio Idea

Amino acid sequence → protein shape → protein function

If the amino acid sequence changes, the protein's shape may change, which can change or destroy its function.

Example:

Mutation → different amino acid → different interactions → altered protein shape → altered function

Key Vocabulary

• Amino acid — monomer of proteins

• R group — variable group that determines amino acid properties

• Peptide bond — covalent bond connecting amino acids

• Polypeptide — chain of amino acids

• Primary structure — amino acid sequence

• Secondary structure — alpha helices and beta sheets

• Tertiary structure — 3D shape of one polypeptide

• Quaternary structure — interaction of multiple polypeptides

• Denaturation — disruption of a protein's shape and function

AP Bio Connection

When a protein's environment changes (such as temperature or pH), the interactions maintaining its shape can be disrupted. This can cause denaturation and loss of function.