Biology 1 Ch. 1-3 College

Scientific Method Steps

Observation → Question → Hypothesis → Prediction → Experiment → Data Collection → Analysis → Conclusion → Theory.

Hypothesis

A testable, falsifiable proposed explanation for a specific observation. Narrow in scope.

Theory

A broad, well-substantiated explanation for a large body of evidence that has withstood extensive testing.

Prediction in Scientific Method

A specific, testable statement about what will happen if the hypothesis is correct.

Independent Variable

The factor the researcher manipulates or changes in an experiment.

Dependent Variable

The factor that is measured or observed; responds to the independent variable.

Control Group

A group that does not receive the experimental treatment; used as a baseline for comparison.

Experimental Group

The group that receives the treatment or condition being tested.

Controlled Variables (Constants)

All other factors kept identical between groups so only the independent variable affects the dependent variable.

Data

Quantitative or qualitative information collected during an experiment.

Atom

The smallest unit of matter that retains the properties of an element.

Proton

Positively charged particle in the nucleus. Number of protons = atomic number.

Neutron

Neutral particle in the nucleus. Number can vary among atoms of the same element.

Electron

Negatively charged particle that orbits the nucleus in energy levels.

Atomic Number (Z)

The number of protons in an atom; defines the element.

Mass Number (A)

The sum of protons and neutrons in an atom's nucleus.

Isotope

Atoms of the same element with different numbers of neutrons.

Electronegativity

The tendency of an atom to attract shared electrons in a chemical bond.

Significance of Electronegativity

Determines bond type and polarity.

Nonpolar Covalent Bond

Electrons shared equally; electronegativity difference < 0.5.

Polar Covalent Bond

Electrons shared unequally, creating partial charges (δ⁺, δ⁻); electronegativity difference 0.5–1.7.

Ionic Bond

Complete transfer of electrons from one atom to another; electronegativity difference > 1.7.

Hydrogen Bond

Weak attraction between a hydrogen atom covalently bonded to O or N and another electronegative atom.

Why Water is Polar

Oxygen is more electronegative than hydrogen, creating partial negative charge on O and partial positive on H.

Four Properties of Water

Cohesion/adhesion, moderation of temperature (high specific heat), expansion upon freezing, solvent of life.

Cohesion

Attraction between water molecules (water–water) due to hydrogen bonding.

Adhesion

Attraction between water molecules and other polar surfaces.

Surface Tension

Result of cohesion; allows insects to walk on water.

Capillary Action

Combined effect of cohesion and adhesion; moves water upward against gravity.

High Specific Heat of Water

Stabilizes temperatures in organisms and environments; helps maintain homeostasis.

Why Ice Floats

Ice is less dense than liquid water due to hydrogen bonds forming a crystalline lattice.

Expansion Upon Freezing Importance

Ice insulates water below; frozen water can crack pipes/rocks.

Water as 'Solvent of Life'

Its polarity allows it to dissolve many ionic and polar substances.

Hydration Shell

Sphere of water molecules surrounding an ion in solution; δ⁺ H faces anions; δ⁻ O faces cations.

Hydrophilic

'Water-loving'; substances that dissolve in water (polar molecules, ions).

Hydrophobic

'Water-fearing'; substances that do not dissolve in water (nonpolar molecules).

Acid

A substance that increases H⁺ concentration in solution; proton donor.

Base

A substance that decreases H⁺ concentration; proton acceptor.

pH Scale

Logarithmic scale (0–14) measuring H⁺ concentration.

Formula for pH

pH = −log[H⁺].

Acidic pH Range

pH < 7.

Basic/Alkaline pH Range

pH > 7.

Neutral pH

pH = 7 (pure water at 25°C).

Buffer

A solution that resists changes in pH when small amounts of acid or base are added.

How Buffers Work

They accept or donate H⁺ ions; usually a weak acid and its conjugate base.

Dehydration Synthesis

Reaction that joins two molecules by removing a water molecule; used to build polymers.

Hydrolysis

Reaction that breaks a covalent bond by adding a water molecule; breaks polymers into monomers.

Isomers

Molecules with the same molecular formula but different structural arrangements.

Structural Isomers

Differ in covalent arrangement of atoms.

Geometric Isomers

Differ in spatial arrangement around a double bond.

Enantiomers

Mirror-image isomers differing around an asymmetric carbon.

Hydroxyl Group

—OH; polar, forms hydrogen bonds; found in alcohols, sugars.

Carbonyl Group

—C=O; aldehyde or ketone; found in sugars.

Carboxyl Group

—COOH; acidic (donates H⁺); found in amino acids, fatty acids.

Amino Group

—NH₂; basic (accepts H⁺); found in amino acids, proteins.

Sulfhydryl Group

—SH; forms disulfide bonds; found in proteins.

Phosphate Group

—PO₄³⁻; negatively charged, energy transfer; found in ATP, DNA, RNA.

Methyl Group

—CH₃; nonpolar, hydrophobic; found in lipids, DNA.

General Structure of Carbohydrates

Composed of C, H, O in ~1:2:1 ratio (CH₂O)ₙ.

Monosaccharide

Simple sugar with 3–7 carbons; monomer of carbohydrates; examples: glucose, fructose.

Disaccharide

Two monosaccharides joined by a glycosidic linkage; examples: sucrose, lactose, maltose.

Glycosidic Linkage

Covalent bond formed by dehydration synthesis between two monosaccharides.

Polysaccharide

Long chain of monosaccharides; examples: starch, glycogen, cellulose, chitin.

Starch

Storage polysaccharide in plants.

Glycogen

Storage polysaccharide in animals; highly branched.

Cellulose

Structural polysaccharide in plant cell walls; humans cannot digest it.

Chitin

Structural polysaccharide in fungi and arthropod exoskeletons.

Difference between Starch and Cellulose

Starch has α-1,4 linkages; cellulose has β-1,4 linkages.

Lipids

Hydrophobic, nonpolar, composed mainly of C and H; not polymers.

Three Main Classes of Lipids

Fats (triglycerides), phospholipids, steroids.

Structure of a Fat (Triglyceride)

One glycerol + three fatty acid chains; formed by dehydration synthesis.

Saturated Fatty Acid

No double bonds between carbons; solid at room temp; examples: butter, lard.

Unsaturated Fatty Acid

One or more double bonds; liquid at room temp; examples: olive oil, fish oil.

Phospholipid

Glycerol + phosphate group + two fatty acid chains; amphipathic.

Amphipathic

Having both hydrophilic and hydrophobic regions.

Importance of Phospholipids

They form the bilayer of cell membranes.

Steroids

Four fused carbon rings; examples: cholesterol, testosterone, estrogen.

Cholesterol

Cell membrane component and precursor to other steroids.

Unsaturated Fats at Room Temperature

Kinks prevent tight packing. Liquid at room temperature

Saturated Fats at Room Temperature

Straight chains pack tightly together. solid at room temperature

Functions of Proteins

Enzymatic catalysis, structural support, transport, signaling, defense, movement, storage.

Amino Acid

Central carbon bonded to amino group (—NH₂), carboxyl group (—COOH), hydrogen (—H), and R group.

R Group

Variable side chain; determines amino acid properties.

Peptide Bond

Covalent bond linking amino acids; formed by dehydration synthesis.

Polypeptide

Chain of amino acids linked by peptide bonds.

Primary Structure of Protein

Linear sequence of amino acids; determined by DNA.

Secondary Structure of Protein

Local folding patterns stabilized by hydrogen bonds; examples: α-helix, β-pleated sheet.

α-Helix

Coiled secondary structure; example: keratin.

β-Pleated Sheet

Folded sheet secondary structure; example: silk fibroin.

Tertiary Structure of Protein

Overall 3D shape of a single polypeptide; stabilized by R group interactions.

Quaternary Structure of Protein

Arrangement of multiple polypeptide chains into a functional protein; example: hemoglobin.

Forces Stabilizing Tertiary Structure

Hydrophobic interactions, hydrogen bonds, ionic bonds, disulfide bridges.

Denaturation

Loss of native protein shape due to disruption of weak interactions; usually nonfunctional.

Determines Protein Structure

Primary structure ultimately determines shape; environment influences folding.

Disease Caused by Amino Acid Change

Sickle cell anemia (glutamic acid → valine in hemoglobin).

Nucleotide

Nitrogenous base + pentose sugar + phosphate group.

Nitrogenous Bases

Adenine (A), Guanine (G), Cytosine (C), Thymine (T), Uracil (U).

Sugar in DNA

Deoxyribose.

Sugar in RNA

Ribose.

DNA

Double helix, antiparallel strands, deoxyribose, bases A, T, G, C.