General Biology Study Guide: Chapters 1–4 (Foundations, Chemistry, Biomolecules, and Cells)

Chapter 1: Introduction – Evolution and the Foundations of Biology

Key Concepts in Biology

This chapter introduces the foundational principles of biology, focusing on evolution, the scientific method, and the basic elements of life.

• Evolution: The process by which different kinds of living organisms develop and diversify from earlier forms. Central to understanding all biological phenomena.

• Natural Selection: Mechanism of evolution where organisms better adapted to their environment tend to survive and produce more offspring.

• Descent with Modification: The passing on of traits from parent organisms to their offspring, with changes accumulating over generations.

• Elements in the Human Body: The majority of the human body's mass is made up of four elements: oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).

The Scientific Method

• Steps: Observation, Hypothesis, Experiment, Data Collection, Conclusion.

• Experimental Variables:

  • Independent Variable: The factor that is changed or controlled in a scientific experiment.

  • Dependent Variable: The factor being tested and measured.

  • Controls: Constants in the experiment to ensure validity.

Energy Transfer and Transformation in Ecosystems

• Energy flows through ecosystems, typically entering as sunlight and exiting as heat.

• Organisms transform energy from one form to another (e.g., photosynthesis, cellular respiration).

Chapter 2: The Chemical Context of Life

Atoms and Subatomic Particles

Understanding the structure of atoms is essential for grasping chemical interactions in biology.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

• Atomic Number: Number of protons in an atom ($Z$).

• Mass Number: Sum of protons and neutrons ($A = Z + N$).

• Isotopes: Atoms of the same element with different numbers of neutrons.

Electron Energy Levels and Chemical Properties

• Electrons occupy energy levels (shells) around the nucleus.

• Valence Electrons: Electrons in the outermost shell, determine chemical reactivity.

Chemical Bonds

• Covalent Bonds: Sharing of electron pairs between atoms.

  • Single Bond: One pair of shared electrons.

  • Double Bond: Two pairs of shared electrons.

  • Nonpolar Covalent Bond: Electrons shared equally.

  • Polar Covalent Bond: Electrons shared unequally, leading to partial charges.

• Ionic Bonds: Transfer of electrons from one atom to another, creating ions.

  • Cation: Positively charged ion.

  • Anion: Negatively charged ion.

Electronegativity and Bond Strength

• Electronegativity: The tendency of an atom to attract electrons in a bond. Increases across a period and decreases down a group in the periodic table.

• Covalent bonds are generally stronger than ionic bonds in biological systems.

Chemical Reactions

• Reactants: Starting substances in a reaction.

• Products: Substances formed by the reaction.

• Chemical Equilibrium: The point at which the rate of the forward reaction equals the rate of the reverse reaction.

Properties of Water

• Four Emergent Properties:

  1. Cohesion (water molecules stick together)

  2. Ability to moderate temperature

  3. Expansion upon freezing

  4. Versatility as a solvent

• Solvent vs. Solute: Solvent dissolves the solute; in biology, water is the universal solvent.

• Acids and Bases: Acids increase H+ concentration; bases decrease it.

• Buffers: Substances that minimize changes in pH.

Chapter 3: Carbon and the Molecular Diversity of Life

Carbon and Molecular Structure

Carbon's ability to form four covalent bonds makes it the backbone of biological molecules.

• Formation of Bonds: Carbon forms single, double, or triple bonds, leading to diverse molecular shapes.

• Geometric Isomers (Cis-Trans Isomers): Molecules with the same covalent arrangements but different spatial arrangements.

• Enantiomers: Isomers that are mirror images of each other.

Dehydration and Hydrolysis Reactions

• Dehydration Reaction: Joins monomers by removing a water molecule.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides joined by a glycosidic linkage (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides.

  • Starch: Storage in plants.

  • Glycogen: Storage in animals.

  • Cellulose: Structural in plant cell walls.

  • Chitin: Structural in fungi and arthropods.

Lipids

• Hydrophobic vs. Hydrophilic: Lipids are hydrophobic (water-fearing), while other molecules may be hydrophilic (water-loving).

• Saturated vs. Unsaturated Fatty Acids: Saturated have no double bonds; unsaturated have one or more double bonds.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

Proteins

• Amino Acids: Building blocks of proteins, linked by peptide bonds.

• Functional Groups: Specific groups of atoms within molecules that have characteristic properties.

• Polypeptides: Chains of amino acids.

• Protein Structure:

  1. Primary: Sequence of amino acids.

  2. Secondary: Alpha helices and beta sheets (hydrogen bonding).

  3. Tertiary: 3D folding due to side chain interactions.

  4. Quaternary: Association of multiple polypeptides.

• Hydrophobic vs. Hydrophilic Monomers: Amino acids can be classified based on the properties of their side chains.

• What Determines Protein Structure? Sequence of amino acids, chemical environment, and interactions among side chains.

Nucleic Acids

• Nucleotides: Monomers of nucleic acids (DNA and RNA).

• DNA vs. RNA: DNA contains deoxyribose sugar; RNA contains ribose sugar.

• Pyrimidines vs. Purines: Pyrimidines (cytosine, thymine, uracil) have a single ring; purines (adenine, guanine) have a double ring.

Chapter 4: A Tour of the Cell

Prokaryotic vs. Eukaryotic Cells

This chapter explores the structure and function of cells, the basic unit of life.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria, archaea).

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles (e.g., plants, animals, fungi, protists).

• Be able to label a cell diagram.

Organelles in Eukaryotic Cells

• Nucleus: Contains genetic material (DNA).

• Nuclear Envelope: Double membrane surrounding the nucleus.

• Endoplasmic Reticulum (ER):

  • Rough ER: Studded with ribosomes; synthesizes proteins.

  • Smooth ER: Lacks ribosomes; synthesizes lipids and detoxifies.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for breaking down waste.

• Phagocytosis: Process by which cells engulf large particles.

• Vacuoles: Storage organelles;

  • Contractile Vacuoles: Pump excess water out of cells (in protists).

  • Central Vacuole: Large storage organelle in plant cells.

• Plasma Membrane: Selectively permeable barrier of the cell.

• Mitochondria: Site of cellular respiration and energy (ATP) production.

• Endosymbiont Theory: Proposes that mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic cells.

Cytoskeleton

• Properties: Provides structural support, cell shape, and movement.

• Three Main Types of Fibers:

  1. Microtubules: Hollow tubes; maintain cell shape, chromosome movement, organelle movement.

  2. Microfilaments: Thin rods; involved in muscle contraction, cell movement.

  3. Intermediate Filaments: Provide mechanical support for the cell.

Word Bank Table

The following table summarizes key terms and their definitions for Chapters 1–4:

Term	Definition
Hypothesis	A testable explanation for an observation or scientific problem.
Inductive Reasoning	Drawing general conclusions from specific observations.
Deductive Reasoning	Making specific predictions based on general principles or theories.
Controlled Experiment	An experiment in which only one variable is changed at a time.
Valence Electron	Electron in the outermost shell of an atom, involved in forming bonds.
Cation	Positively charged ion.
Anion	Negatively charged ion.
Cohesion	Attraction between molecules of the same substance (e.g., water molecules).
Adhesion	Attraction between molecules of different substances.
Hydrophobic	Repelled by water; nonpolar substances.
Hydrophilic	Attracted to water; polar substances.
Acids	Substances that increase the concentration of H+ ions in solution.
Bases	Substances that decrease the concentration of H+ ions in solution.
Buffers	Substances that minimize changes in pH.
Carbohydrates	Organic molecules consisting of carbon, hydrogen, and oxygen; include sugars and starches.
Lipids	Hydrophobic organic molecules, including fats, oils, and phospholipids.
Nucleic Acid	Polymers of nucleotides; DNA and RNA.
Isomers	Molecules with the same molecular formula but different structures.
Cis-trans Isomers	Isomers with different spatial arrangements around a double bond.
Monomers	Small molecules that can join to form polymers.
Polymers	Large molecules made up of repeating monomer units.
Pyrimidine	Single-ring nitrogenous base (cytosine, thymine, uracil).
Purine	Double-ring nitrogenous base (adenine, guanine).
Eukaryotic Cell	Cell with a nucleus and membrane-bound organelles.
Prokaryotic Cell	Cell lacking a nucleus and membrane-bound organelles.
Plasma Membrane	Phospholipid bilayer that surrounds the cell.
Nucleus	Organelle containing DNA in eukaryotic cells.
Ribosomes	Structures that synthesize proteins.
Endoplasmic Reticulum	Network of membranes involved in protein and lipid synthesis.
Golgi Apparatus	Organelle that modifies and packages proteins and lipids.
Lysosome	Organelle containing digestive enzymes.
Mitochondria	Organelle that produces ATP through cellular respiration.
Endosymbiont Theory	Theory that mitochondria and chloroplasts originated from free-living prokaryotes.