General Biology Exam 1 Study Guide: Key Concepts and Molecular Foundations

Themes in the Study of Life

Overview of Biological Organization and Evolution

Biology is the study of living organisms and their interactions with the environment. Understanding the major themes helps students grasp the complexity and unity of life.

• Prokaryotes vs. Eukaryotes: Prokaryotes are unicellular organisms lacking a nucleus (e.g., Bacteria), while eukaryotes have a nucleus and membrane-bound organelles (e.g., Plants, Animals).

• Order of Organization: Biological systems are organized from molecules to biosphere: molecule → organelle → cell → tissue → organ → organism → population → community → ecosystem → biosphere.

• Evolution and Natural Selection: Evolution is the process by which species change over time. Natural selection is a mechanism where organisms better adapted to their environment tend to survive and reproduce.

• Unity and Diversity: All living things share common molecular structures (e.g., DNA), but exhibit vast diversity due to evolutionary processes.

• Steps in the Scientific Method: Observation → Question → Hypothesis → Experiment → Analysis → Conclusion.

The Chemical Context of Life

Elements, Atoms, and Chemical Bonds

Life is composed of chemical elements, and their interactions form the basis of biological molecules.

• Essential Elements: Four elements make up about 96% of living matter: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N).

• Atomic Structure: Atoms consist of protons (positive charge), neutrons (neutral), and electrons (negative charge). Atomic number = number of protons; atomic mass = protons + neutrons.

• Covalent Bonds: Atoms share electrons to form molecules. Example: $H_2O$ (water) is formed by covalent bonds between hydrogen and oxygen.

• Ionic Bonds: Atoms transfer electrons, resulting in charged ions that attract each other. Example: $Na^+$ and $Cl^-$ form $NaCl$ (table salt).

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (often oxygen or nitrogen). Important in water and DNA structure.

Water and the Fitness of the Environment

Properties of Water and Their Biological Importance

Water's unique properties make it essential for life, influencing biological processes and environmental conditions.

• Polarity: Water is a polar molecule, with partial positive and negative charges, allowing it to form hydrogen bonds.

• Cohesion and Adhesion: Cohesion is the attraction between water molecules; adhesion is the attraction between water and other substances. These properties enable capillary action in plants.

• Surface Tension: Water's surface tension allows small objects to float and supports certain organisms.

• pH: pH measures the concentration of hydrogen ions ($[H^+]$) in a solution. Formula: $pH = -\log_{10}[H^+]$

• Buffering: Buffers help maintain stable pH in biological systems by absorbing excess H+ or OH-.

Carbon and the Molecular Diversity of Life

Carbon's Role and Functional Groups

Carbon is the backbone of organic molecules, enabling the diversity of life through its bonding properties.

• Carbon Dioxide and Acidification: CO2 dissolves in water, forming carbonic acid and lowering pH, affecting aquatic life.

• Isomerism: Isomers are molecules with the same formula but different structures. Types include enantiomers (mirror images), cis-trans isomers (differ in spatial arrangement), and structural isomers (differ in connectivity).

• Functional Groups: Groups of atoms that confer specific properties to molecules. Examples:

  • Carboxyl group (-COOH): acidic

  • Carbonyl group (C=O): found in sugars

• Monomers and Polymers: Monomers are building blocks (e.g., glucose), and polymers are chains of monomers (e.g., starch).

The Structure and Function of Large Biological Molecules

Major Classes of Biological Macromolecules

Biological macromolecules are essential for structure, function, and regulation of the body's tissues and organs.

• Carbohydrates: Provide energy and structural support. Monomer: monosaccharide (e.g., glucose).

• Proteins: Perform a wide range of functions, including catalysis (enzymes), transport, and structural support. Monomer: amino acid.

• Lipids: Store energy, form cell membranes, and act as signaling molecules. Not true polymers; include fats, phospholipids, and steroids.

• Nucleic Acids: Store and transmit genetic information. Monomer: nucleotide. Examples: DNA and RNA.

Comparison of Biological Macromolecules

The following table summarizes the monomers and functions of the four major classes of biological macromolecules.

Macromolecule	Monomer	Main Function
Carbohydrates	Monosaccharide	Energy storage, structural support
Proteins	Amino acid	Catalysis, transport, structure
Lipids	Fatty acid (not true polymer)	Energy storage, membrane structure, signaling
Nucleic Acids	Nucleotide	Genetic information storage and transfer

Additional info: Academic context and definitions have been expanded for clarity and completeness.