General Biology Exam 1 Review: Core Concepts and Study Guide

Characteristics of Life

Defining Features of Living Organisms

All living things share a set of fundamental characteristics that distinguish them from non-living matter. Understanding these features is essential for studying biology.

• Cellular Organization: All life is composed of one or more cells, which are the basic units of structure and function.

• Complexity: Living organisms exhibit hierarchical, ordered complexity, with molecules forming cells, tissues, organs, and systems.

• Response to Stimuli: Organisms can detect and respond to environmental changes.

• Growth, Development, and Reproduction: Governed by hereditary information, organisms grow, develop, and reproduce to ensure survival of the species.

• Energy Utilization: Organisms take in and use energy to perform work and maintain order.

• Homeostasis: The maintenance of stable internal conditions despite external fluctuations.

• Evolutionary Adaptation: Populations evolve over generations through changes in genetic composition, allowing adaptation to the environment.

The Scientific Method

Hypotheses, Inductive and Deductive Reasoning

The scientific method is a systematic approach to understanding natural phenomena through observation, hypothesis formation, experimentation, and analysis.

• Hypothesis: A tentative explanation for a specific phenomenon, which can be tested by further investigation.

• Theory: A broader explanation supported by a large body of evidence.

• Inductive Reasoning: Uses specific observations to construct general principles.

• Deductive Reasoning: Applies general principles to predict specific results.

• Reductionism: Understanding complex systems by reducing them to their simpler components.

Experimental Design

Experiments are designed to test hypotheses by manipulating variables and observing outcomes.

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

• Dependent Variable: The factor that is measured or observed.

• Control: Keeping all variables except the independent variable constant to ensure valid results.

• Falsification: The process of disproving a hypothesis through experimental evidence.

Example: Testing the effect of light on plant growth by varying light exposure (independent variable) and measuring plant height (dependent variable), while keeping soil and water constant (controls).

Atoms, Isotopes, and Chemical Bonds

Atomic Structure and Isotopes

Atoms are the fundamental units of matter, composed of protons, neutrons, and electrons.

• Isotopes: Atoms of the same element with different numbers of neutrons. Some isotopes are unstable and undergo radioactive decay.

• Radiometric Dating: Uses the decay of radioactive isotopes to estimate the age of materials. The rate of decay is expressed as the half-life.

Equation:

$N = N_0 \times (1/2)^{t/t_{1/2}}$

Where $N$ is the remaining quantity, $N_0$ is the initial quantity, $t$ is time, and $t_{1/2}$ is the half-life.

Chemical Bonds

Chemical bonds are forces that hold atoms together in molecules and compounds.

• Covalent Bond: Sharing of electron pairs between atoms.

• Ionic Bond: Attraction between oppositely charged ions.

• Hydrogen Bond: Weak attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom.

• Van der Waals Interactions: Weak attractions due to transient polarization of electron clouds.

Electronegativity: The tendency of an atom to attract electrons in a bond. Higher electronegativity means stronger pull on shared electrons.

Water and Its Properties

Emergent Properties of Water

Water's unique properties are essential for life and result from its molecular structure and hydrogen bonding.

• Cohesion: Water molecules stick together due to hydrogen bonding, resulting in high surface tension.

• Adhesion: Attraction between water molecules and other substances, aiding processes like capillary action in plants.

• Temperature Moderation: Water absorbs and releases heat slowly, stabilizing temperatures in organisms and environments. High specific heat and high heat of vaporization are key features.

• Expansion Upon Freezing: Ice is less dense than liquid water, allowing it to float and insulate aquatic life.

• Versatility as a Solvent: Water dissolves many substances due to its polarity, forming hydration shells around ions and molecules.

Example: Water's high specific heat helps maintain stable body temperatures in organisms.

Acids, Bases, and pH

The pH scale measures the concentration of hydrogen ions ($[H^+]$) in a solution.

• Acid: Substance that increases $[H^+]$ in solution.

• Base: Substance that decreases $[H^+]$ (often by increasing $[OH^-]$).

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.

• Buffers: Substances that minimize changes in pH by accepting or donating $H^+$ ions.

Equation:

$\text{pH} = -\log_{10}[H^+]$

Carbon and Molecular Diversity

Carbon's Bonding and Isomerism

Carbon's ability to form four covalent bonds leads to a diversity of organic molecules.

• Isomers: Compounds with the same molecular formula but different structures and properties.

• Types of Isomers:

  • Structural Isomers: Differ in covalent arrangement of atoms.

  • Cis-Trans (Geometric) Isomers: Differ in spatial arrangement around double bonds.

  • Enantiomers: Mirror images of each other, important in biological systems.

• Functional Groups: Specific groups of atoms that confer characteristic chemical properties to molecules (e.g., hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, methyl).

Macromolecules

Polymers and Monomers

Most biological macromolecules are polymers, long chains of repeating subunits (monomers) joined by covalent bonds.

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

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

Carbohydrates serve as fuel and building material. They include sugars and their polymers.

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

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

• Polysaccharides: Long chains of monosaccharides; storage (starch in plants, glycogen in animals) or structural (cellulose in plants, chitin in fungi and arthropods).

Lipids

Lipids are hydrophobic molecules, not true polymers, and include fats, phospholipids, and steroids.

• Fats (Triglycerides): Composed of glycerol and three fatty acids, used for energy storage, insulation, and cushioning.

• Saturated Fatty Acids: No double bonds, solid at room temperature.

• Unsaturated Fatty Acids: One or more double bonds, liquid at room temperature.

• Phospholipids: Amphipathic molecules forming the basis of cell membranes.

• Steroids: Four fused carbon rings; cholesterol is a key example in animal cell membranes.

Proteins

Proteins are polymers of amino acids, performing a vast array of functions in cells.

• Amino Acids: 20 different types, each with a central carbon, amino group, carboxyl group, hydrogen, and R group (side chain).

• Peptide Bond: Covalent bond linking amino acids.

• Levels of Protein Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Local folding (α-helix, β-sheet) via hydrogen bonds.

  • Tertiary: Overall 3D shape due to interactions among R groups.

  • Quaternary: Association of multiple polypeptide chains.

• Denaturation: Loss of protein structure and function due to environmental changes (pH, temperature, etc.).

Nucleic Acids

Nucleic acids (DNA and RNA) store and transmit genetic information.

• Nucleotides: Monomers consisting of a nitrogenous base, a pentose sugar, and one or more phosphate groups.

• DNA: Double-stranded, contains deoxyribose, bases A, T, C, G.

• RNA: Single-stranded, contains ribose, bases A, U, C, G.

• Phosphodiester Bond: Links nucleotides in a nucleic acid chain.

Table: Comparison of Macromolecules

Macromolecule	Monomer	Bond Type	Main Functions	Example
Carbohydrate	Monosaccharide	Glycosidic linkage	Energy storage, structure	Starch, cellulose
Lipid	Fatty acid, glycerol	Ester bond	Energy storage, membranes	Triglyceride, phospholipid
Protein	Amino acid	Peptide bond	Catalysis, structure, transport	Enzyme, hemoglobin
Nucleic Acid	Nucleotide	Phosphodiester bond	Genetic information	DNA, RNA

Additional info:

• Some content was inferred and expanded for clarity and completeness, such as the full definitions of isomer types and the table comparing macromolecules.

• Equations and chemical principles were added to support understanding of radiometric dating and pH.