General Biology: Core Concepts and Practice Questions

Core Concepts in General Biology

Characteristics of Life

All living organisms share certain fundamental characteristics that distinguish them from non-living matter.

• Cellular Organization: All organisms are composed of one or more cells, which are the basic units of life.

• Genetic Information: Organisms possess genetic material (DNA or RNA) that guides growth, development, and reproduction.

• Metabolism: Living things carry out chemical reactions to obtain and use energy.

• Evolution: Populations of organisms can evolve over generations through changes in genetic composition.

• Response to Environment: Organisms can sense and respond to environmental stimuli.

• Reproduction: Organisms reproduce to pass on genetic information to offspring.

Example: Bacteria, plants, and animals all exhibit these characteristics, though they may differ in complexity.

Atoms and Elements in Biology

Atoms are the fundamental units of matter, and elements are substances made of only one type of atom. The properties of atoms and elements are central to understanding biological molecules and processes.

• Atomic Structure: Atoms consist of protons, neutrons, and electrons. The number of protons (atomic number) defines the element.

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

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

• Periodic Table: Elements are organized by atomic number; group number often indicates the number of valence electrons.

Example: Oxygen has an atomic number of 8, so it has 8 protons and, in a neutral atom, 8 electrons.

Chemical Bonds and Molecules

Atoms combine to form molecules through chemical bonds, which are essential for the structure and function of biological macromolecules.

• Covalent Bonds: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bonds: Electrons are transferred from one atom to another, creating charged ions.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

• Double Bonds: Carbon can form up to two double bonds (e.g., in CO2).

Example: Water (H2O) is a polar molecule due to unequal sharing of electrons between hydrogen and oxygen.

Properties of Water

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

• Cohesion: Water molecules stick together due to hydrogen bonding.

• Adhesion: Water molecules stick to other substances.

• High Specific Heat: Water can absorb or release large amounts of heat with little temperature change.

• Density: Liquid water is denser than ice, allowing ice to float.

• Solvent Properties: Water dissolves many substances, making it a universal solvent.

Example: Water's high specific heat helps regulate temperature in organisms and environments.

Acids, Bases, and pH

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or basicity.

• Acid: Substance that increases H+ concentration; pH < 7.

• Base: Substance that decreases H+ concentration; pH > 7.

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

Example: A solution with [H+] = 1 × 10-7 M has a pH of 7 (neutral).

Macromolecules: Structure and Function

Biological macromolecules include carbohydrates, lipids, proteins, and nucleic acids, each with distinct structures and functions.

• Carbohydrates: Energy storage (e.g., starch, glycogen) and structural support (e.g., cellulose, chitin).

• Lipids: Energy storage, membrane structure (phospholipids), and signaling (steroids).

• Proteins: Enzymes, structural components, transport, signaling, and immune response.

• Nucleic Acids: Store and transmit genetic information (DNA, RNA).

Example: Glycogen is an energy storage polysaccharide in animals; cellulose provides structural support in plants.

Protein Structure and Function

Proteins have complex structures that determine their function. Structure is organized into four levels:

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding into α-helices and β-sheets, stabilized by hydrogen bonds.

• Tertiary Structure: Overall 3D shape, stabilized by various interactions (hydrogen bonds, ionic bonds, disulfide bridges, hydrophobic interactions).

• Quaternary Structure: Association of multiple polypeptide chains.

Example: Hemoglobin has quaternary structure, consisting of four polypeptide subunits.

Enzymes and Metabolism

Enzymes are biological catalysts that speed up chemical reactions by lowering activation energy. Metabolism includes all chemical reactions in a cell.

• Anabolic Pathways: Build complex molecules from simpler ones; require energy.

• Catabolic Pathways: Break down complex molecules into simpler ones; release energy.

• Enzyme Inhibition: Can be competitive (inhibitor binds active site) or non-competitive (inhibitor binds elsewhere).

• Feedback Inhibition: End product of a pathway inhibits an earlier step to regulate pathway activity.

Example: ATP synthase is an enzyme that synthesizes ATP during cellular respiration.

Thermodynamics in Biology

Biological systems obey the laws of thermodynamics, which govern energy transformations.

• First Law: Energy cannot be created or destroyed, only transformed.

• Second Law: Every energy transfer increases the entropy (disorder) of the universe.

• Exergonic Reactions: Release energy (e.g., cellular respiration).

• Endergonic Reactions: Require energy input (e.g., photosynthesis).

Example: The process of photosynthesis is endergonic, requiring energy input from sunlight.

Cellular Respiration and Photosynthesis

Cells obtain energy through cellular respiration and photosynthesis.

• Cellular Respiration: Converts glucose and oxygen into ATP, CO2, and water.

• Photosynthesis: Converts CO2 and water into glucose and oxygen using sunlight.

• ATP: The main energy currency of the cell.

Example: Mitochondria are the site of cellular respiration; chloroplasts are the site of photosynthesis in plants.

Practice Table: Comparison of Macromolecules

Macromolecule	Monomer	Main Function	Example
Carbohydrate	Monosaccharide	Energy storage, structure	Starch, cellulose
Lipid	Fatty acid, glycerol	Energy storage, membranes	Triglyceride, phospholipid
Protein	Amino acid	Catalysis, structure, transport	Enzyme, hemoglobin
Nucleic Acid	Nucleotide	Genetic information	DNA, RNA

Additional info:

• Some explanations and examples were expanded for clarity and completeness.

• Table content inferred from standard biology curriculum.