General Biology: Core Concepts and Practice Questions

Introduction to General Biology

This study guide covers foundational topics in General Biology, including the organization of life, chemical basis of biology, cell structure and function, macromolecules, energy transformations, and cellular respiration. The content is structured around key concepts and reinforced with example questions and explanations.

Organization of Life

Biological Hierarchy

• Definition: Life is organized from the simplest to the most complex levels.

• Hierarchy (from least to most inclusive): molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem

• Example: A heart cell (cell) is part of heart tissue (tissue), which forms the heart (organ), part of the circulatory system (organ system), in a human (organism).

Classification of Life

Domains of Life

• Three Domains: Bacteria, Archaea, and Eukarya

• Eukarya: Includes all eukaryotic organisms (cells with nuclei).

• Prokarya: Not a domain; refers to organisms without a nucleus (Bacteria and Archaea).

Chemical Basis of Life

Atoms and Elements

• Atomic Number: The number of protons in an atom ($\text{Atomic Number} = \text{Number of Protons}$).

• Electron Shells: The innermost shell holds 2 electrons; the outermost shell can hold up to 8 electrons.

Chemical Bonds

• Covalent Bond: Forms when two atoms share electrons.

• Ionic Bond: Forms when one atom donates an electron to another.

Compounds and Molecules

• Compound: Contains two or more different elements in a fixed ratio.

• Organic Compounds: Always contain carbon.

Functional Groups

• Hydroxyl Group: -OH

• Amino Group: -NH2

• Carboxyl Group: -COOH

Properties of Water

• Polarity: Water is a polar molecule; oxygen is more electronegative and attracts electrons more strongly than hydrogen.

• Hydrogen Bonding: Responsible for water's unique properties (cohesion, adhesion, high specific heat).

Macromolecules

Carbohydrates

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

• Disaccharides: Formed by joining two monosaccharides via dehydration synthesis.

• Polysaccharides: Long chains of monosaccharides (e.g., cellulose, starch, glycogen).

Lipids

• Phospholipids: Composed of a glycerol molecule linked to one phosphate group and two fatty acids.

• Hydrophobic Nature: Lipids are hydrophobic due to their nonpolar hydrocarbon chains.

Proteins

• Amino Acids: Building blocks of proteins; distinguished by their R groups.

• Peptide Bonds: Formed by dehydration synthesis between amino acids.

Nucleic Acids

• Nucleotides: Consist of a sugar, phosphate group, and nitrogenous base.

• DNA and RNA: Polymers of nucleotides; DNA stores genetic information, RNA is involved in protein synthesis.

Cell Structure and Function

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; include Bacteria and Archaea.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles (e.g., mitochondria, chloroplasts).

Cell Organelles

• Nucleus: Contains DNA; manufactures ribosomal RNA.

• Mitochondria: Site of cellular respiration; produces ATP.

• Chloroplasts: Site of photosynthesis in plants; contain their own DNA and ribosomes.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and stores calcium ions.

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

• Lysosomes: Contain digestive enzymes for intracellular digestion.

Cell Membrane Structure

• Phospholipid Bilayer: Hydrophilic heads face outward toward water; hydrophobic tails face inward, away from water.

• Proteins: Embedded in the membrane; involved in transport, signaling, and enzymatic activity.

Transport Across Membranes

Passive Transport

• Simple Diffusion: Movement of molecules from high to low concentration without energy input or proteins.

• Facilitated Diffusion: Movement of molecules across membranes via transport proteins.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Active Transport

• Definition: Movement of substances against their concentration gradient; requires energy (ATP).

• Example: Sodium-potassium pump in animal cells.

Energy and Metabolism

Thermodynamics in Biology

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

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

• Open vs. Closed Systems: Living organisms are open systems (exchange energy and matter with surroundings).

Enzymes

• Function: Biological catalysts that lower the activation energy of reactions.

• Substrate: The reactant an enzyme acts upon.

Cellular Respiration and Fermentation

Pathways of Cellular Respiration

• Glycolysis: Occurs in the cytosol; breaks down glucose into pyruvate.

• Citric Acid Cycle: Completes the breakdown of glucose; occurs in mitochondria.

• Electron Transport Chain: Uses electrons from NADH to produce ATP; oxygen is the final electron acceptor.

• Overall Sequence: Glucose → NADH → Electron Transport Chain → Oxygen

Fermentation

• Definition: Anaerobic process by which cells generate ATP without oxygen.

• Example: Yeast cells metabolize glucose to produce ATP in the absence of oxygen.

Sample Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Key Definitions and Concepts

• Hypothesis: A proposed explanation for a set of observations.

• Theory: An explanation of an idea that is broad in scope and supported by a large body of evidence.

• Acid: Substance with a pH less than 7; increases hydrogen ion concentration.

• Base: Substance with a pH greater than 7; decreases hydrogen ion concentration.

Additional info:

• Some explanations and context have been expanded for clarity and completeness, based on standard General Biology curricula.