General Biology: Foundational Concepts and Key Topics

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Three Scientific Domains

Overview of the Three Domains of Life

The classification of all living organisms is organized into three major domains based on genetic and cellular differences.

Bacteria: Single-celled prokaryotes with unique cell wall structures.
Archaea: Single-celled prokaryotes distinct from bacteria, often found in extreme environments.
Eukarya: Organisms with eukaryotic cells, including animals, plants, fungi, and protists.

Example: Escherichia coli (Bacteria), Halobacterium (Archaea), Homo sapiens (Eukarya).

Life’s Hierarchical Sequence: Molecule to Biosphere

Levels of Biological Organization

Biological systems are organized in a hierarchy from the smallest chemical units to the entire biosphere.

Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Example: DNA (molecule) is found in the nucleus (organelle) of a liver cell (cell) in a human (organism).

Darwin’s Theory of Natural Selection

Principles of Natural Selection

Natural selection is the process by which organisms better adapted to their environment tend to survive and produce more offspring.

Variation exists within populations.
Some variations are heritable.
More offspring are produced than can survive.
Individuals with advantageous traits are more likely to survive and reproduce.

Example: The evolution of antibiotic resistance in bacteria.

Scientific Method

Steps in the Scientific Method

The scientific method is a systematic approach to inquiry in science.

Problem/Question
Hypothesis
Experimental Design
Collecting and Analyzing Data
Drawing Conclusions
Sharing (publishing results)

Variables:

Independent Variable: The factor that is changed or controlled in an experiment.
Dependent Variable: The factor that is measured or observed.

Example: Testing the effect of sunlight on plant growth (sunlight = independent variable, plant growth = dependent variable).

Basic Chemistry Terminology

Key Terms in Chemistry

Atom: The smallest unit of matter retaining the properties of an element.
Compound: A substance formed from two or more elements chemically bonded.
Molecule: Two or more atoms held together by covalent bonds.
Isotopes: Atoms of the same element with different numbers of neutrons.

3D Structure of an Atom

Nucleus: Contains protons and neutrons.
Electrons: Negatively charged, found in electron clouds/orbitals around the nucleus.

Atomic Number, Mass Number, Isotopes

Atomic Number (Z): Number of protons in the nucleus.
Mass Number (A): Total number of protons and neutrons.
Isotopes: Atoms with the same atomic number but different mass numbers.

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Types of Bonding (Covalent and Ionic)

Chemical Bonds in Biology

Covalent Bonds: Atoms share electron pairs.
Ionic Bonds: Transfer of electrons from one atom to another, resulting in charged ions.
Other Bonds: Hydrogen bonds, van der Waals interactions (important in biological molecules).

Example: Water molecules are held together by covalent bonds; salt (NaCl) is formed by ionic bonding.

Elements in Living Organisms

Major Elements

Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)

These four elements make up about 96% of living matter.

Trace Elements

Definition and Examples

Trace elements are required by organisms in minute quantities but are essential for proper functioning.

Examples: Iron (Fe), Iodine (I), Zinc (Zn), Copper (Cu)

General Structure of an Equation

Chemical Equations

Chemical equations represent the reactants and products in a chemical reaction.

General format: Reactants → Products

Example:

Balancing Chemical Equations

Principles of Balancing

Balancing ensures the same number of each type of atom on both sides of the equation, following the law of conservation of mass.

Adjust coefficients, not subscripts.
Check each element in turn.

pH Scale

Acidity and Alkalinity

The pH scale measures the concentration of hydrogen ions in a solution.

Scale ranges from 0 (most acidic) to 14 (most basic), with 7 being neutral.
Formula:

Example: Pure water has a pH of 7.

Organic Compounds

Major Classes of Organic Molecules

Carbohydrates: Monosaccharides, disaccharides, polysaccharides. Serve as energy sources and structural materials.
Lipids: Fats, oils, phospholipids, steroids. Important for energy storage and membrane structure.
Proteins: Polymers of amino acids. Function as enzymes, structural components, and signaling molecules.
Nucleic Acids: DNA and RNA. Store and transmit genetic information.

Example: Glucose (carbohydrate), triglyceride (lipid), hemoglobin (protein), DNA (nucleic acid).

Hydrolysis and Dehydration Synthesis

Building and Breaking Polymers

Dehydration Synthesis: Joins monomers by removing a water molecule.
Hydrolysis: Breaks polymers into monomers by adding water.

Example: Digestion of starch into glucose monomers.

Microscopy

Principles of Microscopy

Magnification: The increase in apparent size of an object.
Resolution: The ability to distinguish two close objects as separate.

Microscopes are essential tools for studying cells and microorganisms.

Cell Theory

Fundamental Principles

All living things are composed of cells.
The cell is the basic unit of life.
All cells arise from pre-existing cells.

Prokaryotic vs. Eukaryotic Cells

Comparison of Cell Types

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No	Yes
Membrane-bound Organelles	No	Yes
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists

Plant Cells vs. Animal Cells

Similarities and Differences

Feature	Plant Cells	Animal Cells
Cell Wall	Yes	No
Chloroplasts	Yes	No
Central Vacuole	Yes	No (small vacuoles)
Centrioles	No	Yes

Organelles of Eukaryotic Cells

Major Organelles and Their Functions

Endomembrane System: Includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles.
Energy Processing: Mitochondria (cellular respiration), chloroplasts (photosynthesis in plants).
Structure, Support, and Communication: Cytoskeleton, cell wall (plants), plasma membrane.

DNA vs. RNA

Comparison of Nucleic Acids

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Nitrogenous Bases	A, T, C, G	A, U, C, G
Strands	Double-stranded	Single-stranded

Types of Junctions

Cell Junctions in Multicellular Organisms

Tight Junctions: Prevent leakage of extracellular fluid between cells.
Desmosomes: Anchor cells together.
Gap Junctions: Allow communication between animal cells.
Plasmodesmata: Channels between plant cells for transport and communication.