Five Unifying Themes of Biology

Core Concepts in Biology

Biology is guided by several unifying themes that help explain the diversity and unity of life. Understanding these themes provides a framework for studying biological systems.

• Unity and Diversity of Life: All living organisms share common characteristics, yet exhibit remarkable diversity.

• Emergent Properties: New properties arise at each level of biological organization that are not present at the preceding level.

• Levels of Biological Organization: Life is organized from molecules to biosphere, including cells, tissues, organs, organisms, populations, communities, and ecosystems.

• Gene Expression: Genes encode information that is expressed as traits through transcription and translation.

• Interactions: Organisms interact with each other and their environment, affecting survival and evolution.

Scientific Method and Experimental Design

Hypotheses, Variables, and Theories

Scientific inquiry involves forming hypotheses, designing experiments, and analyzing results to draw conclusions.

• Hypothesis: A testable statement that explains observations.

• Experiment: Involves predictions, control variables, and independent & dependent variables.

• Theory: A well-substantiated explanation based on a body of evidence.

• Difference between Hypotheses and Theories: Hypotheses are specific and testable; theories are broad and supported by extensive evidence.

Chemistry of Life

Matter, Elements, and Compounds

All living things are composed of matter, which consists of elements and compounds.

• Subatomic Particles: Protons (positive), neutrons (neutral), and electrons (negative).

• Atomic Number and Mass Number: Atomic number is the number of protons; mass number is protons plus neutrons.

• Periodic Table: Organizes elements by atomic number and properties.

• Valence Electrons: Electrons in the outermost shell, important for chemical bonding.

Chemical Bonds and Water

Chemical bonds hold atoms together and determine the properties of molecules.

• Types of Chemical Bonds: Polar/nonpolar covalent, ionic, and hydrogen bonds.

• Water Properties: Water is polar, forms hydrogen bonds, and exhibits cohesion, adhesion, and high specific heat.

• Acids and Bases: Acids donate H+; bases accept H+. pH scale measures acidity.

• Significance of Stanley-Miller Experiment: Demonstrated that organic molecules could form under prebiotic conditions.

Organic Molecules and Isomerism

Carbon Chemistry and Isomers

Organic molecules are based on carbon and can exist in different structural forms called isomers.

• Isomers: Molecules with the same molecular formula but different structures (structural, cis-trans, enantiomers).

• Functional Groups: Groups of atoms that confer specific properties to organic molecules (e.g., hydroxyl, carboxyl).

Macromolecules

Classes and Functions

Biological macromolecules are large molecules essential for life, including carbohydrates, lipids, proteins, and nucleic acids.

• Monomers and Polymers: Monomers are building blocks; polymers are chains of monomers.

• Dehydration Synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers into monomers by adding water.

• Saturated vs. Unsaturated Fats: Saturated fats have no double bonds; unsaturated fats have one or more double bonds.

• Protein Structure: Primary (sequence), secondary (folding), tertiary (3D shape), quaternary (multiple polypeptides).

• DNA vs. RNA: DNA stores genetic information; RNA is involved in protein synthesis.

Cell Structure and Function

Cell Membrane and Transport

The cell membrane controls the movement of substances in and out of the cell.

• Fluid Mosaic Model: Describes the membrane as a mosaic of proteins and lipids that move fluidly.

• Hydrophobic vs. Hydrophilic: Hydrophobic molecules repel water; hydrophilic molecules attract water.

• Passive Transport: Movement without energy (diffusion, osmosis, facilitated diffusion).

• Active Transport: Requires energy to move substances against their concentration gradient.

• Tonicity: Refers to the relative concentration of solutes (hypertonic, hypotonic, isotonic).

• Bulk Transport: Endocytosis (into cell) and exocytosis (out of cell).

Prokaryotic vs. Eukaryotic Cells

Cells are classified as prokaryotic or eukaryotic based on their structure.

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles (e.g., bacteria).

• Eukaryotic Cells: Have a nucleus and organelles (e.g., plants, animals).

• Organelle Labeling: Be able to identify structures such as nucleus, mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, etc.

Endosymbiont Theory

The endosymbiont theory explains the origin of mitochondria and chloroplasts in eukaryotic cells.

• Endosymbiont Theory: Proposes that mitochondria and chloroplasts originated as free-living bacteria that were engulfed by ancestral eukaryotic cells.

• Evidence: Double membranes, own DNA, and similarities to prokaryotes.

Table: Comparison of Prokaryotic and Eukaryotic Cells

Key Equations

• Dehydration Synthesis:

• Hydrolysis:

• pH Calculation:

Example: The fluid mosaic model explains how proteins and lipids move within the cell membrane, allowing for flexibility and selective transport.