Introduction to Biology & Characteristics of Life

Properties of Life

All living organisms share a set of fundamental characteristics that distinguish them from non-living matter.

• Order: Living things exhibit complex but ordered organization.

• Regulation: Organisms maintain stable internal conditions (homeostasis).

• Growth and Development: Organisms grow and develop according to inherited instructions.

• Energy Processing: Living things acquire and use energy for metabolism and work.

• Response to Environment: Organisms respond to environmental stimuli.

• Reproduction: Organisms reproduce their own kind.

• Evolutionary Adaptation: Populations evolve over generations to adapt to their environments.

Levels of Biological Organization

Biological systems are organized in a hierarchy, from smallest to largest:

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

• Emergent Properties: New properties arise at each level that are not present at the previous level (e.g., life emerges at the cellular level).

Eukaryotic vs. Prokaryotic Cells

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

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles; found in Eukarya (includes kingdoms Plantae, Fungi, Animalia, and Protists).

Classification of Life

• Domains: Bacteria, Archaea (both prokaryotic), and Eukarya (eukaryotic).

• Kingdoms in Eukarya: Plantae, Fungi, Animalia, Protists.

Role of DNA and Gene Expression

• DNA: The molecule of heredity; stores genetic information.

• Gene Expression: The process by which information from DNA is used to synthesize RNA and then proteins.

Central Dogma:

• DNA → RNA → Protein

Energy and Matter in Living Systems

• Energy: Flows through ecosystems (usually enters as sunlight, exits as heat).

• Matter: Cycles within ecosystems (e.g., carbon, nitrogen cycles).

Feedback Regulation

• Negative Feedback: A process in which the end product slows or stops its own production (e.g., body temperature regulation).

• Positive Feedback: A process in which the end product speeds up its own production (e.g., blood clotting).

Natural Selection

• Definition: The process by which organisms with advantageous traits survive and reproduce more successfully.

• Mechanism: Variation exists; environment selects for traits; successful traits become more common in future generations.

The Scientific Process

• Controlled Experiment: Includes independent variable (manipulated), dependent variable (measured), and control group (baseline for comparison).

• Inductive Reasoning: Deriving general principles from specific observations.

• Deductive Reasoning: Predicting specific results from general principles.

Chemistry of Life

Matter, Elements, and Compounds

• Matter: Anything that takes up space and has mass.

• Element: A substance that cannot be broken down by chemical means.

• Compound: A substance made of two or more elements in a fixed ratio; has emergent properties.

Essential and Trace Elements

• Essential Elements: Four elements make up ~96% of living matter: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N).

• Trace Elements: Required in minute amounts (e.g., iron, iodine).

Atomic Structure

• Subatomic Particles: Protons (positive, in nucleus), Neutrons (neutral, in nucleus), Electrons (negative, in orbitals).

• Atomic Number: Number of protons; defines the element.

• Mass Number: Number of protons + neutrons.

Formula:

• Number of Neutrons = Mass Number - Atomic Number

Isotopes

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

• Applications: Used in biological research and medicine (e.g., radioactive tracers).

Electron Energy Levels and Orbitals

• Electron Shells: Electrons occupy energy levels (shells) around the nucleus.

• Valence Electrons: Electrons in the outermost shell; determine chemical properties.

• Orbitals: 3D spaces where electrons are found; shape influences molecular structure.

Chemical Bonds

• 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 ions.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., O or N); important in water and biological molecules.

Chemical Reactions

• Reactants: Starting materials.

• Products: Substances formed.

Example:

Water and Life

Structure and Properties of Water

• Polar Covalent Bonds: Oxygen is more electronegative than hydrogen, creating partial charges (O: δ-, H: δ+).

• Hydrogen Bonds: Form between water molecules due to polarity; responsible for many unique properties.

Cohesion and Adhesion

• Cohesion: Water molecules stick to each other (important for transport in plants).

• Adhesion: Water molecules stick to other substances (e.g., cell walls).

High Specific Heat

• Water absorbs or releases a large amount of heat with little temperature change, stabilizing temperatures in organisms and environments.

Ice Floats

• Hydrogen bonds in ice are more ordered, making ice less dense than liquid water; allows ice to float and insulate aquatic life.

Water as a Universal Solvent

• Solution: Homogeneous mixture of substances.

• Solvent: Dissolving agent (water).

• Solute: Substance dissolved.

• Hydrophilic: Substances that dissolve in water (polar/charged).

• Hydrophobic: Substances that do not dissolve in water (nonpolar).

Acids, Bases, and Buffers

• pH Scale: Measures hydrogen ion concentration; 0-6 acidic, 7 neutral, 8-14 basic.

• Buffers: Substances that minimize changes in pH; crucial for maintaining homeostasis.

Macromolecules

Carbon: The Backbone of Life

• Versatility: Carbon has 4 valence electrons, allowing it to form 4 covalent bonds and a variety of structures (chains, rings, branches).

• Isomers: Molecules with the same formula but different structures; can have different properties.

Functional Groups

• Groups of atoms attached to carbon skeletons that confer specific properties (e.g., hydroxyl, carboxyl, amino, phosphate).

Macromolecules, Polymers, and Monomers

• Macromolecules: Large molecules (carbohydrates, lipids, proteins, nucleic acids).

• Polymers: Long chains of monomers (except lipids).

• Monomers: Building blocks (e.g., monosaccharides, amino acids, nucleotides).

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: Joins monomers by removing water; forms polymers.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

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

• Disaccharides: Two monosaccharides joined (e.g., sucrose).

• Polysaccharides: Many monosaccharides (e.g., starch, glycogen, cellulose, chitin).

• Functions: Energy storage (starch, glycogen), structural support (cellulose, chitin).

Lipids

• Fats: Glycerol + fatty acids; saturated (no double bonds, solid) vs. unsaturated (double bonds, liquid).

• Phospholipids: Glycerol, 2 fatty acids, phosphate group; hydrophilic head, hydrophobic tails; form cell membranes.

• Steroids: Four fused rings; e.g., cholesterol, hormones.

Proteins

• Polypeptides: Chains of amino acids (20 types).

• Structure: Primary (sequence), secondary (α-helix, β-sheet), tertiary (3D folding), quaternary (multiple polypeptides).

• Functions: Enzymes, transport, structure, signaling, defense, etc.

Nucleic Acids

• DNA: Double-stranded, stores genetic information.

• RNA: Single-stranded, involved in protein synthesis.

• Monomers: Nucleotides (sugar, phosphate, nitrogenous base).

• Gene Expression: DNA → RNA → Protein.

Additional info: This guide covers foundational concepts from the first four chapters of a typical General Biology course, including the scientific method, basic chemistry, water's properties, and the structure and function of biological macromolecules.