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 (genes).

• Energy Processing: Living things acquire and use energy to power activities.

• 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.

Example: A plant growing toward sunlight demonstrates response to environment and energy processing.

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 level of the cell).

Cell Types: Eukaryotic vs. Prokaryotic

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

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles. Domain: Eukarya (includes kingdoms: Plantae, Fungi, Animalia, 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 that stores genetic information in all living organisms.

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

Central Dogma:

Energy and Matter in Living Systems

• Energy: Flows through ecosystems (e.g., sunlight → chemical energy → heat).

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

Example: Plants convert sunlight to chemical energy via photosynthesis; animals eat plants and use that energy.

Feedback Regulation

• Negative Feedback: A process in which the end product reduces the initial stimulus (e.g., body temperature regulation).

• Positive Feedback: A process in which the end product amplifies the initial stimulus (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).

• Importance: Controls allow for valid conclusions about cause and effect.

Scientific Reasoning

• 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.

Emergent Properties: Compounds have properties different from their constituent elements.

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).

Bonding Capacity: C (4), H (1), O (2), N (3) bonds; determines molecular structure and function.

Atomic Structure

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

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

• Mass Number: Number of protons + neutrons.

Equation:

Isotopes

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

• Uses in Biology: Radioactive isotopes are used as tracers in medical imaging and research.

Electron Energy Levels and Orbitals

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

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

• Orbitals: 3D spaces where electrons are found; shape affects molecular geometry.

Chemical Bonds

• Covalent Bonds: Atoms share electrons. Nonpolar (equal sharing), Polar (unequal sharing).

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

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

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 the slightly positive H of one water molecule and the slightly negative O of another.

Cohesion and Adhesion

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

• Adhesion: Water molecules stick to other substances (helps water move up plant vessels).

High Specific Heat

• Water absorbs a lot of heat before changing temperature, stabilizing climates and organisms' internal temperatures.

Ice Floats

• Hydrogen bonds in ice are more stable and spread out, making ice less dense than liquid water.

• This insulates aquatic life in winter.

Water as a Universal Solvent

• Solution: Homogeneous mixture of two or more substances.

• Solvent: Dissolving agent (water).

• Solute: Substance dissolved.

• Water dissolves polar and ionic substances (hydrophilic), but not nonpolar (hydrophobic) substances.

Acids, Bases, and pH

• pH Scale: Measures hydrogen ion concentration; ranges from 0 (acidic) to 14 (basic), 7 is neutral.

• Acids: Increase H+ concentration (pH < 7).

• Bases: Decrease H+ concentration (pH > 7).

• 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 essential for life (carbohydrates, lipids, proteins, nucleic acids).

• Polymers: Long chains of monomers (repeating units).

• Monomers: Building blocks of polymers.

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: Long chains (e.g., starch, glycogen, cellulose, chitin).

Lipids

• Fats: Glycerol + fatty acids; energy storage.

• Saturated Fats: No double bonds; solid at room temperature.

• Unsaturated Fats: One or more double bonds; liquid at room temperature.

• Phospholipids: Glycerol, two 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).

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

• Levels of Structure:

  • Primary: Sequence of amino acids.

  • Secondary: Alpha helices and beta sheets (hydrogen bonding).

  • Tertiary: 3D folding (interactions among R groups).

  • Quaternary: Multiple polypeptides joined.

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.