Introduction to Biology & Characteristics of Life

Properties of Life

Living organisms share several fundamental properties that distinguish them from non-living matter.

• Order: Organisms exhibit organized structures, from cells to tissues to organs.

• Regulation: Ability to maintain internal conditions (homeostasis).

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

• Energy Processing: Use and transformation of energy for metabolism.

• Response to Environment: React to stimuli in their surroundings.

• Reproduction: Ability to produce offspring.

• Evolutionary Adaptation: Populations evolve over generations.

Example: Plants grow toward light (response to environment), use sunlight for photosynthesis (energy processing), and reproduce via seeds.

Levels of Biological Organization

Biological systems are structured hierarchically, with each level building upon the previous.

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

• Emergent Properties: New properties arise at each level due to interactions among components (e.g., life emerges at the cell level).

Example: A heart (organ) can pump blood, but individual heart cells cannot.

Eukaryotic vs. Prokaryotic Cells

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

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

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles. Found in Eukarya domain (kingdoms: Animalia, Plantae, Fungi, Protista).

Example: Human cells are eukaryotic; bacterial cells are prokaryotic.

Classification of Organisms

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

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

Role of DNA and Gene Expression

DNA stores genetic information and directs cellular activities through gene expression.

• Gene Expression: Flow of information: DNA → RNA → Protein.

Example: Hemoglobin gene in DNA is transcribed to RNA, then translated to hemoglobin protein.

Role of Energy and Cycling of Matter

• Energy: Originates from the sun (photosynthesis), flows through ecosystems (not recycled).

• Matter: Cycles through ecosystems (carbon, nitrogen, water cycles).

Example: Plants convert solar energy to chemical energy; decomposers recycle nutrients.

Feedback Regulation

• Negative Feedback: Reduces change (e.g., blood glucose regulation).

• Positive Feedback: Amplifies change (e.g., blood clotting).

Natural Selection

Natural selection drives evolution by favoring traits that enhance survival and reproduction.

• Mechanism: Variation → Differential survival → Reproduction → Change in population genetics.

• Environment: Selects for traits best suited to current conditions.

Example: Peppered moth coloration changes in response to pollution.

Scientific Process and Controlled Experiments

• Controlled Experiment: Tests one variable at a time.

• Independent Variable: Manipulated factor.

• Dependent Variable: Measured outcome.

• Control Group: Baseline for comparison.

Inductive vs. Deductive Reasoning

• Inductive Reasoning: Generalizations from specific observations.

• Deductive Reasoning: Predictions from general principles.

Example: Inductive: "All observed swans are white, so all swans are white." Deductive: "If all swans are white, then the next swan observed will be white."

Chemistry of Life

Matter, Elements, and Compounds

Matter is composed of elements, which combine to form compounds with new properties.

• Matter: Anything that occupies space and has mass.

• Element: Pure substance consisting of one type of atom.

• Compound: Substance formed by two or more elements in fixed ratios.

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

Essential and Trace Elements

• Essential Elements: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) — make up most living matter.

• Bonds Formed: C (4), H (1), O (2), N (3).

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

Example: Iron is needed for hemoglobin function.

Atomic Structure

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

• Protons: Determine atomic number and element identity.

• Neutrons: Affect mass number and isotopes.

• Electrons: Involved in chemical bonding.

Atomic Number and Mass Number

• Atomic Number: Number of protons.

• Mass Number: Number of protons + neutrons.

Equation:

Isotopes

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

• Uses: Biological tracers, dating fossils.

Electron Energy Levels and Orbitals

• Energy Levels: Electrons occupy specific energy levels (shells).

• Orbitals: Regions where electrons are likely found; shape affects molecular structure.

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

Chemical Bonds

• Covalent Bonds: Atoms share electrons. Polar (unequal sharing, e.g., water), Nonpolar (equal sharing, e.g., O2).

• Ionic Bonds: Electrons transferred; forms ions (e.g., NaCl).

• Hydrogen Bonds: Weak attraction between partial charges (e.g., between water molecules).

Chemical Reactions

• Reactants: Starting substances.

• Products: Resulting substances.

Example: (cellular respiration)

Water and Life

Polar Covalent Bonds in Water

Water's unique properties stem from its polar covalent bonds.

• Polarity: Oxygen has a greater pull on electrons, creating partial negative charge; hydrogens are partially positive.

Hydrogen Bonds in Water

• Formation: Partial charges allow hydrogen bonds between water molecules.

• Strength: Weaker than covalent bonds, but collectively strong.

Cohesion and Adhesion

• Cohesion: Water molecules stick to each other (surface tension).

• Adhesion: Water molecules stick to other substances (capillary action).

Example: Water moves up plant stems via cohesion and adhesion.

High Specific Heat

• Definition: Water resists temperature change due to hydrogen bonding.

• Impact: Stabilizes climate and organism temperatures.

Ice Floats

• Reason: Hydrogen bonds lengthen, creating a less dense structure.

• Impact: Insulates aquatic life in winter.

Water as Universal Solvent

• Solvent: Dissolves polar/hydrophilic substances.

• Hydrophobic Substances: Do not dissolve (e.g., oils).

• Solution: Mixture of solute (dissolved substance) and solvent (dissolving agent).

Acids, Bases, and Buffers

• pH Scale: Measures hydrogen ion concentration (0-14).

• Acids: pH < 7; Bases: pH > 7; Neutral: pH = 7.

• Buffers: Stabilize pH in organisms.

Example: Blood contains buffers to maintain pH.

Macromolecules

Carbon and Its Versatility

Carbon's unique properties make it the backbone of biological molecules.

• Valence Electrons: Carbon has 4, allowing diverse bonding.

• Variation: Carbon forms chains, rings, and branches.

Functional Groups

• Definition: Groups of atoms attached to carbon skeletons; affect molecular function.

• Examples: Hydroxyl, carboxyl, amino, phosphate.

Macromolecules, Polymers, and Monomers

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

• Polymers: Chains of monomers.

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

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: Joins monomers by removing water.

• Hydrolysis: Breaks polymers by adding water.

Carbohydrates

• Monosaccharides: Simple sugars (glucose).

• Disaccharides: Two monosaccharides (sucrose).

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

• Starch: Storage in plants; Glycogen: Storage in animals; Cellulose: Plant cell walls; Chitin: Fungal cell walls, exoskeletons.

Lipids

• Fats: Glycerol + fatty acids; Saturated: No double bonds; Unsaturated: Double bonds.

• Phospholipids: Hydrophilic head, hydrophobic tail; form cell membranes.

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

Proteins

• Amino Acids: 20 types; differ in side chains.

• Polypeptides: Chains of amino acids.

• Functions: Enzymes, structure, transport, signaling.

• Structure: Primary (sequence), Secondary (folds), Tertiary (3D shape), Quaternary (multiple polypeptides).

Nucleic Acids

• DNA: Double helix; stores genetic information.

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

• Gene Expression: DNA → RNA → Protein.

Example: DNA sequence codes for insulin protein.

Summary Table: Cell Types and Domains

Additional info: Table summarizes classification based on cell structure.