Introduction to Biology

Characteristics of Life

Biology is the study of living organisms and their interactions with the environment. All living things share certain properties that define life.

• Order: Living things are organized, from cells to tissues to organs.

• Regulation: Organisms maintain internal conditions (homeostasis).

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

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

• Response to Environment: Organisms respond to stimuli.

• Reproduction: Living things reproduce, passing on genetic material.

• Evolutionary Adaptation: Populations evolve over generations.

Levels of Biological Organization

Biological systems are organized hierarchically, each level exhibiting emergent properties.

• Levels: 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., a cell is alive, but its organelles alone are not).

• Example: Heart cells can contract, but only the whole heart can pump blood.

Eukaryotic vs. Prokaryotic Cells

Cells are classified as 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 organelles. Found in Eukarya domain (kingdoms: Animalia, Plantae, Fungi, Protista).

Classification of Life

• 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: Information flows from DNA → RNA → Protein.

• Central Dogma:

Energy and Matter in Ecosystems

• Energy: Flows through ecosystems (from sun to producers to consumers), not recycled.

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

• Example: Plants convert solar energy to chemical energy; animals eat plants.

Feedback Regulation

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

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

Natural Selection

Natural selection is the process by which populations change over time due to differential survival and reproduction.

• Mechanism: Individuals with advantageous traits survive and reproduce more.

• Result: Future generations resemble the most successful individuals.

Scientific Process and Controlled Experiments

• Controlled Experiment: Tests one variable at a time; includes control group.

• Variables: Independent variable (manipulated), Dependent variable (measured).

• Importance: Control group allows comparison to determine effect.

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 this swan must be white."

Chemistry of Life

Matter, Elements, and Compounds

Matter is anything that occupies space and has mass. Elements are pure substances; compounds are combinations of elements.

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

• Example: Sodium (Na) and chlorine (Cl) form sodium chloride (NaCl), table salt.

Essential and Trace Elements

• Essential Elements: Four most common: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N).

• Bonds: C (4), H (1), O (2), N (3) bonds; affects molecular structure and function.

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

Atomic Structure

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

• Atomic Number: Number of protons; defines element.

• Mass Number:

• Isotopes: Atoms with same number of protons, different neutrons; used in biology for dating and tracing.

Electron Energy Levels and Orbitals

• Electron Orbitals: Determine molecular shape and function.

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

Chemical Bonds

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

• Ionic Bonds: Electrons transferred; forms ions.

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

Chemical Reactions

• Reactants: Starting substances.

• Products: Ending substances.

• Example: (cellular respiration)

Water and Life

Structure of Water

• Polar Covalent Bonds: Oxygen has greater pull on electrons, creating partial negative charge; hydrogens are partial positive.

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

Cohesion and Adhesion

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

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

• Example: Water movement in plants (transpiration).

High Specific Heat

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

• Impact: Stabilizes temperatures in organisms and environments.

Ice Floats

• Reason: Hydrogen bonds in ice are longer, making ice less dense than liquid water.

• Impact: Insulates aquatic life in winter.

Water as Universal Solvent

• Solution: Homogeneous mixture.

• Solute: Substance dissolved.

• Solvent: Substance doing the dissolving (water).

• Hydrophilic: Polar substances dissolve in water.

• Hydrophobic: Nonpolar substances do not dissolve.

Acids, Bases, and pH

• pH Scale: Measures concentration of H+ ions; ranges from 0 (acidic) to 14 (basic), 7 is neutral.

• Acids: pH < 7; donate H+.

• Bases: pH > 7; accept H+.

• Buffers: Maintain stable pH in organisms.

Macromolecules

Carbon and Its Versatility

• Valence Electrons: Carbon has 4; can form up to 4 bonds.

• Variation: Carbon forms diverse structures (chains, rings, branches).

• Impact: Different structures with same formula (isomers) have different functions.

Functional Groups

• Definition: Groups of atoms attached to carbon skeletons; affect chemical properties.

• 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., glucose for carbohydrates).

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).

• Comparison Table:

Lipids

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

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

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

Proteins

• Polypeptides: Chains of amino acids.

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

• Functions: Enzymes, structure, transport, signaling.

• Protein Structure:

Nucleic Acids

• DNA: Double helix; stores genetic information.

• RNA: Single strand; involved in protein synthesis.

• Gene Expression: DNA → RNA → Protein.

• Comparison Table:

Additional info: Academic context and examples were added to clarify and expand brief points from the original review guide.