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 (Homeostasis): Organisms maintain stable internal conditions.

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

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

• Response to Environment: Organisms respond to environmental stimuli.

• Reproduction: Organisms reproduce their own kind.

• Evolutionary Adaptation: Populations evolve over generations through the process of natural selection.

Example: A plant bending toward light demonstrates response to environment and energy processing.

Levels of Biological Organization

Biological systems are organized into a hierarchy, with each level building on the previous one and displaying emergent properties.

• Levels (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 preceding level (e.g., life emerges at the cellular level).

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

Eukaryotic vs. Prokaryotic Cells

• 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 (includes kingdoms Plantae, Fungi, Animalia, Protista).

Classification of Life

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

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

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.

Flow of Genetic Information:

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).

Feedback Regulation

• Negative Feedback: Reduces the initial stimulus (e.g., body temperature regulation).

• Positive Feedback: Enhances the initial stimulus (e.g., blood clotting).

Natural Selection

• Mechanism: Individuals with traits better suited to their environment are more likely to survive and reproduce.

• Result: Over generations, populations become better adapted to their environments.

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

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

• Matter: Anything that has mass and occupies space.

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

• Compound: A substance consisting of two or more elements in a fixed ratio.

• Emergent Properties: Compounds have characteristics different from those of their elements.

Essential and Trace Elements

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

• Bonding: C (4 bonds), H (1 bond), O (2 bonds), N (3 bonds); the number of bonds affects molecular structure and function.

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

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

• Isotopes: 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 Orbitals: Regions where electrons are likely to be found; determine molecular shape and function.

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

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 charged ions that attract each other.

• Hydrogen Bonds: Weak attractions between a hydrogen atom (partially positive) and an electronegative atom (e.g., oxygen or nitrogen).

Chemical Reactions

• Reactants: Starting materials in a chemical reaction.

• Products: Substances formed by the reaction.

Example:

Water and Life

Structure and Polarity of Water

• Polar Covalent Bonds: Oxygen is more electronegative than hydrogen, creating partial negative (O) and partial positive (H) charges.

• Result: Water is a polar molecule, with an uneven distribution of charge.

Hydrogen Bonding in Water

• Formation: The partial positive hydrogen of one water molecule is attracted to the partial negative oxygen of another.

• Importance: Responsible for many of water's 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).

Example: Transpiration in plants relies on both cohesion and adhesion.

High Specific Heat of Water

• Definition: Water can absorb or release a large amount of heat with only a slight change in its own temperature.

• Impact: Stabilizes temperatures in organisms and environments.

Ice Floats

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

• Impact: Insulates bodies of water, protecting aquatic life in winter.

Water as a Universal Solvent

• Solution: Homogeneous mixture of two or more substances.

• Solvent: Dissolving agent (water).

• Solute: Substance dissolved.

• Hydrophilic Substances: Polar or charged; dissolve in water.

• Hydrophobic Substances: Nonpolar; do not dissolve in water.

Acids, Bases, and Buffers

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

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

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

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

Macromolecules

Carbon: The Backbone of Life

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

• Structural Variation: Different arrangements (isomers) can have distinct properties even with the same chemical formula.

Functional Groups

• Definition: Groups of atoms attached to carbon skeletons that participate in chemical reactions and give molecules 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 repeating units (monomers).

• Monomers: Building blocks of polymers.

Dehydration Synthesis and Hydrolysis

• Dehydration Synthesis: Monomers are joined by covalent bonds; water is released.

• Hydrolysis: Polymers are broken down into monomers; water is consumed.

Carbohydrates

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

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

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

• Functions: Energy storage (starch, glycogen), structural support (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 and hydrophobic tails; major component of cell membranes.

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

Proteins

• Monomers: Amino acids (20 types, differing in R group).

• Polypeptides: Chains of amino acids.

• Levels of Structure:

  • Primary: Sequence of amino acids.

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

  • Tertiary: 3D folding due to side chain interactions.

  • Quaternary: Multiple polypeptides assembled together.

• Functions: Enzymes, structural support, transport, signaling, defense, etc.

Nucleic Acids

• Types: DNA and RNA.

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

• DNA vs. RNA: DNA is double-stranded, contains deoxyribose, bases A, T, C, G; RNA is single-stranded, contains ribose, bases A, U, C, G.

• Function: Store and transmit genetic information; gene expression (DNA → RNA → Protein).

Additional info: This guide expands on the review outline by providing definitions, examples, and context for each concept, ensuring a comprehensive overview suitable for exam preparation.