Introduction to Biology

Features of Life

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

• Order: Organisms exhibit complex but ordered organization, such as the structured arrangement of cells in plants and animals.

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

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

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

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

• Response to Environment: Organisms detect and respond to environmental stimuli.

• Reproduction: Organisms reproduce, passing genetic information to offspring.

Levels of Biological Organization

Life is organized in a hierarchical structure, from the broadest to the most specific levels.

• Biosphere: All environments on Earth that support life.

• Ecosystem: All living and nonliving components in a particular area (e.g., desert, forest).

• Community: All living organisms in an ecosystem.

• Population: Interacting group of individuals of one species.

• Organism: An individual living entity.

• Organ: Structure composed of tissues with a specific function.

• Tissue: Group of similar cells performing a function.

• Cell: Basic unit of life capable of all life processes.

• Organelle: Functional components within cells (e.g., nucleus, mitochondria).

• Molecule: Chemical structure consisting of two or more atoms.

Cell Types & Genetics

• Eukaryotic Cells: Contain membrane-bound organelles, including a nucleus.

• Prokaryotic Cells: Lack a nucleus and other membrane-bound organelles.

• DNA: The hereditary material in cells, composed of four bases: adenine, thymine, cytosine, and guanine.

The Flow of Energy

• Energy flows from the sun to producers (plants), then to consumers (animals), and finally to decomposers.

• First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

• Decomposers: Break down organic matter, recycling nutrients back into the ecosystem.

Regulation in Organisms

• Negative Feedback: A process that reduces the initial stimulus (e.g., insulin regulation of blood glucose).

• Positive Feedback: A process that amplifies the initial stimulus (e.g., blood clotting).

Taxonomy & Species Diversity

• About 1.8 million species have been identified and named, but estimates range from 10 to 100 million total species.

• Each species has a two-part scientific name: Genus and species (e.g., Homo sapiens).

• Taxonomic classification was developed by Carl Linnaeus, using Latin names and grouping by shared features.

Taxonomic Hierarchy

Organisms are classified into a series of hierarchical categories:

• Domain (e.g., Eukarya, Bacteria, Archaea)

• Kingdom (e.g., Animalia, Plantae, Fungi, Protista)

• Phylum

• Class

• Order

• Family

• Genus

• Species

Evolution & Natural Selection

• Evolution: Change in the genetic composition of a population over generations.

• Natural Selection: Mechanism of evolution where individuals with advantageous traits survive and reproduce more successfully.

• Key Observations:

  1. Variation in traits

  2. Competition for resources

  3. Adaptation to the environment

• Example: Darwin's finches evolved different beak shapes to exploit different food sources.

• Unity in Diversity: All life shares common ancestry, but adaptations lead to diversity (e.g., similar forelimb structures in bats, humans, whales).

Scientific Method & Inquiry

• Science is based on observation, hypothesis formation, and testing.

• Hypothesis: A testable and falsifiable explanation for observations.

• Deductive Reasoning: Using general premises to make specific predictions ("if...then" statements).

• Steps of the Scientific Method:

  1. Observation

  2. Question

  3. Hypothesis

  4. Prediction

  5. Experiment or further observation

Chemistry of Life

Matter & Elements

• Matter: Anything that has mass and occupies space; composed of atoms.

• Element: A substance that cannot be broken down into other substances by chemical means; 92 natural elements exist.

• About 20-25% of elements are essential to life; CHON (carbon, hydrogen, oxygen, nitrogen) make up 96% of living matter.

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

• Compound: Substance consisting of two or more elements in a fixed ratio (e.g., water, ).

Atomic Structure

• Atom: Smallest unit of an element, composed of protons, neutrons, and electrons.

• Protons: Positively charged, determine atomic number and identity.

• Neutrons: No charge, contribute to atomic mass.

• Electrons: Negatively charged, orbit the nucleus in electron shells.

• Atomic Number: Number of protons.

• Mass Number: Sum of protons and neutrons.

• Atomic Mass: Total mass of an atom.

Formulas:

• Number of neutrons:

• Uncharged element:

Electron Shells & Energy

• Energy: Capacity to cause change; electrons have potential energy based on their position.

• Electrons in higher shells have more energy.

• First shell holds 2 electrons; outer shells hold up to 8 electrons.

Chemical Bonding & Reactivity

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

• Atoms with full valence shells are inert (noble gases); those with incomplete shells are reactive.

• Atoms form chemical bonds to achieve stable electron configurations.

Covalent Bonds

• Atoms share pairs of valence electrons.

• Single bond: One pair shared ().

• Double bond: Two pairs shared ().

• Nonpolar covalent bond: Electrons shared equally.

• Polar covalent bond: Electrons shared unequally, creating partial charges.

Isotopes

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

• Radioactive isotopes: Unstable, decay spontaneously, used in dating fossils, tracing atoms, and medical diagnostics.

Ionic Bonds

• Formed when electrons are transferred from one atom to another, creating ions.

• Cation: Positively charged ion.

• Anion: Negatively charged ion.

• Ionic bond: Attraction between cation and anion (e.g., NaCl).

Weak Chemical Bonds

• Hydrogen bonds: Weak bonds between a hydrogen atom covalently bonded to one electronegative atom and attracted to another.

• Van der Waals interactions: Weak attractions due to transient local charges.

Water and Its Properties

Importance of Water

Water is essential for life and exhibits unique properties due to its molecular structure and hydrogen bonding.

Four Properties of Water

1. Cohesive Behavior: Water molecules stick together (cohesion) due to hydrogen bonding, aiding transport in plants. Adhesion is attraction between water and other substances. Surface tension is high in water.

2. Ability to Moderate Temperature: Water absorbs and releases heat with little temperature change due to high specific heat. Calorie (cal): Heat needed to raise 1g of water by 1°C.

3. Expansion Upon Freezing: Ice is less dense than liquid water, so it floats. Water is densest at 4°C.

4. Versatility as a Solvent: Water dissolves many substances, forming aqueous solutions. Hydrophilic substances have affinity for water; hydrophobic substances do not.

Acids, Bases, and pH

• Acid: Increases hydrogen ion concentration () in solution. Example:

• Base: Reduces hydrogen ion concentration, often by accepting or releasing . Example:

• pH Scale: Measures concentration; scale from 0 (acidic) to 14 (basic), with 7 as neutral. Each unit change is a tenfold change in concentration.

Organic Chemistry and Biomolecules

Organic Chemistry

• Study of carbon-containing compounds; living things are carbon-based.

• Carbon forms four covalent bonds, allowing for diverse molecules.

• Stanley Miller's experiment demonstrated synthesis of organic molecules under early Earth conditions.

Carbon Bonding Properties

• Carbon can form single, double, or triple bonds, and chains or rings.

• Valence electrons: Hydrogen (1), Oxygen (6), Nitrogen (5), Carbon (4).

• Bond polarity affects molecule properties (nonpolar = equal sharing; polar = unequal sharing).

Isomers

• Structural isomers: Differ in covalent arrangement of atoms.

• Cis-trans isomers: Differ in spatial arrangement around double bonds (cis = same side, trans = opposite sides).

• Enantiomers: Mirror images due to asymmetric carbon ("handedness").

Functional Groups

Groups of atoms attached to carbon skeletons that confer specific properties.

• Hydroxyl (-OH): Polar, forms hydrogen bonds (e.g., alcohols).

• Carbonyl (C=O): Found in ketones and aldehydes.

• Carboxyl (-COOH): Acts as an acid (e.g., amino acids).

• Amino (-NH2): Acts as a base (e.g., ammonia).

• Sulfhydryl (-SH): Forms disulfide bonds in proteins.

• Phosphate (-PO4): Contributes negative charge, involved in energy transfer (e.g., ATP).

• Methyl (-CH3): Affects gene expression and molecular shape.

ATP (Adenosine Triphosphate)

• Primary energy carrier in cells; releases energy when phosphate bonds are broken.

Biological Macromolecules

Macromolecules Overview

• Four major classes: Carbohydrates, Lipids, Proteins, Nucleic Acids.

• Most are polymers made from monomers via dehydration reactions (release water); broken down by hydrolysis (add water).

Carbohydrates

• Composed of carbon, hydrogen, and oxygen.

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

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

• Polysaccharides: Long chains for storage (starch in plants, glycogen in animals) or structure (cellulose in plants, chitin in arthropods).

Lipids

• Hydrophobic molecules, not true polymers.

• Fats: Glycerol + fatty acids; energy storage, insulation, cushioning.

• Saturated fats: No double bonds, solid at room temperature (animal fats).

• Unsaturated fats: One or more double bonds, liquid at room temperature (plant oils).

• Trans fats: Produced by hydrogenation; associated with health risks.

• Phospholipids: Two fatty acids + phosphate group; form cell membranes (hydrophilic head, hydrophobic tails).

• Steroids: Four fused carbon rings; include cholesterol and hormones.

Proteins

• Composed of amino acids (20 types); perform diverse functions (enzymes, defense, transport, support, movement).

• Primary structure: Sequence of amino acids.

• Secondary structure: Coils and folds (alpha helices, beta sheets).

• Tertiary structure: 3D shape due to side chain interactions.

• Quaternary structure: Association of multiple polypeptide chains.

Table: Main Types of Biological Macromolecules

Additional info: Nucleic acids (DNA and RNA) are not detailed in the provided notes but are a key class of macromolecules in biology.