Foundations of General Biology: Organization, Cell Theory, Evolution, and Chemistry of Life

Hierarchy of Biological Organization

Levels of Organization in Biology

Biological systems are organized in a hierarchical structure, from the largest scale (biosphere) to the smallest (atoms). Understanding these levels is fundamental to studying life.

• Biosphere: All living things on Earth and their environments.

• Ecosystem: A community plus its physical environment.

• Community: All populations of different species in an area.

• Population: A group of individuals of the same species.

• Organism: An individual living thing.

• Organ System: A group of organs working together for a function.

• Organ: Structure composed of different tissues.

• Tissue: Group of similar cells performing a specific function.

• Cell: Basic unit of life.

• Organelle: Specialized cell structures with specific functions.

• Molecule: Chemical structure made up of atoms.

• Atom: Smallest unit of matter.

Example: A human (organism) is made up of organ systems (e.g., circulatory system), which are composed of organs (heart), made of tissues (cardiac muscle), which are made of cells, containing organelles, built from molecules, which are made of atoms.

Characteristics of Living Things

Defining Life

Living things share several key characteristics that distinguish them from non-living matter.

• DNA: Contains genetic information; stored in the nucleus. Composed of adenine, thymine, guanine, and cytosine.

• Reproduction: Sexual (requires sperm and egg cells) and asexual (mitosis, binary fission).

• Cells: Basic unit of life. All eukaryotes.

• Metabolism: Chemical reactions in cells; in eukaryotes, ATP is produced in mitochondria.

• Growth and Development: Changes that take place over a lifetime.

• Adaptation and Evolution: Environments influence evolution.

• Homeostasis: Ability to maintain stable internal conditions.

• Response to Stimuli: Reacting to external stimuli, influencing internal processes.

Example: Humans respond to cold by shivering (response to stimulus) and maintain a constant body temperature (homeostasis).

Cell Types

• Prokaryotic Cells: Simple cells without membrane-bound organelles (e.g., bacteria).

• Eukaryotic Cells: Complex cells with membrane-bound organelles (e.g., plants, animals, fungi, protists).

Flow of Energy

• Energy flows from light to chemical energy to heat.

Symbiosis: Interactions Between Organisms

• Commensalism: One organism benefits, the other is unaffected.

• Parasitism: One benefits, one is harmed.

• Mutualism: Both organisms benefit.

Cell Theory

• All organisms are made up of cells (pattern).

• All cells come from preexisting cells (process).

Domains and Classification of Life

Three Domains of Life

All life is classified into three domains based on cellular structure and genetics.

• Bacteria: Most diverse and widespread prokaryotes.

• Archaea: Prokaryotes living in extreme environments.

• Eukarya: Includes all eukaryotic organisms.

Eukarya Domain: Kingdoms

• Kingdom Plantae

• Kingdom Animalia

• Kingdom Fungi

• Protists

Evolution and Fitness

Fitness

Fitness is an organism's ability to reproduce and pass on its genes to the next generation.

Darwin's Theory of Evolution

• Varied population needed for evolution.

• Offspring must be suited to survive and compete for resources.

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

• Population of varied traits → Elimination of individuals with certain traits → Reproduction of survivors → Increasing frequency of favorable traits.

Tree of Life

• Read from left (ancestors) to right (descendants).

• Top to bottom: oldest to most recent species.

Scientific Method

Approaches to Scientific Reasoning

• Inductive Reasoning: Drawing general conclusions from specific observations. May be logically true but not always realistic.

• Deductive Reasoning: Drawing specific conclusions from general principles. Logically and realistically true.

Chemistry of Life

Elements and Compounds

• Living organisms are primarily made of carbon, hydrogen, and oxygen.

• Element: Substance that cannot be broken down chemically.

• Compound: Combination of two or more elements in a fixed ratio.

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

• Atomic #: Number of protons in an atom.

• Mass #: Total number of protons and neutrons.

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

Electron Shells and Chemical Bonds

• Electrons are arranged in shells; first shell holds 2, second and following hold 8.

• Elements in the same column of the periodic table have similar valence electron configurations.

• More right on the periodic table = more electrons to occupy shells.

Types of Chemical Bonds

• Polar Covalent Bond: Unequal sharing of electrons between atoms with different electronegativities.

• Nonpolar Covalent Bond: Equal sharing of electrons between atoms of similar electronegativity.

• Ionic Bond: Attraction between oppositely charged ions (transfer of electrons).

• Van der Waals: Temporary attractions due to spontaneous movement of electrons.

• Hydrogen Bond: Weak bond between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Bond Strength (Weakest to Strongest): Ionic, hydrogen bonding, van der Waals (weakest); covalent (strongest).

Properties of Water

• Cohesion: Water molecules stick together.

• Polarity: Water has a partial positive and negative charge.

• High Heat Capacity: Water absorbs and retains heat well.

• Universal Solvent: Many substances dissolve in water.

• Density: Ice is less dense than liquid water.

• Capillary Action: Water moves up narrow tubes against gravity.

Acids, Bases, and pH

• pH: Measure of hydrogen ion concentration.

• Acid: Increases hydrogen ion concentration (pH < 7).

• Base: Decreases hydrogen ion concentration (pH > 7); used to regulate pH.

• pH 7: Neutral.

Formulas:

• $\text{pH} = -\log_{10}[\text{H}^+]$

Table: Comparison of Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	Absent	Present
Membrane-bound Organelles	Absent	Present
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists