General Biology Study Notes: Taxonomy, Chemistry of Life, Atomic Structure, Chemical Bonds, Acids & Bases, and Buffers

Taxonomy and Classification of Life

Taxonomy: Organizing Species

Taxonomy is the science of classifying organisms into groups based on shared characteristics. This system helps biologists organize and understand the diversity of life.

• Species: The basic unit of classification, defined as a group of organisms capable of interbreeding and producing fertile offspring.

• Domains: The highest taxonomic rank, including Bacteria, Archaea, and Eukarya.

• Kingdoms: Subdivisions within domains, such as Animalia, Plantae, Fungi, Protista, etc.

Example: Humans are classified as Homo sapiens in the domain Eukarya, kingdom Animalia.

Bacteria and Archaea

Bacteria and Archaea are prokaryotic domains, meaning their cells lack a nucleus and membrane-bound organelles.

• Bacteria: Characterized by unique cell wall structures and diverse metabolic pathways.

• Archaea: Often found in extreme environments; cell walls lack peptidoglycan.

Eukarya

Eukaryotes have cells with a nucleus and membrane-bound organelles. They can be unicellular or multicellular.

• Examples: Animals, plants, fungi, and protists.

Scientific Method

The scientific method is a systematic approach to investigation and discovery in science.

• Steps: Observation, hypothesis, experiment, analysis, conclusion.

Chemical Context of Life

Matter and Elements

Matter is anything that occupies space and has mass. Elements are substances that cannot be broken down into simpler substances by chemical means.

• Major elements in biology: C, H, O, N (make up 96% of living matter).

• Trace elements: Na, Mg, K, Ca (essential in small amounts; all have positive charge).

Atomic Structure

Atoms: Basic Units of Matter

An atom consists of a nucleus (protons and neutrons) surrounded by electrons.

• Proton: Positively charged particle in the nucleus.

• Neutron: Neutral particle in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

Atomic Number and Mass Number

• Atomic number: Number of protons; unique to each element.

• Mass number: Sum of protons and neutrons.

Isotopes and Radioactive Isotopes

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

• Radioactive isotopes: Unstable isotopes that decay over time, emitting radiation; used in medicine and research.

Electron Shells and Energy Levels

Electron Shells

Electrons occupy energy levels called shells around the nucleus. The arrangement of electrons determines chemical reactivity.

• Valence shell: Outermost shell; determines bonding behavior.

• Stable configuration: Atoms are most stable when their valence shell is full.

Energy and Electron Excitation

• Electrons can absorb energy and move to higher shells (excited state).

• When electrons return to lower energy levels, energy is released (often as light).

Chemical Bonds and Molecular Structure

Types of Chemical Bonds

Chemical bonds hold atoms together in molecules and compounds.

• Covalent bonds: Atoms share electrons; can be single, double, or triple bonds.

• Ionic bonds: Electrons are transferred from one atom to another, creating charged ions that attract each other.

• Polar covalent bonds: Electrons are shared unequally, resulting in partial charges.

• Nonpolar covalent bonds: Electrons are shared equally.

Electronegativity and Polarity

• Electronegativity: The ability of an atom to attract electrons in a bond.

• Polarity: Molecules with uneven distribution of charge (e.g., water).

Molecular Shapes and Interactions

• Molecular shape: Determined by the arrangement of atoms and electron pairs.

• Hydrophobic interactions: Nonpolar molecules tend to group together in water.

Acids, Bases, and pH

Definitions and Properties

• Acids: Donate H+ ions in solution.

• Bases: Accept H+ ions or produce OH- ions.

pH Scale

• pH: Measure of hydrogen ion concentration; scale ranges from 0 (acidic) to 14 (basic).

• Formula: $pH = -\log[H^+]$

• Each unit change in pH represents a tenfold change in [H+].

Acid-Base Equilibrium

• Equilibrium: $K_{eq} = \frac{[products]}{[reactants]}$

• Water dissociation: $H_2O \rightleftharpoons H^+ + OH^-$

Buffers and Biological pH Regulation

Buffer Systems

Buffers help maintain stable pH in biological systems by neutralizing excess acids or bases.

• Bicarbonate buffer system: $H_2CO_3 \rightleftharpoons HCO_3^- + H^+$

• Buffers resist changes in pH by reversible binding of H+ ions.

Biological Importance

• Maintaining pH is crucial for enzyme function and metabolic processes.

• Blood pH is tightly regulated by buffer systems.

Summary Table: Types of Chemical Bonds

Bond Type	Electron Sharing/Transfer	Example	Strength
Covalent	Shared	H2O, O2	Strong
Ionic	Transferred	NaCl	Moderate
Hydrogen	Attraction between polar molecules	Between water molecules	Weak

Additional info: Some explanations and examples have been expanded for clarity and completeness, including the importance of buffers and the role of electronegativity in bond formation.