Core Concepts in General Biology: Classification, Chemistry, and Biological Molecules

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Biological Classification and Organization

Scientific Naming and Taxonomy

Biological classification uses a hierarchical system to organize living organisms. The scientific name of an organism is based on binomial nomenclature, which includes the genus and species.

Genus: The first part of the scientific name; always capitalized (e.g., Homo in Homo sapiens).
Species: The second part of the name; always lowercase (e.g., sapiens in Homo sapiens).
Example: Homo sapiens is the scientific name for humans, where Homo is the genus and sapiens is the species.

Characteristics of Living Organisms

All living organisms share certain fundamental characteristics, though some features may vary among groups.

Structure and Function of DNA: All living organisms use DNA as their genetic material, which encodes instructions for growth, development, and reproduction.
Other Features: While many organisms are multicellular or reproduce sexually, these are not universal traits.

Levels of Biological Organization

Biological systems are organized into hierarchical levels, from the simplest to the most complex.

Organ System: Groups of organs working together (e.g., digestive system).
Individual: A single organism.
Population: A group of individuals of the same species in a given area.
Biosphere: The global sum of all ecosystems; the most complex level.
Example: The biosphere includes all living things and their environments on Earth.

Cell Theory and Scientific Method

Discovery of the Cell

The invention of the microscope was crucial for the discovery of cells, allowing scientists to observe structures not visible to the naked eye.

Microscope: Instrument that magnifies small objects, leading to the discovery of cells by Robert Hooke in 1665.

Scientific Hypotheses, Theories, and Laws

The scientific method involves forming hypotheses, testing them, and developing theories or laws based on evidence.

Hypothesis: A tentative explanation or assumption made before research is conducted.
Theory: A well-substantiated, unifying explanation for a set of verified facts, supported by extensive evidence.
Law: A statement describing consistent natural phenomena, often expressed mathematically.
Example: The cell theory is a unifying concept in biology, stating that all living things are composed of cells.

Chemical Bonds and Water Properties

Chemical Bonds in Biology

Atoms interact to form molecules through different types of chemical bonds, each with distinct properties and strengths.

Covalent Bond: Formed by the sharing of electrons between atoms.
Ionic Bond: Formed by the transfer of electrons from one atom to another, resulting in oppositely charged ions.
Hydrogen Bond: A weak bond between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).
Van der Waals Interactions: Weak attractions between molecules due to temporary dipoles.

Relative Bond Strengths (Strongest to Weakest):

Bond Type	Relative Strength
Ionic	Strong
Covalent	Strong
Hydrogen	Weak
Van der Waals	Very Weak

Example Sequence: Ionic > Covalent > Hydrogen > Van der Waals

Properties of Water

Water's unique properties are essential for life and are due to its molecular structure and hydrogen bonding.

Hydrogen Bonding: Each water molecule can form up to four hydrogen bonds, leading to high cohesion, surface tension, and heat capacity.
Heat Absorption: Water has a high heat-absorbing capacity due to extensive hydrogen bonding, which must be disrupted before temperature rises.
Hydration Shell: Water molecules form hydration shells around ions (e.g., in salt solutions), stabilizing them in solution.
Example: Salt (NaCl) dissolves in water, allowing water molecules to form a hydration shell around Na+ and Cl- ions.

pH and Acidity

pH is a measure of the concentration of protons (H+) in a solution.

Low pH: Indicates a high concentration of protons (acidic solution).
High pH: Indicates a low concentration of protons (basic solution).
Equation:
Example: The stomach has a low pH due to high H+ concentration.

Antacids and pH Regulation

Antacids such as sodium bicarbonate relieve acid reflux by neutralizing stomach acid and increasing pH.

Mechanism: Sodium bicarbonate reacts with hydrochloric acid (HCl) in the stomach to form water, carbon dioxide, and salt, raising the pH.
Equation:

Biological Molecules and Functional Groups

Functional Groups

Functional groups are specific groups of atoms within molecules that have characteristic properties and reactivity.

Hydroxyl Group: Represented by –OH; found in alcohols and many biological molecules.
Other Examples: –SH (sulfhydryl), –NH2 (amino), –CH3 (methyl).

Polysaccharides and Carbohydrates

Polysaccharides are large carbohydrates composed of many monosaccharide units linked by glycosidic bonds.

Examples: Starch, cellulose, and glycogen are all polysaccharides.
General Formula for Glucose Polymerization: When n glucose molecules (C6H12O6) are joined, the formula is C6nH12nO6n minus water for each glycosidic bond formed.
Example: A polymer with formula C12H22O11 is made from 2 glucose units (as in maltose).

Nucleic Acids and Monomers

Nucleic acids (DNA and RNA) are polymers made up of nucleotide monomers.

Nucleotide: Consists of a phosphate group, a five-carbon sugar, and a nitrogenous base.
Example: ATP (adenosine triphosphate) is a nucleotide used for energy transfer.

Fatty Acids: Saturated vs. Unsaturated

Fatty acids are classified based on the presence or absence of double bonds in their hydrocarbon chains.

Saturated Fatty Acids: Have only single carbon-carbon bonds; solid at room temperature.
Unsaturated Fatty Acids: Have one or more double carbon-carbon bonds; usually liquid at room temperature.
Example: Stearic acid (saturated), oleic acid (unsaturated).

Metabolism and Energy

Cells metabolize certain biomolecules to generate energy, while others serve different functions.

Carbohydrates and Proteins: Both can be metabolized for energy.
Vitamins: Not metabolized for energy; function as coenzymes or cofactors in metabolic reactions.

Summary Table: Key Biological Molecules

Molecule Type	Monomer	Example	Main Function
Carbohydrate	Monosaccharide	Glucose, Starch	Energy storage, structure
Protein	Amino acid	Enzyme, Hemoglobin	Catalysis, structure, transport
Nucleic Acid	Nucleotide	DNA, RNA	Genetic information
Lipid	Fatty acid, glycerol	Triglyceride	Energy storage, membranes