General Biology: Foundational Concepts and Chemical Principles

Foundations of Scientific Inquiry

Occam's Razor and Scientific Models

Occam's Razor is a principle used in science to guide the development of models and explanations. It suggests that, when presented with competing hypotheses, the one with the fewest assumptions should be selected.

• Occam's Razor: Prefers simpler scientific models when multiple explanations are possible.

• Scientific Models: Representations or simulations of natural phenomena used to predict and explain observations.

• Critical Thinking: Science relies on observation, experimentation, and the willingness to revise models based on new evidence.

• Example: In biology, the simplest explanation for a trait's inheritance is often preferred until evidence suggests otherwise.

Cellular Organization

Prokaryotic vs. Eukaryotic Cells

Cells are the basic units of life, and they are classified as either prokaryotic or eukaryotic based on their structural features.

• Prokaryotic Cells: Lack a membrane-bound nucleus and organelles. Examples include Bacteria and Archaea.

• Eukaryotic Cells: Possess a nucleus and membrane-bound organelles. Examples include Plants, Animals, Fungi, and Protists.

• Unique Prokaryotic Features:

  • Cell wall composition (e.g., peptidoglycan in bacteria)

  • Circular DNA located in the nucleoid region

  • Absence of membrane-bound organelles

• Example: Only prokaryotes can fix atmospheric nitrogen directly (e.g., Cyanobacteria).

Unifying Themes in Biology

Major Themes

Biology is organized around several unifying themes that help explain the diversity and complexity of life.

• Interactions: Organisms interact with each other and their environment.

• Circulation: Movement of living things and substances through closed systems (e.g., blood circulation).

• Energy and Matter: Life requires the transformation of energy and matter.

• Organization: New properties emerge at successive levels of biological organization.

• Example: The flow of energy from sunlight to chemical energy in photosynthesis.

Evolutionary Relationships

Cladograms and Domains of Life

Cladograms are diagrams that depict evolutionary relationships among organisms. The three domains of life are Bacteria, Archaea, and Eukarya.

• Cladogram: A branching diagram showing evolutionary relationships.

• Domains:

  • Bacteria: Prokaryotic, diverse metabolic pathways.

  • Archaea: Prokaryotic, often extremophiles.

  • Eukarya: Eukaryotic, includes plants, animals, fungi, and protists.

• Example: Placement of Domain Eukarya on a cladogram based on rRNA sequence analysis.

Atomic Structure and Chemical Bonds

Subatomic Particles

Atoms are composed of subatomic particles: protons, neutrons, and electrons, each with distinct properties.

Particle	Charge	Location
Electron	Negative (-1)	Energy shells around nucleus
Neutron	Neutral (0)	Atomic nucleus
Proton	Positive (+1)	Atomic nucleus

• Example: Hydrogen atom has one proton and one electron.

Hydrogen Bonds in Biology

Hydrogen bonds are weak interactions important in biological molecules, such as water and DNA.

• Hydrogen Bond: Attraction between a hydrogen atom covalently bonded to an electronegative atom (like oxygen or nitrogen) and another electronegative atom.

• Examples in Biology:

  • Between water molecules

  • Between base pairs in DNA

Chemical Bond Types

Atoms and molecules interact through various types of chemical bonds, which determine the properties of compounds.

• Covalent Bonds: Sharing of electron pairs between atoms.

• Ionic Bonds: Complete transfer of electrons from one atom to another, resulting in charged ions.

• Hydrogen Bonds: Weak attractions involving hydrogen atoms.

• van der Waals Interactions: Weak, transient attractions between molecules.

• Example: Sodium chloride (NaCl) forms via ionic bonding.

Ions and Isomers

Formation of Ions

Atoms become ions by gaining or losing electrons. The loss of an electron results in a positively charged ion (cation).

• Cation: Positively charged ion (e.g., potassium ion after losing one electron).

• Anion: Negatively charged ion (gains electrons).

• Isomer: Molecules with the same chemical formula but different structures.

• Example: Potassium (atomic number 19) loses one electron to become K+.

Properties of Water

Heat of Vaporization and Cooling Effect

Water has a high heat of vaporization, which is crucial for temperature regulation in living organisms.

• Heat of Vaporization: The amount of energy required to convert 1 gram of liquid water to vapor without temperature change.

• Cooling Effect: As water evaporates, it absorbs heat from the surface, cooling the organism (e.g., sweating in humans).

• Equation: $q = m imes L_v$ where $q$ is heat absorbed, $m$ is mass, and $L_v$ is latent heat of vaporization.

• Example: Evaporation of sweat helps maintain body temperature.

Organic Molecules and Functional Groups

Bond Types and Isomerism

Organic molecules contain various types of bonds and can exist as isomers, including cis-trans isomers.

• Double Bond: The dashed-line arrow in the diagram indicates a carbon-carbon double bond.

• Cis-Trans Isomers: Isomers with different spatial arrangements around a double bond.

• Example: 2-butene can exist as cis-2-butene and trans-2-butene.

Functional Groups in Organic Chemistry

Functional groups are specific groups of atoms within molecules that determine their chemical properties.

Molecular Formula	Functional Group Name
NH2	Amino
CH3	Methyl
OPO3(OH)2	Phosphate
COOH	Carboxyl
SH	Sulfhydryl
OH	Hydroxyl

• Example: The carboxyl group (-COOH) is found in amino acids.