General Biology Exam Review: Chapters 2–7 Study Guide

Elements, Atoms, and Chemical Bonds

Essential Elements of Life

Living organisms are primarily composed of a few key elements. Understanding these elements and their interactions is fundamental to biology.

• Key Elements: Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N) make up approximately 96% of living matter.

• Valence Electrons: The subatomic particles involved in chemical bonding between atoms are the valence electrons.

Chemical Bonds and Properties

Chemical bonds are the forces that hold atoms together in molecules and compounds. The nature of these bonds determines the properties of substances.

• Covalent Bonds: Atoms share electrons. If shared equally, the bond is nonpolar; if unequally, the bond is polar.

• Hydrogen Bonds: Weak bonds between a partially positive hydrogen atom and a partially negative atom (often oxygen or nitrogen).

• Ionic Bonds: Formed when electrons are transferred from one atom to another, resulting in oppositely charged ions.

• Van der Waals Interactions: Weak attractions between molecules or parts of molecules that result from transient local partial charges.

Key Terms and Definitions

Term	Definition
Energy	The capacity to cause change.
Kinetic Energy	Energy of motion.
Electronegativity	The tendency of an atom to attract electrons in a covalent bond.
Polar Covalent Bond	The sharing of a pair of valence electrons by two atoms causes partial charges.
Nonpolar Covalent Bond	Atoms share electrons equally.
Ionic Bond	Bond between oppositely charged ions.
Hydrogen Bond	Bond between a partially charged hydrogen and another electronegative atom.
Van der Waals Interactions	Weak attractions due to transient partial charges.

Water and Its Properties

Structure and Polarity

Water is a polar molecule, with oxygen being more electronegative than hydrogen, resulting in partial charges.

• Hydrogen Bonds: Form between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another.

Properties of Water (CAVE)

• Cohesion: Water molecules stick to each other via hydrogen bonds.

• Ability to modify temperature

• Versatility as a Solvent: Water dissolves many substances due to its polarity.

• Expansion upon Freezing: Ice is less dense than liquid water due to hydrogen bond arrangement.

Example: The cooling effect from sweating is due to water's high heat of vaporization, which removes heat as water evaporates from the skin.

pH and Buffers

The pH scale measures the concentration of hydrogen ions in a solution.

• pH Equation:

$[H^+][OH^-] = 10^{-14}$

$pH = -\log[H^+]$

• At neutral pH (7): $[H^+] = [OH^-] = 10^{-7}$ M

• Lower pH = more acidic; higher pH = more basic.

Macromolecules: Structure and Function

Types of Macromolecules

Macromolecule	Monomer	Polymer	Type of Bond
Carbohydrates	Monosaccharide	Polysaccharide	Glycosidic linkage
Proteins	Amino acid	Polypeptide	Peptide bond
Nucleic Acids	Nucleotide	Polynucleotide (DNA/RNA)	Phosphodiester bond
Lipids	Glycerol & Fatty acids	Triglyceride	Ester linkage

Polymerization and Hydrolysis

• Dehydration Synthesis: Links monomers together, releasing water as a by-product.

• Hydrolysis: Breaks polymers into monomers by adding water.

Carbohydrates

• Monomers: Glucose, fructose, galactose, etc.

• Polymers: Starch (plants), glycogen (animals), cellulose (plants).

• Structural Differences: Cellulose has β(1→4) linkages; glycogen and starch have α(1→4) linkages.

Lipids

Types of Fat	Description	Form at Room Temp
Unsaturated (Cis)	Cis double bonds	Liquid
Saturated	Maximum number of hydrogens, no double bonds	Solid

• Phospholipids: Composed of a hydrophilic head and hydrophobic tails; form bilayers in cell membranes.

Proteins

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.

• Tertiary Structure: 3D folding due to side chain interactions.

• Quaternary Structure: Association of multiple polypeptide chains.

• Amino Acids: Differ by their side chains (R groups); 20 standard amino acids.

Functional Groups

Group	Structure	Polar or Nonpolar
Hydroxyl	–OH	Polar
Carbonyl	–C=O	Polar
Amino	–NH2	Polar
Sulfhydryl	–SH	Nonpolar
Phosphate	–PO4	Polar
Methyl	–CH3	Nonpolar

• Acidic Group: Carboxyl (–COOH)

• Basic Group: Amino (–NH2)

Isomers

Isomer	Description
Enantiomers	Mirror images; asymmetric carbon with four different groups.
Structural Isomers	Different covalent arrangements of atoms.
Cis-Trans Isomers	Same covalent bonds but differ in spatial arrangement due to double bonds.

Cell Structure and Function

Animal vs. Plant Cells

Animal	Plant
No cell wall, no chloroplasts, small vacuoles	Cell wall, chloroplasts, large central vacuole
Similarity: Both have nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, etc.

Prokaryotic vs. Eukaryotic Cells

Prokaryotic	Eukaryotic
No nucleus, no membrane-bound organelles	Nucleus, membrane-bound organelles
Smaller, simpler	Larger, more complex

Cell Organelles and Functions

• Nucleus: Contains most of the cell's DNA.

• Centrosome: Contains two centrioles in animal cells; important for cell division.

• Lysosome: Contains hydrolytic enzymes for digestion.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

Cell Membranes and Transport

Structure of the Cell Membrane

• Phospholipid Bilayer: Major structural component; hydrophilic heads face outward, hydrophobic tails inward.

• Integral Proteins: Span the membrane; have hydrophobic and hydrophilic regions.

• Peripheral Proteins: Attached to the membrane surface.

Transport Across Membranes

• Simple Diffusion: Small, nonpolar molecules (e.g., O2, CO2) cross freely.

• Facilitated Diffusion: Transport proteins help polar or charged molecules cross.

• Active Transport: Requires energy to move substances against their concentration gradient.

Examples: Glucose and ions require transport proteins; water can cross via aquaporins.

Summary Table: Molecule Transport

Type of Molecule	Can Cross Freely?	Requires Transport Protein?
Small nonpolar (O2, CO2)	Yes	No
Large polar (glucose)	No	Yes
Ions (Na+, K+)	No	Yes
Water	Limited	Yes (aquaporins)

Additional info: This study guide covers foundational topics in general biology, including atomic structure, chemical bonding, macromolecules, cell structure, and membrane transport, suitable for exam preparation in a college-level introductory biology course.