General Biology Practice Exam Study Guide: Foundations of Biological Chemistry and Macromolecules

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Foundations of Scientific Inquiry

Scientific Method and Acceptance of Theories

The scientific method is a systematic approach to understanding natural phenomena through observation, hypothesis formation, experimentation, and analysis. Acceptance of scientific discoveries, hypotheses, or theories is based on rigorous evidence and repeated validation.

Evidence: Scientific claims must be supported by empirical data and reproducible results.
Consensus: Widespread agreement among scientists strengthens the acceptance of theories.
Authority and Belief: These are not sufficient for scientific acceptance without supporting evidence.

Classification of Life

Three Domains of Life

Biological classification divides all living organisms into three major domains: Bacteria, Archaea, and Eukarya. Each domain is distinguished by unique cellular and genetic characteristics.

Bacteria: Prokaryotic, unicellular organisms lacking a nucleus.
Archaea: Prokaryotic, often extremophiles, genetically distinct from bacteria.
Eukarya: Organisms with cells containing a nucleus and membrane-bound organelles.
Viruses: Not classified within the three domains as they are acellular and require host cells for replication.

Atomic Structure and Elements

Valence Electrons and Isotopes

Elements such as carbon, oxygen, hydrogen, and nitrogen are fundamental to life. Their chemical behavior is largely determined by the number of valence electrons.

Valence Electrons: Electrons in the outermost shell, crucial for chemical bonding.
Isotopes: Atoms of the same element with different numbers of neutrons.
Atomic Number: Number of protons in the nucleus, defines the element.
Atomic Mass: Sum of protons and neutrons.

Electron Configuration

The arrangement of electrons in an atom determines its chemical properties and reactivity.

Sodium (Na): Atomic number 11, mass number 23; 11 electrons, 11 protons, 12 neutrons.
Oxygen: Atomic number 8; 6 valence electrons.
Sulfur: Atomic number 16; 6 valence electrons.

Element	Atomic Number	Valence Electrons
Oxygen	8	6
Sulfur	16	6

Chemical Bonds and Water

Covalent and Hydrogen Bonds

Chemical bonds are forces that hold atoms together in molecules. Water's unique properties arise from its molecular structure and bonding.

Covalent Bonds: Atoms share electrons; strong and stable.
Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen).
Water Molecule: Shaped like a tetrahedron, with polar covalent bonds and the ability to form hydrogen bonds.

Bond Type	Strength	Example
Covalent	Strong	H2O (within molecule)
Hydrogen	Weak	Between H2O molecules

Water Properties

Water's ability to form hydrogen bonds leads to high cohesion, surface tension, and its role as a universal solvent.

Polarity: Oxygen is more electronegative, creating a partial negative charge.
Hydrogen Bonding: Enables water to dissolve many substances and maintain liquid state over a wide temperature range.

Acids, Bases, and pH

pH Scale and Hydrogen Ion Concentration

The pH scale measures the concentration of hydrogen ions () in a solution, indicating its acidity or basicity.

pH Formula:
Acidic Solutions: pH < 7, higher
Basic Solutions: pH > 7, lower
Neutral Solution: pH = 7

Solution	pH	Acidic/Basic
Vinegar	~3	Acidic
Black coffee	~5	Acidic
Tomato juice	~4	Acidic
Stomach acid	~2	Acidic
Household bleach	~12	Basic

Organic Molecules and Functional Groups

Functional Groups

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

Hydroxyl (-OH): Found in alcohols.
Amino (-NH2): Found in amino acids.
Carboxyl (-COOH): Found in organic acids.
Phosphate (-PO4): Found in nucleotides.
Aldehyde (-CHO): Found in sugars.

Functional Group	Example Molecule
Hydroxyl	Ethanol
Amino	Methylamine
Carboxyl	Propionic acid
Phosphate	Methyl phosphate
Aldehyde	Propionaldehyde

Macromolecules: Carbohydrates, Proteins, and Lipids

Carbohydrates

Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. They serve as energy sources and structural components.

Monosaccharides: Simple sugars (e.g., glucose).
Disaccharides: Two monosaccharides joined by glycosidic bonds (e.g., maltose).
Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).
Dehydration Synthesis: Formation of covalent bonds by removal of water.
Hydrolysis: Breaking covalent bonds by addition of water.

Type	Example	Bond
Monosaccharide	Glucose	None
Disaccharide	Maltose	Glycosidic
Polysaccharide	Starch	Glycosidic

Proteins

Proteins are polymers of amino acids linked by peptide bonds. They perform diverse functions including catalysis, structure, and transport.

Primary Structure: Sequence of amino acids.
Secondary Structure: Alpha helices and beta sheets formed by hydrogen bonding.
Tertiary Structure: Three-dimensional folding due to side chain interactions.
Quaternary Structure: Association of multiple polypeptide chains.
Peptide Bond Formation:

Lipids

Lipids are hydrophobic molecules including fats, oils, and phospholipids. They are important for energy storage and membrane structure.

Saturated Fatty Acids: No double bonds; solid at room temperature.
Unsaturated Fatty Acids: One or more double bonds; liquid at room temperature.
Phospholipids: Major component of cell membranes.

Nucleic Acids

Structure and Function

Nucleic acids (DNA and RNA) store and transmit genetic information. They are polymers of nucleotides.

Nucleotide: Composed of a sugar, phosphate group, and nitrogenous base.
DNA: Double-stranded, contains deoxyribose.
RNA: Single-stranded, contains ribose.

Additional info:

Some questions referenced diagrams and chemical structures; functional group matching and macromolecule identification are common exam topics.
Practice questions cover foundational concepts in atomic structure, chemical bonding, macromolecule synthesis, and biological classification, all central to General Biology.