General Biology Exam I Study Guide: Foundations, Chemistry of Life, and Cell Membranes

Biology: The Study of Life

Defining Life and Its Characteristics

Biology is the scientific study of life, focusing on organisms and their interactions with the environment. Living organisms share five fundamental characteristics:

• Cells: All organisms are made up of membrane-bound cells.

• Replication: All organisms are capable of reproduction.

• Information: Organisms process hereditary information encoded in genes and respond to environmental information.

• Energy: All organisms acquire and use energy to stay alive.

• Evolution: Populations of organisms are continually evolving.

The Scientific Process

Steps of the Scientific Method

The scientific method is a systematic approach to investigation and problem-solving in biology.

• Observation

• Hypothesis

• Prediction

• Experimental test

• Results

A hypothesis is a testable statement that explains an observation or answers a question. A prediction is a measurable or observable result that would support a hypothesis.

Experimental Design

Attributes of a Well-Designed Experiment

Experiments must be carefully designed to test hypotheses:

• Variables: Characteristics that can change.

• Independent variable: Manipulated by the researcher.

• Dependent variable: Responds to changes in the independent variable.

• Control group: Maintained under standard conditions, not exposed to the independent variable.

• Experimental group: Exposed to the independent variable.

• Blind/double-blind strategies: Reduce bias in data collection.

Water and Carbon: The Chemical Basis of Life

Covalent Bonds and Carbon

Carbon atoms can form covalent bonds with other elements, allowing for complex molecules. Each shared pair of electrons forms a covalent bond, so carbon can make four covalent bonds.

Electrons and Electronegativity

• Electrons: Control how atoms behave and interact.

• Electronegativity: The strength with which atoms pull electrons toward themselves.

Covalent vs. Ionic Bonds

• Covalent bond: Sharing of a pair of valence electrons by two atoms.

• Ionic bond: Attraction between oppositely charged ions after electron transfer.

Potential Energy in Chemical Bonds

• Nonpolar bonds: High potential energy (e.g., C-H bonds).

• Polar bonds: Lower potential energy (e.g., C-O bonds).

Example: Glucose (C6H12O6) contains many C-H and C-C bonds, which store energy. Fats provide about 9 calories per gram, carbohydrates about 4 calories per gram.

Properties of Water

Emergent Properties of Water

• Cohesion, adhesion, and surface tension

• Water as an efficient solvent

• Expansion upon freezing

• Moderation of temperature

• Water and acid-base reactions

Types of Bonds in Water

• Hydrogen bonds: Between water molecules.

• Covalent bonds: Within a water molecule.

Protein Structure and Function

Formation and Breakdown of Polymers

• Dehydration/condensation reactions: Form polymers.

• Hydrolysis: Breaks down polymers.

Levels of Protein Structure

• Primary: Peptide bond

• Secondary: Hydrogen bond

• Tertiary: Hydrogen bond, covalent disulfide bond, ionic bond

• Quaternary: Multiple polypeptide chains

Protein Denaturation

A denatured (unfolded) protein is unable to function normally.

Nucleic Acids and the Genetic Code

Nucleotide Structure and Base Pairing

• DNA bases: A (adenine), T (thymine), C (cytosine), G (guanine)

• RNA bases: A (adenine), U (uracil), C (cytosine), G (guanine)

• Base pairing rules: DNA: C-G, A-T; RNA: C-G, A-U

• Strand direction: 5' end has phosphate group, 3' end has free OH group

Carbohydrates

Glycosidic Linkages

A glycosidic linkage is a covalent bond formed when two monosaccharides join through a dehydration/condensation reaction.

Cellulose vs. Starch

• Cellulose: Structural polysaccharide in plants

• Starch: Energy storage polysaccharide in plants

Lipids and Membranes

Phospholipids and Amphipathic Molecules

Phospholipids are amphipathic molecules with a hydrophilic head (glycerol + phosphate group) and hydrophobic tail (fatty acids).

Biological Membranes

• Phospholipid bilayer: Hydrophilic heads face outward, hydrophobic tails face inward.

• Semi-permeability: Small proteins and molecules can pass through; larger ones are blocked.

Saturated vs. Unsaturated Fats

• Saturated fats: No double bonds, solid at room temperature.

• Unsaturated fats: One or more double bonds, liquid at room temperature.

Transport Across Membranes

Concentration Gradient

A concentration gradient is created by a difference in solute concentrations. Maintaining gradients requires energy.

Passive vs. Active Transport

• Passive transport: No energy required, moves with the concentration gradient (e.g., simple diffusion, osmosis, facilitated diffusion).

• Active transport: Requires energy, moves against the concentration gradient (e.g., protein pumps).

Types of Membrane Proteins

• Channel proteins: No energy needed, open doorway for molecules moving with the gradient.

• Carrier proteins: Bind to specific molecules, change shape, and carry across the membrane.

• Pumps: Move molecules against the gradient, require ATP.

Osmosis and Tonicity

• Osmosis: Movement of water across a semipermeable membrane.

• Hypertonic solution: Higher solute concentration outside the cell; water leaves the cell.

• Hypotonic solution: Lower solute concentration outside the cell; water enters the cell.

• Isotonic solution: Equal solute concentration; no net water movement.

Co-Transport

Co-transport occurs when two or more molecules move across a membrane together, using energy from one molecule moving down its gradient to help another move against its gradient.

Type of Transport	Energy Required?	Direction Relative to Gradient	Example
Simple Diffusion	No	With gradient	O2, CO2
Facilitated Diffusion	No	With gradient	Glucose via carrier protein
Active Transport	Yes	Against gradient	Na+/K+ pump

Additional info: Some explanations and examples have been expanded for clarity and completeness, including definitions and context for key terms and processes.