Section 1 – Evolution, Themes of Biology, and Scientific Inquiry

1.1 The Study of Life Reveals Common Themes

Biology is the scientific study of life, and it encompasses several unifying themes that help organize and explain the diversity of living organisms. Understanding these themes provides a framework for studying biological systems.

• Organization: Life is structured in a hierarchical manner, from molecules to the biosphere.

• Information: Genetic information is stored in DNA and governs the functioning of organisms.

• Energy and Matter: Organisms obtain and use energy and matter to sustain life.

• Interactions: Living things interact with each other and their environment.

• Evolution: The process by which species change over time, leading to diversity and adaptation.

Example: The cellular organization of life, from organelles to cells to tissues.

1.2 The Core Theme: Evolution Accounts for the Unity and Diversity of Life

Evolution is the central concept in biology, explaining both the similarities and differences among living organisms. It is driven by mechanisms such as natural selection, genetic drift, and mutation.

• Unity: All living things share common characteristics due to descent from a common ancestor.

• Diversity: Variations arise through evolutionary processes, resulting in the vast array of species.

• Natural Selection: The process by which traits that enhance survival and reproduction become more common in a population.

Example: The finches of the Galápagos Islands, which evolved different beak shapes to exploit various food sources.

1.3 Scientific Inquiry: Forming and Testing Hypotheses

Scientific inquiry is the process by which scientists investigate the natural world. It involves making observations, forming hypotheses, conducting experiments, and analyzing data.

• Hypothesis: A testable explanation for an observation.

• Experiment: A controlled test to evaluate the validity of a hypothesis.

• Data: Quantitative or qualitative information collected during experiments.

• Conclusion: Interpretation of results to support or refute the hypothesis.

Example: Testing whether light affects plant growth by comparing plants grown in light and darkness.

Section 2 – Carbon Atoms and Large Biological Molecules

2.1 Carbon Atoms Can Form Diverse Molecules by Bonding to Four Other Atoms

Carbon is the backbone of biological molecules due to its ability to form four covalent bonds, allowing for a variety of structures such as chains, rings, and branches.

• Covalent Bond: A chemical bond formed when atoms share electrons.

• Hydrocarbons: Molecules consisting entirely of carbon and hydrogen.

• Functional Groups: Specific groups of atoms that confer particular properties to molecules.

Example: Glucose, a six-carbon sugar, forms a ring structure in solution.

2.2 Key Chemical Groups in Molecular Function

Certain chemical groups are critical for the function of biological molecules. These include hydroxyl, carbonyl, carboxyl, amino, sulfhydryl, phosphate, and methyl groups.

• Hydroxyl (-OH): Found in alcohols; increases solubility in water.

• Carboxyl (-COOH): Acts as an acid; found in amino acids and fatty acids.

• Amino (-NH2): Acts as a base; found in amino acids.

• Phosphate (-PO4): Important in energy transfer (e.g., ATP).

Example: The phosphate group in ATP enables energy storage and transfer.

2.3 Macromolecules Are Polymers Built from Monomers

Macromolecules are large biological molecules formed by joining smaller units called monomers. The four main types are carbohydrates, lipids, proteins, and nucleic acids.

• Polymer: A long molecule consisting of many similar or identical monomers linked together.

• Monomer: The building block of a polymer.

• Dehydration Synthesis: The process of joining monomers by removing water.

• Hydrolysis: The process of breaking polymers into monomers by adding water.

Example: Starch is a polymer of glucose monomers.

2.4 Carbohydrates Serve as Fuel and Building Material

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

• Monosaccharides: Simple sugars (e.g., glucose, fructose).

• Disaccharides: Two monosaccharides joined together (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

Example: Cellulose forms the structural component of plant cell walls.

2.5 Lipids: Diverse Group of Hydrophobic Molecules

Lipids are nonpolar molecules that are insoluble in water. They include fats, phospholipids, and steroids, and serve as energy storage, structural components, and signaling molecules.

• Fats: Composed of glycerol and fatty acids; store energy.

• Phospholipids: Major component of cell membranes; have hydrophilic heads and hydrophobic tails.

• Steroids: Lipids with a four-ring structure (e.g., cholesterol).

Example: Phospholipids form the bilayer of cell membranes.

2.6 Proteins: Diversity of Structure and Function

Proteins are polymers of amino acids and perform a wide range of functions, including catalysis, transport, structure, and signaling.

• Amino Acid: The monomer of proteins; contains an amino group, carboxyl group, and side chain.

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Local folding (e.g., alpha helix, beta sheet).

• Tertiary Structure: Overall 3D shape of a protein.

• Quaternary Structure: Association of multiple polypeptides.

Example: Hemoglobin is a protein that transports oxygen in blood.

2.7 Nucleic Acids: Store, Transmit, and Express Hereditary Information

Nucleic acids are polymers of nucleotides and include DNA and RNA. They store genetic information and are involved in its expression.

• DNA (Deoxyribonucleic Acid): Stores genetic information.

• RNA (Ribonucleic Acid): Transmits and helps express genetic information.

• Nucleotide: Consists of a sugar, phosphate group, and nitrogenous base.

Example: DNA encodes instructions for protein synthesis.

Section 3 – Membrane Structure and Function

3.1 Cellular Membranes: Fluid Mosaics of Lipids and Proteins

Cell membranes are composed of a phospholipid bilayer with embedded proteins, creating a dynamic and flexible structure.

• Phospholipid Bilayer: Two layers of phospholipids with hydrophilic heads and hydrophobic tails.

• Integral Proteins: Span the membrane and are involved in transport.

• Peripheral Proteins: Attached to the membrane surface.

Example: The plasma membrane regulates entry and exit of substances.

3.2 Membrane Structure Results in Selective Permeability

The structure of the membrane allows certain molecules to pass while restricting others, maintaining internal conditions.

• Selective Permeability: Only specific substances can cross the membrane.

• Transport Proteins: Facilitate movement of ions and molecules.

Example: Water passes through aquaporins, specialized channel proteins.

3.3 Passive Transport: Diffusion Across a Membrane Without Energy Investment

Passive transport involves the movement of substances down their concentration gradient without the use of cellular energy.

• Diffusion: Movement of molecules from high to low concentration.

• Facilitated Diffusion: Transport of molecules via proteins.

• Osmosis: Diffusion of water across a membrane.

Example: Oxygen diffuses into cells for cellular respiration.

3.4 Active Transport: Uses Energy to Move Solutes Against Their Gradients

Active transport requires energy (usually from ATP) to move substances against their concentration gradients.

• ATP: The energy currency of the cell.

• Pumps: Proteins that move ions or molecules (e.g., sodium-potassium pump).

Example: The sodium-potassium pump maintains ion gradients in animal cells.

3.5 Bulk Transport: Exocytosis and Endocytosis

Bulk transport moves large molecules or particles across the membrane via vesicles.

• Exocytosis: Export of materials out of the cell.

• Endocytosis: Import of materials into the cell.

• Phagocytosis: "Cell eating"; uptake of large particles.

• Pinocytosis: "Cell drinking"; uptake of fluids.

Example: White blood cells engulf bacteria by phagocytosis.

Section 4 – A Tour of the Cell

4.1 Biologists Use Microscopes and Biochemistry to Study Cells

Microscopy and biochemical techniques allow scientists to observe cell structure and function.

• Light Microscope: Uses visible light to view cells.

• Electron Microscope: Provides higher resolution images.

• Cell Fractionation: Separates cell components for study.

Example: Electron microscopy reveals the detailed structure of mitochondria.

4.2 Eukaryotic Cells Have Internal Membranes That Compartmentalize Functions

Eukaryotic cells contain membrane-bound organelles that perform specialized functions.

• Nucleus: Contains genetic material.

• Endoplasmic Reticulum: Synthesizes proteins and lipids.

• Golgi Apparatus: Modifies and sorts proteins.

Example: Plant cells have chloroplasts for photosynthesis.

4.3 Genetic Instructions Housed in the Nucleus and Carried Out by Ribosomes

The nucleus stores DNA, and ribosomes translate genetic instructions into proteins.

• DNA: Encodes genetic information.

• Ribosome: Site of protein synthesis.

Example: Messenger RNA carries instructions from DNA to ribosomes.

4.4 The Endomembrane System Regulates Protein Traffic and Performs Metabolic Functions

The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles.

• Lysosome: Digests macromolecules.

• Vesicle: Transports materials within the cell.

Example: Secretory proteins are synthesized in the ER and processed in the Golgi.

4.5 Mitochondria and Chloroplasts Change Energy from One Form to Another

Mitochondria and chloroplasts are organelles responsible for energy conversion.

• Mitochondria: Site of cellular respiration; converts glucose to ATP.

• Chloroplast: Site of photosynthesis; converts light energy to chemical energy.

Example: Mitochondria produce ATP during aerobic respiration.

4.6 The Cytoskeleton: Network of Fibres Organizing Structures and Activities

The cytoskeleton provides structural support and facilitates movement within the cell.

• Microtubules: Hollow tubes; involved in cell shape and transport.

• Microfilaments: Thin rods; involved in cell movement.

• Intermediate Filaments: Provide mechanical support.

Example: Microtubules form the spindle during cell division.

Section 5 – Metabolism

5.1 An Organism’s Metabolism Transforms Matter and Energy

Metabolism is the sum of all chemical reactions in an organism, including catabolic (breakdown) and anabolic (synthesis) pathways.

• Catabolism: Breaks down molecules to release energy.

• Anabolism: Builds complex molecules from simpler ones.

Example: Cellular respiration is a catabolic pathway.

5.2 Free-Energy Change of a Reaction Determines Spontaneity

The change in free energy () indicates whether a reaction will occur spontaneously.

• Exergonic Reaction: Releases energy; .

• Endergonic Reaction: Requires energy input; .

Formula:

where is change in enthalpy, is temperature, and is change in entropy.

5.3 ATP Powers Cellular Work by Coupling Exergonic and Endergonic Reactions

ATP (adenosine triphosphate) is the primary energy carrier in cells. It couples energy-releasing reactions to energy-consuming processes.

• ATP Hydrolysis: Releases energy for cellular work.

• ATP Cycle: ATP is regenerated from ADP and inorganic phosphate.

Formula:

5.4 Enzymes Speed Up Metabolic Reactions by Lowering Energy Barriers

Enzymes are biological catalysts that increase the rate of reactions by lowering activation energy.

• Activation Energy: The energy required to start a reaction.

• Substrate: The molecule upon which an enzyme acts.

• Enzyme Specificity: Each enzyme acts on a specific substrate.

Example: Amylase catalyzes the breakdown of starch.

5.5 Catabolic Pathways Yield Energy by Oxidizing Organic Fuels

Cellular respiration is a catabolic pathway that breaks down glucose to produce ATP.

• Glycolysis: Breakdown of glucose in the cytoplasm.

• Krebs Cycle: Further oxidation of glucose derivatives in mitochondria.

• Electron Transport Chain: Transfers electrons to generate ATP.

Formula:

5.6 Fermentation and Anaerobic Respiration Enable ATP Production Without Oxygen

When oxygen is unavailable, cells can produce ATP through fermentation or anaerobic respiration.

• Fermentation: Produces ATP and byproducts (e.g., lactic acid, ethanol) without oxygen.

• Anaerobic Respiration: Uses electron acceptors other than oxygen.

Example: Yeast cells produce ethanol during alcoholic fermentation.