General Biology: Foundations, Chemistry of Life, and Cellular Processes

Nature of Science

Characteristics of Scientific Knowledge

• Empirical Evidence: Scientific knowledge is based on observations and experiments.

• Testability: Hypotheses and theories must be testable and falsifiable.

• Tentativeness: Scientific understanding can change with new evidence.

Role of Models, Theories, and Laws

• Models: Simplified representations of complex biological processes (e.g., cell membrane model).

• Theories: Broad explanations supported by extensive evidence (e.g., cell theory, theory of evolution).

• Laws: Descriptions of observed phenomena, often mathematical (e.g., Mendel's laws of inheritance).

Experimental Design Considerations

• Variables: Independent, dependent, and controlled variables must be clearly defined.

• Controls: Essential for comparison to determine the effect of the independent variable.

• Sources of Error: Random and systematic errors can affect results and interpretations.

Interpretation of Data and Trends

• Data analysis involves identifying patterns, correlations, and causation.

• Statistical methods are used to determine significance.

Correlation vs. Causation

• Correlation: Two variables change together but one does not necessarily cause the other.

• Causation: One variable directly affects another.

How Evidence Supports or Refines Scientific Understanding

• New evidence can confirm, refute, or refine existing models and theories.

Chemistry of Life

Water Properties and Biological Consequences

• Cohesion and Adhesion: Allow water transport in plants.

• High Specific Heat: Stabilizes temperature in organisms and environments.

• Solvent Properties: Facilitates biochemical reactions.

Hydrogen Bonds in Biological Systems

• Hydrogen bonds stabilize DNA structure and protein folding.

Carbon’s Bonding Capacity and Molecular Diversity

• Carbon forms four covalent bonds, enabling complex molecules.

• Isomers: Molecules with the same formula but different structures.

Functional Groups and Their Effects

• Examples: Hydroxyl, carboxyl, amino, phosphate groups affect molecule reactivity and function.

Macromolecule Structure-Function Relationships

• Proteins, nucleic acids, carbohydrates, and lipids have unique structures that determine their biological roles.

Enzyme Action

• Active Site: Region where substrate binds and reaction occurs.

• Induced Fit: Enzyme changes shape to better fit the substrate.

• Factors Affecting Enzyme Activity: Temperature, pH, substrate concentration.

Levels of Biological Organization

• Hierarchical Organization: Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere.

• Emergent Properties: New properties arise at each level of organization.

• Feedback Mechanisms: Maintain homeostasis (e.g., negative feedback in temperature regulation).

• Systems Thinking: Understanding how components interact within biological systems.

• Examples: Photosynthesis connects molecular, cellular, and ecosystem levels.

Microscopy and Cell Observation

Resolution Limits of Light Microscopy

• Light microscopes resolve structures down to ~200 nm.

Comparison of Light and Electron Microscopy

Feature	Light Microscopy	Electron Microscopy (TEM vs. SEM)
Resolution	~200 nm	~1 nm (TEM), 3-10 nm (SEM)
Sample Preparation	Simple, live cells possible	Complex, only dead cells
Image Type	Color, 2D	Black & white, 2D (TEM), 3D (SEM)

Importance of Scale and Magnification

• Understanding cell size and structure requires appropriate magnification and scale bars.

Microscopy and Cell Theory

• Microscopy provided evidence for cell theory: all living things are made of cells.

Interpretation of Micrographs

• Ability to identify organelles and cell structures in images is essential.

Photosynthesis

Energy Transformation and Redox Reactions

• Photosynthesis converts light energy into chemical energy.

• Redox reactions transfer electrons during the process.

Chloroplast Structure-Function Relationships

• Thylakoid membranes contain pigments and electron transport chains.

Light Reactions

• Photosystem II and I absorb light, drive electron flow, and produce ATP and NADPH.

• Electron flow: Water is split, oxygen is released.

• Chemiosmosis: Proton gradient drives ATP synthesis.

Calvin Cycle

• Carbon Fixation: CO2 is incorporated into organic molecules.

• Reduction: ATP and NADPH reduce 3-phosphoglycerate to G3P.

• Regeneration of RuBP: Allows cycle to continue.

Limiting Factors of Photosynthesis

• Light intensity, CO2 concentration, temperature.

Role of Photosynthesis in Global Carbon Cycling

• Photosynthesis removes CO2 from the atmosphere, influencing climate.

Cellular Respiration & Energy Transfer

Redox Reactions and Electron Carriers

• NADH and FADH2 transfer electrons to the electron transport chain.

ATP Synthesis Pathways

• Substrate-Level Phosphorylation: Direct transfer of phosphate to ADP.

• Oxidative Phosphorylation: ATP synthesis powered by electron transport and chemiosmosis.

Chemiosmosis and Proton Gradients

• Proton gradient across mitochondrial membrane drives ATP synthase.

Mitochondrial Structure-Function

• Inner membrane contains electron transport chain and ATP synthase.

Comparison of Aerobic vs. Anaerobic Pathways

• Aerobic: Uses oxygen, produces more ATP.

• Anaerobic: No oxygen, less ATP, produces lactate or ethanol.

Energy Efficiency and Heat Loss

• Not all energy from glucose is converted to ATP; some is lost as heat.

IB-Level Expectations

• Use labeled process diagrams to illustrate mechanisms.

• Show connections between topics (e.g., how photosynthesis and respiration are linked).

• Include cause-effect relationships in explanations.

• Emphasize understanding of why processes occur, not just what happens.