General Biology I: Foundations, Characteristics of Life, and Scientific Method

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Characteristics of Life

Defining Life and Its Properties

Biologists define life by a set of shared characteristics that distinguish living organisms from non-living matter. These features are essential for the study and understanding of biological systems.

Hierarchical Organization: Life is structured in a hierarchy from molecules to organisms:
- Molecules → Macromolecules → Subcellular structures → Cells → Tissues → Organs → Organisms
Metabolism: The sum of chemical reactions that generate energy and build cellular molecules. Example: Cellular respiration and photosynthesis.
Homeostasis: Regulation of internal conditions (e.g., pH, temperature, glucose concentration) to maintain stability. Example: Human body temperature regulation.
Behavior: Organisms perceive and respond to their environment. Example: Plants growing toward light (phototropism).
Growth and Development: Organisms grow and change during their life cycle. Example: Metamorphosis in butterflies.
Reproduction: Production of new organisms, either asexually (offspring identical to parent) or sexually (offspring genetically different). Example: Mitosis (asexual), meiosis and fertilization (sexual).
Evolution: Populations of organisms change over time through descent with modification. Example: Natural selection leading to adaptation.
Cells: All life is composed of one or more cells, the basic unit of life.

Emergent Properties

Definition and Examples

Emergent properties arise at higher levels of biological organization due to interactions among components. These properties are not present at lower levels.

Definition: Properties that emerge only when individual parts interact within a system.
Example: Consciousness in a brain, or a functioning ecosystem.

Central Dogma of Biology

Flow of Genetic Information

The central dogma describes how genetic information is transferred within biological systems.

Process: DNA → RNA → Protein
Transcription: DNA is transcribed into RNA.
Translation: RNA is translated into a polypeptide (protein).

Equation:

Non-Living Infectious Agents

Viruses and Prions

Some infectious agents are not considered living because they lack cellular structure and metabolism.

Viruses: Non-cellular, lack metabolism and behavior outside host cells. Example: Influenza virus.
Prions: Infectious proteins that cause neurodegenerative diseases. Example: Bovine spongiform encephalopathy (mad cow disease), Creutzfeldt-Jakob disease.

Domains of Life

Classification and Characteristics

All living organisms are classified into three domains based on cellular and molecular features.

Domain	Cell Type	Key Features	Examples
Bacteria	Prokaryotic	Unicellular, no nucleus, no organelles, diverse habitats, some photosynthetic, some pathogenic	Escherichia coli, cyanobacteria
Archaea	Prokaryotic	Unicellular, no nucleus, no organelles, extreme environments, no known pathogens	Thermophiles, halophiles
Eukarya	Eukaryotic	Unicellular or multicellular, nucleus, organelles, cytoskeleton	Plants, animals, fungi, protists

Nature of Science

Scientific Principles and Method

Science seeks to explain the natural world through physical principles, laws, and empirical testing. Scientific ideas are subject to change based on new evidence.

Physical Principles: Science relies on observable, quantifiable data.
No Metaphysics: Science does not address ultimate causes or make moral judgments.
Changeable Theories: Scientific theories can be revised or rejected if new data contradict them.

Scientific Method

Steps and Experimental Design

The scientific method is a systematic approach to investigation and hypothesis testing.

Observation: Identify a phenomenon or pattern.
Hypothesis: Formulate a testable explanation.
Experiment: Design controlled experiments to test the hypothesis.
- Independent Variable: Factor changed by the experimenter.
- Dependent Variable: Outcome measured.
- Replicates: Multiple samples per treatment for statistical validity.
- Controls: Baseline group for comparison.
Analysis: Use statistics to interpret results.
Conclusion: Support or reject the hypothesis; repeat or refine experiments as needed.

Example: Testing the effect of Flavobacterium on fish egg survival.

Control group: No added bacteria
Treatment group: Added Flavobacterium
Dependent variable: Number of eggs hatched
Statistical analysis: Compare means between groups

Key Terms and Concepts

Essential Vocabulary

Hierarchy of Order
Metabolism
Growth and Development
Behavior
Reproduction
Evolution
Cells
Central Dogma
Emergent Properties
Virus
Prion
Domains of Life
Natural Selection
Hypothesis
Theory
Replicates
Experimental Controls

Additional info: These notes synthesize syllabus content and foundational biology concepts for exam preparation and course success.