Chapter 1 Notes: The Study of Life (Understanding Science and Organizing Life)
Part 1: Understanding Science
Understanding the purpose of biology: What does it mean to study Biology? The focus is on exploring life through observation, experimentation, and reasoning to build explanations about living systems.
Types of Science
Diagram the relationship between Basic and Applied Science.
Distinguish among different branches of science and how they relate to real-world questions.
Natural Science vs. Physical Science: Natural Science studies life and the physical world (e.g., Biology, Chemistry, Physics, Earth Science, Astronomy); Physical Science focuses on non-biological physical phenomena; Life Science is another term for biology within Natural Science.
The slide classifications emphasize that science covers categories like Biology, Physics, Chemistry, Earth Science, Astronomy, and Math/Science related disciplines.
Basic vs. Applied Science
Basic (Pure) Science:
Goal: Gain knowledge for its own sake.
No explicit product or service in mind; driven by curiosity.
Example motivation: understanding how the world works.
Applied Science:
Goal: Use scientific knowledge to solve real-world problems.
Focused on technology, product development, and addressing specific needs.
Discovering Answers and Types of Scientific Reasoning
Discovery Science (Inductive Reasoning):
Describes natural structures and processes through observations and data analysis.
Specific observations lead to generalizations (e.g., from many observations, a general principle is formed).
Hypothesis-based Science (Deductive Reasoning):
Begins with a general understanding and tests specific questions through hypotheses.
Generalization example: All known living organisms are made of cells.\
Hypothesis example: The cell of a dog contains the same structures as the cell of a cat.
A good hypothesis is:
Testable
Falsifiable
Cannot be proven, only supported or refuted.
The Scientific Method: Discovering Answers
Steps (in order):
Ask a Question
Research that Question
Form a Hypothesis
Experiment
Collect Data
Analyze Data
Form a Conclusion
Communicate Results
Result interpretations:
Support the Hypothesis
Refute the Hypothesis
Support the null hypothesis
Deductive Reasoning in Practice
Logic flows from the general to the specific.
If a hypothesis is supported, we can expect particular outcomes in experiments.
Designing an Experiment
Design focuses on testing the effect of ONE variable.
Structure includes:
Groups: Control and Experimental
Control: all variables constant at a baseline; provides a baseline comparison
Experimental: all variables constant except the independent variable of interest
Variables:
Independent Variable: the variable being manipulated
Dependent Variable: the variable being measured
Controlled Variables: all other variables kept constant across both groups
Purpose: isolate the effect of the independent variable on the dependent variable.
Scientific Theories
A theory is a hypothesis that has been repeatedly tested and not yet falsified.
Characteristics:
Broad in scope
Supported by a large body of evidence
Many repeated and similar experiments by many scientists
Constantly challenged, tested, and modified as new data arise
Notable quote: "You can disprove a theory by finding even a single observation that disagrees with the predictions of the theory" — Stephen Hawking (A Brief History of Time, 1988)
The Four Theories (Foundations of Biology)
The Cell Theory (1839)
Tenets:
All living organisms are made of one or more cells.
Chemical reactions necessary for life take place within the cell.
All cells arise only from pre-existing cells.
Cells contain hereditary information in the form of DNA.
The Gene Theory (1863)
Genes are the basic unit of function and inheritance; they are comprised of specific DNA sequences.
Mendel’s Laws of Inheritance laid the foundation for heredity in the 1850s; Mendel is often called the father of genetics.
Conceptual metaphor: Genes = the functional units that carry information; DNA sequences define genes.
The Chromosome Theory of Heredity (1902)
Chromosomes contain specific genes and are passed from parent to offspring.
Links between Mendelian inheritance and chromosomal behavior during cell division.
The Theory of Evolution (1859)
Evolution = change over time in a population.
Requires variation within populations and descent with modification.
Change in allele frequency within populations typically leads to the development of new species.
Historical context:
Darwin proposed the theory in On the Origin of Species (1859).
Lamarck proposed acquired characteristics (earlier competing idea).
Key definitions by Darwin:
Descent with modification
Natural Selection: differential reproductive success (requires variation)
Variation leads to differential survival and reproduction; traits are passed to offspring more frequently if advantageous.
The Cell in Focus: Organizing Life (Overview of the basis for life)
A concise list of the major ideas:
The cell is the basic unit of life; all organisms are composed of cells (one or more).
Cells perform all life processes and contain hereditary material (DNA).
Cells arise from pre-existing cells (cell division).
The cell is the subunit for all life as we know it.
Part 2: Understanding Life
Organizing Life: Overview
Organizing Life means organizing biological information from the cellular level up to the biome level.
Learning objectives include:
Describe the basic functions all organisms must accomplish.
Compare and contrast prokaryotic and eukaryotic cell types.
Interpret the levels of biological organization (cell to biome).
Accurately interpret a phylogenetic tree to determine relationships among species.
Taxonomy and Classification
Taxonomy: Branch of biology that names and classifies species.
Hierarchical example (Domain to Species):
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Canidae
Genus: Vulpes
Species: vulpes
Phylogeny: Evolutionary Relationships
Phylogeny = the evolutionary history and relationships among organisms or groups of organisms.
Key questions addressed:
What species did an organism evolve from?
What species is an organism most closely related to?
Phylogeny depicts the most recent common ancestor for related species.
Example focus: most recent common ancestors of related species (e.g., badger, otter; coyote, wolf; badger, wolf).
Nature’s Order: Hierarchy of Biological Organization
A hierarchical sequence showing increasing complexity:
atom → molecule → organelle → cell → tissue → organ → organ system → organism → population → community → ecosystem → biosphere
This hierarchy highlights how properties emerge at higher levels that are not evident at lower levels (emergent properties).
Emergent Properties
Novel properties develop at each higher level of organization due to interactions among components.
Examples:
A cell is more than a bag of molecules.
The whole (organism) is greater than the sum of its parts.
The Cell: Basic Units of Life
Core functions all cells must perform:
Response to environmental stimuli
Uptake and processing of nutrients/energy (to be explored further in Chs. 7 & 8)
Regulation/Homeostasis
Growth & Development
Reproduction
Order
Evolution & Adaptation
All life units rely on these functions; cells are the subunits of life as we know it.
Cell Types: Prokaryotes vs Eukaryotes
Key differences between Prokaryotes and Eukaryotes:
Chromosome structure: Prokaryotes have Circular chromosomes; Eukaryotes have Linear chromosomes.
Organelles: Prokaryotes lack a true nucleus; Eukaryotes possess a nucleus and other membrane-bound organelles.
Reproduction: Prokaryotes primarily binary fission; Eukaryotes use Mitosis/Meiosis.
Size: Prokaryotes range roughly from 0.1 \,\mu m \text{ to } 5 \,\mu m; Eukaryotes range roughly from 10 \,\mu m \text{ to } 100 \,\mu m.
Age (origin): Prokaryotes ≈ 3.5 \text{ BYA}; Eukaryotes ≈ 1.5 \text{ BYA}.
Diversity: Prokaryotes — Little; Eukaryotes — Great.
Plasma membrane: Present in both.
Animal vs. Plant Cells: Key Organelles and Features
Common features listed for both cell types: nucleus, nuclear envelope, nucleolus, ribosomes, endoplasmic reticulum (rough and smooth), Golgi apparatus, mitochondria, cytoplasm, cytoskeleton, plasma membrane, lysosomes (animal), peroxisomes, vesicles, ribosomes, etc.
Plant cell-specific features include:
Chloroplasts (site of photosynthesis)
Central vacuole (cell sap; maintains turgor pressure)
Plasmodesmata (cell–cell channels)
Cell wall (rigidity and structural support)
Plasmodesmata connect plant cells
Shared features include: nucleus, mitochondria, Golgi apparatus, ER, ribosomes, cytoplasm, plasma membrane, cytoskeleton, lysosomes (animal-specific in older diagrams; plants have analogous waste-processing organelles).
Cell Type Diversity
Conceptual idea: There is a spectrum from large numbers with high diversity to small numbers with low diversity depending on cell type and lineage.
Endosymbiotic Theory: Eukaryotic Origin
The endosymbiotic theory explains the origin of mitochondria and chloroplasts as former free-living prokaryotes that were engulfed by ancestral host cells.
Evidence highlighted includes:
Early prokaryotic ancestors with two membranes for mitochondria/chloroplasts
Retained bacterial-type chromosome and ribosomes in these organelles
Reproduction by division similar to prokaryotes
Diagrammatic depiction shows a progression from ancient prokaryotes to complex eukaryotic cells through endosymbiotic events.
Unity in Diversity: Common Threads Across Life
Despite vast diversity, all life shares fundamental similarities:
The same genetic material (DNA, and its expression through mRNA and tRNA)
Nearly universal genetic code (A, C, G, T in DNA; corresponding codons in RNA)
The same basic process of gene expression (transcription and translation)
The same molecular building blocks (proteins built from 20 amino acids)
The presence of ribosomes for protein synthesis
The Big Picture: Why These Concepts Matter
Foundational Principles connect micro to macro: cells build tissues, tissues build organs, and ecosystems are shaped by interactions among organisms and their environment.
Understanding the origin and unity of life informs how biologists interpret experiments, design new studies, and assess claims about biology.
The theories discussed (Cell, Gene, Chromosome, Evolution) provide the framework for interpreting all biological phenomena and guide inquiry and ethical considerations in biological research.
Quick Reference: Notable Dates and Concepts (for exam context)
The Cell Theory: 1839
The Gene Theory: 1863
The Chromosome Theory of Heredity: 1902
The Theory of Evolution: 1859
Endosymbiotic Origin of Eukaryotes: evidence supports two-membrane organelles with bacterial ancestry
By Darwin: Descent with modification and Natural Selection as core definitions of evolution
Basic vs Applied science definitions, and Discovery vs Hypothesis-driven science as two complementary ways of building knowledge
Summary Connections to Foundational Principles
Observation leads to generalizations (Discovery Science) which then guide hypothesis formation and testing (Hypothesis-based Science).
The scientific method is iterative: new data can refine or overturn existing theories.
Emergent properties illustrate why studying systems at multiple levels (cell to ecosystem) is essential for understanding biology.
Unity in diversity shows that despite vast differences, life shares fundamental mechanisms, enabling cross-disciplinary insights and shared methodologies.
Key formulas and numbers used in this content are presented in LaTeX where appropriate, such as chromosome sizes, organism sizes, and fossil-era references where numerically specified.
1839, \ 1863, \ 1902, \ 1859