Chapter 1 Notes: Introduction to Life on Earth (Biology Life on Earth with Physiology, 12th edition)
Case Study: The Boundaries of Life
Ebola is a disease caused by viruses; victims show a wide variety of symptoms and Ebola is typically fatal.
Scientists debate whether viruses are living organisms or not, highlighting the boundaries of what counts as life.
1.1 What Is Life?
Biology is the study of life; but defining life is tricky because some entities (e.g., viruses) satisfy only a subset of traditional criteria (reproduce, evolve) and are not universally considered truly alive.
Organisms share a bundle of characteristics that, taken together, define life:
Actively maintain organized complexity
Acquire and use materials and energy (metabolism)
Sense and respond to stimuli (responsiveness)
Maintain homeostasis
Grow and develop
Reproduce (sexually and/or asexually)
Evolve as a population (genetic changes accumulate over time)
1.1 What Is Life?: organized complexity
Organisms maintain organized complexity and are composed of cells, the basic units of life.
Cells are separated from surroundings by a plasma membrane and contain cytoplasm.
Two main cell types:
Eukaryotic cells: have organelles (including a nucleus that houses DNA); can be unicellular or multicellular.
Prokaryotic cells: lack membrane-bound organelles; can be unicellular.
Multicellular: organisms made up of at least 2 cells.
Prokaryotes: typically unicellular.
Eukaryotes: can be unicellular or multicellular.
Analogy: Prokaryotes resemble a building with simple “offices” (membrane invaginations) but no true nucleus or complex organelles; eukaryotes have a nucleus and many specialized organelles.
1.1 What Is Life?: energy demand
Organisms acquire and use materials and energy continuously.
Two main ways to obtain energy:
Photosynthesis (autotrophs): use light to synthesize organic compounds from CO₂.
Consumption of other living or non-living things (heterotrophs): obtain energy by consuming organic material.
Nutrients cycle; energy flows in one direction (heat cannot be reused by living systems).
Important materials (minerals, water, simple chemical building blocks) come from air, water, and living systems; their supply is maintained through nutrient cycling.
1.1 What Is Life?: Autotrophs vs Heterotrophs
Major groups: Phototrophs vs Chemotrophs.
Phototrophs: energy from light; autotrophic (synthesize their own organic compounds from CO₂).
Chemotrophs: energy from chemical reactions (oxidation). Subtypes:
Chemo-lithotrophs (lithos = rock): energy from oxidation of inorganic compounds (e.g., H₂S, NH₃); use CO₂ as carbon source.
Chemo-heterotrophs (organo): energy from oxidation of organic compounds (e.g., glucose, C₆H₁₂O₆); obtain food from living organisms (parasitism) or dead matter (saprotrophs).
Key distinction: how energy is obtained and what carbon source is used.
1.1 What Is Life?: Response to stimuli
Living things continuously use energy to maintain internal conditions (homeostasis).
Animals use specialized cells and organs to detect/respond to stimuli (light, temperature, sound, chemicals).
Plants, fungi, and unicellular organisms also respond to stimuli.
Examples: plants bend toward sunlight as light moves; reptiles use water to regulate temperature; mammals sweat to cool and maintain body temperature and pH.
1.1 What Is Life?: Grow and develop
Growth: organisms increase in size; bacteria grow by enlarging cells and dividing (mostly asexual).
Animals/plants grow by increasing cell numbers via mitosis and meiosis.
Development: growth toward greater complexity.
Levels of biological organization (from simple to complex):
atoms → molecules → cells → tissues → organs → organ systems → organisms → populations → communities → species → ecosystems → biosphere
Many organisms exist as communities and form relationships (symbiosis, parasitism, etc.).
1.1 What Is Life?: Reproduce
Reproduction mechanisms:
Division in half (binary fission)
Production of seeds
Bearing live offspring
1.1 What Is Life?: Evolve: changes in DNA
DNA (deoxyribonucleic acid) is present in every cell and passes to descendants.
DNA encodes proteins via messenger RNA; four-letter code:
DNA molecules are usually highly condensed and bound to proteins; called chromosomes.
Genes are the basic units of heredity.
DNA replication (process called replication) is assisted by enzymes; after replication, cells divide.
DNA changes (mutations) occur by chance during copying and due to DNA damage by mutagens; repair enzymes attempt to fix damage.
Changes can be neutral, detrimental, or beneficial; e.g., some changes in the SARS-CoV-2 genome increased infectivity.
Evolution involves changes accumulating in populations over time.
1.2 What Is Evolution? (4 of 5)
DNA changes arise spontaneously (enzyme errors during replication) or due to mutagens.
Natural selection leads to adaptation: traits that aid survival and reproduction become more common.
Adaptations can be structures, physiological processes, or behaviors.
Populations and species are resilient due to variation and multiple adaptations; allows long-term adaptation to environmental change.
Extinction occurs when adaptive mutations fail to arise or environmental conditions change unfavorably; e.g., dinosaurs.
Evolution has no goal; it is not purposeful but results from differential survival and reproduction.
Common descent with modification explains the diversity of life; all organisms share DNA/RNA as genetic material and adapt over time.
Evolves at the population level, not individuals.
Examples: COVID-19 variants; antibiotic resistance in bacteria.
1.3 How Do Scientists Study Life? (1 of 6)
Life studied at different levels of organization:
Atom → molecule → cell → tissue → organ → organ system → multicellular organism → population → species → community → ecosystem → biosphere
Biologists classify organisms based on evolutionary relationships; three domains:
Bacteria
Archaea
Eukarya
Archaea share features with bacteria and eukaryotes and have unique traits of their own.
Before DNA concepts, Archaea and Bacteria were grouped together based on the absence of a nucleus.
1.3 How Do Scientists Study Life? (2 of 6) The Domains and Kingdoms
Domain Eukaryotes contains four kingdoms:
Protista (unicellular and some simple multicellular forms)
Plantae (multicellular, photosynthetic, CO₂ carbon source, cellulose cell walls)
Animalia (multicellular, heterotrophic, no cell walls, capable of movement)
Fungi (multicellular and/or unicellular; heterotrophic; saprotrophic; absorb nutrients in liquid form)
Domain Bacteria and Domain Archaea are prokaryotic:
No membrane-bound nucleus
DNA is usually circular and single; located in the cell
Ribosomes present; lack other organelles; some membrane invaginations
Eukarya have a membrane-bound nucleus and multiple organelles.
1.3 How Do Scientists Study Life? (3 of 6) Cells and taxonomy
Bacteria and Archaea are prokaryotic; Eukarya are eukaryotic with a nucleus.
Cells distinguish the domains:
Prokaryotes: Bacteria and Archaea
Eukaryotes: all organisms with a nucleus (plants, animals, fungi, protists)
Binomial nomenclature (genus + species) for naming organisms:
Example: Daphnia longispina; genus = Daphnia, species = longispina
Taxonomy order to learn: Species → Genus → Family → Order → Class → Phylum → Kingdom → Domain
The sequence shows increasing inclusivity from Species (most specific) to Domain (most inclusive).
Practice questions illustrate domain/kingdom classifications (e.g., multicellular, photosynthetic, eukaryotic organisms belong to Kingdom Plantae).
1.3 How Do Scientists Study Life? (4 of 6) Domain Eukaryotes and their kingdoms
Domain Eukaryotes includes four kingdoms: Protista, Plantae, Animalia, Fungi.
Protista includes both unicellular and some simple multicellular organisms; can be heterotrophic or autotrophic; possesses variety of cell wall types.
Plantae are photoautotrophic; use CO₂; have cellulose cell walls; limited movement.
Animalia are multicellular, heterotrophic, lack cell walls, capable of movement.
Fungi are both multicellular and unicellular (e.g., yeast); heterotrophic; saprotrophic and/or parasitic; absorb food in liquid form.
1.3 How Do Scientists Study Life? (5 of 6) Prokaryotes vs Eukaryotes; DNA and organelles
Bacteria and Archaea are prokaryotic:
No membrane-bound nucleus
DNA is circular and typically a single molecule
Ribosomes present; no other organelles
Invaginations of membrane form compartments enabling respiration, photosynthesis, etc.
Eukarya have membrane-bound nucleus; linear DNA molecules (multiple chromosomes in humans: 46);
Multiple organelles (mitochondria, chloroplasts in plants, etc.)
Scientists study life by comparing cellular structures and genetic material to determine evolutionary relationships.
1.3 How Do Scientists Study Life? (6 of 6) Binomial nomenclature and examples
Speciation and naming: binomial system (genus + species).
Example: Daphnia longispina; Daphnia = genus; longispina = species.
Species is defined as a population that can interbreed and inhabit a particular environment.
1.4 What Is Science? Principles and Scientific method
Science defined as systematic inquiry through observation and experiment into the physical universe.
Three core principles:
Events have natural causes.
Laws of nature do not change over time or distance.
Findings are value-neutral and verifiable through replication.
The scientific method comprises six interrelated elements (commonly taught as a sequence):
Observation
Question (Inquiry)
Hypothesis
Prediction
Experiment
Data collection and analysis
Conclusion
Details of scientific inquiry:
Starts with observation, leading to a question; form a hypothesis after reviewing prior work and consultation.
A prediction follows from the hypothesis and is tested via designed experiments.
Data collection and analysis occur; conclusions are drawn about the hypothesis' validity.
Deductive reasoning example: If an object exhibits all the characteristics of life, it must be living.
Inductive reasoning (generalizing from specific observations) is also used.
1.4 What Is Science? Details of experiments and theory
Experiments include controls and experimental treatments:
Experimental treatment tests whether a single variable causes the observed phenomenon.
Controls help guard against unnoticed variables (e.g., testing a new drug requires a placebo control).
Some phenomena cannot be studied with experiments due to impracticality or ethical concerns (e.g., certain evolutionary events or some human behaviors).
Science requires repeatability and communication: replication of results and publication or patenting for dissemination.
Theory (not to be confused with a hypothesis):
A scientific theory is a well-supported, general explanation of important natural phenomena, developed from repeated observations/experiments, and not disproven by new evidence.
Theories can be refuted by new data; natural laws describe predictable phenomena (often expressed as formulas).
The cell theory is an example: all living organisms are composed of cells; viruses are not considered alive in some definitions (acellular).
Science is a human endeavor, influenced by curiosity, accidents, and the social context of discovery (e.g., Fleming's penicillin discovery).
1.4 What Is Science? Historical examples and applications
Francesco Redi's experiment (spontaneous generation debate):
Open jars vs sealed jars vs gauze-covered jars; maggots appeared only in open jars (or on gauze where flies could reach meat but not inside the jar).
Conclusion: organisms arise from preexisting life; challenged spontaneous generation; Pasteur later provided decisive evidence.
Penicillin discovery by Alexander Fleming: mold inhibited nearby bacteria; highlighted serendipity and the need for scientific validation.
The cell theory, virus non-living status, and spontaneous generation are discussed as foundational elements of biology.
Biology illuminates life and deepens appreciation of nature.
1.4 Additional figures and notes
Figures referenced in the slides illustrate levels of biological organization (Figure 1-10), domains and kingdoms (Figure 1-11), and examples like Lupine adaptations (Figure 1-14).
Final slide emphasizes copyright and pedagogical use restrictions.
Quick reference: Key terms and concepts
Life criteria: organized complexity, metabolism, responsiveness, homeostasis, growth and development, reproduction, evolution.
Cellular organization: Prokaryotic vs Eukaryotic; nucleus; organelles; unicellular vs multicellular.
Energy and nutrients: photosynthesis; chemo-/photo-/litho-/organo- pathways; energy flow direction.
DNA and evolution: four nucleotides; base-pairing rules; replication; mutagens; natural selection; adaptation; common descent.
Levels of biological organization: atoms, molecules, cells, tissues, organs, organ systems, organisms, populations, communities, species, ecosystems, biosphere.
Domains and kingdoms: Bacteria, Archaea, Eukarya; within Eukarya: Protista, Plantae, Animalia, Fungi.
Scientific method and theory: observation, hypothesis, prediction, experiment, data analysis, conclusion; controls; repeatability; communication; cell theory; spontaneity debates (Redi, Pasteur).
Case study context: Ebola and viruses fuel debate about whether viruses are alive.