Chapter 1: Biology: The Science of Life (Essentials of Biology, 7th Edition)
1.1 The Characteristics of Life
Life is diverse but share organization and key characteristics across all organisms (e.g., bacteria, humans, plants, fungi).
Organization of the organism (levels from small to large):
Cell — the smallest, most basic unit of life; organisms may be unicellular or multicellular.
Tissue — made up of similar cells.
Organ — made up of tissues.
Organ system — organs working together.
Organism — organ systems working together to support an individual.
Population — members of similar organisms within a particular area.
Species — all populations of similar organisms capable of interbreeding.
Community — populations of species interacting within a given area.
Ecosystem — communities interacting with the physical environment.
Biosphere — the zone of air, land, and water at the Earth’s surface where living organisms are found.
Figure 1.2 (Levels of Biological Organization) depicts the hierarchical progression from atoms to the biosphere, including:
Atom — smallest unit of an element; electrons, protons, and neutrons.
Molecule — union of two or more atoms (the same or different elements).
Cell — structural and functional unit of all living organisms.
Tissue — group of cells with a common structure and function.
Organ — tissues functioning together for a task.
Organ system — several organs working together.
Organism — an individual composed of organ systems.
Population — organisms of the same species in a given area.
Species — all populations of a specific type of organism.
Community — interacting populations in a particular area.
Ecosystem — communities plus the physical environment.
Biosphere — global sum of all ecosystems.
Life requires materials and energy to be sustained.
Food provides building blocks and energy sources.
Energy is the capacity to do work.
Metabolism — all chemical reactions occurring in the cell.
The ultimate energy source for nearly all life on Earth is the sun.
Photosynthesis converts solar energy into chemical energy stored in nutrient molecules.
Energy flow in ecosystems:
Energy and chemical flow between organisms defines ecosystem function.
Energy does not cycle; solar energy and producers are needed to sustain ecosystems.
Producers convert solar energy into chemical energy; energy flows to consumers and eventually to decomposers, with some energy released as heat.
Homeostasis:
The maintenance of a stable internal environment within physiological boundaries (temperature, moisture, acidity, etc.).
Response to the environment:
Living organisms respond to energy and nutrient needs by interacting with the environment, often resulting in movement.
Reproduction and development:
All living things reproduce or create offspring similar to themselves.
Bacteria and other single-celled organisms often reproduce by binary fission (splitting in two).
In multicellular organisms, reproduction usually begins with the union of egg and sperm to form an embryo.
Embryo growth follows genes inherited from parents; genes are made of DNA, which serves as the blueprint.
DNA is the blueprint for inherited traits.
Adaptations:
Adaptations are modifications that make organisms suited to their way of life.
Examples: some hawks catch fish, others catch rabbits; adaptations for flight and hunting; high-elevation human populations exhibit adaptations that reduce the amount of hemoglobin in the blood.
1.2 Evolution: The Core Concept of Biology
Evolution is the process by which populations accumulate adaptations over time, making them more suited to their environments.
Evolution explains both unity and diversity of life; an evolutionary tree traces life’s ancestry back to a common ancestor.
Billions of years ago (BYA):
First ancestral cell likely appeared around 3.5–4.0 BYA (bacteria).
Archaea emerged around 2.4–3.0 BYA.
Eukarya emerged around 2.0–2.5 BYA.
Natural selection — a process by which evolution occurs; independently formulated by Charles Darwin and Alfred Russel Wallace.
Darwin’s On the Origin of Species provided substantiating data; evolution is a core concept in biology.
Natural selection in changing environments:
Environments change due to living or nonliving factors.
Individuals with favorable adaptations have higher survival and reproductive success in a given environment.
The traits that increase reproductive success become more common in the population over generations → evolution.
Descent with modification:
Over time, descendants inherit modifications, leading to new species and diversity.
Hawaiian honeycreepers (illustrative example):
All descended from a single ancestral finch.
Bill types diversified to exploit different food sources, yet body shape and nesting behavior show shared ancestry.
Taxonomic organization of life:
Three domains of life: Archaea, Bacteria, Eukarya.
Prokaryotes (Archaea and Bacteria) lack a membrane-bound nucleus.
Eukaryotes (Eukarya) have a membrane-bound nucleus and can be unicellular or multicellular.
Figure 1.6 (An Evolutionary Tree) summarizes major branches:
Bacteria and Archaea split early; Eukarya branched later and diversified into Protists, Plants, Fungi, and Animals.
1.2 Evolution: Organizing the Diversity of Life (continued) — Taxonomy and Diversity
Taxonomy is the discipline of naming and classifying organisms according to rules; systematics classifies organisms by evolutionary relationships.
Classification levels (from broad to specific): Domain, Supergroup, Kingdom, Phylum, Class, Order, Family, Genus, Species.
Table references:
Domain Archaea — Prokaryotes; unicellular; often extremophiles; Example: Methanosarcina mazei; capable of methane production.
Domain Bacteria — Prokaryotes; unicellular; metabolically diverse; Example: Escherichia coli; common in human intestines.
Eukaryotic Supergroups (six): Archaeplastida, Chromalveolata, Excavata, Rhizaria, Amoebozoa, Opisthokonta.
Eukaryotic kingdoms (four): Protists, Plants, Fungi, Animals.
Protists — diverse group, mostly single-celled to simple multicellular; vary in nutritional modes; examples include algae and protozoans.
Plants — multicellular, photosynthetic.
Fungi — decomposers; multicellular forms like molds and mushrooms.
Animals — multicellular, ingest and process food.
Binomial nomenclature:
Each organism has a unique two-part name: genus and species epithet.
Example: ext{Pisum ext{ }sativum}, where first word is genus and second is specific epithet.
1.3 Science: A Way of Knowing
Biology is the scientific study of life. It starts with observations and uses the scientific method.
Inductive reasoning: generating hypotheses by creative synthesis of isolated facts.
Hypothesis: a testable possible explanation for an event.
Flow of the scientific method (conceptual): observe → develop hypothesis → predict → test via experiments → analyze data → draw conclusions → repeatable results.
Figure 1.8 (Flow Diagram for the Scientific Method) illustrates the sequence of steps.
Scientific Method components:
Make a prediction and perform experiments.
Good experimental design: keep all conditions constant except the experimental variable; use a test group and a control group.
Data may show correlation; correlation does not imply causation.
Scientists are skeptics; repeatability is essential.
Develop a conclusion: is the hypothesis supported or not?
Results and methods should be transparent and repeatable.
Scientific theory:
The ultimate goal is to understand the natural world through well-supported explanations.
Examples: Cell theory, Gene theory.
Theory of evolution is a unifying concept in biology; some biologists treat evolution as a principle or law because of extensive supportive evidence.
Controlled study example (ulcer treatment):
Hypothesis: Antibiotic B is better than Antibiotic A for ulcers.
Design: three experimental groups, random assignment to reduce variance; a control group receives a placebo.
Groups: control (placebo), test group 1 (antibiotic A), test group 2 (antibiotic B).
Outcome measures: incidence and healing of ulcers; results presented as data with approximations.
Publication and dissemination:
Scientific studies are published in journals where a peer-review process helps ensure reliability.
The general public often relies on secondary sources derived from scholarly journals.
Scientific findings advance future discovery and discourse.
1.4 Science and the Challenges Facing Society
Technology as application of scientific knowledge for practical purposes.
Technology enables altering organisms and ecosystems to meet societal needs, but raises ethical and ecological considerations.
Climate change:
Primarily due to imbalance in carbon cycling (carbon reservoir turnover).
Atmospheric CO₂ levels have risen from about 280\,\text{ppm} in 1850 to over 400\,\text{ppm} today.
This imbalance leads to climate-related impacts across the globe.
Biodiversity and habitat loss:
Biodiversity = variation in life on Earth; many millions of species exist.
Estimated species: 8.7\times 10^6 (excluding bacteria); about 2.3\times 10^6 have been classified.
Extinction: death of an entire species or taxonomic group; up to 38\% of all species may be in danger of extinction by the end of this century.
The current extinction rate approaches levels seen in the five mass extinctions in Earth’s history, and biodiversity loss threatens ecosystem function and resilience.
Emerging and reemerging diseases:
Emerging diseases are new to humans (e.g., avian influenza, SARS, MERS, SARS-CoV-2/ COVID-19).
They can arise from new exposure to animal or insect vectors; globalization increases worldwide transmission.
Reemerging diseases (e.g., Ebola outbreak 2014–2015) present ongoing global challenges.
Summary connections:
Scientific understanding underpins policy making, public health, environmental stewardship, and technology development.
Ethical and practical implications include balancing innovation with precaution, equity in access, and preservation of ecosystems.
Key terms and concepts (quick reference)
Levels of biological organization: atom, molecule, cell, tissue, organ, organ system, organism, population, species, community, ecosystem, biosphere.
Homeostasis: internal stability within physiological boundaries.
Metabolism: all cellular chemical reactions.
Photosynthesis: solar energy → chemical energy stored in nutrients.
Natural selection: differential survival and reproduction based on heritable traits.
Descent with modification: cumulative inherited changes over generations.
Binomial nomenclature: two-part Latin name for species (genus + species epithet).
Prokaryote vs. eukaryote: cells lacking (prokaryotes) or possessing (eukaryotes) a membrane-bound nucleus.
Taxonomy vs. Systematics: naming/classification vs. evolutionary relationships.
Scientific method elements: observation, hypothesis, prediction, experimentation, data analysis, conclusions, replication, peer review.
Theory (vs. law) in science: well-supported explanations for natural phenomena; evolution as a unifying theory in biology.
CO$_2$ and climate: carbon dioxide as a key greenhouse gas driving climate change; ppm measures.
Biodiversity metrics: estimated total species, classified species, extinction risk percentages.
Emerging/reemerging diseases: definitions and global health implications in a connected world.
Note: All numerical references have been incorporated in LaTeX format where appropriate, e.g., 280\,\text{ppm}, >400\,\text{ppm}, 8.7\times 10^6 species, 2.3\times 10^6 classified, 38\% at risk. Throughout, definitions and examples reflect the content provided in the transcript, organized into a study-friendly bullet-point format for exam preparation.