8/26 /25 Chapter 1 Notes: Biology — The Study of Life

1.1 The Characteristics of Life

  • Life exists almost everywhere on Earth and exhibits a great variety of diverse life forms. All living things share certain characteristics in common.

  • Life is organized.

  • Life requires materials and energy.

  • Life has the ability to reproduce and develop.

  • Life responds to its environment.

  • Life maintains an internal environment.

  • Life has the capacity to adapt.

Levels of Biological Organization

  • A cell is the smallest unit of life.

  • A tissue is a group of similar cells that perform a specific function.

  • Several tissues join to form an organ.

  • Organs work together to form an organ system.

  • The biosphere encompasses regions of the Earth’s crust, waters, and atmosphere inhabited by living organisms; within it, ecosystems, communities, populations, species, and organisms are organized in a hierarchical structure.

Levels of Biological Organization (detailed)

  • Cell

    • The structural and functional unit of all living organisms.

  • Molecule

    • Union of two or more atoms of the same or different elements.

  • Atom

    • Smallest unit of an element; composed of electrons, protons, and neutrons.

  • Tissue

    • A group of cells with a common structure and function.

  • Organ

    • Composed of tissues functioning together for a specific task.

  • Organ System

    • Composed of several organs working together.

  • Organism

    • An individual; complex individuals contain 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

    • A community plus the physical environment.

  • Biosphere

    • Regions of the Earth’s crust, waters, and atmosphere inhabited by living organisms.

  • Examples: jaguar, E. coli, sequoia, Earth, mushroom, Homo sapiens, Euglena.

  • The chart can be visualized as: Atom → Molecule → Cell → Tissue → Organ → Organ System → Organism → Population → Species → Community → Ecosystem → Biosphere.

1.1 The Characteristics of Life (continued)

  • Life requires external materials and energy sources to maintain organization and carry out life activities. Energy is the capacity to do work.

  • Life can reproduce and develop, with fertilization and cell division leading to development in multicellular organisms.

  • Genes and DNA:

    • Genes are units of information within an individual's DNA that are passed to offspring during reproduction.

    • DNA (deoxyribonucleic acid) is present in all organisms and directs cellular functions.

    • Variation arises when genes are recombined, expressed differently, or mutated.

1.1 Reproduction, Development, and Genetics

  • Life has the capacity to reproduce and develop: life arises only from life; development proceeds from fertilization through juvenile stages to adulthood.

  • Genes and DNA: inheritance and variation via genetic recombination, gene expression, and mutations.

  • Scientific note: Genetic variation underpins population change over generations via natural selection.

1.1 Response to Environment; Homeostasis; Adaptation

  • Responds to external stimuli by moving toward or away from stimuli; movement contributes to behavior.

  • Behavior is directed toward avoiding injury, acquiring food, or mating.

  • Homeostasis: staying the same; organisms maintain a relatively constant internal environment (example: human body temperature fluctuates slightly during a day).

  • Adaptation: over nearly 4 billion years, life has faced changing environments. Adaptations are features that improve an organism's fit to a given environment.

  • Natural selection is the differential reproductive success of adapted individuals, leading to changes in a population’s trait frequencies over time. Evolution is the change in trait frequencies in populations and species over time.

1.2 The Classification of Life

  • Definitions:

    • Taxonomy: discipline of identifying and grouping organisms.

    • Systematics: study of evolutionary relationships among organisms.

  • Classification structure: species, genus, family, order, class, phylum, kingdom, supergroup, domain.

  • Domains (largest category): Archaea, Bacteria, Eukarya.

  • Prokaryotic domains (Archaea and Bacteria):

    • Cells lack a true nucleus.

    • Bacteria: absorb, photosynthesize, or chemosynthesize food; E. coli as example; diverse habitats.

    • Archaea: live in extreme environments (low O2, high salt, high temp, high acidity); unique chemistry; absorb or chemosynthesize food.

  • Eukarya: all eukaryotic organisms with cells that contain a true nucleus.

  • Eukaryotic Supergroups and Kingdoms (historical perspective):

    • Protista: algae, protozoans, slime molds, water molds.

    • Plantae: multicellular, photosynthetic organisms (algae, mosses, ferns, conifers, flowering plants).

    • Fungi: molds, mushrooms, yeasts, ringworms; mostly multicellular filaments; absorb food.

    • Animalia: multicellular; ingest food; animals include sponges, worms, insects, fishes, frogs, turtles, birds, mammals.

  • A modern taxonomy addition: supergroups based on DNA analysis.

    • Eukaryotic supergroups include Archaeplastida, Chromalveolata, Excavata, Rhizaria, Amoebozoa, Opisthokonta.

  • Protists (kingdom Protista): diverse group of mostly single-celled organisms; some photosynthetic, some must acquire food; includes algae, protozoans, water molds.

  • The other three kingdoms (Plants, Fungi, Animals) evolved from protists.

  • Additional levels of classification include Domain, Supergroup, Kingdom, Phylum, Class, Order, Family, Genus, Species.

  • Table 1.2: Classification of Humans (example of taxonomic levels and features):

    • Domain: Eukarya → Cells with nuclei

    • Supergroup: Opisthokonta → Possess cells with flagella

    • Kingdom: Animalia → Multicellular, motile, ingestion of food

    • Phylum: Chordata → Dorsal nerve cord

    • Class: Mammalia → Hair, mammary glands

    • Order: Primates → Adapted to climb trees

    • Family: Hominidae → Walk erect

    • Genus: Homo → Large brain, tool use

    • Species: Homo sapiens → Body characteristics similar to modern humans

  • Binomial nomenclature:

    • Scientific names are two-part: Genus name + specific epithet; Genus capitalized; both words italicized.

    • Examples: Homo sapiens, Pisum sativum, Felis domesticus.

1.3 The Process of Science

  • Biology is the scientific study of life; scientists test hypotheses using the scientific method.

  • Key components:

    • Observation: curiosity about nature; use of senses; technology (e.g., microscope) to extend observations.

    • Hypothesis: inductive reasoning to develop a general explanation; a falsifiable statement; past experiences may influence hypotheses; hypotheses should be testable.

    • Predictions and Experiments: deductive reasoning using if-then logic; provides testable predictions.

    • Experimental design:

    • Independent variable (experimental variable): factor being tested.

    • Dependent variable (responding variable): result or change observed.

    • Control: not exposed to the experimental variable.

    • Groups: Control group (no treatment) and Experimental group (receives treatment).

    • Model organisms and systems: fruit fly Drosophila melanogaster, mouse Mus musculus; computer models for climate change.

    • Data presentation and statistics: data are presented in tables/graphs; standard error (or standard deviation) measures uncertainty; statistical significance assesses whether results are due to chance.

    • Scientific papers: studies are peer-reviewed; rejected or revised before publication.

    • Scientific theory: concepts that join well-supported hypotheses; e.g., cell theory, homeostasis, evolution; the theory of evolution as the unifying concept of biology.

  • Example: Helicobacter pylori and ulcers (illustrative experiment)

    • Experimental background: ulcers commonly linked to H. pylori; antibiotics treat ulcers.

    • Hypothesis: antibiotic B is a better treatment than antibiotic A.

    • Prediction: antibiotic B yields better ulcer healing than antibiotic A.

    • Experiment design (simplified): three groups – control (placebo), test group 1 (antibiotic A), test group 2 (antibiotic B).

    • Method: treat subjects for 2 weeks with the designated substance; examine stomach/intestinal linings for ulcers.

    • Results (example data): after 2 weeks, percentage cured: Control = 10%, Test Group 1 = 60%, Test Group 2 = 80% (data shown with error bars).

    • Conclusion: data support the hypothesis that antibiotic B is a better treatment than A.

1.3 The Process of Science (data handling and reporting)

  • Data are represented in various formats (tables, graphs).

  • Statistical concepts help evaluate data; e.g., standard error and statistical significance.

  • Scientific studies are usually written as research papers and peer-reviewed before publication; acceptance may require revisions.

1.4 Science and the Challenges Facing Society

  • Major contemporary challenges:

    • Climate change

    • Biodiversity and habitat loss (extinction risk)

    • Emerging and reemerging diseases

Climate Change

  • Definition: changes in Earth’s climate cycles due to human activity; more CO2 is released than removed.

  • Historical CO2 levels: $$ ext{CO}_2(1850) \

mnemonic for help you remember the order of taxonomic classification in biology

Domain - dear

Kingdoms- king

Phylum - phillip

Class - came over

Order - over

Family -for

Genus -great

Species - sphagetti