Biology Life on Earth: Intro & Foundations (Notes)

How Do Scientists Study Life? (1.1)

• Life can be studied at different levels:

  • Atom, molecule, cell

  • Tissue, organ, organ system

  • Multicellular organism, population, species

  • Community, ecosystem, biosphere

Levels of Organization (continued)

• Levels of organization outline:

  • All matter is formed of elements.

  • An atom is the smallest particle of an element retaining the properties of an element.

  • Atoms combine to form molecules.

  • Molecules provide the building blocks for cells, the smallest unit of life.

  • Some life forms are single-celled; multicellular life forms consist of tissues, which form organs, which form organ systems.

  • Multicellular organisms are composed of multiple organ systems.

  • Species: organisms capable of interbreeding.

  • Population: group of same-species organisms in a given area.

  • Community: interacting populations.

  • Ecosystem: community plus nonliving environment.

  • Biosphere: Earth's living and nonliving components.

Scientific Principles Underlie Inquiry

• Natural causality: all events have natural causes.

• Natural laws: uniform in space and time; apply to every time and place.

• Human perception: scientists assume people perceive natural events similarly; science requires objectively gathered data.

• Historical approaches to life:

  • Supernatural explanations (e.g., Greek gods) vs. natural causality.

  • Corollary: evidence from nature has not been deliberately distorted to fool us.

Uniformity of Natural Laws (continued)

• Natural laws are uniform in time and space; this underpins understanding of events such as evolution that occurred before humans recorded them.

• Creationism vs. uniformity: Creationists argue species were created by direct intervention, contrary to observed ongoing natural processes.

The Scientific Method (six steps)

1) Observation of a specific phenomenon.

• Observation leads to a question.

• Question leads to a hypothesis (based on prior observations) offered as an answer to the question.

• The hypothesis leads to a prediction (usually in the form "if … then …").

• The prediction is tested by controlled manipulations called experiments.

• Experiments yield results that support or refute the hypothesis, leading to a conclusion.

2) Scientific experiments test the assertion that a single independent variable causes a particular observation (the dependent variables).

• Controls (negative & positive) are incorporated to keep untested variables constant.

• The scientific method is illustrated by experiments by Redi and Andersson.

Experimental Design Elements (pp. 14–15)

• Independent variable: the variable deliberately changed by the experimenter.

• Dependent variable(s): the variable measured.

• Negative control: a baseline where no effect is expected.

• Positive control: a baseline where a known effect is expected.

• Standardized variables: factors kept constant across all groups.

• Example shown: Farmer Fred’s fertilizer trial comparing Fertilizer X (historical), Fertilizer Y (new), and no fertilizer (zilch) across fields Y, X, Z respectively.

• Ind Var, Dep Var, NC, PC, Standardized variables labeled in the example:

  • Independent variable: $IV$

  • Dependent variable(s): $DV$

  • Negative control: $NC$

  • Positive control: $PC$

  • Standardized variables: $SV$

The Experiments of Francesco Redi and Malte Andersson (Fig. E1-1, E1-2)

• Redi: early demonstration that maggots arise only when flies can access meat; challenged spontaneous generation.

• Andersson: discussed in context of experimental controls; details in figures.

The Scientific Method in Everyday Problems (Fig. 1-4)

• Everyday problem example: starting a late-for-appointment car.

• Premature conclusion example: attributing failure to a dead battery without proper controls.

• To fix: establish a control, reinstall old battery, check cables, then test again; if car still fails, conclude battery is likely the issue.

Limitations of the Scientific Method

• Unable to guarantee control of all untested variables.

• Conclusions remain tentative; hypotheses must be testable and falsifiable.

• Science cannot prove that something never happened; no supernatural explanations in science.

• Communication is crucial: results must be communicated for repetition and verification.

Science as a Human Endeavor

• Scientists have personalities and are subject to pride, ambition, fear, and errors.

• Accidents, luck, intelligence, and controversy drive advances.

• Fleming and Penicillin (1920s–1930s):

  • Fleming observed a mold (Penicillium) contaminating a culture and noticed inhibited bacterial growth.

  • He hypothesized the mold produced an antibacterial substance.

  • Further tests with pure Penicillium led to the discovery of penicillin, the first antibiotic.

  • Pasteur’s quote: "Chance favors the prepared mind".

Penicillin Kills Bacteria (Fig. 1-5)

• Petri dish with streaked bacteria.

• Mold produces a substance that diffuses and inhibits bacterial growth around its colony.

Scientific Theories

• A scientific theory is not the same as a guess; it is a broad, well-tested explanation of natural phenomena.

• Theories are extensively tested and can be modified in light of new evidence.

• Examples of widely accepted theories: atomic theory, gravitational theory, cell theory.

• New data can prompt revisions (e.g., prions case).

• Prions: infectious proteins that cause disease; discovery reshaped understanding of infectious diseases (e.g., scrapie, mad cow disease).

Reasoning in Science

• Deductive reasoning: applying a general rule to generate a hypothesis for a specific case.

• Inductive reasoning: creating a general rule from many observations.

• The slide hints at a D =, I =, G =, S = analogy (Deductions, Inductions, and Generating hypotheses/Rules) to illustrate reasoning, though details are not fully provided in the transcript.

Evolution: The Unifying Theory of Biology (1.2)

• Definition: Evolution is the process by which modern organisms descended, with modifications, from preexisting forms of life.

• Evidence: abundant support since Darwin and Wallace in the mid-1800s.

• Misconceptions: evolution is not "just a theory" in the colloquial sense; in science, a theory is a broad, well-supported explanation.

• Dobzhansky quote: "Nothing in biology makes sense, except in the light of evolution."

Darwin & Wallace: Three Natural Processes Underlie Evolution

1) Genetic variation among members of a population due to differences in their DNA.
2) Inheritance of those variations by offspring.
3) Natural selection of individuals whose survival and reproduction are enhanced by favorable variations.

Genetic Variability

• Arises from DNA segments; mutations alter genetic information.

• Mutations sources: irradiation, copying mistakes during DNA replication.

• Effects of mutations: no effect/neutral, decreased function, death, or increased survival and reproduction (rare).

• Mutations accumulate over millions of years, leading to differences among individuals within a species.

Natural Selection and Adaptation

• Individuals with variations that better meet environmental challenges leave more offspring.

• Adaptations: structures, physiological processes, or behaviors that aid survival and reproduction.

• Environment-specific: a trait beneficial in one environment may be detrimental in another.

• Biodiversity arises from a variety of habitats and adaptive processes.

• Humans influence the rate of environmental change and extinction.

What Are The Characteristics of Living Things? (1.3)

• Defining life: life is the quality distinguishing actively functioning beings from a dead body; the concept is nuanced.

• Core properties of living things:

  • They grow

  • They can reproduce themselves

  • They use energy

  • They are complex, organized, and composed of cells

  • They maintain homeostasis (constant internal conditions)

  • They respond to stimuli

  • They acquire and use materials and energy

  • They grow and develop

  • They reproduce

  • They have the capacity to evolve

Cell Theory and Cellular Organization

• Living things are composed of cells; cell theory states the cell is the basic unit of life.

• A single cell has internal structure:

  • Genes (DNA) contain information to control life of the cell

  • Organelles perform specialized functions

  • A plasma membrane encloses cytoplasm and organelles from outside environment

Homeostasis

• Maintenance of relatively constant internal conditions.

• Examples: thermoregulation via sweating, cooling, metabolism, or thermostat adjustments.

• Organisms may still grow and change while maintaining homeostasis.

Response to Stimuli

• Sensing and responding to internal and external environmental stimuli.

• Sensory organs detect light, sound, chemicals; internal receptors detect stretch, temperature, pain, etc.

• Plants and bacteria also respond (e.g., phototropism toward light; chemotaxis toward nutrients).

Acquisition of Materials & Energy

• Organisms require nutrients and energy to maintain organization, grow, and reproduce.

• Nutrients come from air, water, soil, or other organisms and are recycled.

• Energy acquisition:

  • Autotrophs: capture light energy via photosynthesis or derive energy via chemosynthesis.

  • Heterotrophs: obtain energy by ingesting molecules from other organisms.

• All life ultimately relies on energy from the sun (directly or indirectly).

Growth, Development, Reproduction, and Evolution (1.3)

• Growth: organisms become larger over time by producing more cells or enlarging cells.

• Development: progression through life stages.

• Reproduction: genetic material (DNA) passed to offspring, ensuring continuity of life.

• Evolution: genetic composition of a population changes over generations; mutations and variable offspring drive evolution.

How Do Scientists Categorize the Diversity of Life? (1.4)

• Three domains: Bacteria, Archaea, Eukarya.

• Key distinguishing characteristics:

  • Cell type: prokaryote vs. eukaryote

  • Number of cells: unicellular vs. multicellular

  • Energy acquisition: autotroph vs. heterotroph

• Protists (Protista) are a diverse group within Eukarya that includes both uni- and multicellular organisms.

Domains, Cell Types, and Organization

• Prokaryotic cells: lack a nucleus and membrane-bound organelles; 1–2 micrometers in diameter; domains Bacteria and Archaea.

• Eukaryotic cells: have a nucleus and organelles; larger; domain Eukarya.

• Unicellular organisms are found in Bacteria, Archaea, and some Protists; multicellular organisms are in Eukarya (Fungi, Plantae, Animalia).

• Energy strategies:

  • Autotrophs: photosynthetic or chemosynthetic; self-feeding

  • Heterotrophs: obtain energy by consuming others

• Protists: a catch-all term for diverse unicellular and some simple multicellular organisms within Eukarya.

Table 1-1: Some Characteristics Used in Classification

• Domain and Kingdoms overview (summary):

  • Bacteria: Cell Type — Prokaryotic; Cell Number — Unicellular; Energy — Autotrophic or heterotrophic

  • Archaea: Cell Type — Prokaryotic; Cell Number — Unicellular; Energy — Autotrophic or heterotrophic

  • Eukarya: Cell Type — Eukaryotic; Cell Number — Unicellular or multicellular; Energy — Autotrophic or heterotrophic

  • Fungi: Eukaryotic; Multicellular; Heterotrophic

  • Plantae: Eukaryotic; Multicellular; Autotrophic

  • Animalia: Eukaryotic; Multicellular; Heterotrophic

  • Protists: Mostly Eukaryotic; Unicellular to some multicellular; Autotrophic or heterotrophic

• Note: The Protists are a diverse collection; some classify them into multiple kingdoms under discussion.

Connections to Foundational Principles

• The cell theory: the cell is the basic unit of life.

• The flow of energy and recycling of nutrients are fundamental to living systems (Fig. 1-10).

• Evolution provides a unifying framework for understanding diversity and the relationships among organisms.

Summary Connections and Practical Implications

• In lab and field studies, expect integration of:

  • Core concepts: cell theory, energy flow, homeostasis, evolution, and classification.

  • Experimental design: IV, DV, controls, and standardized variables.

  • Ethical and privacy considerations: FERPA, intellectual property, and proper use of material.

• Real-world relevance:

  • Understanding disease (e.g., antibiotics and prions) requires integrating evolution, cell biology, and biochemistry.

  • Biodiversity and human activity: human-driven environmental changes influence selection and extinction rates.