Biology: The Study of Life and Scientific Inquiry

What is Biology?

• Biology is defined as "the study of life."

• It involves posing questions about the living world and seeking answers through systematic scientific inquiry.

What is Life? The Six Characteristics of Living Organisms

An organism is a living thing that exhibits a set of fundamental characteristics:

1. Organized & Complex

• Life is fundamentally organized and complex, especially when compared to nonliving matter such as salt or the ocean.

• Even simple single-celled organisms are highly structured, containing atoms of dozens of different elements that form a cell, which is the basic unit of life.

2. Acquire & Use Materials & Energy

• Organisms continuously use energy to maintain their organization and complexity, which naturally tend to break down.

• Almost all energy sustaining life originates from the sun.

  • Energy Flow:

    • Plants (producers) directly capture solar energy through photosynthesis, trapping and storing it for their own use.

    • When plants are consumed, this stored energy transfers to consumers.

    • Energy flows from the sun to plants and then to all other forms of life.

    • Some heat energy is lost at each step of this transfer. Nutrients, however, are recycled.

• Homeostasis and Material Cycling:

  • Homeostasis is the ability of an organism to maintain its internal environment within specific limits necessary to sustain life.

  • Organisms obtain materials (e.g., water, minerals, elements) that constitute their bodies from the air, water, soil, and other living things.

  • These materials are continuously exchanged and recycled among organisms and their surroundings.

3. Sense & Respond to Stimuli

• Living things can detect and react to changes in their environment (stimuli).

• Animals use specialized cells to detect various external and internal stimuli, including light, temperature, sound, gravity, touch, and chemicals.

• Plants, fungi, and unicellular organisms also demonstrate responses to stimuli (e.g., a water flea's antennae and eyes respond to stimuli).

4. Grow

• At some point in their life cycle, every organism grows, including unicellular organisms.

• Animals and plants grow by increasing the number of cells in their bodies through cell division, and sometimes by increasing the size of individual cells.

• In multicellular organisms, growth is often accompanied by development, where a growing organism becomes progressively more complex.

5. Reproduce

• Organisms reproduce in diverse ways, such as dividing in half, producing seeds, or bearing live young.

• The consistent outcome is the creation of new individuals of the same type as the parent organism.

• Offspring inherit characteristics from their parents, which are encoded in DNA.

• DNA, contained within each cell, provides detailed instructions for building and maintaining an organism.

6. Evolve

• Organisms, specifically populations, evolve, meaning they change over time.

Science vs. Religion

• Science and religion are not mutually exclusive or contradictory; they address different realms.

• Religion, belief, or faith operates outside the boundaries of scientific inquiry.

• Science only deals with testable explanations for natural phenomena.

• Science does not test faith or beliefs that cannot be empirically tested.

The Boundaries of Life: Viruses

• Viruses present a fundamental question about the definition of life.

• Characteristics viruses possess that align with living things:

  • They respond to stimuli (e.g., binding to cells).

  • They reproduce (but only inside a host cell of a different organism).

  • They evolve, notably in response to medications, which explains the need for new flu shots annually.

• Characteristics viruses do NOT possess, leading most to consider them non-living:

  • They do NOT obtain or use energy or materials independently; instead, they hijack other cells' machinery and resources.

  • They do NOT grow.

  • They do NOT actively maintain themselves.

• Viruses are simpler than a cell, often consisting merely of a protein coat surrounding a small amount of genetic material. Some have even been synthesized in a laboratory.

  • As virologist Luis Villarreal stated, "Viruses are parasites that skirt the boundaries between life & inert matter."

• Ethical Question: Should scientists be allowed to synthesize viruses in labs? This raises important ethical considerations.

The Boundaries of Life: Prions

• Prions are Proteinaceous Infectious Particles.

• They are anomalous in that they interact with normal proteins, causing them to misfold, leading to disease.

• Prions cause transmissible spongiform encephalopathies (TSEs), which are neurodegenerative diseases affecting the brain, spinal cord, and other tissues.

• Examples: Scrapie in sheep, Mad Cow Disease (Bovine Spongiform Encephalopathy), Creutzfeldt-Jakob Disease in humans, and Chronic Wasting Disease in cervids.

Studying Life at Different Levels: Biological Organization

Biologists classify the living world into different levels of organization to facilitate understanding:

• Atom: The smallest particle of an element that retains its chemical properties.

• Molecule: A combination of atoms.

• Cell: The smallest unit of life.

• Tissue: A group of similar cells specialized to perform a specific function.

• Organ: A structure typically composed of several tissue types that together form a functional unit.

• Organ System: Two or more organs working collaboratively to execute a specific bodily function.

• Multicellular Organism: An individual living thing composed of many cells.

• Population: All the individuals of a single species living within a specific area at the same time.

• Species: All organisms that are similar enough to breed and produce fertile offspring.

• Community: Populations of different species that live in the same area and interact with one another.

• Ecosystem: A community of organisms interacting with each other and with their nonliving physical surroundings.

• Biosphere: Consists of all life on Earth and the nonliving portions of Earth that support life.

The 3 Domains of Life

Life is broadly categorized into three domains based on cellular and genetic characteristics:

• Bacteria: Single-celled prokaryotes (organisms without a membrane-bound nucleus or organelles).

• Archaea: Single-celled prokaryotes, often found in extreme environments, distinct from bacteria.

• Eukarya: All eukaryotes (organisms whose cells have a nucleus and other membrane-bound organelles).

  • The Domain Eukarya includes four main kingdoms:

    • Plantae: Plants.

    • Fungi: Fungi (e.g., mushrooms, yeasts).

    • Animalia: Animals.

    • Protista (protists): A diverse group, mostly single-celled eukaryotes.

Binomial System of Nomenclature

• Common names (e.g., monkey, cactus, cougar, water flea) are widely used but can lead to confusion as they may refer to more than one species or vary geographically.

• Science requires precision, hence the binomial system for scientific names.

• Each species receives a unique two-part scientific name, always italicized:

  • The first part is the genus (capitalized).

  • The second part is the specific epithet (unique to each species within the genus, not capitalized).

• Example: Daphnia longispina for a water flea.

The Scientific Method

Science is a systematic inquiry, through observation and experiment, into all aspects of the physical universe.

Steps of the Scientific Method

Consists of six core elements:

1. Observation: Noticing a phenomenon.

2. Question: Posing a question about the observation.

3. Hypothesis: A proposed, testable explanation for the observation; an answer to the question.

4. Prediction: An anticipated outcome if the hypothesis is correct, formulated as an "if…then" statement.

5. Experiment: A carefully designed test of the prediction.

6. Conclusion: A determination of whether the results support or do not support the hypothesis.

Experimentation: Variables and Controls

• Variable: A factor in an experiment that is deliberately manipulated or changed to test a hypothesis.

• Control: A portion of an experiment where no variable is changed. Control groups are crucial to guard against the effects of unnoticed variables, allowing for comparison with experimental groups.

• Ideally, experiments and their results should be repeatable by others to ensure reliability.

The Nature of Scientific Proof

• In science, a hypothesis is never "proven true" beyond a shadow of a doubt.

• Instead, experiments attempt to fail to prove a hypothesis incorrect.

• Extensive testing in various ways can significantly increase confidence in a hypothesis's validity, but scientific "truth" is always conditional, based on the weight of available evidence.

Experiment Example: Widowbirds in Africa

• Observation: Male widowbirds have extravagantly long tails, while females do not.

• Question: Why do males have long tails?

• Hypothesis: Males have long tails because females prefer to mate with long-tailed males.

• Prediction: If females prefer long-tailed males, then males with artificially lengthened tails will attract more mates.

• Experiment:

  • Captured male widowbirds and divided them into four groups:

    1. Experimental Group (Shortened): Tails trimmed to half their original length.

    2. Experimental Group (Lengthened): Tail feathers from Group 1 were glued onto these males, doubling their tail length.

    3. Control Group (Re-glued): Tails cut and then re-glued to their original length (to control for the stress of manipulation).

    4. Control Group (Captured & Released): Males captured and released without any tail manipulation.

  • The experimental variable was the length of the tail.

  • Controlled variables included location, season, time, and weather.

  • After releasing the males, the number of nests (indicating mates) on each male's territory was counted.

• Results:

  • Males with extra-lengthened tails had the most nests (average of about two nests per male).

  • Males with shortened tails had the fewest nests (average of less than half a nest per male).

  • Control males (re-glued and captured/released) had an intermediate number of nests (average of about one nest per male).

• Conclusion: The results supported the hypothesis that female widowbirds prefer to mate with long-tailed males.

  • This does not constitute "proof," but rather indicates strong support for the hypothesis. Further experiments could provide additional information or potentially alter understanding.

What is a Scientific Theory?

In science, the term "theory" has a much stronger and more rigorous meaning than in everyday language.

Key Characteristics of a Scientific Theory

• It is NOT a mere hypothesis or a guess.

• It is NOT a simple fact.

• A scientific theory is a general and reliable explanation of important natural phenomena developed through extensive and reproducible observations and experiments.

• Scope: Much broader in scope than a single hypothesis.

• Generality: General enough to a spawn many new, testable hypotheses.

• Evidence: Supported by a significantly greater body of evidence than a single hypothesis.

Theories Can Change

• Scientific theories are dynamic; if compelling evidence emerges that renders a theory invalid, it must be modified or discarded.

• Example: Prions. Before the 1980s, all known infectious disease agents replicated using genetic material (DNA or RNA). The discovery of prions, which are simply proteins capable of causing disease without DNA or RNA, forced a modification of this understanding. This new evidence led to an expansion of the theory regarding infectious agents.

Nature of Science (General Principles)

• Ideally, scientific experiments, observations, and ideas are repeatedly tested.

• Consistent results, especially when replicated by different researchers, increase confidence in the findings.

• Scientific work must be rigorously communicated to others to be useful. This includes:

  • Publication in peer-reviewed scientific journals.

  • Presentation at scientific conferences.

  • Detailed publication of methods to ensure reproducibility.