Biology Basics: Life, Organization, Evolution, and the Scientific Method

What is biology?

• Biology is the study of living organisms and their interactions with one another as well as the non-living parts of their environment.

• Recap slides are designed to be the best study guide for exams; most exam questions come straight from recap slides.

• Any definitions that are underlined on slides are definitions you should know for exams.

• Memorization is important; tools like Quizlet/flashcards are encouraged.

• The instructor emphasizes that slides contain most information, and students don’t need to copy everything in real time.

Living organisms and interactions

• A living organism is a form of life; an organism interacts with other living things (e.g., fiddler crab vs. seagull) and with the non-living abiotic environment (soil, air, water).

• Abiotic environment refers to non-living components.

• Example given: fiddler crab (a living organism) interacts with a seagull (predator) and the environment.

• The study of biology includes both biotic interactions and abiotic interactions.

Levels of biological organization (and the place of atoms/molecules)

• Biology can be studied at multiple levels of organization and hierarchical levels:

• Atoms and molecules are smaller than cells but are not alive, so they do not count as levels of biological organization.

• Cells are the smallest unit of living material that can perform all eight characteristics of life.

• Organisms can be unicellular or multicellular (many cells organized to form tissues, organs, organ systems).

• Scientists classify cells as prokaryotic or eukaryotic:

  • Eukaryotic cells have membrane-bound organelles, including a nucleus.

  • Prokaryotic cells lack a nucleus and membrane-bound organelles.

• Levels of organization (from smallest to largest within individuals):

  • Cells → Tissues → Organs → Organ systems → Organism

• Multicellular organisms are built from cells that form tissues, organs, and organ systems.

• The first five levels (cells, tissues, organs, organ systems, organism) pertain to the individual.

Key definitions and examples for levels of organization

• Cell: the smallest unit of living material that can perform all eight characteristics of life; cells are the basic unit of life. An organism is made of cells.

• Tissue: a group of similar cells performing related functions; e.g., epithelial tissue (epithelium) makes up skin.

• Organ: a collection of tissues that perform a common function.

• Organ system: multiple organs that perform related functions.

• Organism: the individual living thing.

• Population: all individuals of the same species living in a specific geographic area.

  • Key points: must be the same species and occupy the same geographic area (e.g., humans in a classroom).

• Community: all populations inhabiting the same area (multiple species).

• Ecosystem: community plus the non-living environment (soil, water, air, minerals, etc.).

• Biosphere: the planet; the collection of all ecosystems.

Distinguishing population, community, ecosystem, and biosphere

• Population vs. Community:

  • Population = all individuals of the same species in a given area.

  • Community = all populations (multiple species) in a given area.

• Ecosystem vs. Community:

  • Community = all living populations in an area.

  • Ecosystem = community plus the non-living environment.

• Biosphere = the planet; all ecosystems together.

• Teacher notes: these concepts form a ladder from individuals up to the biosphere and are important for tests (e.g., be able to contrast population vs. community).

The eight characteristics of life (the umbrella of life)

• There are eight characteristics; all must be present for something to be considered alive:

• $1)$ Order and organization

• $2)$ Sensitivity or response to the environment (stimuli)

• $3)$ Reproduction

• $4)$ Adaptation

• $5)$ Growth and development

• $6)$ Regulation (homeostasis)

• $7)$ Processing of energy

• $8)$ Evolution

• If any one is missing, the entity is not considered living.

• Note: this list is introduced early and will be revisited in more detail later in the course.

Deep dive into the first five levels and why they matter

• The first five levels focus on an individual:

  • Cells are the smallest units of life; they perform all eight life characteristics.

  • Tissues, organs, organ systems organize cells into functional units.

  • The organism is the complete living individual.

• Visualizing the hierarchy helps understand how smaller components create larger functions.

• A common teaching point: “you cannot have a tissue without a cell; you cannot have an organ without tissues,” etc.

Characteristics of life in more detail

• 1) Order and organization: the hierarchical organization (cell → tissue → organ → organ system → organism).

• 2) Sensitivity to or response to environment (stimuli): organisms respond to environmental cues; example: plants tracking the sun (positive response).

• 3) Reproduction: both unicellular and multicellular organisms reproduce (cell division is a basic mechanism); offspring production.

• 4) Adaptation: a living organism can adjust to its environment; adaptations enhance survival and reproduction; example: lantern fish with rod-dominated retinas adapted for deep-sea darkness.

• 5) Growth and development: genetic instructions drive growth and development, ensuring offspring resemble parents to a degree; genetics will be covered later in the course.

• 6) Regulation/homeostasis: organisms regulate internal conditions to maintain stability; example: dog panting to cool down.

• 7) Processing energy: all organisms require energy; some capture energy via photosynthesis (plants) and others obtain energy by consuming food (herbivores, predators).

• 8) Evolution: populations change over time via evolution; natural selection acts on variation to produce adaptation; evolution happens over long timescales.

Energy processing in more detail (photosynthesis vs. heterotrophy)

• Plants can capture energy from the sun via photosynthesis to produce chemical energy.

• General idea: energy intake is required for metabolism and growth; some organisms make their own food, others obtain it by eating.

• Photosynthesis equation (simplified):

• $6\,CO<em>2 + 6\,H</em>2O + \text{light energy} \rightarrow C<em>6H</em>{12}O<em>6 + 6\,O</em>2$

Evolution and natural selection: three primary types

• Evolution occurs through natural selection, which comes in three primary forms:

• $\text{Stabilizing selection}$: natural selection favors the average, reducing extremes.

• $\text{Directional selection}$: natural selection favors one extreme or the other.

• $\text{Diversifying (disruptive) selection}$: natural selection favors the extreme variants and not the average.

• These three forms are distinct; some discussions also mention other forms (e.g., frequency-dependent or sexual selection) but they may not be the focus here.

Stabilizing selection (example: robin eggs)

• Concept: the population shifts toward the average; extremes are selected against.

• Example: robins typically lay about four eggs; producing more than four eggs can lead to malnourished chicks due to resource limitations; producing fewer than four may lead to too few offspring surviving.

• Graphical intuition: original population (blue bell curve); after stabilizing selection, population shifts toward the center (average).

• Takeaway: extremes are less fit; the average is favored for survival and reproductive success.

Directional selection (example: moth coloration during the Industrial Revolution)

• Concept: selection favors one extreme due to environmental change.

• Example: pre-industrial moths were light-colored, blending with light backgrounds; post-industrial soot darkened the environment, and darker moths became better camouflaged; over time, the population shifted toward darker coloration.

• Takeaway: selection favors one end of the trait spectrum, leading to a shift in the population mean in one direction.

Diversifying (disruptive) selection (example: rabbits with color morphs)

• Concept: selection favors both extremes and not the average.

• Example: white rabbits vs. gray and spotted morphs; predation pressures favored camouflage in multiple distinct color forms, producing a bimodal distribution.

• Takeaway: extremes are favored in different microhabitats or under different selective pressures, increasing trait diversity.

Key differences among the three forms of natural selection

• Stabilizing selection: favors the average, reduces variation toward the center.

• Directional selection: favors one extreme (either high or low) and shifts the mean in that direction.

• Diversifying (disruptive) selection: favors both extremes and can increase bimodality; the average is disfavored.

• Quick recap: stabilizing = average, directional = one extreme, diversifying = extremes.

The scientific process: inductive vs deductive reasoning; the scientific method

• Types of reasoning:

• Inductive reasoning: using related observations to arrive at a general conclusion (specific observations → general rule).

• Deductive reasoning: starting from a general principle to predict specific results (general rule → specific predictions).

• Examples:

• Inductive: waking up tired and coffee reducing tiredness for multiple people → conclude coffee reduces tiredness (tentative).

• Deductive: all plants rely on photosynthesis → if you find a cactus (a plant), it must rely on photosynthesis.

• The scientific method (a defined process with experimentation and observation):

• Observation → Question → Hypothesis (testable and falsifiable) → Prediction → Experiment → Analysis → Conclusion/Report results.

• If results do not support the hypothesis, revise and test a new hypothesis.

• Hypotheses are testable and falsifiable; experiments have:

  • Variables (what can change)

  • Experimental group (the treatment/what is being manipulated)

  • Control group (reference, no manipulation)

• Determining success: compare experimental vs. control groups; if they differ in a way that supports the hypothesis, it is supported.

• After analysis, report results; if unsupported, revise the hypothesis.

• Historical note: Francis Bacon is often credited with formalizing the scientific method.

Basic science vs applied science

• Basic science: seeks to understand fundamental principles and knowledge for its own sake, regardless of immediate practical application.

• Applied science: uses basic knowledge to solve real-world problems or improve human conditions.

• Relationship: most applied science is built on foundational basic science; both are important.

• Coastal science example: oyster restoration illustrates basic science informing applied practice.

  • Basic science discovered cues used by oyster larvae to settle (e.g., recognizing adults); applied science uses that knowledge to design oyster reefs using concrete, old oyster shells, etc., to promote reef formation and larval settlement.

Recap and exam-oriented cues

• Expect exam questions that distinguish population vs. community, and ecosystem vs. biosphere.

• Underlined definitions on slides are likely to appear in exams.

• Recap slides are emphasized as the primary study guide for exams.

• A reminder: you do not need to copy every slide in real time; the slides will be accessible on Canvas for study.

Quick references to keep in mind

• Eight life characteristics: $1$ Order & organization, $2$ Sensitivity/response, $3$ Reproduction, $4$ Adaptation, $5$ Growth & development, $6$ Regulation/homeostasis, $7$ Energy processing, $8$ Evolution.

• Levels of organization (for individuals): cells → tissues → organs → organ systems → organism; then populations, communities, ecosystems, biosphere.

• Prokaryotic vs Eukaryotic cells: nucleus and membrane-bound organelles present in eukaryotes; prokaryotes lack a nucleus and membrane-bound organelles.

• Energy in biology: photosynthesis vs. heterotrophy; chemical energy intake through metabolism.

• Evolutionary modes of natural selection: stabilizing, directional, diversifying.

• The scientific method relies on testable, falsifiable hypotheses and controlled experimentation with proper comparisons between experimental and control groups.

If you want, I can convert any section into a shorter study-card version or expand any of the examples (e.g., more on the ocean ecosystem context) for targeted study prep.