Biology: An Introduction to Biology

Principles of Biology and Levels of Organization

  • Biology defined: The study of life.
  • Investigations of living things can lead to discoveries with far-reaching benefits.
    • Example: Salicylic acid (aspirin) from the willow tree.
    • Example: Blood pressure medicine (ACE inhibitor) from poisonous snakes.
  • The study of life has revealed a set of unifying principles.
    • Principles 1 through 6 define the basic features of life.
    • Principle 7 and beyond are also important in all fields of biology.

Unifying Principles of Biology

  • Principle 1: Cells are the simplest units of life.
    • The cell theory is a foundation of biology.
      • All organisms are composed of one or more cells.
      • Cells are the smallest units of life.
      • New cells come from pre-existing cells by cell division.
  • Principle 2: Living organisms use energy.
    • The maintenance of organization requires energy.
  • Principle 3: Living organisms interact with their environment.
    • Includes both living (e.g., predator) and non-living components (e.g., light).
  • Principle 4: Living organisms maintain homeostasis.
    • The amount of variability for a parameter may differ between species (e.g., body temperature in a mammal versus a reptile).
  • Principle 5: The genetic material (DNA) provides a blueprint that allows organisms to grow, develop, and reproduce.
  • Principle 6: Populations of organisms evolve from one generation to the next and are related by an evolutionary history.
    • All organisms contain genetic material composed of DNA (deoxyribonucleic acid).
    • The genetic information of a population can change over time.
    • DNA sequences, the fossil record, and other lines of evidence document evolution.
  • Principle 7: Structure determines function.
  • Principle 8: New properties of life emerge from complex interactions.
  • Principle 9: Biology is an experimental science.
  • Principle 10: Biology is a quantitative science.
  • Principle 11: Biologists use models and simulations to test experimental predictions and convey their ideas.
    • A model is a conceptual, mathematical, or physical depiction of a real-world phenomenon.
  • Principle 12: Biology affects our society.

Levels of Biological Organization

  • The organization of living organisms can be analyzed at different levels of biological complexity, ranging from atoms to the biosphere:
    • Atoms
    • Molecules
    • Cells
    • Tissues
    • Organs
    • Organ systems
    • Organism
    • Population
    • Community
    • Ecosystem
    • Biosphere

Biological Evolution

  • Unity and diversity are terms often used to describe life.
    • Unity refers to the common characteristics displayed by all forms of life (Principles 1-6).
    • Diversity refers to the many different forms of unicellular and multicellular life.
  • Evolution: The changing genetic composition of a population over time; the underlying factor that explains the unity and diversity of modern species.

Evolutionary History

  • Life began on Earth as primitive cells between 3.5 to 4 billion years ago (bya).
  • Evolutionary history helps us understand the structure and function of an organism.
  • Evolutionary change involves modifications of pre-existing characteristics; structures may be modified to serve new purposes.
    • Example: Walking limbs were modified into a dolphin’s flipper or a bat’s wing.

Mechanisms of Evolutionary Change

  • Evolutionary change occurs by two mechanisms: vertical descent with mutation and horizontal gene transfer.

Vertical Descent with Mutation

  • Involves transfer of genetic information from parents to offspring.
  • A progression of changes within a lineage can be documented.
  • New species evolve from pre-existing species by the accumulation of mutations.
  • Natural selection drives an increased frequency of beneficial mutations in a population over time.

Horizontal Gene Transfer

  • An organism incorporates genetic material from another organism without being the offspring of that organism; this is a distinct process of exchanging genetic information that is relatively rare.
  • Can occur between different species.
  • Example: Genes that confer antibiotic resistance are sometimes transferred between different species of bacteria.

Natural and Artificial Selection

  • Evolution via natural selection results in adaptations that favor reproductive success.
  • Adaptation: A characteristic in a species that is the result of natural selection; adaptations affect survival and reproduction.
  • Artificial selection: A human-driven form of selection (e.g., human choices of desirable traits led to various breeds of dogs).

Tuskless Elephants

  • The frequency of tuskless elephants appears to be increasing due to poaching.
  • The tuskless condition is an adaptation that may lessen poaching.
  • Less than 2% of elephants in well-protected populations are tuskless.
  • Approximately 50% of the survivors of a poached population were tuskless.
  • All tuskless elephants are female (females normally have tusks).
  • The tuskless gene is found on the X chromosome; female elephants have two X chromosomes (XX) whereas males have only one (XY).
  • Tuskless (T) is a dominant allele.
  • Female tuskless elephants have the genotype X^TX^t.
  • Males cannot be tuskless because a single T allele is lethal.

Classification of Living Things (Taxonomy)

  • Taxonomy: The grouping of species based on common ancestry.
  • Classification involves sorting at multiple levels, where species are placed into progressively smaller groups that are more closely related to each other evolutionarily.

Domains of Life

  • The largest groups are the three domains of life:
    • Bacteria (unicellular prokaryotes)
    • Archaea (unicellular prokaryotes)
    • Eukarya (unicellular and multicellular eukaryotes)
  • The smallest group is the species; each species has a unique scientific name.
  • Genus name is capitalized; species descriptor (specific epithet) is not capitalized.
  • Both names are italicized (e.g., Amphiprion ocellaris, commonly known as the Ocellaris clownfish).

Taxonomic Hierarchy Example

  • The example given for Amphiprion ocellaris is:
    • Domain: Eukarya
    • Supergroup: Opisthokonta
    • Kingdom: Animalia
    • Phylum: Chordata
    • Class: Actinopterygii
    • Order: Perciformes
    • Family: Pomacentridae
    • Genus: Amphiprion
    • Species: ocellaris

Biology as a Scientific Discipline

  • Science is the observation, identification, experimental investigation, and theoretical explanation of natural phenomena.
  • Many scientists utilize model organisms in their research and use a scientific method to test hypotheses.
  • Different branches of biology study life at different levels using a variety of tools.
    • Examples: Ecology, anatomy, physiology, cell biology, molecular biology, and systems biology.
  • As new tools become available, they allow scientists to ask new questions.

Levels of Investigation in Biology

  • Ecologists study species in their native environments.
  • Cell biologists often use microscopes to learn how cells function.
  • Molecular biologists and biochemists study the molecules and macromolecules that make up cells.
  • Anatomists and physiologists study how the structures of organisms are related to their functions.
  • Systems biologists may study groups of molecules.

Hypotheses and Theories

  • A hypothesis is a proposed explanation for a natural phenomenon.
    • Based on previous observations or experiments.
    • Must yield predictions that can be shown to be correct or incorrect (must be testable and falsifiable).
    • Additional observations or experiments can support or reject a hypothesis, but a hypothesis is never really proven.
    • Observation: Maple trees lose their leaves during autumn.
    • Hypothesis: Maple trees drop their leaves in autumn because of shortened hours of sunlight.
    • Alternative hypothesis: Maple trees drop their leaves in autumn because of colder temperatures.
  • A theory is a broad explanation of some aspect of the natural world that is substantiated by a large body of evidence.
    • Allows us to make many predictions.
    • Biological theories incorporate observations, hypothesis testing, and the laws of other disciplines (physics and chemistry).
    • Theories are viewed as knowledge.
    • Two key attributes of a theory:
      • Consistent with a vast amount of known data.
      • Able to make many correct predictions.
    • Example: DNA is the genetic material.
      • An overwhelming body of evidence supports this theory.

Scientific Approaches

  • Biologists do not follow a rigid path to discovery; rather they:
    • Ask questions
    • Make observations
    • Conduct experiments
    • Ask modified questions
    • Learn from failure (lots of “trouble-shooting”)
    • Repeat experiments
    • Analyze data
    • Try new experimental approaches
    • Communicate their findings, and more…
  • Researchers typically utilize 2 general approaches: discovery-based science and hypothesis testing.

Discovery-Based Science

  • Involves the collection and analysis of data without having a preconceived hypothesis.
  • Goal is to gather information.
    • Example: Investigating a newly discovered gene without already knowing the function.
    • Example: Testing drugs to look for action against disease.
  • Discovery-based science often leads to hypothesis testing.

Hypothesis Testing (Scientific Method)

  • Designed to be an objective way to gather knowledge.
  • The steps involved:
    1. Observations are made regarding natural phenomena.
    2. These observations lead to a testable hypothesis that tries to explain the phenomena.
    3. Experiments are conducted to determine if the predictions are correct.
    4. The data are analyzed (involves use of statistical analysis).
    5. The hypothesis is supported or rejected based on the data.
  • Data are often collected in parallel control and experimental groups.
    • Groups differ by a single factor.
  • Prediction: Exposure of trees to shorter amounts of daylight will cause leaves to fall.

Models in Biology

  • A model is a conceptual, mathematical, or physical depiction of a real-world phenomenon.
  • Biologists use models to convey their ideas, evaluate experiments, and make predictions that apply to research studies.
  • Models are evaluated by their consistency with experimental data.
  • Models take many forms, including:
    • Structural models
    • Mechanistic models
    • Mathematical models
    • Temporal models
    • Hierarchical models

Biology as a Social Discipline

  • In addition to being a scientific discipline, biology is also a social discipline.
  • Biologists engage in a variety of interpersonal interactions and communication practices.
  • Within a research laboratory, undergraduate students, graduate students, postdocs, technicians, and the Principal Investigator (PI) all work together.
  • Different labs collaborate on projects.
  • Research papers are peer-reviewed.
  • At meetings, scientists discuss new data – and debate!
  • You can discuss science without having “all the answers.”