Chapter 1 - An Introduction to Biology Notes

Principles of Biology and Levels of Organization

• Biology is 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.

• Biologists have described a set of principles that apply to all fields of biology; principles 1 through 6 define the basic features of life.

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.

  • This 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.

  • All organisms contain genetic material composed of DNA (deoxyribonucleic acid).

• Principle 6: Populations of organisms evolve from one generation to the next and are related by an evolutionary history.

  • 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 is the underlying factor that explains the unity and diversity of modern species; it's the changing genetic composition of a population over time.

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: 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; 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.

  • An adaptation is a characteristic in a species that is the result of natural selection; adaptations affect survival and reproduction.

• Artificial selection is a human-driven form of selection (e.g., human choices of desirable traits led to various breeds of dogs).

• Tuskless elephants appear 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 XTXt.

• Males cannot be tuskless because a single T allele is lethal.

Classification of Living Things (Taxonomy)

• Taxonomy is 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 (ex: Amphiprion ocellaris, commonly known as the Ocellaris clownfish).

Taxonomic Hierarchy

• Each species is placed into a taxonomic hierarchy:

  • Domain

  • Supergroup

  • Kingdom

  • Phylum

  • Class

  • Order

  • Family

  • Genus

  • Species

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:

  • Ecology

  • Anatomy

  • Physiology

  • Cell biology

  • Molecular biology

  • Systems biology

• As new tools become available, they allow scientists to ask new questions.

Scientific 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.

  • Example:

    • 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; the 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.

    • Observations are made regarding natural phenomena.

    • These observations lead to a testable hypothesis that tries to explain the phenomena.

    • Experiments are conducted to determine if the predictions are correct.

    • The data are analyzed (involves the use of statistical analysis).

    • 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.

Model-Based Learning

• 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

Science 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.”