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Biology 1116 Outline

Biology 1116 Lecture Notes

Chapter 1: Biology: Exploring Life


  • Life’s levels of organization define the scope of biology
  • Living organisms and their environments form interconnecting webs
  • Cells are an organism's basic unit of structure and function
  • Unity in diversity: all forms of life have common features
  • Biological diversity can be arranged into 3 domains
  • Evolution explains the unity and diversity of life
  • Scientists use two main approaches to learn about nature
  • Biology is connected to our lives in many ways

Life’s levels of organization define the scope of biology

  • Life is organized into several structural levels forming a hierarchy. Biology is the scientific study of all these hierarchical levels of biological organization (Fig 1.1)
    • Ecosystem (biotic and abiotic components of a particular area)
    • Community (all organisms in a particular area)
    • Population (all individuals of a particular species in a particular area)
    • Organism
    • Organ systems
    • Organs
    • Tissues
    • Cell (basic unit of living matter)
    • Organelles
    • Molecules
    • Atoms
    • Subatomic (electrons, protons and neutrons)
  • Life’s hierarchy builds from molecules to ecosystem.
  • Most biologists specialize in the study of life at a particular level.
  • The deepest insights into biology often come from discovering connections between various levels in the hierarchy of life.
  • Each level in nature’s hierarchy has unique structures, and a set of functional properties result from that structure.
  • Each level has "emergent properties" which are not present at lower levels. Emergent properties arise from the interaction of component parts: The whole is greater than the sum of its parts.

Living organisms and their environments form interconnecting webs

  • At highest level in nature’s hierarchy (the ecosystem) interactions between organisms make up a web of relationships connecting all organisms and the components of the environment.
  • Environment = everything external to organism (or gene). Includes both biotic and abiotic factors.
  • Fig 1.2: Highlights differences between flow of chemical nutrients and flow of energy within an ecosystem.
    • Energy flows through an ecosystem. In contrast, chemical nutrients are cycled in an ecosystem.
    • Ecosystems gain and loose energy constantly.
    • Ultimately all energy entering an ecosystem is derived from the sun by photosynthesis. All energy eventually leaves an ecosystem as heat (this energy can not be harnessed to do useful work).
    • Primary producers: includes plants, algae, and some bacteria (Photosynthetic).
    • Primary consumers: Animals and protists that eat primary producers.
    • Secondary consumers: eat primary consumers
    • Decomposers: Fungi and bacteria. Nutrient recycling is essential.
  • The web of relationships among plants, animals, microorganisms, and the physical environment give an ecosystem structure (structure as applied to an ecosystem is more abstract than that of physical entities).
  • Interactions account for the passage of chemical nutrients and energy throughout the ecosystem.


  • The cell is the lowest level of structure capable of performing all the activities of life. Fundamental unit of life.
    • Cell theory (Shleiden and Schwann): All living things consist of cells, and all cells are derived from preexisting cells. Ability of cells to divide to form new cells is the basis for all reproduction and development.
    • All cells are enclosed by a membrane which regulates passage of materials between the cell and its surroundings.
    • All cells have DNA at some point in their life cycle. DNA, an information encoding molecule, is the heritable material that directs the cell's activities.
    • Two major kinds of cells (based on structural organization):(Fig 1.3)
      • Prokaryotes: includes eubacteria, and archaea. Lack internal compartmentalization. Simpler in structure. Very small.
      • Eukaryotes: Have extensive compartmentalization due to presence of organelles. Larger and more complex than prokaryotes.

Unity in diversity: all forms of life have common features

  • Life on earth is monophyletic: we all share a common ancestor. Life’s diversity is united by common features whose foundation resides in the genetic information in DNA.
  • Some common features of all life (Fig 1.4).
    • Composed of one or more cells.
      • all cells are DNA based (4 nucleotides)
    • Universal genetic code. Specifications differ but not the language. Information in DNA underlies all properties that distinguish life from nonlife.
    • Ability to reproduce. Reproduction underlies the capacity of species to evolve (i.e. change through time).
    • Evolution and natural selection.
    • Order: all living things exhibit highly ordered complex organization.
    • Homeostasis: ability to keep internal environment constant, despite external environmental fluctuations.
    • Response to external stimuli.
    • Growth and develepoment
    • Energy utilization
  • Evolutionary connections among all life forms account for the paradox of unity in diversity.

Biological diversity can be arranged into 3 domains

  • A hallmark of life on earth is its incredible diversity. There are tens of millions of species.
  • To make the enormous diversity of life more comprehensible, taxonomists have devised ways of grouping organisms.
  • Because organisms are grouped according to their similarities, taxonomy often reflects evolutionary history.
  • The tree of life has three main branches (Domains)

  • 1. Bacteria
    • most ancient, diverse, and ubiquitous.
    • lack internal compartmentalization nucleus nor membrane-bound organelles.
  • 2. Archaea
    • inhabit extreme habitats.
    • thermophiles, halophiles, methanogens
    • most closely related to Eukaryotes.
  • 3. Eukarya
    • includes protists, algae, plants, fungi, and animals
    • cells contain a nucleus + membrane-bound organelles.
  • Each Domain is divided into kingdoms. E.g. Domain eukarya contains various kingdoms Protista, Fungi, Plantae, and Animalia.

Evolution explains the unity and diversity of life

  • Charles Darwin: 1859 published "On the Origin of Species by Means of Natural Selection".
  • Theory of evolution by Natural Selection has revolutionized biology. Provides a framework with great explanatory power. Unifies all disciplines of biology.
  • Biology without evolution does not make sense.
  • Natural Selection (Fig 1.6b)
    • Occurs as heritable variations are exposed to environmental factors that favor the reproductive success of some individuals over others.
    • Results from responses of organisms to interactions with biotic and abiotic factors in environment.
    • Note: populations and species evolve, but not individuals. Evolution is the change in "allele" frequencies over time.
  • Adaptations = Set of features evolved by natural selection enabling organisms to be well suited to their particular environment.

Scientists use two main approaches to learn about nature

  • Science is a way of knowing. It's an investigative process which can be applied to almost any discipline. Biology is the scientific investigation into the workings of nature at all levels of organization.
  • Two main approaches used:
    • Discovery science: Mostly descriptive (e.g sequencing of human genome, describing newly discovered species, etc...). Uses inductive reasoning (derivation general principles from large number of specific observations).
    • Scientific method. 5 key elements:
      • 1. Observations
        • from others or results from previous experiments.
      • 2. Questions
        • about unclear aspects of observations: How? When? Why?
      • 3. Hypotheses
        • tentative explanations of a phenomena phrased in such a way as to be testable.
      • 4. Predictions
        • logical, testable outcomes of the hypotheses developed by the use of deductive reasoning, eg. if .... (statement of hypotheses) is true, then ... (predictions).
      • 5. Tests
        • determine if predictions are supported (fail to falsify).
        • experimental tests differs from the control test by a single factor, called the variable.
        • a control is a replica of the experiment in which the special treatment being studied is omitted. Controls clarify experimental results by establishing a standard for comparison. Without a control, it is not possible to say if experimental outcome is due to variable tested or some other variable.
  • The scientific process simply falsifies or supports hypotheses. Science never proves anything. Hypotheses are never proven with absolute certainty, only with a certain statistical degree of confidence. Gradually, as repeated testing supports a particular hypotheses, we come to have greater confidence in the hypotheses.


  • Science is an adaptable process, not rigid. (eg, controls can not always be used especially where experiments are done in nature).
  • Science is tentative, it does not prove, only falsifies.
  • Science requires critical thinking at every step.
  • Cumullative (often observations are simply previous results).
  • Self-critical: always open to revision by additional data. It is a social activity with a self-correcting mechanism.
  • Science itself is devoid of moral content. However, the knowledge that we gain from applying scientific method to the uncovering of the mysteries of nature does help humans decide what is "right" or "wrong". Do not look to nature for a moral compass.
  • Many questions lie outside the realm of science. There are limits to science. Only deals with observable, quantifiable, testable phenomena in the natural world. Not for use with the "supernatural". Will not answer the question "Does God Exist?"
  • "Freedom in science is essential." Is it?

Biology is connected to our lives in many ways

  • Some of the biggest challenges facing humanity have biological underpinnings. A basic understanding of biology is necessary for an informed position on many issues.
  • Some of these issues include: human population growth, climate change, pollution, endangered species, genetic engineering, nutrition, medical advances, disease, etc...
  • Biology- from molecular to ecosystem levels- is directly connected to our lives.
  • Evaluating reports on problems of this magnitude requires critical thinking and familiarity with many aspects of biology (politicians and lawers should be biologically literate).
  • Biology offers us a deeper understanding of ourselves and the planet.
  • Practical implications of biology: Technology = application of scientific knowledge.
  • Potent combination of science and technology has had profound effects on society. Many effects have been beneficial. Others have inerdvertantly been harmful (e.g. reduction of death rates through better health care has led to human over population of earth, possibly beyond it's carrying capacity).


This Page last updated Jan 2009. For more information contact Mário Moniz de Sá