Chapter 1:Ten Themes in the Study of Life

 

A. What is life?

To biologists, life reflects its ancient molecular origins and its degree of organization.

B. Life's major themes:

1. Each level of biological organization has emergent properties.

2. Cells are the basic unit for both structure and function.

3. DNA is the genetic material and is the heritable information.

4. Structure and Function are related at all levels of organization.

5. Open systems: A way of sensing and responding to specific changes in the environment.

6. A way of capturing and using energy and materials (regulation of biochemical reactions)

7. Unity and Diversity.

8. Evolution is the central theme of biology.

9. Science is a process of inquiry (the scientific method).

10. Science and technology are functions of society,

I. Energy and Life’s Organization

A. Levels of Biological Organization

1. The cell, composed of "biological molecules," is the basic unit of life.

2. Multicelled organisms have increasingly complex levels of organization that result in tissues >>> organs >>> organ systems >>> organisms >>> populations >>> communities >>> ecosystems >>> biosphere.

B. Interdependencies Among Organisms

1. Energy flows from the sun.

  • a. Plants (producers) trap this energy by photosynthesis.
  • b. Animals (consumers) feed on the stored energy in plants, using aerobic respiration.

    c. Bacteria and fungi (decomposers) break down the biological molecules of other organisms in order to recycle raw materials.

  • 2. All organisms are part of webs that depend on one another for energy and raw materials.

    II. DNA, Energy, and Life

    A. Nothing Lives Without DNA

    l. Living and nonliving matter are composed of the same particles, operating according to laws governing energy.

  • a. Deoxyribonucleic acid, or DNA, is the special molecule that sets the living world apart from the nonliving.

    b. DNA carries the hereditary instructions for assembly of proteins.

  • 2. Each organism is part of a reproductive continuum that extends back through countless generations.

  • a. Each organism arises through reproduction in which DNA instructions are transmitted from parents to offspring.

    b. DNA also guides development of a fertilized egg into a multicelled organism.

  • B. Nothing Lives Without Energy

    1. Energy, the capacity to do work, is transferred throughout the universe.

    2. Metabolism refers to the cell's capacity to extract and convert energy from its surroundings and use energy to maintain itself, grow, and reproduce.

  • a. Plants acquire energy from sunlight and transfer some of the energy into ATP are energy transfers.
  • 3. Organisms can sense changes in the environment and make controlled responses to them.

  • a. Receptors detect specific information about the environment.

    b. Special cells receive stimuli and make appropriate responses.

  • c. Homeostasis is the maintenance of a tolerable internal environment.

    III. If So Much Unity, Why So Many Species?

    A. All organisms are made of the same materials and function according to the same laws of energy.

    B. Yet there is much diversity, a fact that has led humans to develop classification schemes

  • 1. All organisms can be identified by a genus and species name; example: Quercus alba (white oak).

    2. Groupings from least inclusive to most inclusive are: genera >>> family >>> order >>> class >>> phylum >>> kingdom.

    3. Six kingdoms are presently recognized:

  • a. Archaebacteria&endash;the most ancient of bacteria, many anaerobic.

    b. Eubacteria&endash;more recently evolved bacteria.

    c. Protista&endash;one-celled organisms; producers or consumers.

    d. Fungi&endash;molds, mushrooms; mostly decomposers.

    e. Plantae&endash;familiar multicellular plants; mostly producers.

    f. Animalia&endash;multicellular animals from sponges to humans; consumers.

  • 4. Bacteria and Archaea are prokaryotic (lacking a nucleus); all other kingdoms are in Eukarya and are eukaryotic (having a true nucleus).

  • IV. An Evolutionary View of Diversity

    A. Mutation&endash;Original Source of Variation

    1. Hereditary instructions are encoded in molecules of DNA.

    2. Variations in hereditary instructions arise through mutations.

  • a. Mutations are changes in the kind, structure, sequence, or number of parts of DNA.

    b. Many mutations are harmful.

    c. Some may be harmless or even beneficial.

  • 3. An adaptive trait is any trait that helps an organism survive and reproduce under a given set of environmental conditions.
  • B. Evolution

    1. The frequencies of genes and the effects they cause can change over time.

  • 2. Evolution is the change that characterizes populations through successive generations.
  • C. Natural Selection

  • 1. Charles Darwin reasoned that the practice of artificial selection used by pigeon breeders could serve as a model for his theory of natural selection.

    2. The main points of his theory are these:

  • a. Members vary in form and behavior; much of the variation is heritable.

    b. Some varieties of heritable traits will improve survival and reproductive chances; i.e., they are more adaptive.

    c. Those with improved chances will be more likely to reproduce (differential reproduction) and pass the adaptive traits on with greater frequency in future generations (natural selection).

    d. Any population evolves when some forms of traits increase in frequency and others decrease or disappear over generations.

    e. Evolutionary processes help explain life’s diversity.

  •  

    V. The Nature of Biological Inquiry

    A. Observations, Hypotheses, and Tests

  • 1. Biology is an ongoing record of discoveries arising from methodical inquiries into the natural world.
  • 2. Explanations are sought using the following approach:

  • a. Ask a question.

    b. Develop hypotheses (educated guesses) using all known information.

  • c. Make a prediction of what the outcome would be if the hypothesis is valid (deductive, "if-then" reasoning).

    d. Test the predictions by experiments, models, and observations.

    e. Repeat the tests for consistency.

  • f. Report objectively on the tests and conclusions.

  • B. About the Word "Theory"

  • 1. A theory is a related set of hypotheses that form an explanation about some aspect of the natural world.

    a. A theory has broader application than a hypothesis.

  • b. A theory is not "absolute truth"; scientists are "relatively" certain it is (or is not) correct.
  • 2. The fact that an idea, or even a theory, might be subject to change is a strength of science, not a weakness.

  • VI. The Limits of Science

    A. Science is limited to questions that can be tested.

    B. The external world must be the testing ground for science.