Lecture Outline

Why Biology?

A. To biologists, life reflects its ancient molecular origins and its degree of organization. Life is:

1. An outcome of ancient events by which nonliving materials became assembled into the first living cells.

2. A way of capturing and using energy and raw materials.

3. A way of sensing and responding to changes in the environment.

4. A capacity to reproduce, grow, and develop.

5. Life evolves, or changes over time.

1.1 DNA, Energy, and Life

A. Nothing Lives Without DNA

1. Living and nonliving matter are composed of the same particles, operating according to laws governing energy—the capacity to make things happen, to do work.

a. Deoxyribonucleic acid, or DNA, is the special molecule that sets the living world apart from the nonliving by carrying the hereditary instructions for assembly of new organisms.

b. The flow is from DNA to RNA to protein.

2. Inheritance is the acquisition of traits through the transmission of DNA from parents to offspring.

a. Each organism arises through reproduction—the production of offspring by one or more parents.

b. DNA also guides development—the transformation of a new individual into a multicelled adult.

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

B. Nothing Lives Without Energy

1. Energy, the capacity to do work, moves through the universe in a series of transfers.

2. Metabolism is the cell’s capacity to:

a. obtain and convert energy from its surroundings,

b. use energy for maintenance, growth, and reproduction.

3. Receptors and the stimuli they receive allow controlled responses to be made to heat and cold, harmful substances, and varying food supplies

4. Homeostasis refers to a state in which the conditions of the “internal environment” are maintained within tolerable limits.

a. Increased sugar causes insulin release, which stimulates cells to take up sugar.

b. Decreased blood sugar causes another hormone to call on stored sugar reserves.

1.2 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 complex molecules of other organisms to simple raw materials suitable for recycling.

2. All organisms are part of webs that depend on one another for energy flow through them and recycling of raw materials among them.

1.3 If So Much Unity, Why So Many Species?

A. Attempts to clarify the diversity of life forms led to classification schemes.

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

2. A three domain system of classification has been proposed: bacteria, archaea, and eukarya.

3. Six kingdoms are presently recognized:

a. Archaebacteria—anaerobic bacteria.

b. Eubacteria—autotrophs and heterotrophs.

c. Protista—one-celled organisms.

d. Fungi—molds, mushrooms.

e. Plantae—familiar multicellular plants.

f. Animalia—multicellular animals from sponges to humans.

B. Both types of bacteria are prokaryotic, meaning they do not possess a nucleus; all other groups are eukaryotic, having a true nucleus that houses the DNA.

1.4 An Evolutionary View of Diversity

A. Mutation–Original Source of Variation

1. Reproduction involves inheritance of instructions that 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. The environment tests the combination of patterns expressed in each organism and may prove the trait adaptive—increases survivability and reproduction.

B. Evolution Defined

1. Suppose a DNA mutation gives rise to a different form of a trait in a few members of a population.

2. The change in the frequency of the features in a population is evolution.

C. Natural Selection Defined

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; present-day overuse of antibiotics illustrates Darwin's model even more.

2. The key points of his theory are as follows:

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.

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

d. Over time the character of a population may change and lead to different lines of organisms (evolution).

1.5 The Nature of Biological Inquiry

A. Observations, Hypotheses, and Tests

1. Biology, like all science, pursues a methodical search for information that reveals the secrets of 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. Predict what the outcome would be if the hypothesis is valid (deductive, “if-then” reasoning).

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

e. Repeat the tests for consistency.

f. Examine alternative hypotheses in same manner.

g. Report objectively on the tests and conclusions.

3. Problem solving involves logic.

a. Inductive logic derives a general statement from specific observations.

b. Deductive logic allows inferences to be made about specific predictions that follow from a hypothesis.

4. Experiments involve tests in which conditions are carefully controlled.

a. Control groups are used to identify side effects during a test that involves an experimental group.

b. The experimental group experiences all of the same conditions as the control except for the variable being studied.

B. About the Word “Theory”

1. A theory is a related set of hypotheses that form a broad-ranging explanation of many phenomena.

2. Theories are accepted or rejected on the basis of tests and are subject to revision.

3. Scientists must be content with relative certainty, which becomes stronger as more repetitions are made.

4. Scientists must be prepared to change their minds in light of new evidence.

1.6 Focus On Science: The Power Of Experimental Tests

1.7 The Limits of Science

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

1. Subjective questions do not readily lend themselves to scientific analysis and experiments.

2. All of human society must participate in moral, aesthetic, and other such judgments.

B. Science may be considered controversial when it offers explanations for an aspect of nature previously considered supernatural.

1. Copernicus correctly stated that the earth circled the sun—a heresy in his day.

2. The external world, not internal conviction, must be the testing ground for science.