Introduction
Biology is the subject of life and
living organisms. By studying the hundreds of thousands of living organisms with
which humans share this earth, biologists try to answer questions about
diversity and about the common characteristics of living organisms. We shall
look at some of these "themes" of biology this term; others will have to wait
for other courses... First, however, let's try to list some of the
characteristics of living organisms, and then look a bit at how science asks
questions about the world in which we live. These two topics are addressed in
the introductory chapter of your textbook.
Characteristics of
Life
Living Organisms are virtually everywhere on earth, and are found in
all sizes, shapes and colors. From bacteria to Aspen groves, blue whales and
California Redwoods, there is a remarkable array of living organisms to catalog
(or classify) and observe on earth.
All of us have some understanding of what it is to be alive and what
non-living stuff is. However, coming up with a good definition of life is not so
easy. There are a number of things we can state which are characteristics of
living organisms, the sum of which can be of help to us in distinguishing life
from non-life:
- Living organisms have an organized structure composed of cells.
- Living organisms acquire energy and materials from their surroundings, and
use energy to process acquired materials to those needed to survive.
- Living organisms have the ability to adjust to changing conditions by
actively maintaining their structure and internal environment, a process
called homeostasis.
- Living organisms have growth and development.
- Living organisms respond to environmental stimuli.
- Living organisms have the capacity for reproduction using the information
in the molecules of DNA
- Life has the capacity to change genetically from generation to generation
-- to evolve.
Although both living and non-living things share the
same fundamental properties of matter and energy (which we shall look at) living
organisms and non-living materials differ in the degree to which energy is used
and materials are organized. To help us determine how life and non-life can be
distinguished we study some of the following common "features" of living
organisms (the unity of life):
- Organisms are made of cells, the fundamental unit of all living organisms
- Organisms routinely repair and replace cells and tissues
- Organisms have common metabolic and homeostatic processes such as
photosynthesis and cell respiration
- Organisms share a common molecular basis of inheritance (DNA)
Much
of biology focuses on the linking of life processes:
- The dependence of life processes on each other
- The interaction of organisms with their environment
- The changes that occur in groups of organisms through time
- The mechanisms of evolution as a foundation for change
While
looking for the unity of life processes, we recognize the great diversity of
appearance and behavior of species on this earth, as well. Species differ
greatly in their adaptations to the many distinct environments on earth. Both
the unity and diversity of organisms can be explained by the mechanisms of
evolution.
Diversity of Life
For thousands of years humans have categorized
living organisms into groups sharing some kind of common features. In the
1700's, Linnaeus proposed a hierarchical scheme which we continue to follow. For
some time, biologists grouped organisms into general groups, called
Kingdoms, based on broad general features (which are not so easy to see
all of the time). Recently, biologists added a new category above Kingdom,
called Domain. There are three Domains:
- Domain Archaea
- Domain Eubacteria
- Domain Eukarya
- Kingdom Plantae
- Kingdom Animalia
- Kingdom Fungi
- Kingdom Protista
At times during Biology 101, we will
have reason to look a little more closely at the characteristics of these
domains and kingdoms, and for those who go on to study diversity in other
courses, you'll have the opportunity for greater observations. Table 1.1 on
page 8 of your textbook lists some of the characteristics used in the
Classification of the Domains and Kingdoms. In addition, chapters 18 - 22 of
your text discuss the diversity of organisms found within the kingdoms and
domains.
How Biologists Ask Questions
Each of us is curious about
any number of things. Often when we are curious we ask questions to try and find
out whatever it is that we are curious about.
Biologists try and find answers to their questions about living things by
using the scientific method of problem solving, or some variant of this method,
to study the processes of life.
Scientific Principles A Scientific Principle is an idea supported by
repeated experiments and observations. The assumptions behind which scientific
principles are based have been thoroughly tested and found valid over many
years.
- Principle of Natural Causality
Events can be traced to natural causes.
- Principle of Uniformity of Space and Time
Natural laws do not change
with time or distance (geography).
- Principle of Uniform Perception
Humans perceive natural events in the
same way., and this perception provides humans with reliable information about
the world around us.
How the Scientific Method Works
- Find something about which you are curious and ask a question about it
- Make observations about whatever it is you are questioning to produce a
"model" or preliminary explanation for your question
- Based on your observations, make a testable hypothesis (reasoned
guess) by using the information available to make a general statement (called
the hypothesis)
- Predict what will happen if the hypothesis is correct
- Test the hypothesis by models, controlled experiments and observations
- Repeat tests to see if results are consistent with the hypothesis
- Objectively note results and drawing conclusions
- Examine alternative hypotheses in the same manner
Science is
limited to questions that can be tested. Other fields may look at issues and
ideas which are untestable. These ideas are not appropriate for science.
Evolution as the Guiding theme of Biology
The processes of
evolution outline the mechanisms by which species genetically change from
generation to generation, in response to the "forces" of their surroundings
which favor some genetic trait over another less suited to the surroundings in
which the organisms live. We shall spend some time this term looking at the
mechanisms of evolution, as well as seeing the results of evolution as we study
the structure and functioning of cells.
This term, in Biology 101 we will look at some of these life processes.
Chapter One of your text reviews many of the ideas I've mentioned here. Read
this chapter with thought. Much of what is written there may help you think more
deeply and with greater understanding of what we are to do in Biology 101 as
well as in subsequent biology courses you will take.
