This is an introductory biology course -- spend what time remains today considering various aspects of science in general and of the science of biology in particular.
Science: "knowledge about the natural world attained through study."
Science is a way in which we can find order in the world around us -- science provides tentative explanations of how the natural world is organized and how it functions.
Sciences that you are probably familiar which include chemistry, physics, geology, mathematics, and biology.
Biology can be defined as "the science of life."
What do we mean by "life?" I suspect that we have an intuitive feeling for what is "alive" what is not.
Nonetheless, it's useful to consider some of the characteristics of living things.
All living things have five common characteristics:
1. they are organized.
2. they respond to environmental stimuli.
3. they metabolize.
4. they reproduce.
5. they are adapted to the environment.
Living things are organized -- both living and nonliving things are ultimately composed of atoms that are subject to the same laws of physics and chemistry. However, atoms are organized differently in living and nonliving things.
Nonliving things tend to be homogeneous (e.g. a glass of water = H20), while living things are heterogeneous and consist of many different kinds of atoms.
Biological systems are organized in a hierarchical fashion -- each level is made up of less complex levels lower in the hierarchy.
Let’s look at this hierarchy:
1. The cell is the basic unit of life -- living organisms are composed of one or more cells -- some organisms (e.g. bacteria) are single cells, while others (e.g. ourselves) are multicellular
2. In multicellular organisms, different kinds of cells form tissues that have specific functions (e.g. nerve, muscle, bone tissue)
3. tissues form organs (e.g. the brain).
4. organs form organ systems (the nervous system).
5. organ systems are organized into organisms.
6. organisms of the same kind form a population.
7. populations at a specific place form a community.
8. a community and its physical environment forms an ecosystem.
9. all ecosystems on earth together make up the biosphere.
In this class, we will take a "levels of organization" approach, beginning with nonliving levels (atoms and molecules) and finishing with ecosystems.
Living things respond -- living things interact with their environment and must respond to environmental changes in order to maintain a constant internal state and to survive -- ability to maintain a constant internal state is called homeostasis -- signals of environmental change are called stimuli -- e.g. light, temperature, nutrients, wastes etc. -- response may be behavioral or physiological -- e.g. dog sleeping on a heating vent -- may respond behaviorally by moving to another part of the room; may respond physiologically by panting to cool itself.
Living things metabolize -- in order to maintain their organization and their homeostasis, living things must metabolize --
Metabolism: chemical conversion of nutrient molecules (food) into useable energy and building materials -- energy and building materials used for growth, repair, reproduction, movement, and other processes.
Living things reproduce -- each type of organism has the potential to reproduce -- offspring have same general characteristics as their parents because reproduction insures that the genetic message carried in molecules of DNA is passed from one generation to the next -- individual organisms die, but reproduction insures that their species will persist through time -- if individual death rates exceed individual reproductive rates, then extinction of populations and species occurs.
Living things are adapted -- living things possess traits (structures, behaviors, physiology) called adaptations that help them to survive in their specific environment -- adaptations are the result of evolutionary processes, which we will discuss later in the semester -- e.g. various modification of forelimb structure for locomotion in mammals: cat, bat, mole, seal, and whale -- features of desert plants to conserve water.
These then are some of the characteristics common to living things.
Scientists obtain knowledge in an organized, systematic fashion using a general approach called the scientific method.
Scientific Method: a general "problem-solving" procedure -- five steps.
1. observation -- observe some natural phenomenon or occurrence.
2. hypothesis -- a tentative explanation for the phenomenon.
3. prediction -- a hypothesis makes a prediction -- e.g. "if hypothesis X is operating, then outcome Y should be observed.
4. experiment -- testing the predictions and the hypothesis.
5. decision -- evaluation of experimental results (data).
A few general comments about the scientific method and then an example:
1. hypotheses must be testable and at least potentially falsifiable -- this is what separates the sciences from such other fields as religion, philosophy, metaphysics and art.
2. a hypothesis can be supported or falsified (refuted), but it can never be proven.
3. If experimental results falsify the hypothesis, the scientist begins again by formulating another hypothesis, designing an experiment, etc.
4. If results support the hypothesis, the scientist may design another different experiment to further test the hypothesis.
5. Hypotheses that have been repeatedly tested and not falsified, may be elevated to a theory -- "it's only a theory" is actually saying that the hypothesis is supported by all available evidence -- theories, if they continue to be tested and supported -- may be elevated to "laws "or "principles" -- e.g. law of gravity, principle of evolution.
Scientists publish their hypotheses, experiments, and conclusions in books and journals -- become part of the public record -- one scientist will read another's hypothesis and test it -- perhaps refute it and provide an alternative hypothesis to be tested. In this fashion, science progresses and our knowledge about the natural world increases.
Now, a simple example of the scientific method in action:
1. observation -- lemming populations in the arctic undergo "cycles" in numbers every 3.5-4 years (Graph N vs. time).
2. hypothesis -- a tentative explanation of the observation -- "peak populations destroy their food resources and this leads to starvation and a decline in numbers."
3. prediction -- there are several we could make -- here's one: "if extra food is supplied to lemming populations, then the cycles should be destroyed."
4. experiment -- test the prediction/hypothesis as unambiguously as possible -- general experiment would be to supply extra food, hypothesis would be supported if peak population continued and refuted if decline occurred anyway --
Experimental design -- experiments should be as powerful and unambiguous as possible
1. experiments should include control and replication
a. should have control populations that don't receive extra food.
b. should have several control and experimental populations (replicates) -- e.g. results from an experiment using 5 control populations and 5 experimental populations would be more powerful than an experiment with one experimental population only or 1 experimental pop. and 1 control.
4. decision -- do the data from the experiment support or refute our hypothesis? We would probably use some type of statistical analysis to help us make this decision -- e.g. did addition of food seem to prevent decline in numbers? If so, the hypothesis is supported. If not, we would formulate a new testable hypothesis -- e.g. predators build up and reduce the lemming populations.
This a "real life example" -- lemmings do display these cycles -- excess food has been supplied experimentally and the cycles occur anyway -- thus, the "food hypothesis" is not supported.
One last word about the science of biology and this class.
Obviously, we are living things -- thus, biology and this class in biology should be very relevant to us -- indeed, it would be difficult to find a topic more relevant than biology!!
Our day-to-day life as organisms consists largely of biological phenomena and interactions -- hunger, illness, sex, confrontations with our conspecifics.
On a larger scale, many of the problems and pressing questions that face us as a culture or species are biological and their solutions will come from the work of biologists -- AIDS, cancer, feeding the world’s population, habitat destruction and the extinction of the earth's biota, applications of genetic engineering, to name just a few. Hopefully you will find this course both relevant and interesting.
Next time: Chemical Foundations for Cells.