Dynamic Menu
Week 12 Assignment
Jim Rieger
This is an example of a dynamic menu. I've included some crazy text so that you may see the scroll feature of the menu.
Introduction
Biology is the scientific study of living things.
Biologists goals are to understand how organisms function and to use that knowledge to help solve problems.
What Is Life?
Life can be defined as an organized genetic unit capable of metabolism, reproduction, and evolution.
(See Video 1.1.)
Metabolism involves conversions of matter and energy
An organisms metabolism is its total chemical activity and consists of thousands of individual chemical reactions.
These reactions must be coordinated for an organism to function.
Genes provide this control and coordination.
The internal environment of an organism must remain within a given range of physical and chemical conditions for that organism to remain healthy.
Homeostasis is the maintenance of a relatively stable internal condition, such as temperature.
Metabolic adjustments to internal conditions allow organisms to maintain homeostasis.
Reproduction continues life and provides the basis for evolution
The combination of reproduction and errors in the duplication of the genetic material results in biological evolution.
Variations in the physical environment have helped drive the diversification of life.
No single living thing can perform well in all environments.
The differences among living things that enable them to live in different kinds of environments and adopt different lifestyles are called adaptations.
Identification of the processes that result in biological evolution was one of the great scientific advances of the nineteenth century.
(See Videos 1.2 and 1.3.)
Levels of Organization of Life
Biology can be visualized as a hierarchy of units that include molecules, cells, tissues, organs, organisms, populations, communities, and the biosphere. (See Figure 1.6 and Animated Tutorial 1.1.)
The organism is the central unit of study in biology.
To understand organisms, biologists must study them at all levels of organization, from low to high.
(See Videos 1.6 and 1.7.)
Biology is a Science
Conceptual tools guide scientific research
Underlying most scientific research is the hypothesis-prediction (HP) approach, which allows scientists to modify and correct their beliefs as new observations and information become available.
There are five parts to the HP system:
Making observations.
Asking questions.
Forming hypotheses, or tentative answers to the questions.
Making predictions based on these hypotheses.
Testing the predictions by making additional observations or conducting experiments.
If the results of continued testing support the hypothesis, it may come to be considered a theory.
If the results do not support the hypothesis, it may be modified or abandoned in accordance with the new information.
Hypotheses are tested in two major ways
Most tests of hypotheses are of two types: controlled experiments and the comparative method.
Controlled experiments allow scientists to keep all factors, other than the one hypothesized to be causing the effect, constant.
The most powerful controlled experiments have the ability to demonstrate that the hypothesis or prediction made from it are wrong.
In cases in which hypotheses cannot be tested with controlled experiments, scientists may use the comparative method.
In this approach, scientists make predictions about patterns that should exist in nature if a hypothesis is correct, and then gather data to determine if those patterns do exist.
The HP method was used by researchers to investigate why amphibian populations are declining dramatically in many places on Earth.
Step 1: Making observations:
A group of scientists observed that amphibian populations are declining seriously in some parts of the world including western North America, Central America, and northeastern Australia, but not in others, such as the Amazon Basin.
Observations also showed that the declines were greater in the mountains than in adjacent lowlands.
Step 2: Asking questions:
Two questions are suggested by these observations.
Why are amphibian declines greater at high elevations?
Why are amphibians declining in some regions but not others?
Steps 3 and 4: Formulating hypotheses and making predictions:
To develop hypotheses about the first question, scientists identified environmental factors that change with elevation.
In temperate regions, summer levels of UV-B radiation increase about 18 percent per 1,000 meters of elevation gain.
One hypothesis suggested that declines in the populations of some amphibian species are due to global increases in UV-B radiation resulting from reductions in atmospheric ozone concentrations.
A prediction that can be made from this hypothesis is that experimentally reducing UV-B over ponds where amphibian eggs are incubating and larvae are developing should improve their survival.
Step 5: Testing hypotheses:
The UV-B exposure hypothesis was tested by comparing the responses of tadpoles of two species of frogs that live in Australian mountains.
One species, Littoria verreauxii, had disappeared from high elevations; the other, Crinia signifera, had not.
Scientists predicted that L. verreauxii tadpoles would survive less well than C. signifera if exposed to UV-B radiation typical of high elevations. Experiments confirmed this observation. (See Figure 1.9.)
Individuals of both species survived well when raised in tanks with filters that blocked UV transmission.
These results supported the hypothesis.
Several other hypotheses have been proposed to account for regional differences in amphibian population declines, including adverse effects of habitat alteration by humans and agricultural pesticides. (See Figure 1.10.)
Thanks for viewing this dynamic menu page!