GRADE: Eighth

CONTENT STANDARDS: Life science

CONTENT TOPIC: Regulations and Behavior

CONCEPT: Organism's response to environmental changes.

CONTENT OBJECTIVE: 8F3.00 To understand how organisms change their internal environment to keep up with changes in the external environment

INSTRUCTIONAL OBJECTIVES: The learner will

3.01 Define a stimulus
3.02 Explain homeostasis in living organisms
3.03 Define natural selection

I. Stimuli Response
II. Homeostasis
III. Natural Selection
IV. Peppered Moth

TN COMPONENT OF SCIENCE: Unifying concepts of science TN GOAL:

To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical and earth/space science.

2:5 Change-Interactions within and among systems may result in changes in the properties, position, movement, form or function of systems.

2.5a Everything is constantly changing; rates of change vary over a wide scale with a great variety in patterns of change.

BENCHMARK: New information can modify existing scientific knowledge

BENCHMARK: Selective breeding has resulted in new varieties of plants and domestic animals. Various changes occur as an organism progresses through its life cycle.

TIME REQUIRED:

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white paper, black construction paper, white, gray and black moths

Today we are going to discuss how the peppered moth evolved from being light-colored to dark-colored to blend with its surroundings.

All living things respond to their environment or surroundings. This response may be fast or slow. A stimulus is anything that causes an organism to react. Examples of stimuli include heat, light, gravity, or sound.

Generally speaking, organisms will react to a stimulus in a way that will increase its chances for survival. Homeostasis is defined as the ability of an organism to maintain internal equilibrium by adjusting its physiological processes to preserve the conditions necessary for life.

Most organisms can produce more offspring than are able to survive. Those organisms inheriting the characteristics necessary for survival are favored by being allowed to live and possibly reproduce, thus passing these characteristics along through future generations. This process is known as natural selection. Often, natural selection is referred to as "survival of the fittest."

In the early 1850s, the peppered moth, Biston betularia, was present in the English countryside. This moth was mostly light-colored. The light-colored moth could land on trees and not be seen by its predators. However, as the industrial revolution progressed, the tree trunks began to darken due to the pollution in the country. Now, the light-colored moths stood out and were easily eaten by their predators. As the light-colored months diminished in numbers, the moth population as a whole became darker. The offspring of this new population were also of the dark coloration. The moths were now much closer in coloration to their surroundings and it was much easier for them to go unnoticed by their predators. The change in coloration provided a measure of protection not possessed by the original population as the degree of pollution increased.

In the last few years, pollution control has resulted in much lighter tree trunks once again. As was predicted, the light-colored moths have become more common once again.

Have students prepare model posters to illustrate the natural selection of the peppered moth. Have them use a white paper or posterboard and a black paper or posterboard. Provide a stencil or pattern of a moth or let the students draw their own. They need to make white with dark spots, gray with spots and dark colored moths. Have them scatter them onto the posterboard to visual how predators could pick out and destroy the various moths on the two backgrounds.

Explain to the person behind you what allowed the peppered moth to survive a change in the environment.

1. Stimulus-anything which causes an organism to react.

2. homeostasis-a process by which an organism responds to environmental stimulli in order to preserve conditions necessary for life.

3. Natural selection-a process whereby an organism which survives will reproduce and cause changes in the environment.

McLaren, James E. and Lissa Rotundo. Biology. Massachusetts: D.C. Heath and Co., 1985, pg. 214.
Miller, Kenneth R. and Joseph Levine. Biology. New Jersey: Prentice Hall, 1991, pgs. 30 & 31.
Raven, Peter H. and George B. Johnson. Biology. Iowa: Wm.C.Brown, 1995, pgs.388 & 389.

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