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6-8 > Animals
Grade level: 6-8 Subject: Animals Duration: Two class periods
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Body by Design: Form & Function

Students will understand the following:
1. Symbiosis is a kind of partnership between two organisms in nature.
2. Mutualism is a symbiotic relationship in which both organisms benefit.
3. Commensalism is a symbiotic relationship in which one organism benefits and the other neither benefits nor is harmed.
4. Parasitism is a symbiotic relationship in which one organism benefits and the other is harmed.

For this lesson, you will need:
Computer with Internet access
Books and articles concerning symbiotic relationships in nature
Index cards for note-taking

1. Provide your students with the following background information:
  • Leafcutter ants bite off pieces of leaves and carry them back to their underground nests. A type of fungus grows on the leaves; the ants care for and cultivate the fungus—and then eat it. You might say the ants and the fungi have a partnership.
  • Other pairs of organisms have also developed partnerships. Each pairing is called a symbiosis.There are three types of symbiotic relationships: mutualism, in which both organisms benefit from the pairing; commensalism, in which one organism benefits and the other neither benefits nor is harmed; and parasitism, in which one organism benefits and the other organism is harmed.
2. Divide the class into small discussion groups to talk briefly about the symbiotic relationship between leafcutter ants and the fungi they cultivate and eat. Suggest to the class that two types of symbiosis may be at work (first commensalism, in which the ants cultivate the fungi, and then parasitism, in which the ants eat the fungi).
3. Invite your students to use the research materials you have provided to find information about several other pairs of organisms that practice symbiosis. If possible, each student should find at least one example of each of the three types mentioned above. Students should take notes on index cards and use their notes later in group discussions.
4. Have the groups reconvene to discuss what the group members have learned from their research. Each member should report orally on her or his findings. Then the group can hypothesize how the symbiotic partnerships might have evolved.
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Adaptations for Older Students:
Have each student develop and write his or her own hypothesis about how particular symbiotic relationships might have evolved.
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Discussion Questions

1. Discuss why evolution is described as an “ongoing play without a script or a director.”
2. Compare and contrast the way in which lizards and mammals run and breathe.
3. Discuss why it was important for evolution that reptiles developed waterproof skin.
4. Debate this statement with your classmates: “People may think that humans are the dominant species, but perhaps insect exoskeleton bodies are the shape of things to come.”
5. Explain how you can tell an animal’s position on the food chain by the placement of its eyes on its head.
6. Cheetahs, bison, and leafcutter ants all have very strong jaw muscles, but they use them differently. Contrast how and why these animals use their jaws.
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You can evaluate your students on their research and hypotheses using the following three-point rubric:
  • Three points:at least one example of each type of symbiosis; all examples correctly categorized by type; soundly reasoned hypotheses about how each relationship evolved
  • Two points:at least one example of two of the three types of symbiosis; most examples correctly categorized by type; soundly reasoned hypotheses about how each relationship evolved
  • One point:few examples of symbiosis; some examples incorrectly categorized; weak hypothesis about how the relationship evolved

You can ask your students to contribute to the assessment rubric by determining how many examples should be required and what would constitute a well-reasoned hypothesis.

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Under Cover
Each animal’s covering—whether it is skin, fur, feathers, scales, or something else—is instrumental in determining the niche that the animal fits into. For example, the frog is covered with skin that is porous to air; therefore, the frog must live in an area where it can stay constantly moist and where it can hibernate through the winter by burying itself in the mud at the bottom of a pond. Have students choose another animal species and research where it lives, what it eats, and what eats it. They should identify the role its covering plays in allowing it to be successful in that habitat.

Design an Animal
Obtain pictures of a fish, frog, snake, weasel, and leopard. Give one copy to each student and assign to each student one body part to alter: legs, covering, wings, mouth, or eyes. Tell the students to use the picture as the model and to change only the assigned body part. They can do this by tracing the unchanged part of the animal on a fresh sheet of paper and drawing the new body part on that sheet. Encourage students to be creative—they may change the color, size, shape or covering pattern. When the altered animal pictures are complete, ask students to identify any new behaviors or capabilities their newly invented animals will possess and to explain the form and function of the new feature. Students should then name the new animal and share it with the class. As a class, discuss whether the new animal’s habitat, diet, or range would differ from that of the original.

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Suggested Readings

The Robot Zoo: A Mechanical Guide to the Way Animals Work
John Kelly, Philip Whitfield. Turner Publishing, Inc., 1994.
The authors have transformed and illustrated 16 animals as carefully planned and engineered machines that help us understand how animals move, eat, breathe, and function.

Animals on the Inside: A Book of Discovery & Learning
Andres Llamas Ruiz. Sterling Publishing Co., 1994.
Check out these cross-sections of animals! Great pictures and supporting text help you understand how different animals function.

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Zoological Society of San Diego
Comprehensive site that covers information on mammals, birds, reptiles, and amphibians. This site is very well organized for student research.

Hinterland Who’s Who
This great research site is sponsored by the Canadian Wildlife Service.

National Wildlife Federation
Comprehensive site on wildlife that has education lessons and environmental information and materials.

Zoos and Aquariums of American Zoo and Aquarium Association
An excellent resource for photos, text, and graphics on dozens of animal species.

Animal Diversity Web
Organized and run by the University of Michigan Department of Zoology, this site includes information on animal distribution, natural history, and conservation with pictures and sounds.

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Click on any of the vocabulary words below to hear them pronounced and used in a sentence.

speaker    chitin
Definition:A horny polysaccharide that forms part of the hard outer integument of insects, arachnids, and crustaceans.
Context:Insects, crabs, and lobsters have external skeletons all containing a tough but pliable material called chitin.

speaker    evolution
Definition:A theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations.
Context:Bone and muscles eye and mouth, they all come from thousands of generations of slow tinkering by evolution. It is a natural process no human can match.

speaker    keratin
Definition:Any of various sulfur-containing fibrous proteins that form the chemical basis of horny epidermal tissues, such as hair and nails.
Context:Fur, feathers, scales, and beaks all are made from a versatile group of proteins called keratin.

speaker    pigment
Definition:A coloring matter in animals and plants in a cell or tissue.
Context:Red is a pigment that only plants can create.

speaker    species
Definition:A category of biological classification ranking immediately below the genus or subgenus, comprising related organisms or populations potentially capable of interbreeding.
Context:Over a million different species of animals exist on this earth.

speaker    vertebrate
Definition:Any animal in the subphylum (Vertebrata) of chordates that possess a spinal column (including mammals, birds, reptiles, amphibians, and fishes).
Context:Animals that have internal backbones are called vertebrates.

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This lesson plan may be used to address the academic standards listed below. These standards are drawn from Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education: 2nd Edition and have been provided courtesy of theMid-continent Research for Education and Learningin Aurora, Colorado.
Grade level:6-8
Subject area:science
Understands how species depend on one another and on the environment for survival.
Benchmark 1:Knows how an organism’s ability to regulate its internal environment enables the organism to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.

Benchmark 2:Knows that organisms can react to internal and environmental stimuli through behavioral response (e.g., plants have tissues and organs that react to light, water, and other stimuli; animals have nervous systems that process and store information from the environment), which may be determined by heredity or from past experience.

Benchmark 3:Knows ways in which species interact and depend on one another in an ecosystem (e.g., producer/consumer, predator/prey, parasite/host, relationships that are mutually beneficial or competitive).

Grade level:6-8, 9-12
Subject area:science
Understands the basic concepts of the evolution of species.
(6-8)Knows basic ideas related to biological evolution (e.g., diversity of species is developed through gradual processes over many generations; biological adaptations, such as changes in structure, behavior, or physiology, allow some species to enhance their reproductive success and survival in a particular environment).

(9-12)Knows that heritable characteristics, which can be biochemical and anatomical, largely determine what capabilities an organism will have, how it will behave, and how likely it is to survive and reproduce.

(9-12)Knows that natural selection leads to organisms that are well suited for survival in particular environments, so that when an environment changes, some inherited characteristics become more or less advantageous or neutral, and chance alone can result in characteristics having no survival or reproductive value.

(9-12)Knows that the basic idea of evolution is that the Earth’s present-day life forms have evolved from earlier, distinctly different species as a consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.

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Susan L. Mealiea, life science teacher, Woodbridge High School, Woodbridge, Virginia.
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