Introduction
Modern systems of classifying organisms are based on evolutionary theory. One way to discover how groups of organisms are related to each other (phlogeny) is to compare the anatomical structures (body organs and parts) of many different organisms. Corresponding organs and other body parts that are alike in basic structure and origin are said to be homologous structures (for example, the front legs of a horse, wings of a bird, flippers of a whale, and the arms of a person are all homologous to each other). When different organisms share a large number of homologous structures, it is considered strong evidence that they are related to each other. When organisms are related to each other, it means they must have had a common ancestor at some time in the past. Your task is to find homologous structures among different invertebrates and thereby be able to explain how invertebrates are related to each other.
Guiding Question
How are invertebrates related to each other?
Questions
1. What features
characterize an animal?
2. How is the system of classification of organisms that was developed by
Linnaeus different from the current systems of classification?
3. What is your opinion of the statement: "Phylogeny recapitulates
ontogeny"?
4. How do protostomes differ from deuterosomes?
5. What are the eight major phyla among invertebrates and what homologous
structures characterize each phylum?
6. What is the difference between a primitive
character and a derived
character?
7. How can primitive characters and derived characters be used to make a Venn
diagram that illustrates evolution theory? Give an example.
8. What is cladistics?
9. What is a cladogram? Give an example.
10. What is a dichotomous key? Give an example.
Internet Resources
Ontogeny
Recapitulates Phylogeny
Cladistics 1
Cladistics
2
Cladistics 3
How to Make a
Cladogram 1
How
to Make a Cladogram 2
How
to Make a Cladogram 3
How
to Make a Dichotomous Key 1
How to
Make a Dichotomous Key 2
How to Make a
Dichotomous Key 3
How to Make a Dichotomous
Key 4
Activities
1. Among the eight phyla, describe the evolution of the following features:
A. level of body organization
B. germ layers
C. symmetry
D. cephalization
E. body cavity
F. segmentation
G. digestive system
H. circulatory system
I. respiratory system
J. excretory system
K. nervous system
L. reproduction
M. support, skeletal system
2. Do an arbitrary
classification of twenty different invertebrates that is based on a dichotomous
grouping.
3. With your twenty organisms, construct a Venn diagram that reflects
evolutionary theory.
4. With your twenty organisms, construct a cladogram
that reflects evolutionary theory.
5. Research how evidence from the DNA of invertebrates has caused revisions in
evolutionary theory.
6. Create a lesson that would teach students how to make a cladogram.
David Lauter, Teacher, and Yvette Yip, AP student, collaborated to develop this web hunt.