Here is a lesson for use during units on classification. Students should find it challenging, fun, and rewarding!
Classification and Cladistics - Who is Related?
Standards addressed in this lesson:
NGSS: Science and Engineering Practices (9-12):
Practice 2. Developing and using models
Modeling in 9–12 builds on K–8 experiences and progresses to
using, synthesizing, and developing models to predict and show relationships
among variables between systems and their components in the natural and
designed worlds.
Develop, revise, and/or use a model based on evidence to
illustrate and/or predict the relationships between systems or between
components of a system.
NGSS: Disciplinary Core Ideas (9-12)
LS3: Heredity: Inheritance and Variation of Traits
LS3.B: Variation of Traits
Environmental factors also affect expression of traits, and
hence affect the probability of occurrences of traits in a population. Thus the
variation and distribution of traits observed depends on both genetic and
environmental factors. (HS-LS3-2),(HS-LS3-3)
Learning Outcomes
Students will be able to:
Develop a model of evolutionary relationships of marine organisms.
Describe how groups with similar traits are related based on common ancestry
Infer how environmental factors affect traits of organisms.
Essential Question
How have the traits of marine organisms changed as life has advanced, and how do we use them to develop a model of how these animals evolved?
Students will be able to:
Develop a model of evolutionary relationships of marine organisms.
Describe how groups with similar traits are related based on common ancestry
Infer how environmental factors affect traits of organisms.
Essential Question
How have the traits of marine organisms changed as life has advanced, and how do we use them to develop a model of how these animals evolved?
Lesson Description
Cladistics and Taxonomy are two sciences that are constantly
evolving, and as such are always a source of debate and disagreement in the
scientific community. In the present
day, the use of DNA analysis has answered many questions about relationships
between animals and their lineages, however this wasn’t always the case. While the Linnean system is still used
occasionally as a kind of file cabinet for classifying species, organizing
organisms into clades according to their lineages is becoming far more common
as DNA gives us direct solid evidence.
It wasn’t always this way, however, and scientists often struggled to
classify animals as they had little more to go on than physical features and appearances.
During
this project, students in small groups will be tasked with taking a group of 30
marine organisms and organizing them into a cladogram, which shows not only
relationships but shared traits possessed by different clades. The goal is to get them as close as possible
to what their DNA suggests without having any DNA data available – they can
only go by physical appearance like scientists years ago. They are given a couple starter traits to
look for: symmetry and overall body plan.
Grouping
for this project can be done with mixed, heterogeneous groups or by using
homogeneous groups of students of similar level. The general design is for heterogeneous
groupings with students supporting each other, however uniform groups can be
used with varying levels of difficulty added for more advanced students.
The Lesson in Action
The
students are given a large piece of butcher or construction paper, and the 30
organisms on a sheet of paper. They cut
out the 30 organisms and start to organize them into groups. During this period, students should question each other to try and figure out which animals form groups of closely related organisms. Some of the questions they should ask:
What is the general shape of the organism?
What supporting structures does the organism possess? (shells, bones, exoskeletons)
How does the organism move?
Where does the organism likely live?
How does the organism get its energy?
Does the organism have advanced features? (warm blood, intelligence, social groups)
Other questions can be suggested as necessary. Students will struggle at first, so I suggest they break them into the two large groups of vertebrates and invertebrates, and then go through the questions from there.
Once the students are satisfied with their classification, they should arrange them on the butcher paper and insert lines in the form of a cladogram showing what they think their relationships are according to their traits. On the lines of the cladogram, they should be noting the traits of each group, gleaned from the questions they asked. Major traits that are conserved should go on the main line of the cladogram, while minor group traits go on the branches.
What is the general shape of the organism?
What supporting structures does the organism possess? (shells, bones, exoskeletons)
How does the organism move?
Where does the organism likely live?
How does the organism get its energy?
Does the organism have advanced features? (warm blood, intelligence, social groups)
Other questions can be suggested as necessary. Students will struggle at first, so I suggest they break them into the two large groups of vertebrates and invertebrates, and then go through the questions from there.
Once the students are satisfied with their classification, they should arrange them on the butcher paper and insert lines in the form of a cladogram showing what they think their relationships are according to their traits. On the lines of the cladogram, they should be noting the traits of each group, gleaned from the questions they asked. Major traits that are conserved should go on the main line of the cladogram, while minor group traits go on the branches.
Once
they get their cladogram complete, they write two paragraphs which describe
their classification system and why they put each animal where they put
it. The paragraphs should explain which major traits have appeared as new animal groups evolved, as well as which specialty traits the groups of organisms possess.
Information Sharing
At the culmination of the project, students should share their findings with other groups. Constructive discussion should take place, and as the students present their cladograms and paragraphs, the teacher should be recording which groups were popularly formed by the students and the reasons those groups chose them. After the data are shared, the teacher should show the students a cladogram of the true evolutionary relationships. While very few student groups will come close to the true cladogram, let them know that science is trial and error, and without DNA evidence scientists made the same classifications they did for years. Students should then write a short reflection comparing their findings to the true cladogram, and evaluate what they learned and would do different if they were presented with this project again.
Optional, for one to one classes: After the final discussion, students should be invited to paste their paragraphs into iBooks author, along with a photograph of their cladogram. The teacher can then assemble these into an iBook for the period, which can be published on iTunes.
Information Sharing
At the culmination of the project, students should share their findings with other groups. Constructive discussion should take place, and as the students present their cladograms and paragraphs, the teacher should be recording which groups were popularly formed by the students and the reasons those groups chose them. After the data are shared, the teacher should show the students a cladogram of the true evolutionary relationships. While very few student groups will come close to the true cladogram, let them know that science is trial and error, and without DNA evidence scientists made the same classifications they did for years. Students should then write a short reflection comparing their findings to the true cladogram, and evaluate what they learned and would do different if they were presented with this project again.
Optional, for one to one classes: After the final discussion, students should be invited to paste their paragraphs into iBooks author, along with a photograph of their cladogram. The teacher can then assemble these into an iBook for the period, which can be published on iTunes.
Lesson Pacing
The lesson takes two to three block periods
- Project explanation by instructor: 10-15 minutes
- Prepare cutouts and classify into groups: 30-40 minutes
- Affix cutouts to butcher paper, draw in cladogram, and label traits: 20-30 minutes
- Writing of descriptive paragraphs: 20-30 minutes
- Presentation of cladograms and findings: 5-10 minutes per group
- Project wrap-up, comparison to true cladogram: 20-30 minutes
- Student reflections: 15 minutes
This project is largely student based, the instructor should support the students as needed, but let them work through things without offering too much information
Grouping and Differentiating the Project
Groups can be done many ways, but generally I let the students choose their own groups provided the makeup of the group is acceptable. All groups must be cleared through me before they start the project.
The project can be differentiated in several ways. I generally ensure heterogeneous groups, where the more capable students are helping their peers who are more challenged with the project. Alternatively, groups can also be homogeneous, with more detail being required of advanced students, while certain aspects of the project can be removed for lower grade levels or for classes with students with learning challenges. Layers of difficulty can also be added/removed from the project, such as:
Grouping and Differentiating the Project
Groups can be done many ways, but generally I let the students choose their own groups provided the makeup of the group is acceptable. All groups must be cleared through me before they start the project.
The project can be differentiated in several ways. I generally ensure heterogeneous groups, where the more capable students are helping their peers who are more challenged with the project. Alternatively, groups can also be homogeneous, with more detail being required of advanced students, while certain aspects of the project can be removed for lower grade levels or for classes with students with learning challenges. Layers of difficulty can also be added/removed from the project, such as:
- requiring multiple traits for each group, or simply requiring students to only include major traits
- requiring advanced students to try and figure out what the animals are without research, while allowing challenged students the scaffold of iPads or other research methods
- adding or removing elements from the written paragraph according to student needs
A link to the project and the animal cutouts can be found here:
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