ALEX Lesson Plan

Under the Unity and Diversity DCI, students are asked to evaluate data comparing similarities in developing embryos across different organisms. While this is a classic component of understanding evolution, the modern, real-world reason to learn it is to understand the why and how of using model organisms like zebrafish. Students will learn about how model organisms have been used to find treatments to medical problems in the past, how they are used and selected now, and will be able to draw their own conclusions about the similarities among vertebrates vs. other types of animals. This is a stand-alone lesson/investigation but it would be a great bridge between genetics and evolution and could connect to 7th-grade content. 

This lesson results from a collaboration between the Alabama State Department of Education and ASTA.

Leprosy articles (suggested Taken from their families: The dark history of Hawaii's leprosy colony from cnn.com by Meera Senthilingam; linked in instructions) 
Embryology sheets (stages strips, 8 words, student worksheet)
Optional: play dough or clay in 3-4 colors

Ability to play/display video clips using any device

Internet access

Armadillo videos, developing embryo videos, zebrafish embryo videos 

Embryo Stage sheets will need to be cut into 3 strips and prepared for groups. Cards with 8 different organisms represented in embryo sheets will need to be cut up so that students can move them around to assign one to each animal. This is easy to modify for individuals, pairs, or groups by simply making more or fewer copies; if you can laminate them you can have a reusable set.

Here is what you (the teacher) need to know about embryology: All chordates share 4 common characteristics at some point in their lives—a post-anal tail, pharyngeal slits/pouches/gills, a dorsal hollow nerve cord, and a notochord. Vertebrates further have in common some kind of rigid (flexible cartilage still counts!) backbone. The fact that this is common to all chordates suggests both points of divergence and a common ancestor. It is therefore considered to be a strong piece of evidence for evolution. Further evidence comes from the fact that these structures are vestigial in some animals, humans, for example, lose their tail during development and while the notochord is responsible for directing a lot of development, it does not persist into our mature forms.

So, this information is the basis of what the standard is asking you to teach; it is a classic part of the evidence for evolution and should be included in the discussion. However, I find this has little concrete meaning to 7th graders and propose to give it much more meaning and context by connecting it to model organisms. The reason we can use animals as model organisms is because we share both DNA and structures, and we know in nature there is a huge connection between structure and function. The reason we share these structures during development is likely due to a common ancestor and so we can research things like development of the nervous system, effects of drugs on embryo development, genetic interventions, etc. on animals that are similar but much less unethical to experiment on than human embryos.

I. Engage

1. Tell students today they will learn about an animal that is both a life-threatening menace and life-saving hero-- ask if they have any guesses?

Confirm or deny guesses by showing them Rollie the Armadillo video and then Armadillo vs. Dog.

Have students practice a quick Claims Evidence Reasoning by supporting either the claim that they are playing or the claim that they are fighting using evidence from the video. 

2. Now we've clearly established armadillos are cute and vicious to toy bears. But how do they help or hurt humans?

Engage students in a close read (stop and ask questions periodically) about the former Hawaiian Leper colony Kalaupapa.

In the article, it mentions armadillos, ask students what they think it means.

3. Give students a leprosy fact sheet located in the attachments. Have them read and summarize as a group.

Key points: leprosy is a bacteria that only grows in humans and armadillos (and some lab mice). Due to the fact it would only grow in armadillos, they were used to study the bacteria, research a vaccine, and develop effective treatments. Leprosy used to mean a life of exile. Now, thanks to armadillos and scientists, people can be screened, be given vaccines or treated so they have normal lives. 

II. Explore

4. Ask students what made the armadillo a successful substitute for humans in researching leprosy-- make a group list on the board (similar temperature, smaller, easier to take care of, not [as] unethical to infect/test on them). Determine some things were similar and some were different in a good way. 

FQ: If one organism has similarities to humans that enable us to study diseases without researching on humans, could there be other organisms with similarities?

Let's consider Motor Neuron Disease. 

Motor neuron disease http://www.ninds.nih.gov/disorders/motor_neuron_diseases/detail_motor_neuron_diseases.htm

It is a problem with the motor neurons—the cells that connect your brain to your muscles and tell them to move. We don’t understand it well in humans—to be able to study the disease in an animal, what characteristics would the animal need to have in common with us?

Example answers: Brain, nervous system, motor neurons, muscles

Suggested questioning: What are the components of the nervous system?

It happens that many animals have similar types of nervous systems to us. It turns out that even though many animals look very different as adults, we are very similar as we develop.

FQ: What are the similarities and how long to they last?

Let’s consider some animals. Ask student to name some cool animals; keep going until you have a big list. Ask students to group the animals by big categories (birds, mammals, fish, reptiles, insects, etc).

We know that all living things are made of cells and all cells come from other cells. So, we all started as one cell. Did that first cell look the same? Probably. So that one cell divides into two, and they each divide into four and so on. Do you think the balls of cells look the same? Probably. Anyone remember one of the names for that? We’re going to use embryo, which means a developing baby. Let’s take a look at embryos for different organisms. See if you can figure out which is which?

5. Students get a copy of "early stage embryo" strip, animal cards, and student embryology sheet (attached). Once students have completed early they get the "mid" strip, then the "late". It should be nearly impossible to tell which is which in early, some indication in middle, and they should be able to figure it out by late. It is important for them to get the strips independently so that they have to think about similarities and differences among stages. 

6. Ask students to identify what was similar among all of the embryos (this will be quick as the drawings don't have a lot of detail).

III. Explain

7. The students are ready for some vocabulary now. All of the animals in guess the embryo are chordates, and we could specify that they are all vertebrates. What makes a chordate is that it has 4 features during development. In some animals these stay, in others they go away, but all chordates have them at some point.

a. A [post anal] tail (just the word "tail" is fine). You can really play this up with students joking about how they used to have a tail.

b. A dorsal hollow nerve cord. Dorsal, like a dorsal fin, means back. Theirs became their spinal cord and brain

c. A notochord. For some animals, this is like a spinal cord. For us it directs a lot of early development and then goes away

d. Pharyngeal (gill) slits. The term "gill" is misleading because we didn't all have gills in development-- it's more about structures that later develop in your head and neck (See pictures in ppt).

8. If you want, students can use dough or clay to make model chordate embryos to show these 4 structures. Here's a college-level lesson; you could have students do much less detail.

9. Have students watch a couple of embryonic development animals: Zebrafish   Chicken   Elephant (this one is amazing). Note how short a time it takes the zebra fish to develop and how long it takes the elephant.

IV. Elaborate 

10. Back to our question about motor neuron disease, what we are looking for is a model organism-- something that will function like a human. Do we now know of some other animals that have similar nervous system development to humans? Yes-- fish, salamander, turtle, etc. Ask students to select one of the animals from the embryo activity to be a model for humans. They should consider which animals have short life cycles, are cheap and easy to take care of, and would be most ethical to experiment on. Ask students to explain their reasoning. 

11. Explain that there are many animals used as model organisms but one of the most popular for development and embryology is the zebra fish-- they are cheap and easy to care for, produce a lot of eggs, have a very short life cycle, and are close enough to humans to be a good model. They are used to study things like cancer, diabetes, and motor neuron disease.

Evaluate

See attached "Student-Embryology-Sheet-and-Assessment." If students create a model it should clearly illustrate the 4 chordate embryo characteristics. 

Guess the embryo is a formative assessment, attached in the same document is a summative assessment. 

Students should be able to answer the following questions.

EQ: What is a model organism and how can we select one that is an appropriate model for humans?

EQ1: What kinds of animals are closely related to humans? What are the key characteristics that determine “relatedness”?

EQ2: What kinds of characteristics/traits are important for a model organism to share? Are they always the same or does it vary depending on what is being studied?

EQ3: How does understanding embryological similarities among humans and other vertebrate’s impact medical research and technology?

EQ4: How will understanding embryological similarities and differences among humans and other animals affect our understanding of the process of evolution?

Connecting this to standards about evolution would be a good next step now that students have a clear understanding of the similar development of chordates and a little exposure to the development of other animals. 

Students could examine additional pictures of embryos to look for more patterns. There are some color and more dimensional images of comparative embryology online that may make similarities and differences more evident.