Dichotomous Key

 Dichotomous Key

One of the things we teach seventh graders in Texas is how to use a Dichotomous Key. We also provide them with a chance to create a Dichotomous Key because what better way to understand something than to create it.

Prior to creating a Dichotomous Key we have the students work with several of varying difficulty. My colleagues and I have located one with aliens, one with little creatures like gremlins and one that is emojis and we also use a leaf key which is scientifically inclined. We copy them so there are 2 keys per page and create a little booklet where the keys are in order from easiest to most difficult. I normally practice part of the first one with the students and then I go over the scientific one together as a class and we work the final key together. This normally takes only one and a half 45 minute class periods to complete.

Next we move on to creating a Dichotomous Key. For my regular education classes I begin with the worksheet shown above. We work on the first three sections together as a class and then I have them work on the rest with their partners. This takes up the other half a class period from the previous day.

This year I tried something new with my Pre-AP classes. Rather than begin the creation process with the worksheet I decided to begin with  a hands on activity. As a class we reviewed the Dichotomous Key creation guidelines in their notes, then I provided the students with a baggie that help 9 pieces of uncooked pasta in 3 different colors. I then encourage the students to remove the pasta from the bag and to physically separate the pasta into groups. Since there are 9 pieces of pasta and 3 colors their first instinct is to split the pasta into 3 groups by either pasta type or pasta color. This causes them to pause and really think about how they can separate them into 2 groups to comply with the options available on each section of the key.

This activity gives them a really good opportunity to truly break down the process and consider how it works. The other thing that works well in this activity is having the students work together because they do not always agree with one another about how the groups should be split so then we are able to have a conversation about how this can occur in the real world and how scientists might have to deal with these things. 

I have heard of doing this same type of activity with 15 bean soup although I think that might work better for older students. You could also make this simpler by using pasta that is only one color so the students only group them by size or shape or you could simplify the activity by using pasta that splits evenly in half each time like using small, medium and large macaroni and small, medium and large shells.

Once I have completed this activity I give the partners a worksheet with 10 creatures, they must color and name the creatures and then they must create their own Dichotomous Key. I encourage them to cut the creatures out and physically separate them into groups. The physical separation seems to help the students with the Dichotomous Key creation. I allow the student groups 2 class days to use to complete their assignment.

All in all I use a week of class time to take notes, practice using the key, and then practice creating a key. 

Frog Dissection Lab

 Frog dissection Lab

The final component in our human body system unit is frog dissection. We have one prep day where we go over a power point that shows the students the steps to take in order to dissect the frog. I express to them how important it is to keep each body system intact and to observe it thoroughly before moving to the next system. We discuss how dissecting the frog gives us a better look at body systems. Then I show them a video on YouTube of a science teacher dissecting a frog so they get an additional look at the process. I also have them color a picture of an open frog showing it's digestive system and they create a Venn diagram and compare the frog digestive system to the human digestive system. this gives them a chance to see how many organs we have in common.

On day two of frog dissection the students are actually allowed to dissect the frog. Since I teach at a Title 1 school we only have enough frogs for one frog per group of four students. Some of the students are frightened or disgusted so they prefer to simply watch, but sometimes they all want to participate so they take turns since there are plenty of cuts to make and organs to remove. We do not have scalpels so we only use tweezers, scissors and probes during the dissection. I encourage the students to remove each organ, discuss the name of the organ and the body system that the organ comes from. I feel that this steps causes them to slow down in their excitement and really take a look at the body systems.

I have struggled with classroom management this year and with students unwillingness to complete assignments so this year I have large groups of students who were not able to participate in the actual frog dissection since it is a privilege, however I did not want them to miss out on the experience entirely so I decided to add some stations to frog dissection this year. 

I went to the local grocery store and I got several types of organ meat. Here in San Antonio we eat several dishes that require organ meat so I had no problems finding hearts, liver, brains, intestines and bones. I set out the various types of organ meat and I had a short question at each station. I asked the students to be sure to hold the organs, look at their structures and talk about why they might feel different from one another. I wish we could afford more gloves and more time in the lesson because I really would have liked to let the students spend a whole day just on this task. As it was they ran through it very quickly but they did gain quite a bit of joy and excitement from the task.

 I would like to do this again next year, I am going to work on it some this summer and determine what I can do to tweak this or see if I can write a grant to get more gloves so I spend an extra day on this. I would love to rewrite the whole system and spend 12-15 weeks just on human body systems but that's not going to happen just yet so I need to try to fit it in the best way I can. I do want to ensure this is meaningful to their learning and not just really fun to do.

On a final note I am not opposed to fun and I think one way to truly ensure that students recall some of their learning is by making learning fun. I always try to dress up for any large event we have. This year I found a frog hat at Target during Halloween in the costume section. I wore the hat all day and it really caught their attention. The students were so excited when they saw me in the hallway because they knew it was frog dissection day. In previous years I have used a frog puppet to read a body system book to the glass or to give directions during the human body system unit. I try to make sure everything ties together so they have some recall and for many of the students it works. (I know because I ask them science questions in the hallway when they come to visit me as 8th graders.)