I start by handing out several strips of paper to each table group. I ask each student to think of and write one type of garbage (ex: apple core, tissue, etc.) on each strip, filling up as many strips as they can. Once they have come up with as many garbage items as they can, I have them work in pairs to sort these trashy items into two different groups, using any criteria they find suitable.
After providing time for students to sort their trash, I tell them that we will be learning about two different types of garbage - biodegradable and non-biodegradable. I have the students use a dictionary or an electronic device to look up the prefix "bio", the root word "degrade", and the suffix "able", and then challenge them to try to figure out what these pieces mean together. I call on a few volunteers to share their guesses.
After hearing their responses, I explain to the students that, in simplest terms, “biodegradable” means a material that is able to degrade or break down. Things that are biodegradable are often made of organic materials, or things naturally occurring in our environment. Examples of biodegradable materials are apple cores, bones, paper, cotton, flowers, food, some types of serving utensils, and paper plates. I hold up a banana and explain that the banana peel we throw away after eating this banana is biodegradable and will take approximately 3 days to degrade.
“Non-biodegradable” refers to materials that are not broken down by organisms. Non-biodegradable objects are usually synthetic and produced in a lab. Examples of non-biodegradable materials are plastic, glass, polyester some clothing items, and aluminum cans. I hold up a plastic bottle and explain that items like this are non-biodegradable and will take many, many years to break down!
Next, I hold up a disposable diaper (which I usually fill with melted chocolate, for "gross factor") and pose the following question, allowing students to write a guess on a sticky note and place in a jar on my desk:
How many years do you think it takes for a disposable diaper to biodegrade?
(I will reveal the answer at the end of class.)
Next, I pass out the Degrade Times worksheet. In this part of the activity, students have the choice of working alone or in pairs to learn about the time it takes for various objects to decompose. They will start out by making a guess as to the decomposition times for each object.
Once they have written down their guesses, they will conduct some research online to find the actual time needed. Each student will also select two of their own items to guess and research the decomposition time to add data to their worksheet.
After completing our research, we compile our data and record the average decomposition times for each item in a graph, using either paper or the Create A Graph website. After we decide, as a class, which graph is most suitable for the purpose, I usually have several volunteers come up and record the the data points, one-by-one. (Another option, which requires significantly more time, is to provide each group of students with the data for one object and to have them create an individual graph for all of the decomposition times collected by the students for that object.)
Next, we display our graph and try to identify any patterns or trends.* We discuss the discrepancies between items and why they may have such different rates of decomposition. Students will quickly start to discern between the biodegradable and non-biodegradable items, based on the amount of time it takes them to decompose, but they may also realize that size, density, mass, and a variety of other factors could affect the decomposition rate.
*If you teach math, this is a great tie to address the following math standards by delving deeper into the data you have collected:
Considering what has been taught so far, students should have a pretty good understanding of which materials biodegrade, and at what pace. I assess their understanding by handing out one page of the Garbage Sort Worksheet to each student. I have students cut out and sort the images of the eight trash items in ascending order, according to the time it will take them biodegrade. Once they have sorted the four items, they must meet with a partner and try to integrate each other's items into one larger sort. Finally, they do it one more time with the other two students at their table. By the time they have gone through this third round, they have sorted all 16 items on the four pages. We discuss the way each group has sorted their items, justifying their thoughts with evidence from the research they completed earlier in the lesson.
What happens to the items that don't biodegrade, or that take very long to decompose? Students will start to wonder about this, and you may hear this question buzzing around the class. To demonstrate what happens to the garbage that doesn't decompose, I play Video Field Trip: Landfill.
How Does a Modern Landfill Work also does a great job of describing how a landfill works. It is a perfect addition to the lesson if time permits.
I assess the overall understanding and sense of personal responsibility students have gained from the lesson by having them reflect on three of the following questions (projected on the board):
Finally, at the end of class, I pull the sticky notes out of the jar on my desk that contained student guesses about how long it takes the diaper to decompose. I read through the responses and we sort them by sticking them on the board in ascending order to form a line plot. Finally I reveal the answer: 500-600 years! I like to give a little "prize" to the student who guesses the closest. (They get to keep the dirty diaper!)