Lesson 1 of 4
Objective: Students will be able to develop a model to describe the cycling of water through Earth's systems .
This lesson is designed to connect to the following NGSS and Common Core Standards:
MS-ESS2-4 Develop a model to describe the cycling of water through Earth's systems driven by energy from the sun and the force of gravity.
MS-ESS3-3 Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.
CCSS.ELA-LITERACY.WHST.6-8.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/ experiments, or technical processes.
Science and Engineering Practices:
Developing and Using Models (SP2):
- Develop and/or use a model to predict and/or describe phenomena.
- Develop a model to describe unobservable mechanisms.
- Develop and/or use a model to generate data to test ideas about phenomena in natural or designed systems, including those representing inputs and outputs, and those at unobservable scales.
Energy and Matter: Flows, Cycles, and Conservation: Tracking energy and matter flows, into, out of, and within systems helps one understand their system’s behavior.
- Within a natural or designed system, the transfer of energy drives the motion and/or cycling of matter.
I teach this mini-unit on water quality in connection with my unit on weather and the movement of matter and energy through earth's systems. This lesson represents the first of the second Essential Question in the Unit Plan.
I begin with introducing the Essential Question for the unit and breaking down the vocabulary in the question. I ask the students to turn to their Literacy Unit Plan and read the Essential Question, "How can we interpret data about how human activities affect Earth’s systems in order to develop technologies to monitor and minimize the effects?".
I take time to have the students explain what "interpret data", "human activities", "Earth's systems", "monitor", and "minimize the effects" mean. Asking students to share their understandings of each of each of these will help prime their brain for the lessons ahead and ensure that they understand the purpose of their learning.
Then, I have students rank themselves on each of the skills included in the unit plan. Students rank themselves on a scale of 1 to 4 (4 being mastery). Students will continue to update these scores over the course of the unit. I emphasize to them that it is ok not to be at a "4". Learning is about growth! We will use this starting point to track the growth in their learning.
Notice in the student work below, that the student updates his scores over the course of the unit as he grows in his level of mastery.
Mini Water Cycle Model
I project this image of the water cycle from the USGS. The image is set up so that you can print a poster or picture if you want a classroom or students copy. For my students, the water cycle is something that they have learned about in the past. So, in this lesson, this is just a quick review.
I remind students that one of the learning targets they have to master is:
I can model how the cycling of water through Earth’s systems is driven by the sun and the force of gravity.
I ask, "Looking at this image of the water cycle, how do you think that the sun and force of gravity influence the cycling of matter?" Students respond with the idea that energy from the sun can cause evaporation. I make sure to follow up with the idea that it is also the loss of energy that causes condensation. Without you pointing this out, many students will only focus on the idea of evaporation when they think of energy in the water cycle. Students also respond by saying that water moves down towards lower elevation due to gravity. As a class we reflect on the idea that the lakes, oceans, and rivers that we have been to are all at lower elevations.
Then, I provide students with a gallon size zip lock bag, a sharpie, a small beaker, tape, food coloring, and water. I ask students to develop a model of the water cycle on a small scale using the materials provided. I ask that they label their model with a sharpie so that it is clear where evaporation, condensation, precipitation, infiltration, surface runoff, and ground water will be represented in their model.
Students create their models, tape them to the window, and we observe the process each day and try to identify each aspect of the water cycle as it occurs in our model.
Each year, I contact my local water treatment plant and they lend this groundwater simulator for me to use. Reach out to your local water treatment plant; I am sure they have educational materials and resources that they would be happy to share with your as well! You can also purchase groundwater simulators at any online science education store; however, they are expensive. Reach out to any agency or business that is in your area that deals with water treatment/water quality. Maybe you will be as lucky as me to find someone that will either let you borrow or come present this model to your students! You can also purchase a "make your own", which is a bit less expensive.
While students in 7th grade often feel comfortable with the water cycle, I find that they have a difficult time picturing groundwater and its movements. This model does a fabulous job giving students insight into how water travels below the ground.
First, I model surface runoff for students and emphasize gravity's role in causing water to flow towards lower elevations.
Then, I emphasize that groundwater is always moving. That means that if one area is polluted, that pollution can travel miles down the road. In addition, I take this time to show students what groundwater actually looks like. We talk about aquifers and how water is actually stored in between particles of sand, dirt, rock, etc.
This sets the students up for seeing what happens if groundwater is polluted. I place food coloring in the groundwater so that we can see the pollution travel through the watershed.
I point out that the groundwater is moving towards lower elevations due to gravity. I introduce the idea of point source and non point source pollution. Point source pollution is pollution that goes directly into the water from specific, identifiable source. For example, an oil tanker spills in an ocean or a pipe dumping sewage into a river would be examples of this. Non point source pollution is often carried through surface runoff and can come from multiple sources. Substances are picked up by surface runoff and carried into the water.
I then begin asking students for ideas about what we could do to help clean up this pollution in the ground water. One of the first ideas that they typically share is the idea of adding more water, or diluting the water. Students quickly see that while adding more water does clean up the original area, it also causes the pollution to spread faster towards areas of lower elevation.
Next, I show students that now people that are drinking water from the wells down the road from the original source of pollution now would have the contaminants in their well water. I ask students if they have any other ideas that could help clean up the groundwater. Students often say, "Add chemicals." Then, I add bleach water to the model and the pollution does begin to disappear. As I work to rid the model of the pollution, we talk about the limitations and consequences of solving the problem in this way. Students often note how long the process takes, how much money it would cost, and how adding chemicals could impact wildlife negatively.
Water Drop Stories
In my class, we have spent a large amount of time working on informational writing. In tracking energy as it cycles through Earth's systems, I take the opportunity for students to write creatively. These creative stories are a type of a model in my mind, a way of representing science content through a story. Each year, students get excited about this writing. I often find that students go above and beyond what my expectations are and enjoy connecting to their creative side after all of the informational writing we have completed.
Water Drop Story Prompt:
Pretend you are a drop of water. Tell a story describing your journey through the water cycle.
Questions to consider:
What state of matter do you begin as (solid, liquid, or gas)?
What does it feel like to evaporate?
What causes you to evaporate?
What type of precipitation will you fall as?
Where will you fall?
How will you reach the ground water?
Are there other molecules with you?
What is it like to be in a cloud?
What happens to you that makes you fall as precipitation?
(Yes, you can use any tense of the word. So, for evaporation, you can use the word “evaporate” or “evaporated.” Also, the present tense form of condensation is “condense.” IT IS NOT CONDENSATE! Similar to condense, the present tense form of transpiration is “transpire.”)
Here is a look at one of my students stories of the water cycle from the perspective of the water drop.
To close, I explain that protecting our fresh water is extremely important and that in the upcoming lessons we are going to be investigating how we can help keep our fresh water clean. To emphasize the need for this work, I show the students 1000 mL of water. I explain that this amount of water is going to represent all of the water on earth. It includes the oceans, lakes, rivers, groundwater, ice caps, etc. Then I pour 30 mL into a graduated cylinder. I explain that this represents the amount of that water that is fresh water. I remind them that the water left in the beaker is not available for us to drink as it is salt water. Then, I pour 6 mL of that water into a smaller graduated cylinder. I explain that this is the amount of fresh water that is not locked up in ice caps and glaciers that we actually have access to. I emphasize that this small amount of water is cycling through earth's systems and is therefore a very precious resource and something we have to protect.