In this activity, students filter different substances through a plastic window screen, different sized hardware cloth and poultry netting. Their model shows how the thickness of a filter in the kidney is imperative in deciding what will be filtered out and what will stay within the blood stream.
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- Colorado: Math
- a. Find equivalent forms of commonly used fractions, decimals, and percents using models, drawings, and computational strategies (Grade 5)  ...show
- Colorado: Science
- Common Core State Standards for Mathematics: Math
- 3. Solve multistep word problems posed with whole numbers and having whole-number answers using the four operations, including problems in which remainders must be interpreted. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding. (Grade 4)  ...show
- 2. Write simple expressions that record calculations with numbers, and interpret numerical expressions without evaluating them. For example, express the calculation "add 8 and 7, then multiply by 2" as 2 × (8 + 7). Recognize that 3 × (18932 + 921) is three times as large as 18932 + 921, without having to calculate the indicated sum or product. (Grade 5)  ...show
- 7. Add, subtract, multiply, and divide decimals to hundredths, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. (Grade 5)  ...show
- International Technology and Engineering Educators Association: Technology
- Next Generation Science Standards: Science
- Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. (Grades 3 - 5)  ...show
- Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem. (Grades 3 - 5)  ...show
- Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved. (Grades 3 - 5)  ...show
- Explain the role of the kidney as a filtering system for blood.
- Describe the by-products of the excretory system.
- Model the filtering function of a kidney on a larger scale.
- Give examples of filters designed by engineers, such as dialysis machines.
- Six inch square pieces of each of the following:
- plastic window screening
- hardware cloth (½" mesh)
- hardware cloth (¼" mesh)
- hardware cloth (1/8" mesh)
- poultry netting (1" holes)
- 1-2 sheets of newspaper (to cover desk)
- 2 measuring cups or bowls (about 4 cups each)
- Large funnel (large enough to have large pebble flow through the neck)
- ½ cup sand
- ½ cup small pebbles in various sizes from 1/8" to >1"
- ½ cup water
- 4 copies of the Filtering System Journal
- 4 copies of the Filtering Worksheet
- Duct tape
- round coffee filter (optional)
- 2 Tbsp. flour (optional-only add if using coffee filter)
|Dialysis:||The process of separating substances in solution by diffusion through semipermeable membranes.|
|Dialysis Machine:||Equipment that filters blood when the kidneys cannot.|
|Hemodialysis:||The process that refers specifically to purifying blood by dialysis.|
Before the Activity
- Cut screening, poultry netting, and hardware cloth to the proper size.
- Bind the poultry netting and hardware cloth with duct tape to cover sharp edges (see Figure 4).
- Assemble all necessary materials.
- Prepare overhead of the Excretory System (attached).
With the Students
- Show students the Excretory System overhead. Ask students to help you identify the location of the kidneys, bladder and ureters. Have students write down these terms under the Vocabulary section of the Filtering System Journal.
- Remind students that the kidneys are a filtering system for the blood. Explain that engineers design dialysis machines for people whose kidneys are not working properly. Have students write a few sentences about how the kidney functions under "I've Learned" on their journal sheets.
- Explain that this activity is a model for how the kidney cleans the blood. Students should be clear that this is just a model and that the kidney does not actually filter solids, except for blood cells. The products filtered through the screens in the activity are meant to represent the waste products in the blood, which are excreted in urine. Urine contains glucose, sodium, potassium, bicarbonate, water, acid, blood cells, protein and urea (which is what makes urine yellow).
- Students should mix the sand, pebbles, flour (optional) and water in the first measuring cup or bowl, as shown in Figure 4.
- The students should take turns filtering the water mixture through the funnel, poultry netting, different-sized hardware cloth, window screening and coffee filter (optional), from large-filter holes to small-filter holes (see Figure 6). The screening should be held over the second measuring cup/bowl. Students should then pour the mixture from the full measuring cup/bowl onto the screen over the empty container and then back again, using a different screen each time.
- Students should complete the Observations section of the Filtering System Journal.
- Discuss with the students what they have learned and have them work through the Filtering Worksheet. Ask the students how the filter model they created might be used by engineers in creating dialysis machines. Have students write down any other things they have learned in their Filtering System Journal under the "I've Learned" section, and answer any questions the students may have written in the "Questions I Have" section of their journal.
Activity Embedded Assessment
U.S. Department of Health and Human Services, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC), NIH Publication No. 06–4281, March 2006, "Prevent Diabetes Problems: Keep Your Kidneys Healthy," http://diabetes.niddk.nih.gov/dm/pubs/complications_kidneys/
U.S. Department of Health and Human Services, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC), NIH Publication No. 03–4666, September 2003, "Treatment Methods for Kidney Failure: Hemodialysis," http://kidney.niddk.nih.gov/kudiseases/pubs/hemodialysis/
Jessica Todd, Emily Weller, Sara Born, Abigail Watrous, Denali Lander, Malinda Schaefer Zarske, Janet Yowell
© 2006 by Regents of the University of Colorado.
Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
Last modified: October 5, 2015