Excretory System - Removal of Waste to Live

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SWBAT explain how the structure and function of excretory system impacts our daily lives.

Big Idea

Students use a model to describe how structure and function of excretory system (i.e. kidney) affects our daily lives.


10 minutes

To engage students in this lesson I show them this picture of a city infested with trash.

After 5 seconds for observation:

I ask students to predict what would happen if our trash were never picked up and removed?  Most students answer that the city would become "dirty", "disgusting", and it would probably lead to disease and infection.

After students have been given enough time to share out their answers, I do a raised hand survey to ask if they believe our bodies produce waste. The results are pretty mixed. I follow the survey by asking, "How do you think wastes are removed from our bodies?"  Depending on prior knowledge, students might reply by explaining that "going to the restroom" is one way we remove wastes from our bodies.  

To close the discussion, I show students the picture (below) of the excretory system and have them record the following definition:  

The excretory system is a passive biological system that removes excess, unnecessary materials from an organism, so as to help maintain homeostasis within the organism and prevent damage to the body. 

I emphasize two things here:

1) Homeostasis - this one of the characteristics of living things we reviewed in a prior lesson.

2)  Explain that the excretory system is a great example of how organs from other systems (i.e. lungs/respiratory system, large intestine/digestive system) interact with one another to stabilize body systems and ultimately ensure organism survival. (MS-LS1-3 - Body is a system of interacting subsystems composed of a group of cells) (CCC -Systems and System Models -Systems may interact with other systems; they may have sub-systems and be a part of larger complex systems.)


I end this part of the lesson by showing students the video (below) of Esmeralda

Esmeralda is a dialysis patient who is fighting for her life due to kidney failure.  The objective of this video is to connect what they're learning in class to a real life application by bring relevance and connecting with them at an emotional level.  Many of my students have family members who have diabetes, which is the number one cause of renal failure in the United States.  


30 minutes

The video is very powerful, and I think it motivates students as they now conduct a Kidney Filtering activity. This activity connects the science we are covering to engineering - design. 


Engineers design many different filters that help people live healthier lives. Engineers design filters to clean water, and they also design special filters called dialysis machines. This equipment, actually a special filter, cleans blood for people (i.e. Esmeralda) whose kidneys are not working properly.


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.  (SP2 - Developing and Using Models - Modeling in 6–8 builds on K–5 experiences and progresses to developing, using, and revising models to describe, test, and predict more abstract phenomena and design systems.  Develop and use a model to describe phenomena. Develop a model to describe unobservable mechanisms.) 

Learning Objectives

After this activity and accompanying worksheet, students should be able to:

  • 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.


Each group needs:

  • Six inch square pieces of each of the following:
  1. plastic window screening
  2. hardware cloth (½" mesh)
  3. hardware cloth (¼" mesh)
  4. hardware cloth (1/8" mesh)
  5. 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

To bind the screens for safety:

  • Duct tape


As a quick introduction/motivation I hand out to each student a copy of the Kidney Model. This handout discusses how engineers have designed various filters to solve a variety of problems including dialysis machines for patients with end-stage renal disease.  This a good way of promoting engineering careers through demonstrating how engineers help saves lives, like Esmeralda's.


Pre-Activity Assessment

Vocabulary: Have students write down the terms kidneys, excretory system, ureters and bladder under the Vocabulary section of the Filtering System Journal.  Writing acts as a record, now the thinking begins. Students discuss with a neighbor what these terms mean and write short definitions in their notes next to the terms.

Activity Embedded Assessment

Worksheet/ Observations: Explain to students that engineers and scientists record their observations while they are working with a model. Using the Filtering System Journal, remind them to write down anything they notice during the activity in the "Observations" section of their journal, and any questions they might have in the "Questions I Have" section. It is important to review their questions, as well as observations, to gauge their mastery of the subject.

Post-Activity Assessment

Discussion: Lead a discussion out loud, asking students what they have learned about filters and engineering. Have students write down the things they have learned in their Filtering System Journal under the "What I've Learned" section. Make sure to answer any questions the students may have written in the "Questions I Have" section of their journal. 


I have included Excretory System Overhead and Filtering System Worksheet which are mentioned in Kidney Model under procedure.


5 minutes

To give students a quick overview of the excretory system, I use a video. 

We watch* the video to answer the following questions. 

1)  What is excretion?

2)  What is the process that results in wastes being removed from body surface to water in unicellular organisms?

3)  What is the chief organ of the excretory system?

4)  What organs make up the excretory system?

5)  Kidney is the basic _____________ unit.

6)  Draw a kidney including the NEPHRONS.

7)  Why are nephrons crucial for kidney function?

8)  What does urine contain?  How is urine removed from the body?

9)  What is the reason we are able to control the urge to urinate?

*There are a few ways to do this. Students can watch the video twice, first reviewing the questions and then watching straight through for comprehension and next to stop and start so that they can respond to questions. If you decide to stop and start the video, how it is done is also important. If the video is stopped just as the information that can answer one of these questions is presented, students tune out until the video stops. If students are told they are accountable for the answers, but you are only going to stop and start it according to time (for example, every two minutes), there is a tendency to pay more attention.

Consider also how to have students respond. If group thinking really helps your students to develop meaning, particularly if vocabulary is difficult for them, then taking the responses orally and encouraging them to build off of each other is a better way. You can record the "final" determination for each answer on the board, and students can then put these into their notebooks. Otherwise, consider having your students respond in writing. Practicing writing is an important skill.


10 minutes

In this section of the lesson students visit cK12.  In this website students are required to read a text dealing with the following learning objectives.

Learning Objectives

  • Identify the functions of the excretory system.
  • List the organs of the excretory system.
  • Describe the parts of urinary system.
  • Outline how the kidneys filter blood.
  • Identify three disorders of the urinary system.

Students use Stop and Jot as a reading strategy.  

Objective of Strategy

Strengthen ability to analyze word meaning from context and introduce students to unfamiliar vocabulary. Further solidify understanding by defining new vocabulary words as well as generating personal examples of words and concepts.

Instruction of Strategy

Students will read through a concept listing words they don’t understand and write down the sentence they are used in; then they will define the word; lastly, they will give an example of the word or concept from the text or their own experience. 

At end of lesson students answer the following questions:

 Review Questions

  1. What are the functions of the excretory system?
  2. List the organs that make up the excretory system.
  3. What is the difference between the urinary system and the excretory system?
  4. What is urine made up of?
  5. Outline how the kidneys filter blood.
  6. What is the purpose of the urinary bladder?
  7. The walls of the urinary bladder are stretchy, what do you think is the advantage to having these stretchy walls?
  8. What connects the kidneys to the urinary bladder?
  9. What does antidiuretic hormone do?
  10. What is a urinary tract infection?
  11. Why is kidney failure such a serious health problem?


5 minutes

In this section of lesson students are given a Writing Task.  Students are required to create an informative pamphlet/newsletter on the following topics: (W.7.2 - Write informative/explanatory texts to examine a topic and convey ideas, concepts, and information through the selection, organization, and analysis of relevant content.)

1) Overview of Excretory System

2) Kidney Disease

3) Role of Engineering in Dialysis Machines

Students must cite resources they used to create pamphlet/newsletter in the reference section of their pamphlet/newsletter. (Note: Students are required only to create either a pamphlet or newsletter, not both).

I have attached examples of possible pamphlet layouts below:

Possible Newsletter Layout

 Students are scored using the following Rubric.