Lesson 5. Lesson 5: Homeostasis in Other Body Systems

Eleanor Kemp
Biology, Environmental Science
2-3 periods
High School Honors Biology
v1

Overview

In order for students to gain a deeper understanding of homeostasis in the human body, groups will design their own experiment (with parameters) to test how internal conditions remain stable as external conditions change. 

In each of these experiments, you can use whatever resource you would like for your lab set up.  The following are general outlines for each: 

Temperature Investigation: 

Test subject should submerge hand in ice water (no longer than 30 seconds).  Two temperature probes are required, one taped to the hand that is in ice water (make sure to cover with tape as much as possible so that the probe is recording temperature of skin rather than water), and one in the crook of the elbow of the same hand (this represents core). Temperature recordings should be taken continuously over time (preferably 5 minutes or longer) to show the body attempting to recover surface temperature and maintain core.

Pulse/Breathing Rate: 

Students can pick whatever exercise they want to do for this investigation, but make sure they are very clear on how to record pulse & breathing rate (read for 30 sec intervals and multiply by 2).  Again, the readings should take place for up to 5 minutes (preferably longer) after the exercise to show the systems returning to stability.  

pH:

Various homogenates can stand in for the living system - a potato "smoothie", a liver "smoothie," even whole milk should work.  The general set up is 2 test cups (less than 25 mL each) of homogenate and 2 test cups of distilled water.  2 members can test the effect of 1.0M HCl and 2 members can test 1.0M NaOH.  Acid/base is added 5 drops at a time to homogenate/water and pH is tested after each addition of drops (30-35 drops total).  Again, more is better, but 30-35 drops should be enough to show the change in water and the relative stability of living system.  NOTE: remind students to "swirl" after adding drops and not to insert pH strip/meter in the same place as drops were added.  The homogenates sometimes separate out into water and living cells, so make sure they are stirring to maintain a fairly consistent mix. 

Standards

Next Generation Science Standards
  • Life Science
    • [HS-LS2] Ecosystems: Interactions, Energy, and Dynamics
  • NGSS Crosscutting Concept
    • Patterns
    • Causation
    • Systems
    • Stability and Change
  • NGSS Practice
    • Analyzing Data
    • Asking Questions, Defining Problems
    • Using Models
Computational Thinking in STEM
  • Data Practices
    • Analyzing Data
  • Modeling and Simulation Practices
    • Using Computational Models to Understand a Concept
  • Systems Thinking Practices
    • Investigating a Complex System as a Whole
    • Understanding the Relationships within a System

Credits

Unit designed by Eleanor Kemp a teacher at Lindblom.

Acknowledgement

These lessons utilize resources from Project Neuron, a curriculum program developed by the University of Illinois, and HASPI (Health and Science Pipeline Initiatives). 

Activities

  • 1. Does the human body maintain a stable internal temperature?
  • 2. Does the human body maintain stability in complex systems?
  • 3. Does the human body maintain a stable pH?
  • 4. Collecting and Analyzing Data
  • 5. Evaluating the claim: human body systems maintain homeostasis

Student Directions and Resources


In this exploration, you and your group members will design an investigation to see if the human body maintains homeostasis as external conditions change.  In order to do this, you may choose one of the following conditions to test:

  1. Internal temperature
  2. Internal O2/CO2 balance (heart/breathing rate) 
  3. Internal pH 

No matter which investigation your group chooses, everyone is collecting data to evaluate the following claim: 

Human body systems are regulated so that an internal stability is maintained as the external environment changes. 

All data collected will be graphed, so similarities should exist within the data so we can provide multiple lines of evidence to evaluate the claim (our body has multiple systems, so for this claim to be accepted/rejected, we should see a similar pattern in multiple investigations). 

 

If you are testing temperature, go to the next page (page 2). 

If you are testing pulse/breathing rate, skip to page 3. 

If you are testing pH, skip to page 4. 

ONCE YOU ARE APPROVED TO CONDUCT EXPERIMENT, EVERYONE SHOULD GO TO PAGE 5. 

1. Does the human body maintain a stable internal temperature?


For this investigation, you are testing whether or not the human body maintains a stable internal body temperature as external temperatures change.  To help you design your experiment, read the purpose and materials list below: 

Purpose:

The purpose of this investigation is to see if our internal temperature (core body temperature) remains constant when our body surface is exposed to changing external temperature. 

Materials:

  • 2 temperature probes (1 flexible wire, 1 standard probe)
  • Ice bath
  • Timer
  • Tape
  • Towel

NOTE: A temperature probe placed on the inner elbow will give a reading that represents core body temperature. 


Question 1.1

How do you plan on changing the external environment of system (your independent variable)?  



Question 1.2

How do you plan on measuring the effect of your change to the system (your dependent variable)? 

Don't forget: you should be taking TWO measurements!



Question 1.3

Now that you have identified the cause-effect relationship you are testing, make a hypothesis about what you think will happen during the experiment. Remember that your hypothesis should be an if-then statement and should include some form of explanation.  

Here is an example hypothesis: 

If a shell-less egg is placed in distilled water, then the mass of the egg will increase because water moves across the cell membrane by diffusion. 

NOTE: You might not be able to give a full scientific explanation at this point, but you should be able to provide a reason why you think something will happen!



Question 1.4

In the space below, provide a summary (or numbered list) of how you will conduct your investigation.  Make sure you are SPECIFIC in terms of units, time, etc. 

You should use the body outline below to sketch where you will place your temperature probes and how you manipulate the external environment. 

Note: Draw your sketch in the sketchpad below


2. Does the human body maintain stability in complex systems?


For this investigation, you are testing whether or not the human body maintains stability of two complex systems as external conditions change.  To help you design your experiment, read the purpose and materials list below: 

Purpose:

The purpose of this investigation is to see if two of our internal systems (circulatory and respiratory) maintain stability as external conditions change.  

Materials:

  • 1 test subject
  • Timer
  • Diagnostician to measure breathing rate
  • Diagnostician to measure pulse

NOTE: 

  • Pulse can be taken at the wrist or via the carotid artery (underneath the jawline, by the lymph nodes).  The test subject may take their own pulse. 
  • Breathing rate = 1 inhalation and 1 exhalation as one breath.  The test subject should NOT record their own breathing rate
  • Measurements should be recorded for 30 seconds and multiplied by 2 to determine rate (per minute)

Question 2.1

How do you plan on changing the external environment of the system (your independent variable)?  



Question 2.2

How do you plan on measuring the effect of your change to the system (your dependent variable)?

Don't forget: you should be taking TWO measurements!



Question 2.3

Now that you have identified the cause-effect relationship you are testing, make a hypothesis about what you think will happen during the experiment. Remember that your hypothesis should be an if-then statement and should include some form of explanation.  

Here is an example hypothesis: 

If a shell-less egg is placed in distilled water, then the mass of the egg will increase because water moves across the cell membrane by diffusion. 

NOTE: You might not be able to give a full scientific explanation at this point, but you should be able to provide a reason why you think something will happen!



Question 2.4

In the space below, provide a summary (or numbered list) of how you will conduct your investigation.  Make sure you are SPECIFIC in terms of units, time, etc. 

Please make sure to explain what type of physical activity your test subject will be performing, specify times, units, modes of data recording, roles, etc. 

3. Does the human body maintain a stable pH?


For this investigation, you are testing whether or not the human body maintains a stable pH as external conditions change.  To help you design your experiment, read the purpose and materials list below: 

Purpose:

The purpose of this investigation is to see if the pH of a living system maintains stability as external conditions change.  

Materials:

  • 2 cups of distilled water (no more than 25 mL per cup)
  • 2 cups of living homogenate (no more than 25 mL per cup)
  • 1.0M solution of HCl (Hydrochloric Acid, a strong acid)
  • 1.0M solution of NaOH (Sodium Hydroxide, a strong base)
  • 2 droppers
  • pH strips/pH meter 

NOTE: 

  • The pH scale is a logarithmic scale which measures how acidic/basic a solution is and ranges from 0 to 14.  The pH of distilled water is about 7.0, and blood is about 7.35
  • The stronger an acid is, the lower the number on the pH scale.  A very strong acid like HCl may register a pH as low as 1-3, depending on its concentration. 
  • The stronger a base is, the higher the number on the pH scale.  A very strong acid like NaOH may register a pH as high as 11-13, depending on its concentration. 
  • STRONG ACIDS AND BASES CAN CAUSE BURNS AND DAMAGE TISSUES - BE CAREFUL WHEN USING!


Question 3.1

How do you plan on changing the external environment of the system (your independent variable)?  



Question 3.2

How do you plan on measuring the effect of your change to the system (your dependent variable)?

Don't forget: you should be taking TWO measurements!



Question 3.3

Now that you have identified the cause-effect relationship you are testing, make a hypothesis about what you think will happen during the experiment. Remember that your hypothesis should be an if-then statement and should include some form of explanation.  

Here is an example hypothesis: 

If a shell-less egg is placed in distilled water, then the mass of the egg will increase because water moves across the cell membrane by diffusion. 

NOTE: You might not be able to give a full scientific explanation at this point, but you should be able to provide a reason why you think something will happen!



Question 3.4

In the space below, provide a summary (or numbered list) of how you will conduct your investigation.  Make sure you are SPECIFIC in terms of units, time, etc. 

Please make sure to explain the exact method you are using to manipulate the control and the experimental group (how are you adding drops, what are doing to cup, how many drops, etc), how you are collecting data (again, anything you are specifically doing when you are conducting test), etc. 

4. Collecting and Analyzing Data


Once your teacher has approved your experimental design, you may conduct your experiment.  Remember that any QUANTITATIVE data should be recorded in a data table.  If you are unsure how to set up your data table, remember that every investigation is designed to demonstrate the stability/change of the system over time. In the case of the pH investigation, you are observing the stability/change of the system with the addition of drops of a solution. 

QUALITATIVE data should be recorded as observations below/beside the data table in your journal. 

Once you have recorded your data, you will graph it using Google Sheets (or other appropriate spreadsheet program) and upload it to Google Classroom (or CT-Stem website, depending on teacher preference). 

Remember the following when graphing;

T - does your title describe a cause/effect relationship between the variables you tested?

A - did you plot the correct variable on the correct axis? (http://mathbench.umd.edu/modules/visualization_graph/page02.htm) 

L - are both of your axes correctly labeled with units? 

K - did you provide a key? 

5. Evaluating the claim: human body systems maintain homeostasis


Even though you and your classmates completed different investigations, all of them should have provided you with experimental evidence to support the claim that living systems maintain a stable internal environment even as the external environment changes. 

A secondary claim could be made that living systems maintain stable internal conditions in response to changing external conditions. 

Look at the graphs below to help you answer the following questions. 


Question 5.1

What similarities do you see in the three graphs?  Be as specific as possible - refer to things like time, internal/external conditions, etc. 



Question 5.2

Using data from the graphs above (or the ones that you created), determine the set point for the following internal conditions: 



Question 5.3

Does the evidence in the graphs support the following claim? Use scientific reasoning to support your answer. 

Living systems maintain a stable internal environment even as the external environment changes. 

 

​



Question 5.4

Does the data in the graph support the following claim? Use scientific reasoning to support your answer. 

Living systems maintain stable internal conditions in response to changing external conditions. 



Question 5.5

Which of the claims from the previous questions is best supported by data in the graphs? Use evidence to explain your reasoning.