Acid-base (pH) balance / Homeostasis

Engaging activities to support your teaching of acid-base balance and homeostasis found below:
1) Human Demo of Osmosis
2) Buffer Ball (respiratory buffering system)
3) Homeostasis Activity
4) Song about homeostasis

1) Human Demo of Osmosis
Preparation: Acquire a cubicle style divider, or several easels.
Instruct 2/3 of the class to wear blue shirts and 1/3 to wear white shirts.  The blue shirts are water molecules and the white shirts are the solute of your choice.  (Alternatively, have white and blue paper that can be taped onto shirts – but shirts are better – less trees!)
Divide an open space in half by placing the divider perpendicular to the viewers.  Place the divider at the front of the room (you could also use several large easels) leaving a space behind the divider or between dividers if you are using 2.  Hang a sign on the divider facing the viewers : “Membrane”
List on the blackboard how many blues and how many whites there are in total.
Distribute the people unevenly.
Announce how many of each (water vs. solute) there are on each side.
Instruct them that only the water can move and must distribute  itself so that it is in the same ratio to solute on both sides.
You might choose to have a few students play director at a time – figuring out how to fix the ratio and sending people from one side of the membrane to the other.  If you have time for several groups or all of the students to be the directors, it will facilitate everyone’s understanding.  For added fun have the students vibrate and gently bounce off one another on their own side.
On the 2nd or third attempt, when things are going a bit smoothly, video the entire production.  Then watch it as a class and discuss.  OR put it on Blackboard and let them watch it there.  If you watch it in class, you will probably have to watch it once without discussion to allow them to giggle and point end enjoy.  Then watch again and review what is happening.


· Many students do not understand the chemistry involved in acid/base balance – buffering systems.  Here’s a fun way to help them understand.  I call it Buffer Ball:

Get yourself 3 nerf balls (or other soft balls) of different colors.  Designate the projectiles as H+, ‘combine,’ and ‘dissolve.’  Write on them if possible.
Then have the students make themselves signs that include name and formula for other players in the buffer system : carbonic acid, bicarbonate, carbon dioxide and water.
Designate an area of play.
Have some of the participants sit on the sidelines with a stack of signs so they can adopt molecular status as needed.
Toss the balls to the players in the area of play.
Whoever catches a ball should react appropriately depending on the label of the ball.  If they catch and react with an H+, then they should step to the sidelines and exchange places with a student wearing the appropriate sign for what they have become.  The player who has just left the field of play then tosses the ball to someone else.
If a player catches the ‘combine’ or ‘dissolve’ ball and can do so, they should either find another player with whom they can combine and together go to the sidelines so that the new molecule can take their place – OR, in the case of dissolve, go to the sidelines and have 2 people take their place with appropriate signs.
If the caught ball has no effect on the catcher, he or she should toss it to someone else in the field of play.
There is room for a lot of variation and manipulation with this idea.  You can flood the system with CO2 as if the person has COPD and hoards CO2, or you could reduce the amount of CO2 present as if the person is hyperventilating.
You could establish the number of signs in a plausible ratio for a body with normal pH, or just play to give the students the idea of the chemistry involved and the constant shuffling that makes a buffer system work.

3) Homeostasis activity
· The following is a fun and valuable interactive illustration of the body working to maintain homeostasis in an ordinary college student’s day.  The material is a little advanced as it asks what organs / body systems affect the changes required to maintain homeostasis, but it clearly illustrates how a body recognizes change and how systems are in place to bring the body back into safe parameters.  It also provides explanations and second chances to the user.  This activity combines story-telling with A&P and the hero of the story is a college sophomore at the University of Wisconsin.

4) Homeostasis – song from “Groovin’ in the Hippocampus”
You are welcome to play my songs in the classroom and to hand out or project the lyric sheet, but please do not make a song available to the students to download for free.  They can download a copy from a link on the home page of this site.

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