LESSON 5: ARE WE ROBOTS? (What is respiration?) SUMMARY Respiration is an important and necessary part of being alive. Respiration is defined as the movement of oxygen from the outside air to the cells within ​
tissues​
, and the ​
transport​
of ​
carbon dioxide​
in the opposite direction. ​
Just like students, microbes exhale carbon dioxide, which forms an acid that can cause certain acidity indicators (like cabbage juice) to turn colors as the acidity increases. In this lesson students will learn about the similarities between microbes and students. For example, though soils are loaded with microbes, it can be very hard to visualize the number of microbes in soils or to measure soil breath. Students will use ​
an acidity indicator​
­­cabbage juice­­to show that microbes, just like the combination of baking soda and vinegar, or dry ice sublimating into carbon dioxide gas, or an Alka Seltzer tablet added to a liquid, can generate carbon dioxide! ESTIMATED TIME 30­50 minutes LEARNING OBJECTIVES Learners will learn... Learners will be able to... 1. Microbes are living organisms smaller than 1. Demonstrate that we can measure our eyes can see. Because soils are home microbial activity by measuring the gases to quadrillions of living bacteria, soils are the microbes produce. alive. 2. Demonstrate that some liquids can serve 2. Microbes breathe just like we breathe. as acid indicators, allowing us to visually 3. One of the gases that microbes “exhale” is “see” carbon dioxide (via different acidities) carbon dioxide (CO​
), which can make as different colors. 2​
solutions ​
more acidic​
. NEXT GENERATION SCIENCE STANDARDS PS1.A: Structure and Properties of Matter ● Matter of any type can be subdivided into particles that are too small to see, but even then the matter still exists and can be detected by other means. A model showing that gases are made from matter particles that are too small to see and are moving freely around in space can explain many observations, including the inflation and shape of a balloon and the effects of air on larger particles or objects. (5­PS1­1) ● The amount (weight) of matter is conserved when it changes form, even in transitions in which it seems to vanish. (5­PS1­2) PS1.B: Chemical Reactions​
No matter what reaction or change in properties occurs, the total weight of the substances does not change. (Boundary: Mass and weight are not distinguished at this grade level.) (5­PS1­2) Disciplinary Core Idea Biodiversity and Humans There are many different kinds of living things in any area, and they exist in different places on land and in water. (2­LS4­1) Adaptation For any particular environment, some kinds of organisms survive well, some survive less well, and some cannot survive at all. (3­LS4­3) <​
greenhouse gases​
[H​
O, CO​
] combine to form carbonic acid [H​
CO​
], conservation of mass [solid to 2​
2​
2​
3​
gas]> BACKGROUND INFORMATION FOR TEACHERS Respiration is an important and necessary part of being alive. Respiration is defined as the movement of oxygen from the outside air to the cells within ​
tissues​
, and the ​
transport​
of ​
carbon dioxide​
in the opposite direction. ​
Just like students, microbes exhale carbon dioxide, which forms an acid that can cause certain acidity indicators (like cabbage juice) to turn colors as the acidity increases. When we breathe we are actually inhaling one gas (oxygen) from the air and exhaling two gases (carbon dioxide, water vapor). Here is a simplified equation for breathing, or what some biology teachers call respiration: sugar (=chemical energy) + oxygen →
water vapor + carbon dioxide (+ heat energy)
All life, including plants and microbes, breathes. Most of that life­­except for very unusual types of bacteria­­release carbon dioxide as part of exhaled breath. When carbon dioxide mixes with water, it makes the water more acid, by forming carbonic acid. water vapor + carbon dioxide → (carbonic) acid
This means that if we could just measure the pH (acidity) of a solution next to anything with microbes in it, including soils, we can show that that ‘anything’ is alive! (Soils, unfortunately, have fairly slow breathing rates so in this exercise, we will focus on getting students comfortable with different ways to generate carbon dioxide [human breath, dry ice, baking soda + vinegar], and then monitoring for a color change as a solution of cabbage juice gets more acidic. Similarly, we can always add an antacid (base) to make the cabbage juice less acid!) This is why we will use an acid indicator (cabbage juice) that switches from blue to purple to pink as it gets more acid. blue​
​
purple The photo at the top of the next page shows the 3 colors that cabbage juice can turn: ​
pink​
or ​
. These colors represent different acidities, and we will use this property of cabbage juice to understand how one of the gases in your breath can create an acid. When you first boil red cabbage, the juice is blue as on the left. From an acidity perspective, it’s not very acid. Then, as more acid is added to the juice, it first turns purple (in the middle), and then turns pink (at the right). You can get the cabbage juice to turn different colors depending on whether you add a base (like Tums, an antacid, or in this example, a solution of diluted baking soda and water) or an acid (like vinegar, or some gases like carbon dioxide!). Sidenote: Throughout UTRAC, we feel it’s important for students to understand ​
why we eat food​
, and by extension, why microbes eat their food, something we can call “soil organic matter.” It is NOT because the gases we produce when we (and our internal microbes) digest the food are acidic. Food is consumed in order to fuel­­energetically­­life. Food starts as chemical energy and is transformed by life mostly into heat energy. Of course some of the chemical energy is also transformed into kinetic(moving) energy. The easiest way to tell a living cockroach from a dead cockroach is that a living cockroach will move if you try to catch it! The speed of a cockroach represents kinetic energy, which it obtains from its food. So food is consumed to transform its energy to be used, and the mass of the food is converted into solids or liquids or gases.(NOTE: Make sure the students are clear on the facts that the food’s energy remains energy, and its mass remains mass. You CANNOT transform the food’s mass into energy or vice versa.) So what gases are produced in our (or cockroach or microorganism) breath? MATERIALS AND PREPARATION ● Print out of pH scale; ideally in color but not necessary since the colors do not match the colors of the acid indicator (cabbage juice). ● At least one small souffle­type ​
cup​
per student; at least one straw per student. ● Cabbage juice; ideally fresh (royal blue). ¼ red cabbage microwaved for 5 minutes in 2 C water can be diluted 1 part cabbage juice to 3 or 4 parts water. This will NOT stay royal blue for long. This lesson as outlined includes a comparison of FRESHLY made (royal blue) vs. OLD (purple) cabbage juice and serves as the central mystery in Experiment 4. ● Vinegar is acetic acid; it will turn the cabbage juice from blue to purple to pink, depending on how much is added. ●
●
●
●
●
Baking soda is sodium bicarbonate, or NaHCO3, which will make a solution less acid (more basic). Depending on how much you add, it will turn the cabbage juice from pink to purple to blue. Other means of generating carbon dioxide (e.g., Alka Seltzer, dry ice). Other types of acids (e.g., lemons). Syringes for drop­by­drop dispensing of anti­acid (baking soda) or acid (vinegar) solutions. Sealable plastic containers to explore whether the production of CO​
in a confined space can be 2​
sufficient to change the acidity of fresh cabbage juice. INTRODUCTION: ​
10​
minutes 1. Ask students: “Does anyone know what an acid is? In what context have you heard the word used? What kinds of things (products or substances) does the term acid bring to mind?” The students may state that acids are dangerous, can cause burns, are in soda, or citric juices, etc. Explain to the students that an acid can break molecules (molecules are the smallest piece that you can break something into and still have it be same substance) apart in order to mix and react with them. This is very destructive and can cause effects we associate with acids like stinging and chemical burns. There are different levels of acids ranging from strong to weak. 2. Ask students: “Does anyone know what a base is? In what context you have heard the word used? What kinds of things, if any, does the term base, basic or alkali bring to mind?” Many students will not have much knowledge, so explain that bases can be dangerous and can cause burns, and that many cleaning agents utilize bases. 3. Ask the students: “Does anyone know what pH is?” Explain that the strength of an acid or base is measured on a scale called the pH scale. The scale ranges from 0 to 14 with the middle value, 7, being neutral (neither acidic nor basic). Zero is the strongest acid and 14 is the strongest base. ​
For this lesson, it is not important that the students be able to associate different acidities with different numbers, or that this scale is logarithmic­­every shift of a single unit (7 to 6) represents a 10­fold shift in acidity. So going from pH 7 to pH 5 is a 100­fold increase in acidity. 4. Show the students a print out of the pH scale below and point out where various everyday substances fall on the scale. Your stomach (and its microbes) can produce an acidity of 2 on this scale, 1,000,000 (1 million) times more acid than seawater (pH 8)!! A lemon has an acidity of about pH 2, same as your stomach; acetic acid (vinegar) can have a similar pH. TEACH: ​
40​
minutes First Experiment ­­ Are you a robot? 1. Tell the students you are going to use a special potion to examine acid levels and that the first thing you are going to test is ­­​
Are you a robot? 2. Pass out a small souffle cup filled with ​
BLUE​
cabbage juice and a straw to each student. *** DO NOT use the purple cabbage juice, as this will be a useful demonstration later!!!! The purple cabbage juice is OLD cabbage juice, and students will need to figure out why ­­all on its mysterious own­­ the juice turned purple. Nothing nothing nothing has been added to the originally blue cabbage juice!!!! 3. Ask the students to be thinking how an acid test would prove whether or not they are robots. 4. Once each student has a souffle cup of ​
BLUE​
liquid and a straw, instruct the students to ​
blow into the liquid slowly and to keep blowing, while observing whether any changes are happening. Tell them NOT TO DRINK the liquid (though it’s only cabbage juice!). Second Experiment: What GAS in your breath causes the color change if you’re NOT a robot? ​
If something in your breath means that a student is NOT a robot, which of the two gases produced during breathing (water vapor and carbon dioxide­­nevermind nitrogen gas [N​
] or oxygen gas [O​
, which explains 2​
2​
why CPR works]) sugar (=chemical energy) + oxygen →
water vapor + carbon dioxide (+ heat energy) ​
is​
responsible for the color change? 1. Have students fill a souffle cup ⅓ full with blue cabbage juice and slowly add water. 2. Does the color change? (It should only dilute the juice, not change its acidity, and so color.) 3.
Have the students think of ways to add carbon dioxide to a ½ full cup (blue cabbage juice) to see if the same color change occurs (blue→ purple → pink). For example, they could add an Alkaseltzer, which releases CO​
bubbles into solution. Or they could add a small chip of dry ice, which will also 2​
generate CO​
in solution. **** They can build mini­volcanoes (souffle cup size) inside one of the 2​
plastic totes provided to create CO​
and see if that CO​
released is enough to change the color of 2​
2​
royal blue cabbage juice inside the same sealed container!!!! ***** Third Experiment: How can you make the acid disappear? 1. Have students troubleshoot ways they might make the acid color (pink or purple) disappear, and return the cabbage juice to blue (least acid). Hints: they could add baking soda or a solution of baking soda dissolved in water. 2. Could CO​
work as an antacid, turning an already acid solution (pink) into a less acid solution 2​
(purple or blue)? Try it with dry ice or Alka Seltzer. (CO​
does NOT work as an antacid.) 2​
Fourth experiment: Why did we bring purple cabbage juice to afterschool? If you compare the royal blue and light purple cabbage juice bottles (left to right in the image below), it would be correct to say that the light purple cabbage juice bottles have been acidified. But how????? microbes are everywhere​
. Don’t forget that ​
The bottle of blue cabbage juice contains more than just cabbage juice! It contains billions of microbes. But they haven’t been breathing for very long, so the solution is still not acid­­so it is blue. As microbes continue to breathe, however, they produce carbon dioxide, which turns the color of the cabbage juice purple over time. The more purple cabbage juice is just cabbage juice that has been growing microbes for about 1 week, just like the moldy bread had been growing microbes for a long time, creating those powerful smells, and all that dampness inside the bread bag. If there is enough cabbage juice, kids can take a small amount home to watch it turn colors over the weekend! (If they freeze the cabbage juice while it is blue, it will remain blue because freezing minimizes microbial activity.) WRAP­UP: 10 minutes ● Explain to students that in the same way the carbon released from their breath acidified the liquid, the ocean is currently becoming more acidic from absorbing carbon that is being released from sources such as the burning of fossil fuels. Ocean acidification is the ongoing decrease in the ​
pH​
of the ​
Earth​
's oceans, caused by the uptake of ​
carbon dioxide​
(CO2​
​
) from the ​
atmosphere​
. An estimated 25% of the carbon dioxide from human activity released into the atmosphere dissolves into oceans, rivers and lakes the very same way that the CO2 ​
​in breath dissolves and causes a color ●
change. Explain that the acidification of the oceans could have an impact on what kinds of plants and animals can live in the ocean and also could impact our climate. For example, many microbes that photosynthesize in the ocean take in carbon dioxide and release oxygen. They help maintain the oxygen / carbon dioxide balance. If many of those microbes die because they cannot tolerate the increasing acidity of the ocean, that will cause even more carbon dioxide (a greenhouse gas that keeps heat in) to be in our atmosphere and therefore increase global temperatures. Remind students that this week they have learned that microbes are small, essentially shrinky­dinked­to­invisibility! Just because the color is changing does not mean that mass is disappearing. All that is happening is that the acid indicator in cabbage juice (anthocyanin is a type of pigment) is changing color as the acidity levels change.