Advanced fermentation bag module

Research teams present preliminary findings during an informal data presentation session.
Teams are asked to restate their “claim" or hypothesis, describe or prepare a data table or graph with their data and provide their reasoning for their results using the data they collected.

EXTEND:

(Optional-time permitting) Students may refine or extend their investigations
to explore new questions or collect new data with revised procedures based on what
they learned in their first investigation.

EVALUATE:

Students summarize findings across all research investigations. Teachers
may provide an exit slip or ask students to provide a brief response to questions from
the investigation.

Engineering estimation

Designing experiments and recording observed measurements requires creative scientific skills. Using experimental data to make estimation and predictions is equally creative for combining science, engineering, math and statistics.

Watch this video of a person estimating the number of grains of sand in the Sahara desert.

If you found this video clever and want to learn how to think like this, try this problem below. You should also let your teacher know you like this or send us a message here to chat more about professions that seek people with this curiosity for scientific estimation.

Thinking creatively like this by combining biology with math, chemistry and physics are skills anybody can learn.

And there are professions that seek people who can creatively combine these skills to solve societal challenges facing people, animals, habitats.

If you like these types of challenges but think you're not good in math, chemistry and physics to be any good, give yourself the chance to apply these skills in real world problems. You might find with after a few years of practice, you'll be doing these things in your head.

The story and challenge...

You know that ethanol is a type of alcohol can kill the coronavirus.

And you now know that yeast can metabolize sugar to create ethanol.

So what if in a future coronavirus pandemic, there was a shortage shortage of ethanol, what would you do?

But before you started telling people you could help, you wanted to not overpromise how much you could help. So you decide to estimate how much ethanol you could produce in ziplock bags

How would you estimate this?

In this experiment you found in 30 minutes that ______________ grams of yeast + _____________ grams of sugar made a ziplock bag fill with carbon dioxide.

But how do you figure out how much ethanol is in the bag?

Well, what would you do if you had this stoichiometric equation?

What if we were to say that all of the grams of glucose were converted to ethanol? How many grams of ethanol would you estimate are in your bag?

How many glucose molecules are in a gram of glucose?

So if 1 mole of glucose has a molar mass of 180 grams/mol, then how many glucose molecules are in 1 gram?

(1 grams glucose)/(180 grams glucose/mol) = 0.0055 moles

How many glucose molecules are in 0.0055 moles?

• 3.34 x 10²¹ molecules of glucose

If yeast converts 1 molecule of glucose into 2 molecules of ethanol, how many ethanol molecules are in the bag containing 1 gram of glucose? 6.68 x 10²¹ molecules of ethanol

If you have a different mass of glucose in your bag, how many grams of ethanol are in your bag?

(0.0055 mol of glucose) x (2 mol of ethanol/1 mol of glucose) = 0.011 mol of ethanol

(0.011 mol of ethanol) x (46 grams of ethanol/mol of ethanol) = 0.506 grams of ethanol

How many liters of ethanol is in your bag?

What physical property has an equation that relates mass to liters?

(0.506 grams of ethanol)x(789.3 grams of ethanol/liter of ethanol) = 0.000641 liters of ethanol = 0.641 mL

We're estimating. So how many significant digits should you report? 0.641 mL, 0.64 mL, 0.6 mL?

So if a nurse in a hospital needs to wash their hands with 100 mL of alcohol before touching a patient and one nurse typically attends to 100 patients per day, how much ethanol does one nurse need per day?

How many bags of yeast+glucose do you need to need to produce enough ethanol for one nurse?

If there are 100 nurses in the hospital, how many bags of yeast+glucose do you need to make per day to provide for all the nurses?

If ethanol occupies 0.641 mL in the bag, how would you calculate how many liters of carbon dioxide is in the bag?

If you had a bucket and water, how might you experimentally calculate how much carbon dioxide is in the bag?

First measure the mass of the bucket on a scale.

Next fill the bucket to the rim with water measure the mass again.

Subtract the difference. This is equal to the mass of water.

From the density equation, you can calculate the volume of water in a bucket even if it has tapered or irregular shape.

Without spilling any water, remove the bucket from the scale and place it in a location where it's okay for things to get wet.

Now ensure your ziplock bag is sealed tight. Slowly submerge it into the bucket of water. The displaced water will spill onto the floor.

Remove the bag from and gently place the bucket with remaining water back onto the scale.

Subtract this mass measurement from the original mass of the empty bucket.

Subtracting the mass of the full bucket of water from the mass of the bucket after water was displaced by the bag gives you the mass of water that would have occupied the volume of the ziplock bag.

Using the density of water equation, you can now solve for volume of the ziplock bag containing CO2.

Subtract the volume of ethanol you calculated above from this experimental volume measurement of the bag. This gives you approximately the volume of CO2. (A small difference will be due to the volume in the bag occupied by the yeast and water)

Now rearrange the ideal gas law to find the number of moles of carbon dioxide: PV = nRT

You can make some measurements about the temperature and atmospheric pressure in the room.

Compare the number of moles and mass of CO2 calculated experimentally to the number of moles and mass of CO2 you calculated using the stoichiometry equation method.

Why might it not be safe to use alcohol produced by yeast without purification?

If it takes 30 minutes for yeast to reproduce and we stop the experiment at 29.999 minutes, then is the final number of yeast cells greater, equal to, or less than the initial number of yeast cells?

If we approximate a yeast cell as having a mass of 60 picograms (pg) 60x10^-12 and we placed 1 gram of yeast into the bag, then approximately how many yeast cells are in the bag at time = 29.999 minutes?

(1 gram yeast)/(6.0x10^-11 grams per yeast cell) = 1.67 x 10²² yeast cells

If after 29 minutes there is 6.68 x 10²¹ molecules of ethanol then on average how many molecules of ethanol did each yeast cell produce in the 29.999 minute time period?

(6.68 x 10²¹ molecules of ethanol)/(1.67 x 10²² yeast cells) ~ 4 x 10^-1 ethanol molecules per yeast cell per ~30 minute time period. Let's allow ourselves to round this to 5 x 10^-1 ethanol molecules per yeast cell per ~30 minute time period. Or 0.5 ethanol molecules per yeast cell per ~30 minutes. 0.5 or 1/2 is an easier number to keep in our memory.

It is still odd to think about 0.5 molecules being produced per yeast cell in 30 minutes. A more intuitive way to express this is to say in a 30 minute time period only half of the yeast cells produce an ethanol molecule.

An analogy is to think about baking cakes. Imagine a 24 hour bake-a-thon consistin of 10 bakers. You stop in to the competition for 30 minutes and count how many cakes are completed in the 30 minutes you are present. If 10 bakers completed 5 cakes in 30 minutes, we could say that each baker baked 0.5 cakes in 30 minutes. That's an odd way to think about making cakes. Just like it's odd to think about 1/2 of a molecule of ethanol being produced in 30 minutes. Another more intuitive way to express this is to say that if in a randomly selected 30 minuted time period you only saw 5 cakes being made by 10 bakers, we could estimate that it takes each baker 60 minutes to make a cake.

So if we've rounded to 0.5 molecules of ethanol produced by 1.67 x 10²² yeast cells in a 30 minute time window, then we can say that it takes 60 minutes for each yeast cell to produce one molecule of ethanol.

You can develop a deeper appreciation for individual cells by using basic math, physics, chemistry and biology principles to each cell's capability.

Step back for a moment and ask yourself these questions:

1. Did you find it interesting to measure the height of the bag when using different feedstocks?
2. How did estimating the amount of ethanol molecules help you apply your experimental observations to an societal challenge such as coronavirus hospital hygiene?
3. If you someone were to say to you that a kilogram of yeast could provide enough ethanol to fill a 10 liter fuel tank in 5 hours, would you be able to estimate whether their statement is plausible?
4. Without experimental data to provide evidence, can you think of another way to make estimates to check the plausibility of claims such as ethanol for biofuels and hospital hygiene?

Commentary and modifications

With the constrains of a typic science classroom, there is rarely enough time, money for supplies or capability for students to do more than surface-level investigations. In this lab, teachers may allow students to design most phases of a true investigation including how to collect data, design and standardize procedures and ask questions that lead to investigations.

Adding cereal as a feedstock to this lab added high interest for students and
provided a surprising nding. In their lab, students found that Cheerios produced more CO2 than Corn Pops. This led to a better comparison of the sugar content by weight andvolume on the cereal labels.

When time is limited, teachers may select the data collection method of choice using 9" balloons (check for latex allergies) or probes (CO2/pressure) from the lab.

To further limit time, teachers may choose to allow a group brainstorm of research questions and then select one or two from the list that all groups will investigate.