Ocean Acidification Experimental Design Lab

Students learn not only about the effects of increasing acidity in the ocean on marine organisms, but also practice their experimental design skills in this Ocean Acidification Lab.  In addition, the lab helps students practice NGSS Science and Engineering Practice #3: Planning and Carrying Out Investigations.  Click for a copy of the lab.

Materials Needed for Ocean Acidification Experimental Design

A box of donated shells
  1. Shells:  MUST BE MOLLUSCA (Flat shells like clams, mussels, and scallops). NO GASTROPODA (Snails). Too much solution gets stuck way up in the Gastropod shells and will actually cause the mass to increase and not decrease due to water weight.   Ask students to donate shells. Many have boxes in the garage that are no longer wanted. You can also go to a seafood restaurant and ask for their clam, mussel or oyster shells. I like to eat pasta with mussels at home so I save my shells sometimes.  You can also buy at craft stores, but they are usually very small and not the best for the lab, but will do in a pinch.
  2. Soaking cups or small beakers. I use soaking cups since I don’t have enough beakers for multiple classes to soak for several days. I buy small plastic cups at Smart N Final (a restaurant/public supply store). The 5 1/2 oz size is a good size for this lab. Plastic drinking cups are fine as well.  I allow students to have 4 cups per group (I have groups of 4 kids).
  3. Vinegar as the acid.  Some teachers use other acids, but since I don’t teach chemistry, I find vinegar the easiest and it doesn’t have to be specially disposed of.
  4. pH meter: You can use pH paper in a pinch, but a meter will help the kids with more exact pH measurements.  The other problem with pH paper is that vinegar drops the pH so rapidly that many of the cups will have a similar pH and students need to see the slight different that a pH meter will show. The probe that I use is  $15-20 on Amazon.  Pocket Size pH Meter Digital Water Quality Tester 
  5. Two graduated cylinders per group. Use one for water and one for vinegar to avoid cross-contamination.
  6. Two plastic disposable pipets per group (optional). Helps students measure precisely using the graduated cylinders.
  7. Water: I use tap water since my tap water is slightly basic which mimics the ocean. Tap water also has minerals which is similar to the ocean. If you can, collect ocean water for more authentic results.
  8. Scale: Any electric scale is good as long as they go to the tenth place in grams. I have a set of pocket scales that I ordered using a Donors Choose grant. If you have some money, pocket scales are inexpensive $10-15 and nice for groups to have their own.  Amazon sells them for cheaper than science supply companies. I have this type of scale in my lab
  9. Sharpie to mark the cups
  10. Hammer (optional) for shells that are too big for the cups.

Need idea for funds to purchase new equipment?  Read about my favorite sources for funding.

Supplies needed
Some shells are too big for soaking cups.
Use a hammer to break into pieces
Each cup gets a piece

Pre-Lab

Students discuss the design in their groups and fill in the lab paper. I have all the materials they can use in the middle of their table to look at as they brainstorm. The visuals are good for many students such as English Learners and Resource kids. I let them handle the materials also as they figure out how to set up the lab.

Students must get 3 different signatures/initials from me. Most groups need to refine their initial question to make it more “high-school” level. (NGSS SEP #1).  I ask them to use words such as “increasing” and “decreasing”.  This also helps them refine their language in a way that is beneficial on AP® Exam FRQs.

  • One cup must be a control with water and shell only.
  • Students may not use more than 50% vinegar. (You can even make this number smaller)
  • Students need to figure out the total ml of solution in each cup as a constant. They can do this by testing how much solution is needed to cover the shells using a graduated cylinder.
  • Its best to direct the students to use % of vinegar in their cups instead of designing around pH. If students want 4 cups with pH of 7,6,5,4 for example, this is very difficult as it requires a titration and will take students FOREVER in the lab to make their cups. Instead, students should have cups with 0% vinegar, 5%, 10%, 25% etc.  They can decide which ones–that’s the point of experimental design.

A procedure is optional for my students.  I have them outline what’s going in each cup (amount of water and vinegar) and many draw pictures on their paper.  Once they have this information, a procedure is usually not necessary. But that’s up to you.

Lab

Students need to find 4 shells that are as identical as they can find (species, thickness etc).  They can also take a larger shells and break into 4 pieces.  The mass of each doesn’t have to be the same, because students are measuring percent change.

Students need to record the mass of the shells before soaking.

Students prepare the four cups using the materials.

After making concentrations, students record pH of the soaking cups.
Students need to rinse pH probes after using each time. Otherwise, trace amounts of vinegar will skew the results of subsequent cups. Make sure the students face the pH meters downwards or water will damage the electronics. (Learned the hard way)
Finished cups labeled with a sharpie
My students store in trays. Use whatever you have for storage.

Shells stay in solution for 3-4 days (or longer)

Three to Four Days Later (or more)

  1. Students remove shells from soaking cups.
  2. Students need to measure the pH again.  This is a great time to talk about buffering!
  3. Students dump solutions in the sink and replace shells in their cups (make sure they don’t mix them up)
  4. Allow shells to dry for 2-4 days.  Shells MUST dry all the way or the students will measure an increase in mass due to water weight.

Buffering (from my chemistry buddy, Laura Solarez)

The pH will rise during the soaking time due to the release of Calcium Carbonate from their shells. The resistance to a pH change with the addition of acid is known as buffering.  This is an important concept when teaching about acid rain or acid mine drainage.

As the calcium carbonate from the shells dissolves, it binds with the acid, neutralizing it.  In this lab, CaCO3 + HC2H3O2 (vinegar) –> CaC2H3O2 + CO2 + H20.  The bubbles seen in the cups are CO2 and H20 as the reaction occurs.

Calcium carbonate is the same component of limestone that is added to reduce the amount of acid in lakes from acid deposition.

In water saturated with CO2, in the oceans, the calcium carbonate can form calcium bicarbonate, but it is still weakened and will degrade the shells.  If the water is acidic, it will try to neutralize the acid, breaking down into CO2 again and adding more CO2 to the oceans.

Three to Four days later (or more) when the shells are completely dry.

Students now measure the mass of their shells and calculate percent change.

After shells have dried for 3-4 days, students take the mass again.

Assessment can follow in many different ways as you prefer.  Graphing, analysis questions, referencing articles about ocean acidification, formal lab write-up, Claims Evidence Reasoning, etc.

I like to do group lab reports for this lab.  You can read about how I do that here.

 

 

 

Owl Pellet Dissection-Trophic Levels and Energy Loss

Owl pellet dissection is used to teach ecology topics such as food webs, biomass pyramids and energy loss.

Buying Pellets and Materials.

Both small and large pellets work with this lab. I’ve used small when my funds are more limited and large when they’re not. Large pellets give more prey per pellet which is fun for the kids.  If you don’t have enough science funds, here’s some suggestions on where to find additional money for your science classroom.

I buy one pellet per team of 4 students due to cost. This is not ideal, but they are only dissecting to count the prey–not to identify all the bones or do anything else with them.

The pellets are sterilized, but I provide gloves for kids who prefer gloves. My pictures show dissection trays, but they’re not necessary. A paper plate or a paper towel works just as well.

Pre-Lab

Since I try to teach inquiry-style with the 5E learning cycle, I don’t want to pre-load information into the kids’ brains. I do, however, want them to see where owl pellets come from and basic dissecting techniques. I assign these videos the night before on Edpuzzle, but these can also be shown in class prior to the lab.

Phenomena-based video of baby owl regurgitating a pellet.

Basic information and dissection techniques.

Dissecting pellets

There are many variations of the owl pellet lab which are wonderful.  My copy is a 5E learning cycle which was adapted from the original creator.

Kids can use their fingers or tweezers to take the pellet apart. Provide reference sheets. Many can be found for free online.

Bone sorting chart found on Pinterest. I added some more info (like the size of mouse vs. rat skull or “2 per animal”) before copying.

I altered this reference sheet to help kids correctly identify a mouse vs. a rat. I make kids measure as they don’t readily know how large 1 cm is.

Mice skulls are usually 1 cm. Many students tell me they have a mouse and I say “have you measured it?”. When they do, they find out its a small rat.

I combine ecocolumn data along with owl pellets at the same time so 4 kids have more tasks to do. Two kids take ecocolumn data while the other 2 kids in the group dissect the pellet.

After about 20 minutes both pairs are finish and all 4 of them will do calculations and answer questions on their owl pellet papers together.

Calculations and Analysis Questions

(I want to give a shout-out to the original creator of this lab–the famous Dr. E)

Students take their data and fill in a chart. The entire chart is NOT filled in.  Most of the prey will be a rat or mouse. Students always think they found something else like a mole or shrew, because it sounds more interesting, but unless they can ID a skull, it  probably isn’t. (I have some kids who think they have a shrew, because the ribs they find are so skinny….)

Sample data. Point out to students that they will have zeros for some rows animals.

Next, the students create a numbers pyramid and a food web. I draw a pic on the lab white board to help them.

This is in the lab to help them with the numbers pyramid and food web. The food web is partially complete.

For the food web, you can choose to have students create a food web from just the prey found in their pellet or from all the prey the owl could eat.  I choose the first option (but am thinking of switching to the second for next year to give them more practice with a more complicated food web).

Next comes a biomass pyramid which is the crux of this lab in terms of calculating energy loss.  Students need to complete the biomass chart and then draw a pyramid. I have detailed instructions on the lab paper on how to do that since it confuses them.  

Sample paper with biomass chart, biomass pyramid and energy loss calculations.

Working in groups for the questions is helpful so they can hash out what the correct answers should be and learn better. I flipped my class last year so I have the luxury of time to allow an extra day to do this.  Students are often confused that the energy “loss” from the prey to the owl is over 99%. They need to understand that 90% energy “loss” is an average and they will hypothesize why the loss is this lab is so much higher (the owl doesn’t weigh very much for being a top predator).  Its good for them to question their numbers, however, if they seem “off” as that is a good skill for the math is this course.  But, in this case, its correct.

The questions also discuss that energy is not really “lost”, but becomes heat and an unusable form for food in ecosystems–1st and 2nd laws of thermodynamics.

Normally, I have the kids write a conclusion and submit through Turnitin.com, but this year, I had them do an oral conclusion on Flipgrid. The results were much stronger in terms of understanding energy loss than if they did the conclusions by themselves.  Much of the AP® Exam is higher level thinking and students can help build these skills by working together.