Educator How-To: Cross-curricular Education Gets Cheesy

As educators, we all want students to understand the world holistically, but we still tend to teach each subject independent from all other subjects. Food is an effective way to capture the attention of students and provide a useful tool for creating a more global and cross-curricular learning environment. This global approach to learning has been shown to produce deeper understanding of the concepts being taught.

Making cheese, which seems on its face to be a fun break or a supplemental activity, can be used to discover important concepts and ideas that span an entire range of subjects.  These subjects include, but are not limited to, chemistry, history, and geography. Hands-on learning activities help to create interest and to create better retention of learned material.cheese meme

In that spirit, try one of my favorite activities. I use this activity at the Houston Museum of Natural Science to make learning and discovery memorable. It is a culminating activity for my Iron Age lab. It’s simple, affordable, and the kids love it! Why not give it a try?

A Little Bite of Cheesy History

Milk has been a major source of nutrition from the earliest of times. Milk is full of protein, fat, calcium and other important vitamins and minerals. It just so happens that it’s also full of water and sugars, which have no real nutritional value and cause the milk to spoil quickly without refrigeration. With the invention of cheese, man found an ingenious way to prolong the shelf-life of milk.

Because bacteria love a moist and nutrient-rich environment, milk spoils easily. In antiquity, there was no refrigeration, so unless it was cold outside, fresh milk could not be saved from day to day. No one knows how, but our ancestors figured out the trick to preserving milk. They discovered that calves have a substance called rennet in their stomachs that separates the milk solids and fats from the water in the milk they suckle from their mothers. We know that animal stomachs were used to transport and hold liquid, so it’s possible the milk turning to curds and whey was a fortuitous accidental discovery.

cheese

Goat stomach still used to make cheese in Sardinia. Photo by Ivano Atzori.

The first cheesemakers found that if they added some rennet to fresh milk, it would soon separate into two separate parts. We call these two parts the curds (where the good stuff is) and whey (mostly made up of water and some sugars). They learned that they could extract even more moisture from the curds if they cut them up and added salt to them, which also had the benefit of adding flavor to the cheese. Heating and pressing were also used to expel additional liquid from the curds. If left to age, molds and bacteria colonized the cheese, making it even more tasty! Thus was born an easy-to-make, non-perishable, transportable food for everyone!

Tasty Science: Make Your Own Ricotta!

Let’s get started! Here’s what you need:

  • 4 cups whole milk
  • 2 cups heavy cream
  • 1 teaspoon kosher salt
  • 3 tablespoons good white wine vinegar
  • Measuring cups
  • Measuring spoons
  • Pots
  • Hot plates (or a stove)
  • Mixing spoons
  • Large bowls
  • Sieves
  • Cheesecloth
  • Water
  • Paper towels

First, set a large sieve over a deep bowl. Dampen two layers of cheesecloth with water and line the sieve with the cheesecloth. Next, pour the milk and cream into a pot and stir in the salt.

Bring to a full boil over medium heat, stirring occasionally. Then, turn off the heat and stir in the vinegar. Allow the mixture to stand for one minute until it curdles. It will separate into thick parts (the curds) and milky parts (the whey).

Pour the mixture of curds and whey into the cheesecloth-lined sieve and allow it to drain into the bowl at room temperature for 20 to 25 minutes, occasionally discarding the liquid that collects in the bowl. The longer you let the mixture drain, the thicker the ricotta.

Transfer the ricotta to a bowl, discarding the cheesecloth and any remaining whey. Use immediately or cover with plastic wrap and refrigerate. The ricotta will keep refrigerated for four to five days.

This is a basic but tasty cheese and anyone can be successful in making it. If you decide to incorporate this activity into your classroom, please share your “cheesy” pictures with HMNS on Facebook or Instagram under the hashtag #HMNS. 

The Eyes Have It: Evolutionary Development and DNA

Today’s guest blogger is Neal Immega. He has a Ph.D. in Paleontology and is a Master Docent here at HMNS. In his post below – originally printed in the Museum’s volunteer newsletter – Neal discusses Evolution Development and DNA.

Popular media crime shows, like CSI: Crime Scene Investigation, show amazing applications of DNA technology. For example, a person can be traced to a specific location by means of cells he left on a door knob.

A new science called “Evo-Devo,” shorthand for Evolutionary Development, can tell us even more amazing information. Evo-Devo techniques probe deeply into the structures of DNA to look at how DNA actually codes for the growth of body parts, telling us more about the animal kingdom than we ever dreamed possible. It shows genetic similarities between very different organisms and lets us understand how two organisms, like mice and men, can have DNA that is 85% similar and, yet, code for very different organisms.

We all know the basics of DNA molecules, where the genetic code is stored by a very long sequence of four proteins strung together in various arrangements. That is the easy part! What we need to
worry about is how these genes blueprint a living being. Geneticists, like Sean Carroll (whose popular books are listed in the references box), have discovered that the DNA code is made up of some large master programs that control things, such as eyes, and lots of very small programs (they call them switches) that control what kind of eye will be displayed.

Normal Fruit Fly
Image courtesy of The Exploratorium

Let’s confine ourselves to understanding and experimenting on simple life forms, such as fruit flies. To figure out which specific piece of DNA causes some feature to appear in a developing embryo, geneticists experimentally inactivate a segment of DNA, transplant the complete strand (including the inactivated segment) back into the egg, fertilize that egg, and then see what turns up missing. If that missing part is not vital for survival, the egg might even grow into an adult fly. Compare the drawings of a normal fly with the one below it where the master program for eyes has been deleted.

Eyeless Fruit Fly 
Image courtesy of The Exploratorium

Such experiments have found that the master program for making eyes can cause an eye to grow on a fly’s leg, body, antenna, or inside the body, depending on where it is placed on the DNA strand. Check out the drawing showing the results of moving the master program for legs to the site of the antenna. Note that the extra legs are fully formed but lack the neuron connections to the brain and so are not functional. (In the references box is a link to an electron microscope image of a real fruit fly that shows a mutation in which eyes replace antennae.)

Various mollusks (like clams, snails, and octopuses) grow eyes that vary in complexity from very simple sensitive pits to complex eyes that would compete well with human eyes. The EXACT SAME eye master program from a fruit fly can replace the eye master program for a squid, and it will grow a perfectly functional squid eye. You might be tempted to say that fruit flies and squids are cousins.

Fruit fly with extra legs
replacing the antennae 
Image courtesy of The Exploratorium

That is an amazing statement, but to take it even further, the same experiment with a mouse eye master program will grow fly eyes on flies and squid eyes on squids. They only differ by the small switch segments. These experiments establish a link between vertebrates and invertebrates that paleontologists are unlikely to find in the rock record. This also helps explain the amazing degree of structural similarity between mice and men—although many of the master programs are similar, the really critical parts of the DNA are the small switches that control the details.

Mollusks have just one master program that is controlled by different switches. Pectens, for example, have the most complex vision arrangement of any animal with three different types of eyes on its body. The DNA can be experimentally adjusted to grow any of these eyes anywhere on the body. Random mutations could thus cause novel arrangements, and survival would judge their fitness—evolution in action.

The switch concept explains how mice, chimps, and humans can have a similar number of genes. The switches control the result of the master programs. You can pick up any modern textbook and read that men and chimps have nearly identical genes. It is the switches that make us different and that provide the evolutionary means for dramatic changes, good and bad.

The fossil record is full of cases where a dramatic new species just appears. Paleontologists have often wondered if this was caused by a missing rock interval, by migration, or by rapid evolution. The concept of rapid evolution has often been discounted because it seemed to violate the incremental nature of evolution. We now can see how rapid evolution may just be a single point mutation in a switch. There are numerous biological examples where altering one protein is lethal, as in Tay-Sachs disease, or altering another might bear strongly on survival, as in changing
the color of hair from white to black.

Geneticists can now explain things in a way that profoundly affects how we think about evolution. Biologists and paleontologists have always wondered if evolution had to generate complex structures like eyes from scratch for each phylum. The reuse of master programs from very simple life forms through complex ones means that evolution can build on what went on
before. Critics of evolution often claim that eyes are too complex to have evolved. (The “half-an-eye-is-nogood” argument is derived from the first sentence of the Darwin quote in the box below.) Now, with Evo-Devo tools, we can see commonalities between the genetics of simple life forms and complex life forms– between clams and people.

The possibilities just became more complex.

REFERENCES:
Wyoming Dinosaur Center: http://www.wyodino.org/

Sean B. Carroll:
Endless Forms Most Beautiful: The New Science of Evo-Devo, (paperback) 2006
The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution,
(paperback) 2007
Remarkable Creatures: Epic Adventures in the Search for the Origins of Species, 2009

Lynn Helena Caporale:
Darwin in the Genome: Molecular Strategies in Biological Evolution, 2002

SEM (scanning electron microscope) photograph of eyes replacing antenna in a fruit fly by Naoum
Salame. http://1tv4.sl.pt

Fly Eye Genetics:
http://www.pbs.org/wgbh/evolution/library/04/4/text_pop/l_044_01.html
Renowned scientist Dr. Walter Gehring discusses master control genes and the evolution 
of the eye.

Darwin, 1859, The Origin of Species, http://darwin-online.org.uk/contents.html. In most editions, the quote appears on pp143-4.