Biolo-TREE

Something new I did this year was to offer my students a little extra credit opportunity during the month of December.  I was inspired by some ideas I saw online to give students the chance to create a biology themed Christmas tree ornament.  I really didn't feel that I had time in class to make this a class project, so I decided to offer extra credit to any student who took the initiative to make an ornament outside of class.  To make it a little more fun, I brought in a small artificial tree that was in our basement at home and decorated it with an extra string of lights.  I made a small star for the top and told the students that any ornaments that were turned in would be placed on our classroom Biolo-Tree.

The assignment was presented to students the first day we returned from Thanksgiving break, December 3, and they were given until the last day before winter break, December 20, to complete the ornaments.  At first, the ornaments were a bit slow coming in, but this past week has seen a rush of them!  Some are large, some small, but every one made me smile, especially since it was not a required assignment.  I took a picture of each ornament to share here:

Lastly, here are a few pictures of the tree decorated with all the ornaments.  

Happy Holidays!

Cell Activities

Hello again!  Lately we have been discussing the structure of cells and the functions of many of the cellular organelles and other structures.  We discussed a bit of history behind the discovery and naming of cells and how the three statements that are part of cell theory were developed.  Students learned that all living organisms are made up of one or more cells, that cells are the basic units of structure and function in organisms, and that all cells come only from the reproduction of existing cells.  A kind of fun video that we watch to introduce this concept can be found here:
https://ed.ted.com/lessons/the-wacky-history-of-cell-theory

One of the ideas we talk about is that cells are very diverse in their shapes, sizes, and internal organization due to the fact that different cells have different jobs- and that it is the job of a cell that determines its physical features.  Form follows function, biologists like to say!  However, we also talked about how all cells have several structures, including a cell membrane, ribosomes, DNA, and cytoplasm.  Additionally, while cells vary greatly in size, almost all cells are microscopic.  Students learned that this is due to surface area-to-volume ratio.  As a cell grows, both its surface area and its volume increase, but volume increases much faster than surface area.  This means that the smaller a cell is, the greater its surface area-to-volume ratio.  In other words, a small cell will have less surface area overall than a larger cell, but it will have more surface area relative to its volume.  This is important because cells need to take materials like nutrients and water in through their surface and also need to remove wastes through their surface.  The larger the volume of the cell, the greater its needs will be- so large cells would likely not have enough surface area to meet their needs!

To demonstrate this idea, we did a short lab activity in which students created three differently sized cell models- a large one, a medium-sized one, and a small one.  Students measured the cells and calculated surface area.  They then filled each cell model with sand and measured the volume of sand that the cell model could hold.  Students used their calculated surface area and measured volume to calculate surface area-to-volume ratios for each cell model.  Students found that even though the largest cell had the greatest surface area and the greatest volume, the smallest cell had the greatest surface area-to-volume ratio and would therefore be most efficient at moving materials into and within the cell.

Students prepare cube-shaped cell models of different sizes, then calculate surface area for each cell model.

Getting sand ready to fill cell models!

We continued our discussion of cells by learning how all cells are considered to be either prokaryotic or eukaryotic.  Organisms with prokaryotic cells include bacteria and archaea, and these cells do not have a nucleus or other membrane-bound organelles. Organisms with eukaryotic cells include protists, fungi, plants, and animals.  These cells have a nucleus and several other membrane-bound organelles that perform various functions for the cells.  We reviewed the functions of the major organelles in cells to realize how these cells are able to perform their life functions!

The last full school day before the holiday break we did an activity that allowed students to be a bit creative and which I hope they enjoyed!  Students either selected or were assigned one cellular structure and created an Instagram post (a "Cell-fie!) that the structure might share.  I think most students enjoyed working on something a little bit different, and I have fun seeing how creative they can be!  Here is just a sampling:

#Chloroplast

#Ribosomes

#Endoplasmic Reticulum

#Mitochondria

#Cilia

#Golgi

#Vacuole

#Nucleus

#Vacuole

#Cell Wall

McMush

Before the Thanksgiving break we did a lab that had a definite gross-out factor, called McMush.  This lab allowed students to use various reagents to test food samples for some of the macromolecules we have been studying in class.  We began the lab with known solutions of glucose, starch, protein, and oil (lipid).  For each macromolecule, students did a test with a reagent on the known solution to determine what the positive result would look like, and compared this to a test on water which we know does not contain any of the macromolecules.  Students then recorded the results for a positive and negative test for each molecule.  They found that Biuret solution causes a dark violet color in the presence of proteins, that Benedict's solution and heat causes a white and then orange color in the presence of glucose, that iodine causes a dark purple/black color in the presence of starch, and that Sudan III stains the oil which then forms a red layer on top of water.

Getting the test tubes set up!

Students compare known positive and known negative samples to observe the effects of the reagents.

A student adds Benedict's reagent to a carbohydrate solution.

After obtaining this new knowledge about how various reagents react with macromolecules, students were ready for the "fun" part.  Before beginning the lab, I had ground up a McDonald's Happy Meal (minus the toy) in a blender for several minutes.  I made a big show of putting the different parts of the Happy Meal into the blender- first the cheeseburger, which I broke up into smaller pieces before adding the the blender, followed by french fries, apple slices, and finally the drink- chocolate milk!  Once everything was added, I blended it all together for several minutes to make a goopy liquid that we called "McMush!"  Each student lab group measured out four small portions of the McMush to test for four different macromolecules- simple carbohydrates, starch, protein, and lipids.  Students used the same four reagents from the earlier tests, since they now knew what a positive test for each macromolecule would look like.  It was fairly gross, but I think most students got a kick out of it!

The McMush after it has been blended!

As you might expect, we found that the McMush tested positive for all four macromolecules.  We discussed how the simple carbohydrates likely came from the apples and the chocolate milk, that the starch likely came mainly from the french fries, that the protein mainly came from the hamburger patty and the chocolate milk, and that the lipids came from the burger and the fries.  We discussed how the reagents we used in this lab can be used for testing foods for various molecules in many situations, including when people have special diets that require them to consume or avoid consuming particular things.  We connected this to patient case studies we have been working on in class that involve individuals whose symptoms are related to the various macromolecules in their diets, casuing disorders such as lactose intolerance, celiac disease, and diabetes.  We also discussed how we did not test for the fourth macromolecule, nucleic acids, because these molecules (DNA and RNA) are not nutrients we get from foods the way carbs, lipids, and many proteins are.  All in all, a fun and educational way to spend the last few days before the break!