Sewer Bugs: Observation, Inference and Density

This demonstration is often used to catch students' attention.  You can use it as such, or turn it into an observation activity for your students.

In the classic set-up: 
Before your students arrive, you'll pour some Mountain Dew into a glass (another light colored soda would work as well, but there's just something about that neon yellow color of Mountain Dew... ) and add a handful of raisins.

The raisins should start traveling up and down in the soda.

When the students arrive, you show them your sewer bugs, making up a story about how you acquired them and so on.  At the end of the story, you drink the bugs (remember, you know it's just soda and raisins) - disgusting your students and forever imprinting yourself on their brains!

As a student activity: 
Provide your students with the supplies.  Let them set it up and observe carefully to see if they can determine how the "bugs" are traveling.

The explanation: 
Raisins have lots of nice bumps and creases to which the carbon dioxide bubbles (found in the soda) can adhere.  The carbon dioxide bubbles decrease the density of the raisin, allowing it to rise to the surface.  When the raisin reaches the surface of the soda, the bubbles pop.  The density of the raisin increases and it drops.  Carbon dioxide bubbles once again adhere to the raisin and the cycle continues.

Capillary Action in Action

You'll Need:
Water
Food Coloring
Overhead transparency* (You can use one that's been printed on that you no longer need, as I did)
Paperclips
Small, shallow dish (or a jar lid works)

Cut the transparency in half.  Stack the two pieces on top of each other, roll them into a tube and paperclip at each end.

Place some water in the shallow dish.  Add several drops of food color (don't use yellow for this demonstration, you need something darker to show up).

Stand the tube you made in the dish of liquid and watch what happens.  You may want to roll up a piece of plain white paper and slip it inside your tube to improve visibility.

As you watch, you'll see the colored water creep up the tube.  You're seeing evidence of adhesion - water's desire to stick to things other than itself.  So much so that it overcomes gravity to keep working its way up the tube. 

Didn't photograph real well, but the color did make it all the way up the tube. 

*Does my knowledge and use of transparencies make me old?  I feel like all the new teachers out there are laughing at me and my out-dated ways.  That no one uses an overhead any more, they all project things using their computers and SmartBoards.  Regardless, don't get rid of your overhead projectors, there are cool science demonstrations you can do with an overhead that you can't do with your fancy computers!  :)

Electricity: Light a Lightbulb

Once your students understand the basic idea of a circuit, see if they can get a lightbulb to light.

Each student/pair/group will need a lightbulb (small ones work well), a D battery, and some wires with the ends stripped off (wires will aligator clips on the end work well if you have them).

Unless students have done this before, it will likely take them some time to figure it out. 

The trick is this...

Look closely to the filament in the lightbulb.  One end of it is attached to the bottom of the lightbulb and the other end is attached to the side of the lightbulb. 

So, in order to make a complete circuit, a wire needs to go from the battery to the side.  Then another wire needs to go from the bottom of the lightbulb back to the battery. 

It can be tough to hold everything in place, but once you get everything lined up, it works! 

After students have figured it out, usually through trial and error, I draw a giant lightbulb on the board and illustrate the circuit.

Turn Your Students Into a Protein

This one takes a little prep work the first time 'round.  But after that, you're set forever.  It's a great way to include a little kinesthetic activity into the study of DNA.

First, the prep work: 
On a long strip of paper* write out a string of DNA bases (actually, you're making the mRNA).  You want to make sure your letters are evenly spaced - I actually marked the paper.

Keep a codon chart handy - make sure you begin with a start codon and don't come to a stop codon immediately.  And, don't make the mistake of using T instead of U, as someone did...

Now you need to make a ribosome through which your strip of paper can fit.  I made mine out of fun foam.  It has magnets on the back, so it sticks to the white board.  Cut the window in the ribosome, so that you can see 3 bases at a time (hence the reason for evenly spacing your letters).  Use this picture to guide you:

Now you need to make the amino acids.  Once again I used fun foam.  I wrote the amino acid on the foam, punched holes in it and strung string through the holes so the students could wear them. 

For the activity: 
Draw a huge circle on the board - a cell.  Sketch in a nucleus and stick your ribosome in the middle as well. 

Show your students the mRNA (your paper strip) moving from the nucleus to the ribosome.

Feed the mRNA into the ribosome.

Have your students translate the first 3 mRNA bases into an amino acid.

Have a student put the appropriate amino acid placard on and stand in front of the room.

Move the mRNA to the next three bases.  Determine the amino acid.  Have another student put on the appropriate placard, then stand next to the first student and hold his/her hand.

Proceed this way until you come to a stop codon, or until you've made your point.

Your students will have a better feel for how a ribosome translates mRNA, how proteins are formed, and understand that proteins are long chains of amino acids. 

* I got a few sentence strips from an elementary teacher in my building - they're the perfect size and shape for this, I didn't have to cut them, and they have lines marked on them!

******
I learned this from a fellow teacher at a NJ Science Teachers Association Convention several years ago.  I don't know who that teacher is - but if you're out there, please let me know - I'd like to give you credit.

Earth: Apple Activity

Consider the Earth as an apple.

With a knife, slice the apple into quarters.

Set aside three of the quarters - these represent the oceans.

You have one quarter remaining - this represents the total land area.

Slice the remaining quarter in half.

Set aside one of those pieces - this represents the land that's inhospitable to people: polar areas, deserts, swamps, very high/rocky mountains.

You have 1/8 of the apple/Earth left - this represents the land area where people live.

Slice this piece into four sections.

Set aside three of those sections - they represent  the areas that are too rocky, too wet, too cold, too steep or with too poor of soil to grow food.  It also contains cities, suburbs, highways, schools, parks, factories, parking lots and other places where people live but don't grow food.

You have 1/32 left of the apple/Earth.  Carefully peel this small piece. 

This tiny bit of peel represents the surface of the Earth's crust, the soil upon which all people depend.  It is less than 5 feet deep and represents the total portion of the Earth suitable for producing food.

******
Presented by Audrey H. Brainard (Hands-On-Science) during the 200 Maitland Simmons Life Science Institute.

Air Pressure: Bell Jar Demonstrations

If your school has a bell jar and vacuum pump, break them out!  Try some of my favorites:

- 1 -
Fill a small beaker part way with water.  Have some students touch the water - it's cool/room temperature.  Place the water in the jar and turn on the pump... the water quickly boils.  Remove the water and have students touch it again - it's still cool/room temperature!  With no air pressure, water boils at room temperature! 

 - 2 -
Fill a small balloon with just a small amount of air (just enough so there's air in there, not enough to even stretch the balloon).  Place the balloon in the jar and turn on the pump.  The balloon will expand!  Without air surrounding it, the air molecules trapped in the balloon will begin to expand, thus expanding the balloon!

 - 3 -
Place a marshmallow in the jar and turn on the pump.  The marshmallow will grow right before your eyes!  It's like the balloon above - there's air trapped in the marshmallow that expands when outside air pressure is removed.  Eventually the sugar structure will be stretched to its breaking point and the marshmallow will stop expanding.  When you return the air pressure, the marshmallow will be completely crushed - there's no structure to support/trap air molecules any more.

For some extra fun, pick up some extra Marshmallow Peeps during the holidays!

 - 4 -
Place a small dollop of shaving cream in a small beaker.  Set the beaker in the jar and turn on the pump.  The shaving cream will expand, out of the beaker and will fill the whole bell jar (be careful - turn off the pump before the shaving cream gets into the pump - that would be disastrous).  The shaving cream has air trapped inside of it.  It behands in the same manner as the marshmallow. 

You can also use whipped cream for this, but I find ath shaving cream cleans up very quickly and easily. 

**I've been told that you can do the marshmallow "trick" in one of the vacuum systems for food preservation (the kind that pulls the air out of a jar).  Not having such a system, I haven't been able to confirm, but that information came from a very reliable student.

Balancing Act

If you drop a paperclip into a cup of water, it will sink to the bottom, because paperclips are more dense than water.  But, if you're careful, you can take advantage of water's unique properties and make the paperclip "float" on the surface.  

Fill a cup with water - the fuller the cup, the easier to do this.

Use a fork to gently place a paperclip on the water's surface.  You want to place the whole paperclip on the water at one time.  You don't want one part of the paperclip poking through the water. 

This definitely takes some practice and can be a test of patience.  I have never been able to get more than one paperclip to rest on the surface of the water, but I've seen others do multiple paperclips at the same time. 

If you get frustrated watching someone else get their paperclips to stay on the surface while you can't, place a drop of soap in thier water while they're not looking...


Water molecules like ot stick to one another, creating a membrane-like surface across the top of the water.  If you place the paperclips just so, that strong surface tension will support the paperclips (they aren't actually floating - they are still more dense than water).  Soap breaks water's surface tension, so you won't get soapy water to support anything.