Looking for some activities to jazz up your class lecture on the cell and biology?  Here are a few hands-on teaching activities for middle school or high school:

Here are some cool cells to look at under a microscope:

• Cheek cells
• Onion cells
• Thin smears of ripe versus green banana, stained lightly with iodine.  Says Karen Kalumuck:  “You should see sickle-shaped structures that are amyloplastics – starch storage organelles.  You’ll see more of these in one of the types of bananas than the other, and can correlate with taste.  Predict which banana will have more darkly staining amyloplasts?  What happens to the starch?
• Compare tomato cells with pulp cells.  The skin cells are bricklike, providing structure, whereas the pulp cells are like balloons, to store starch with the lowest surface area to volume ratio.

No access to a microscope? Check out the Exploratorium’s Microscope Imaging Station — you can see videos of sea urchin cells dividing, stem cells, a zebrafish heart cell beating, and more. Any of the images here can be used in educational settings.

You can also build a cell model, and “scale up” cell and organelle dimensions to human scale.  If a cell was the size of my head, how big would a mitochrondria be?  Or, build a 3D diaorama inside a shoebox.  One teacher uses the analogy of a school — the nucleus is the principal’s office, the DNA is the school files, the teachers are the ribosomes, the students would be proteins, and the school bus is a vesicle.  Or, list a set of different analogies (the cell is like “The Simpsons”, the cell is like “a city”)  and let students choose, and make their set of analogical functions.

You can also model a cell membrane using soap film. You can stick a wet finger through a bubble film, just like plasma membranes are selectively permeable.   See this activity here.

This Traits of Life website at the Exploratorium has a set of online interactives and downloadable posters and articles.

You can do a play or drama about the cell — here’s an example about the Immune System from our teaching tips podcast.

Create a bingo or board game where students read off the functions of the parts of their cells, and then place those parts on the cell diagram.

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I’ve got a new podcast posted, this one with my esteemed colleague Valerie Otero of the University of Colorado at Boulder.  She tells us why she thinks that the idea of student “misconceptions” is very dangerous — and gives us a new way to think about student ideas in the classroom, and some activities to address them.  This is in the Beyond Penguins and Polar Bears episode on Keeping Warm, and targets common student ideas about heat.  Still, the general message about misconceptions is, I think, one that every teacher should hear.

Listen to Warm Blankets and Cold Breezes (10 minutes)

You can also read this month’s content article on heat (what is it?  How do people and animals keep warm?) written by moi.

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A while back I blogged about a cool opportunity to get anything (yes, anything!) scanned on a Scanning Electron Microscope. Posted from the ASPEX website, here is a toy bunny, macrosize, and microsize:

Though how anyone could give up that cute wittle bunny is beyond me.

You can still send them samples (which I just think is so cool, and would be a great class activity), and they’ve just started a Name that Sample contest. The first correct answer wins a USB stick.  Here’s this week’s image:

They’ve already got a bunch of comments on there — go ahead, give it a shot!  This could be a good exercise in size and scale.  This is magnified 110X, and the whole thing is about 1000 micrometers across, or 1 millimeter.  So, the first guess on the site of “a blade of grass” is waaay off in order of magnitude (a blade of grass is probably about 10 mm).  Besides, it doesn’t even look like a blade of grass to me.  It also says that “Carbonaceous phases would be represented in darker tones where as Metallic features would be displayed in brighter tones.”  So perhaps this is metallic?  Lots of people have guessed that it’s some sort of adhesive being pulled apart.  But I’m not so sure that that “stretching” is actually dynamic.  SEM requires time to take, so whatever it is, it has to be sitting still while the image is being taken.  And the features are so regular…

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In optics experiments, you often need to create lines of light.  You can do this with light boxes, but they’re expensive, and tend to  have too many rays to be useful.  Laser light boxes are great, but again, spendy.

One teacher recommends using laser levels. These are the things made to help you hang pictures on a wall, so they’re level. Less than $20!  It’s made of a bright laser, with a cylindrical lens, which spreads the dot into a line.  You can see a demo here.

Zeke writes:

They create bright, dead straight, easy to use lines of light.  They do seem useful for Snell’s Law, but it isn’t always obvious how to do it. The most common way is to use a semi-circular dish. You might find that your biology teacher has absonded with them, too. Filled with plain Jello, the rays are really clear. You can’t see the protractor I photocopied and placed under the tray, but it works great. You can also fill them with other substances like water and corn syrup to demonstate different indexes of refraction. However, ray needs something to scatter it so you need to stir in some milk or other colloid. Another option is to get a fine grit sand paper and roughen the bottom of the dish. This will scatter the light through diffuse reflection.

I also like to use plastic bars. You might already have glass plates, but they are surely too thin. The ray of light made by the laser level is thick and if the object is too thin, the ray will go over the top making for a confused appearence.

I made the plastic bar by buying a thick hunk of clear plastic from the discard bin at TAP Plastic. I had them cut it into pieces. I bought six grits of sand paper and progressively sanded the bars until they were clear. The final bit required a liquid polish. The people at TAP explained how to do it to me.

It’s pretty cool and can show total internal reflection really great.

Here’s a video from Teacher Tube:

Have fun,

Many thanks to Marc “Zeke” Kossover for this information.

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Ok, it probably wouldn’t be very yummy, but here’s another hands-on activity you can use that’s rather Halloween-like.  Called “Make a ‘mummy’”, this Exploratorium activity is a great way to demonstrate how mummification works, by drying out the tissue in a fish using baking soda.  Egyptians used a specific type of salt to do this, but baking soda will do the trick, giving you a tough leathery fish.

If you’d just left your fish out on a shelf, exposed to the air, bacteria and fungi would have begun to decay the fish, creating strong, unappetizing odors. Since all living things require water to survive, removing the water from the fish greatly inhibited the growth of these organisms, decreasing the unpleasant effects of rotting.

For an inquiry activity, try substituting salt for baking soda. Which one works best?  (Hint:  It’s not the salt).

Make him a little pyramid home. Imagine his little fishy afterlife.  Bury some fishy mummy friends for him to play with.

From Platonides on Flickr

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Extremepumpkins.com

With halloween fast approaching, it’s time to take advantage of a frivolous holiday to do some fun science stuff.

No post about Halloween would be complete without a reference to the Grossology site. Scroll down for  “lab activities”:  This gets high marks from one teacher who says, “It has the simpliest of the slimey things, glue slime, and fake blood.”

In that vein, read the post on “how to make slime” over at Schooner of Science.  The Schooner also has a recent post on zombies — an interesting story about the origin of zombies and a toxin-like powder which may, or may not, have put people into a zombie-like state.

The “whoosh bottle” is also somewhat spooky as a demonstration.  And you get to talk about gas laws  and combustion, too.

Fire is always fun.  If you google Exploding Pumpkin Experiment or Flaming Pumpkin Experiment, you can find some great things to do with those leftover jack-o-lanterns after Halloween.  Here is Steve Spangler’s version of an Exploding Pumpkin that carves itself.  Most people just have the pumpkin shoot flame from its mouth. You can get lycopodium powder (from Flinn Scientific, for example), and use a syringe to spray it along candles at the bottom of a pumpkin’s mouth, creating a fireball coming out of the mouth.  Obviously, t there are safety measures to consider.  The video below has the best explanation of how to do this that I found.

And here are a few suggestions from veteran teacher Raleigh McElmore:

Slime:  If you can score a magnetic stirring hot plate you can easily get Poly vinyl alcohol at a chemcial supply store and make up some great slime at 40 gr/L and mixing it with a bit of Sodium Borate (known as “Borax” and in many supermarkets detergent aisle) at 40 gr/L.

Your own grossology:  In elementary school I always filled a big pyrex bowl with peeled grapes that had been soaked in red food coloring. This brings out the “veins” in the grapes and I announced that “eyeball soup” would be shared with the students. A chunk of dry ice, the grapes and fill the bowl with cheap fruit punch gives you a seething and bubbling drink with “eyeballs” floating around.  Or you can, for realism, use sheep eyeballs. Give them to your star pupils. I’ll keep an eye out for you.

And to keep them on their toes:

A great magic trick that Penn and Teller invented is to bring two cans of sparkling soda (not anything else as this is messy). Give one can to a quiet student tell them to keep the can totally quiet. Give the other can to a hyperactive sort and tell them to “shake the can as hard as you can without touching anything”.  Did I mention that this should be done outside, oh yeah, do it outside.

Take the highly shaken can, put it in plain sight and say that this is the season for strange things. Tell the students that you will change fizz in the shaken can to the quiet can. Gently touch the quiet can and touch the shaken can. Mumble incantations about AYP and other scary things. Waste at least 30 seconds in mindless babble and then take the “quiet can” and hold it high while you open it. Curve your fingers behind it and squeeze the can as you pop the lid. It will shoot fizz all over everybody as you have secretly crushed the can. After you have sprayed everyone dramatically throw the can into a nearby garbage can to avoid students seeing the crushed can.

Then quietly open the shaken can. The gas will have gone back into solution by then and it won’t do anything. Explain to the students that teachers are given these powers, but only to be used for the good. Drink the calm can and draw attention from the garbage can with the crushed evidence.

Need more ideas?  Here are some links here and here and here.

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Our latest podcast in the Beyond Penguins and Polar Bears webzine has been posted.  This is a bimonthly webzine for elementary educators, to integrate polar science into their teaching.   This month’s webzine is on arctic peoples, and the podcast features a story on how light disappears and reappears in the arctic each year, that you can play right in your classroom.  Plus, suggestions on how to use this story with your elementary students.

The Boy Who Found the Light

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If you’re looking to beautify your classroom, here are some links to some free science posters. No guarantees as to quality, but these links should be a helpful start!

http://www.johnny-lin.com/posters.html#powersoften
http://www.tufts.edu/as/wright_center/products/svl/posters/posts.html
http://www.mii.org/teacherhelpers.php
http://www.surfnetkids.com/games/Science_Games/
http://www.scattercreek.com/~zimba/freeforteachers.htm#posters

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Here’s today’s science classroom activity.  We’re surrounded by the crushing weight of layers of atmosphere above us, but we don’t feel it.  Why?  Our perception is tuned to differences, not absolutes.  If we were in a completely pink world, we would notice anything that wasn’t pink, but (I’m pretty sure) after a few minutes, we would become blind to pink itself, just like you don’t hear the noise of a fan in the room until it stops.

Similarly (though through different mechanisms), we’re not constantly aware of the intense pressure pushing in on our bodies.  (Would we really turn into mush in a vacuum?  No… read more about the effects of a vacuum on the human body here).  Thank goodness, because it’s quite startling.  I know, because I’ve felt it, in this wonderful science classroom experiment.

All you need is a big trash bag and an industrial strength vacuum cleaner, and a willing victim (er, “faithful subject of science.”) The victim (aka “subject) gets inside the bag, and once you suck all the air out of the bag with the vacuum cleaner, they’ll feel an intense pressure.  SAFETY FIRST!  Read this PDF writeup of the activity (from the Exploratorium’s Eric Muller) for all the ins-and-outs and safety factors in doing this with your kids.  (Words to the wise — don’t put your head inside the bag!)  It’s stunning — try it if you can.

Why do we feel this pressure?  Stop and think about it a moment.  What changed when we sucked the air out of the bag?  There’s the same atmospheric pressure outside the bag (14.7 PSI at sea level), that didn’t change, there’s still the weight of the atmosphere pressing down on you.  What changed is the pressure inside the bag.  What does that have to do with anything?

The high pressure outside the bag pushes the bag’s surface against your body, and the bag stretches against your skin.  We feel this stretching of the bag as it pushes on our skin and the little hairs on our body.  We don’t feel the pressure without the bag, because though the air pushes against our skin, it pushes the same in all directions.  The bag lets us feel what is already there — the weight of the air!

You can extend this activity a bit by measuring the pressure inside the bag (at the Exploratorium it was 1 PSI). Eric says:

Paul Doherty and I used a barometer watch to measure the pressure inside the bag when doing research on this activity. Some one that goes to the mountains a lot might be able to loan you one or you can buy one. You can also just get a barometer.  I found a bunch for sale on eBay. Lastly, you can make a home-made barometer.  If you do a Google search, there are a variety of easy to make barometer designs (but you still might need a good barometer to calibrate your homemade one)

Paul D. has a similar activity to let you feel the pressure in water with a plastic bag.  Stick your hand in a pail of water.  You don’t feel any pressure.  But stick your hand in a plastic bag and stick it in the water, and you’ll feel an intense pressure (that gets stronger with depth) as you put your hand in the bag.  Paul D. explains:

Why do you need the glove or the bag?
Human sensors detect differences or changes in a signal. When you stick your ungloved hand into the water the water exerts a uniform force on your hand. It flows around every hair and every wrinkle in your skin. Now a single hair is bent to the side. When this happens you cannot feel the pressure exerted by the water.

However when you wear the bag or the glove they will bend down the hairs on your hand, and the glove and the bag may have folds that exert uneven forces on your skin. So that you can “feel” the force exerted by the water.

Cocktail Party Physics has a great old post on the history of measuring pressure (fascinating stuff, really).  And Eric has more activities here.

A few relevant science toys from Arbor Scientific

One of Paul Hewitt’s favorite demos to show that suction cups stick because of the air pressure pushing (rather than a “sucking force”) is this atmospheric pressure mat.  You can lift a whole lab stool once you stick this down on it.  A similar but smaller version is these atmospheric pressure cups.

A vacuum chamber/pump will let you reduce the pressure on anything (they suggest marshmallows), explore gas laws, etc.    See the website for some example class activities. They also have a class set.

They’ve also got a durable hand-held vacuum pump for expelling air from any other kind of container.  (Good for the “coin and feather fall at same rate in vacuum” kind of demo).

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This week’s episode of my Science Teaching Tips podcast actually features, well, me! Yay. It’s nice to record myself, not always other people, though the folks at the Exploratorium are so darned clever and fun, I feel it’s my mission to document every last scrap of their wisdom and energy. I’m trying…

So, this time I give you a way to adapt a great Exploratorium exhibit to something you can do at home with a friend and a set of keys.  It’s about how we localize sound, which is something very important for people who use sound to navigate (like blind people).  So, find out more about the perception of sound by listening in to this week’s episode.  For those of you who haven’t listened before, these are just 5 minutes long!

Listen to Find that Sound.

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