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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This session is about how using discrepant (or “surprising”) events to teach physics

There’s quite a bit of evidence showing that students don’t really get what we want them to get from demonstrations, but they do like them.  They get a lot more out of them if we ask them to predict the results of the demonstration in advance.  The Detroit area physics teachers went a step further and gave a popular session on “discrepant events” — using demonstrations with surprising results and asking students to first predict what will happen.  He often phrases the questions as mutliple choice and students vote with a show of hands (though clickers could be a great way to do this too).  You can find these at dmapt.org. Here are some examples:

Hoop and a disk

When you roll a hoop and a disk down a ramp, which one will win?  It’s the disk, because it’s harder to get going because it has a higher moment of inertia.  He had a few variations on this — a disk and a sphere, same mass (sphere wins), or a large sphere (2M) and a small sphere (M) (both roll at the same rate).

Springs

When you hang two masses from a bar using springs, and let one mass bounce, what will happen to the other mass?  (they resonate, so the 2nd mass starts to bounce and the 1st mass slows.  What if we change the 2nd mass so it’s not the same as the first mass?  We don’t get resonance in that case.  What if we use 2M on one spring, and make the 1st spring twice as long?  We get resonance again!

Projectile motion

We manage to hit one of those little troll dolls (a “conTROLLed experiment?”) with a ball launched from a little ball launcher.  If he changes the angle, will he still hit the doll?  Well… he cheated… the ball launcher has an angle-o-meter on the back, and he used comlementary angles (eg., 60/30) to manage to hit the target even with the changed angle.  A good activity for the first day of class.

Bike tire

Suspend a bike wheel from a string and get it spinning vertically.  What will happen when you let it go?  (It keeps spinning and precesses).  This one’s hard to describe in words…

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Here is a very nice review (from a teacher’s listserv I’m on) about what sounds like a great book for the chemistry teacher:

A good book about Chemistry for the middle school and high school:  “A Demo a Day, A Year of Chemical Demonstrations”, by Gross, Bilash and Koob.  It has “Separating Metallic Iron from Cereal”, the simplest form of which is to put iron-fortified cereal in a plastic bag with a magnet and shake.  “Many cereal companies add fine powdered iron to their cereals as the U.S.RDA for iron.  Most people assume that cereals are fortified with a soluble ionic form of iron and not iron in its elemental form.  Once ingested, the iron will react with the acid in one’s digestive tract to form iron ions which in turn may be absorbed into the body.”

“Potato Candle” describes how to make a candle using a cylinder of potato as the candle wax and a Brazil nut for the wick.  It is designed to show the importance of observation, while grabbing the students’ attention.  The teacher who wrote this demo was big on showmanship;  after simply telling the students that they are observing a candle, he turns out the lights and asks them to write their observations.  He blows out the candle before it burns out and asks them to read their work aloud.  “Someone will see the wax melting, the braided wick, the carbon dioxide and water vapor coming off.  Remind them about observation and interpretation and how they might have to change their conclusions on the basis of new evidence.”

“If you have timed this correctly, there will only be about one minute left in the period.  Now eat the candle and walk out of the room – never tell them what it was!!!  This will convince your classes that you are an eccentric.  There is a lot to be said for this.”

There’s good variety in this book, so you might like to look at it.

I notice that there are similar books of demonstrations for the physical sciences, biological sciences, etc.  But they appear to be out of print! If anyone knows a good source for these, please post it!  Flinn Scientific appears to carry it (and here’s the Physical Science book).

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A few cool things about science that relate to the holidays.  I wrote this *before* Christmas, but, oh well, better late than never?

Dot Physics has a wonderful post on why Christmas tree lights stay lit even when one of them burns out, which is an unusual way for a series circuit to work.  Some nice explanations using Kirchoff’s laws make this a wonderful little post to stimulate a science lesson for the season.

From Sebastien Martin

I have an old post on why it’s a myth that no two snowflakes are the same shape.

And Morning Coffee Physics has a delightful little post on why snow sparkles. This is just my kind of science — gorgeously explanatory post about something we see every day.

Sebastien Martin at the Exploratorium has some beautiful images on his Flickr site showing how they used Christmas lights to demonstrate resonance and harmonics (see picture at right).

Steve Spangler Science gives you some ideas to deck the halls…holiday decorations with science.

And then of course there’s the old favorite Instant Snow (video on Teacher Tube).  Insta-Snow is made from sodium polyacrylate, a water-absorbing polymer.

And on the Ellen show….

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Here are some great gems from some really old posts over at Swans on Tea. Thanks to Rhett at DotPhysics for the technical assistance.

Robots doing amazing things:

Carbon dioxide is heavier than air (neat thing to try at home)

Weird psychology trick (how does he do that?)

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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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This is the last in a series of three posts on Dan Schwartz’s work on preparation for future learning, or helping students learn skills instead of rote facts so that they can apply their knowledge to new situations. All pictures in this post are courtesy of Dan Schwartz.

Contrasting cases

In the previous post, I showed Dan’s use of contrasting cases in helping students understand density and ratios. Why is it important to show students different cases, instead of the best single example of something? Well, he said, think about perception. Consider this circle:

We immediately recognize it as a circle. It is, after all, not a square.

But, in fact, it is many things. It’s a empty circle. It’s a circle created with a black line. It’s a largish circle. Here are a bunch of contrasts to this circle:

We’re abstracting “circle-ness” from the single example, but that’s because we recognize circle-ness already. These contrasting cases would be important if we were first learning about circles.

Here are some contrasting cases of something familiar to us:

After all, what is the best way to teach Japanese speakers to say the sound “L,” which doesn’t exist in their language? Give them the purest example of an “L” sound that you can find? No, it’s to let them hear “R” and “M” and all the other sounds, so they know what the “L” is NOT in addition to what it IS.

But, this is what we do in instruction! We give students the purest example of something that we can. Consider, for example, this picture.

This is a perfect example of this breed. Now, tell me which one of the following is the same breed?

An expert will look at the width of the ears, the curve of the nose. But a novice can’t look at these pictures and see the immediate resemblance to the example picture. (I forget which one was the correct answer, but I think it’s the last one. The hair length is an extraneous feature, the ear shape is most important.)

It would have helped if, first, an expert had used the following picture with contrasting cases to help you learn about ear shape (what does “rounded” ear shape look like? How wide is “wide”?). You need to be oriented to understand the key structures in what you’re seeing. You can’t just look at the picture below and learn from it, though — a bunch of different examples are confusing to a novice. The expert’s role is to help them make sense of the different cases.

An example activity

Here, for example, is his activity where he asks students to invent a reliability index for a pitching machine. He gives them several different cases so they have to find a general solution which fits all these cases. This, after all, is what we do in science – to find a general solution that fits many cases.

In my previous post, I gave his activity for teaching density using clowns in buses.

The way he uses these in the classroom is to have students explain their classmates’ solutions to each other. That means that each student’s solution has to be written clearly enough so that someone else can understand it. This act of public “publishing” of the results gives students a bit more motivation to come up with a good solution. On the other hand, the goal of this task is NOT to come up with the “right” solution! It’s to prepare students to understand the expert solution (in this case, the idea of variance) when it’s presented.

Expert blind spot

As experts in a subject, we know an amazing amount. What we’ve learned has been compressed into a bunch of huge steps. We don’t recognize the huge number of things that we’re doing when we do what seems to us to be a single step (such as computing a ratio). We need to decompile our knowledge for the novices. In order to do this, it’s good to have an intelligent novice around — someone to ask us a bunch of questions at every step so that we can see what it is that we are doing in any task. Once you’ve discovered some key, fundamental idea that is needed to solve the problem, that’s a great place to put an invention activity. Examples are density, vectors, variance, and other fundamentals.

What these activities are not:

• Not just brainstorming
• Not puzzlers
• Requiring a flash of insight to solve
• Not pure “discovery” tasks
• Not to replace standard instruction

What these activities ARE:

• Students make answers for one case, and recognize it doesn’t generalize to the others
• Learning is incremental
• Students don’t have to find the right solution to benefit from them
• Students should start to notice the variables that matter
• Students are told to invent a form of representation
• They are visual
• These activities are used strategically to communicate fundamental key ideas (like density). Not used for everything.
• Prepares student for standard instruction

To make these cases yourself:

• Think about your own knowledge to isolate key concepts
• Think of each case as an experimental treatment to isolate a key variable
• Or, think of formulas or units and make sure they contrast for each case
• Have some sense of likely misconceptions so you can create cases that will highlight probable “traps” students might fall into
• Make them approachable. You don’t have to be as frivolous as the clowns example, but it should be done in a context that’s different from what you want students to learn (like physics). Then you can help students map it into the new context.

What about assessment?

Dan’s main point is that our assessments need to change in order to use this kind of instruction. If we value students’ showing that their learning is adaptive, we have to give them a chance to demonstrate this on a test, to demonstrate an expert level of perception.

What do I mean by expert level of perception?

What do the images below say to you?

The novice answer (“car,” “bird”) is not very precise.

The expert answer (“2007 BMW X5″ or “indigo bunting”) is much more precise, and relies on deep recognition of various features. We should test students on this more broad ability to apply their knowledge. For instance, geology students should be able to extract some important features from this picture of a landslide:

This doesn’t have to be a perceptual test — in the previous post, the “green people” vs. “blue people” example relied on students ability to recognize the variability in a data set.

I think this stuff is incredibly powerful. Let me know of any more activities that you come up with or you know about!

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A fabulous science activity from Sebastien Martin over at the Exploratorium, via teacher Bree Barnett — visualizing kinetics with LED lights. See detailed instructions and more pictures over at that blog post.

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A teacher asked for a good experiment to show 8th graders that gas has mass.  “We have used balloons in the past,” she says, “but some of the kids still don’t make the connection.”

Paul Doherty replied:

I like to get a big weather balloon from a surplus store , inflate it until it is 1 meter in diameter or a little more and then a second balloon that is deflated.

Have a kid stand and throw the empty balloon at the back of their head…they feel almost no force.

Then throw the full one. It packs a noticeable punch due to the mass of moving air. the mass approaches a kilogram.

Of course you cannot weigh it using a scale due to buoyancy. You can only feel the mass by accelerating it or decelerating it.

And Eric Muller added:

Get some dry ice. It is solid Carbon Dioxide and it has noticeable mass. Lots of stores around the bay area sell dry ice. Many Safeways, Albertsons, bait shops, liquor stores, ice distributors and welding supply companies carry dry ice.

Weigh (or Mass) a chunk of dry ice. Put the chunk in a plastic bag and tie it off. It will sublimate and turn into a gas. The bag will expand noticeable. A solid, 44gram chunk of dry ice (that’s the size of a couple of fingers) will expand to around 22.4 liters of gas.

Gas has mass!

Pressure Pumper

Here’s a cheap little toy from Arbor Scientific that also shows that air has mass — pump air into a small bottle using the pressure pumper. Why does it increase in mass?

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A neat observation from one of the staff physicists at the Exploratorium:

Here is a little game to play with farsighted and nearsighted glasses. Ask all your students who wear glasses to put them on and stand up. Walk up to each of them, look into their eyes and you will be able to tell them if they are nearsighted or farsighted.

If they are farsighted (and therefore have convex lenses) you will see the contour of their cheeks move OUT when viewed through their glasses. If they are nearsighted (and therefore have concave lenses) you will see the contour of their cheeks move IN when viewed through their glasses. This is a nice opportunity for a ray diagram or two! Astigmatism, graded lenses and bifocals can make this more difficult, but it is fun to try. The stronger the prescription the better. Holding far and nearsighted glasses up to colored lights or shadows also produces discriminating effects.

This could be a great “nature of science” activity! Tell them you have mystical powers and can see the shape of their retina (or some such garbage) just by looking deeply into their eyes. (Of course, it won’t work with any students who wear contacts! Why not? Can they guess how you do it?)

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