A classic investigation into the chemistry of bones.

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This activity is from my Experiment of the Week Newsletter. It is free, and will let you know about new resources on this site.

This time, we are going to take a look at a classic science experiment that has been used for a LONG time. In fact, it was already an old classic when I was a kid, and that was quite a while ago.

The experiment involves the link between our senses of taste and smell. Often it is done with apples and potatoes, but there is enough textural difference that you can often tell which is which. I have found that the results are much stronger with flavored candy. To try this, you will need:

• candy that has the same shape and texture, but comes in different flavors.

OK, lets begin with the standard experiment. Be sure that your pieces of candy will all feel the same in your mouth, and that they have distinctive flavors. If you don't see the candy, the taste should be your only clue to what flavor it is.

If you have a friend to help, then close your eyes, hold your nose, and have her give you one of the pieces of candy. Keeping eyes and nose tightly closed, put the candy in your mouth. You will taste a sweet taste, and probably some sour too, but you may be surprised that you can't tell if the candy is cherry, lime, orange, or some other flavor.

Then move your hand away from your nose, so you can breath normally. Yum! You get a sudden burst of flavor, telling you exactly what kind of candy it is. The reason for this is that your tongue has flavor receptors for basic flavors, such as sweet, salty, sour, bitter, and umami (the savory taste of meat.) Most of the other flavors that you taste are tied in with your sense of smell. If you can't smell them, then you don't taste them. That is why food tastes so bland when you have a cold.

But wait a minute! Your parents probably taught you to chew with your mouth closed. How can the smell get out of your mouth to go up your nose, so you can smell it? And your mouth stayed closed when you released your nose, but you still got that sudden burst of flavor. What is really happening?

Well, the smell of the food does have to reach your nose for you to taste all of those subtle flavors, but there is another path that those smells can take. Instead of inhaling those smells through your nose, you are exhaling them. As you breath out through your nose, your breath carries the smells from your mouth into your nose. You were not holding your nose to prevent you from inhaling the smells. Instead, you were blocking the way, so you could not exhale the smells through your nose.

Now that you are tasting the flavor, hold your nose again. After a second or two, the flavor disappears again.

So what if you just held your breath instead of holding your nose? Try that.

No, really. Try it and see for your self.

What did you find? Even holding your breath, you probably still tasted some of the flavor. Why? Think about what happens when you chew or swallow. Your mouth changes shape, your throat moves, your tongue moves around. All of that movement causes the air in your throat to move, forcing some of it up into your nose. It carries some of the smell to your nose even if you don't exhale. By blocking your nose, you pressurize it, preventing the air from your mouth from moving up.

OK, take it one more step. Hold your nose until the flavor goes away. Then release your nose, and inhale. While you are inhaling, keep your mouth closed. You probably won't taste the flavor. Then exhale. Ahh, there is the flavor again. The main path that the smells take to let you taste your food is up through the back of your throat. It is not inhaling that brings you the flavor. Exhaling is what gives you those wonderful flavors.

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As we saw in the Scavengers and Decomposers video, mushrooms play a major role in the food web as decomposers, breaking down wood and other plant material, and putting some of that energy back into the food web. There are over 14,000 species of mushrooms, and many of them look very similar. We use many different characteristics to identify them, including their shape, their color, their texture, where they grow, and many other things. One important test that can help identify a mushroom is its spore print. Spore prints are easy to make, and some are quite beautiful.

To make a spore print, you will need:

• white paper
• black paper
• one or more mature mushrooms
• scissors or a knife
• clear, acrylic spray (optional)

First you will need some mushrooms. They need to be mature, which means that they have opened fully, often into the shape of an open umbrella. If you don't have any mushrooms growing around your house, you can usually buy them at your local grocery store. You don't want the small, white, button mushrooms. They are not mature yet. Instead, look for the pancake shaped Portabella mushrooms. That is what the button mushrooms would look like if they grew and matured.

Looking at the underside of the mushroom, you may see many thin ridges and grooves radiating from the center. These are the gills. No, they are not used for breathing like the gills of a fish, but they have a similar shape. The gills are where the spores are produced. OK, so what are spores? Spores do much the same job for mushrooms that seeds do for flowering plants. The difference is that mushroom spores are very tiny (You usually need a microscope to see an individual spore.), they don't contain the stored food that seeds have, and they don't have to be pollinated. Each tiny spore is capable of growing into a new mushroom. Not all mushrooms have gills. Some have pores or other openings, but they can still produce spore prints.

If possible, collect two specimens of each type of mushroom. Why? Some mushrooms have white spores, while others have dark colored spores, so for each kind of mushroom, we will put one on white paper and the other on black paper. If the mushroom has white spores, they will be hard to see on the white paper, but will stand out on the black paper. If the spores are dark, then the white paper will make them easy to see.

You want the mushroom to lie flat on the paper, so use scissors or a sharp knife to remove the stem. As you do that, watch closely. Many mushrooms will change color when they are cut or broken. This mushroom was white when it was first cut, but within seconds the cut changed to a dark, rusty red. That color change is another useful trait that can help you identify mushrooms. Not all mushrooms have dramatic color changes, so if you are using a Portabella, you will probably not see much at first, but it will slowly darken.

Place the mushrooms with the gill side down on the sheets of paper. Put them in a place where they will not be disturbed, and let them sit overnight. The spores are so small that even a gentle breeze can carry them away, so if you have a fan or air vent nearby, you should cover the mushrooms with a bowl or a box. As the mushroom sits there, it releases spores, which fall onto the paper.

By the following morning, you will probably be able to see a dusting of spores on the paper at the edge of the mushroom. Very carefully, lift the mushroom off of the paper, being sure not to let it shift or slide. Underneath, you should find a spore print in the shape of the mushroom, usually showing the pattern of the gills.

Different mushrooms form different colored spores. This one had spores that were a very nice green color. You can preserve your spore print by very gently spraying it with a clear, acrylic spray. This spray is often used to protect art projects. Don't hold the spray can too close, as that will blow away many of the spores, and form drips that will mess up your spore print.

On the sheet of paper, write the date and location where the mushroom was collected. You might want to attach a photograph or drawing, and any other information about color changes when cut, texture, shape, etc. If you are able to identify your mushroom, then write its common name and its scientific name on the paper too. You may want to start a collection of mushroom spore prints, and might even decide to become a Mycologist, a scientist who studies mushrooms and other fungi.

This video is part of the new Food Web Curriculum Unit. While there is still a LOT of content to be added, you can look around the unit on the Food Web page.

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Home - The Food Web

A food web is a way of seeing how energy is transferred from organism to organism. All living things need energy. They use it to move, to grow, to reproduce. That energy has to come from someplace. Drawing a food web is a great way to get an idea of how that energy is captured by producers, and passed from organism to organism. It helps us see that even things that we usually don't like, such as weeds and mosquitos, play an important role in the ecosystem.

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At some time in your life, you have probably heard that in a fall, cats always land on their feet. Is that true? Well, usually it is. Cats have the amazing ability to turn themselves right side up as they are falling. That does not mean that a fall will not injure them. If you fell off a tall building, would landing on your feet keep you from being injured? No. The same is true for cats. Landing on their feet lets their legs flex to absorb some of the impact, and keeps the impact from directly hitting more delicate bones, but cats do not have any magical protection against injury from falling.

What is amazing is the way that they perform this trick of landing on their feet. They do it by combining fast reflexes with the laws of physics. To get an idea of how they do it, you will need:

• a chair that swivels easily. Common office chairs work very well for this.
• an open area with plenty of room, so you don't break any lamps, furniture, or legs.

OK, lets start by thinking about what the cat has to accomplish. It is falling, which means that it does not have anything to push or pull on to turn itself. Instead of falling, you can get an idea of the problem that they face by sitting in the swivel chair. Make sure that you have plenty of open space around you by holding your feet straight out and turning in a complete circle. You want at least a foot or two of open space between your feet and the closest thing you could bump into.

Now lets get an idea of the challenge the cat faces. Sit cross legged in the chair, so your feet do not stick out. Put your arms in your lap, with your elbows tucked in against your side. Your challenge is to turn the chair around so that you are facing the opposite direction by twisting your body from side to side. Don't move your arms or legs. You can twist at the waist and your neck, but nothing else. DON'T HURT YOURSELF! You will find that you can turn the chair slightly to the right by twisting your body to the left. The problem is that when you twist back to the right, the chair spins back to the left, winding up back where it started. Wiggling the chair back and forth is no problem, but you don't get very far towards turning the chair around.

To see how the cat manages its trick, lets try something different. Keep your elbows at your side, but extend your hands out to the side. Then try twisting again. This time you will notice that the same motions cause you to swivel back and forth farther. Extend your arms all the way out, and try it again. Now, you are really moving back and forth. As you move your arms further and farther from your body, you can use their inertia (resistance to changes in motion) to push against.

You still have the problem that you are twisting back and forth. Remember that you are a falling cat, and you need to turn yourself so you can land on your feet. That leads us to your next step.

Extend your arms all the way out, and then twist to your left. That swivels the chair and your body to the right. Now, before you twist the other direction, pull your arms back in close to your body. Since your arms are in close, you can turn back without swiveling the chair back in the other direction. You have turned part of the way around, and you are back into the position to do it again. Extend your arms again, and repeat the process. It took me three arm swings to turn my chair around so that I was facing in the opposite direction.

Cats do this maneuver even better because they are incredibly flexible. They extend their front legs while pulling in their back legs, and then twist in the direction they want to turn. Very quickly, they pull in their front legs, and extend their back legs, making another quick twist that lets them wind up facing as much as 180° from their original direction.

Although cats are incredibly fast at this, it still takes time. Cats that fall from a very short distance do not have enough time to twist around. Also remember that landing on their feet does not mean that they don't get hurt during a fall. Their reflexes and flexibility can help them land in the best position, but they can still suffer injuries and broken bones from a fall; so you should not use your cat as an experimental subject.

If you want to experiment further, try holding a weight in each hand as you do the experiment. Do you think that will make it work better or worse? Try experimenting with different arm motions. I had interesting results from making the same motions that you would use for paddling a canoe.

In a recent video, we dissected a roast chicken, seeing how the muscles connected to bones to power its wings. This time, we are going to explore a very different arrangement for flight by examining the flight of insects. To try this, you will need: - 2 popsicle sticks or tongue depressors - a hollow, rubber ball - a sharp knife - an adult to use the shape knife (Adults are easier to bandage if they cut themselves.)
Lets start by thinking about bird wings. As we saw in the Bird Bones video, they are made up of several bones, connected at joints, and powered by muscles. An insect's wings are very different. Each wing is all one piece, made of chiton, the same substance that makes its exoskeleton. The wings do not have any joints or muscles. So how do they move?
We can see that by constructing a model, a representation of the insect that will help us understand what is happening. Sometimes scientists use computer models, developing computer programs to simulate a specific event. Other times they construct models from materials to allow them to test ideas. That is what we will do. You need a rubber ball that is hollow, not solid rubber. You can find these in the toy department in many stores. Pick a point on the ball and carefully use the knife to make a cut that is about as long as your popsicle stick is wide. Carefully, insert the end of a popsicle stick into the cut.
Looking at the ball, imagine the face of a clock. Turn the ball until the stick is about at 2:00 on the imaginary clock face. Then make a mark on the ball at about the 10:00 point. Make another cut there, and insert the other stick. Your model butterfly is now complete.
The ball represents the body of the insect. Instead of having muscles attached directly to their wings, most insects move their wings by changing the shape of their bodies. Muscles attach to the top and bottom of the body. Contracting those muscles flattens the body, causing the wings to move up. You can see that by squeezing the ball from top to bottom.
By relaxing those muscles and contracting others, the body changes shape again, moving the wings downwards. You can see that relaxing the hand that is squeezing top to bottom, and instead squeezing the ball from side to side. As the insect flies, its body is flexed by muscles, causing the wings to move up and down. By controlling how much each set of muscles contracts, the insect can change the movement of its wings to control its flight.

This method of flight is used by most insects, including bees, wasps, flies, butterflies, and moths. There are a few insects, most notably Dragonflies and Damselflies, that do have muscles attached to the base of their wings. This lets them control each wing independently, making them very agile fliers.

This week's experiment comes from an email I got from a student. (Thanks Darius!) He wanted to know what causes your knuckles to pop. To try this, you will need:

- your hands

First, not everyone's knuckles will pop, and some pop more than others. Other joints in your body may also pop, some for the same reason as your knuckles, and some for other reasons.

There are different techniques for popping your knuckles, but they all work in basically the same way, by forcing the two bones of the joint to move farther apart. Probably the simplest way to do this is to interlace the fingers of your hands. Then turn your hands so that your palms are away from your body, and gently bend your fingers backwards. THIS SHOULD NOT HURT. DO NOT FORCE YOUR JOINT TO THE POINT WHERE IT IS PAINFUL. As the pressure builds, you should hear a pop from one or more of your knuckles.

If you search the internet for the answer to this question, you will find all sorts of answers, ranging from good explanations to wild guesses and pure fiction. The most comprehensive answer that I found was from "A bioengineering study of cavitation in the metacarpophalangeal joint" by
A. Unsworth, D. Dowson, AND V. Wright, from the Bioengineering Group for the study ofHuman Joints, the University of Leeds. If you want to read the article, you can find it here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1005793/

If you don't want to wade through the article, the sound is caused by a process called cavitation. OK, so what is cavitation?

Lets think for a moment about the properties of liquids. Liquids take on the shape of their container, but they maintain their volume. You can't squeeze water into a smaller space, or stretch it to fill a larger space. If you try to stretch water into a larger space, at first, nothing seems to happen, but you are reducing the pressure of the liquid. When the pull gets strong enough, and the liquid pressure is low enough, some of the liquid changes to a gas, forming a bubble. Unlike the liquid, the gas in the bubble can be stretched into a larger space. That reduces the pull on the liquid, which raises its pressure. At that point, the gas in the bubble almost instantly changes back to a liquid, collapsing the bubble.

The same thing happens when you pop your knuckles. As you apply pressure to your knuckle joint, it forces the ends of the bones apart. Surrounding the joint is a liquid called synovial fluid. Moving the bones apart pulls on the fluid. If it was a gas, it would expand to fill the space as the bones separate. Since it is a fluid, it stays the same size, and its fluid pressure decreases. As you pull harder, the fluid's pressure gets lower and lower, until it reaches the point where the pressure is low enough to let some of the liquid change to a gas, forming a bubble. The bubble expands in response to the pull, which lowers the stress on the fluid. That lets the fluid's pressure go back to normal, which lets the gas change back into a liquid, and the bubble collapses. That collapse produces a loud sound.

Cavitation can be seen in other situations where liquids are subjected to very low pressures. Submarines have to be careful about cavitation from their propellers, as the sound can give away their position. An animal called the Pistol Shrimp snaps its claw fast enough to cause cavitation, producing a sound that is loud enough to stun or kill nearby fish.

Another question that frequently pops up with this subject is why you can usually only pop a joint once, and then you have to wait 20 to 30 minutes before it will pop again. When the low pressure causes the bubble of water vapor, it also causes some of the dissolved gases in the fluid to form bubbles. These bubbles, made up mostly of carbon dioxide, do not instantly collapse, remaining until the gases are reabsorbed back into the fluid. This usually takes 20 to 30 minutes. If you try cracking the joint again before those bubbles are reabsorbed, the bubbles of gas expand, preventing the pressure buildup that causes cavitation.

The other question that comes up frequently is whether knuckle cracking causes arthritis or other damage. Not many studies have been done, but those that have been done do not show any link between knuckle popping and arthritis.

Have a wonder-filled week.

Dissect a bird to compare its skeleton with ours.

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Link to Producers

Link to Primary Consumers

Take the next step up the foodchain to take a look at predators.

The idea for this week's experiment came to me while I was moving our stuff into the hotel where we will be staying for the next 3 weeks. The room is on the second floor and we do not travel light. Basically we take everything except the kitchen sink. We would probably take that as well, but it is too hard to disconnect. After the 14th trip up the stairs, I started to think about muscles and how they get tired. One thing lead to another, and soon I had this week's experiment written. Why do your muscles get tired? And more important, why does your heart, which is also a muscle, not get tired? To find out, you will need:

- you

Your heart is a group of muscles which pump the blood through your body. To get an idea of its size, make a fist. That is about the same size as your heart. Pretending for a minute that your fist is your heart, lets take the idea a little farther. Open you hand about half way and then close it again. If you do that over and over, you can imagine that it is your heart beating. You can even make heart sounds (bump-bump) if you (bump-bump) want to. (bump-bump)

Keep this pretend heart beating as you read this. Soon your hand will begin to get tired. If you keep opening and closing your hand even after you are tired, it will begin to hurt. Why?

When you move your muscles, a chemical reaction takes place. Normally, this chemical reaction needs oxygen. We get this oxygen when we breath. The air moves into your lungs and the oxygen is absorbed by your blood. Your blood carries the oxygen to your muscles. As long as the muscle has plenty of oxygen, everything is fine and it can keep on moving.

If the muscle uses up oxygen faster than the blood can deliver it, then what happens? The muscle does not instantly shut down when the oxygen runs out. Instead, a different chemical reaction takes over. It lets your muscles move even if they do not have enough oxygen. The problem with this backup system is that the reaction makes a chemical called lactic acid. This acid irritates the muscle, making it hurt. If you overdo it, your muscles will be sore the next day. Keep overdoing it and you can damage the muscle.

If your heart is made of muscle, why doesn't it get tired? After all, your heart beats all day and all night, for your entire life. A large part of the answer has to do with blood. Your heart is between your lungs. Blood picks up oxygen from the lungs and flows directly to the heart. This insures that the heart always has plenty of oxygen, so it does not get tired. The one exception is if the blood vessels that lead to your heart get blocked. Then the heart muscles run low on oxygen and get tired. The pain that you feel is what tells you that you are having a heart attack.

Athletes exercise regularly to increase the blood flowing to their muscles. If the muscles get more blood, they get more oxygen. Then they can work harder and longer before they get tired. Right now, I could use some extra oxygen, so I could unload the rest of our stuff.

How do you feel? No, I don't mean are you happy or sad? Touch the back of your hand. Did you feel it? How? When you touched your hand, you pressed on nerves in your skin. These nerves reacted and sent a message to your brain, telling you that something touched your hand. Some parts of your skin have more nerves than others. This week, we are going to examine how these nerves are arranged. You will need:

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This week's experiment is one that we used for teaching about birds back when I worked in the Education Department at the Memphis Pink Palace Museum. On our trip, we went by to say Hi to old friends, which brought back tons of great memories. This is one of the fun things my brain dredged up.

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