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CHECKING THE PULSE OF EARTHWORMS
Now we will pretend to be earth-worm experts! Maybe we should start a fan club. We could call our club the "Benevolent and Paternal Order of Earthworms."
This project seems to be a little cruel, if you don't know at the beginning, that earthworms can live equally well underwater, underground, and above ground. They don't have organs for breathing. The oxygen they need to live is absorbed through their skin, directly into their blood.
We have four jars of the same size and shape. We will fill two with water. We also have four earthworms that are the same size. Each worm will be placed into a jar.
One jar with water and one without (but both having worms) will be placed onto a shelf where they will be left alone. We want to make sure that they will not be in direct sunlight. The worm in the jar without water would be dehydrated (means "dried out," pronounced "dee-HIGH-dray- ted") if it were in direct sunlight. If the worm's skin were to become dry, the gases could not pass through it, it would receive no oxygen, and it would die.
The other pair of jars, one with and one without water, both with worms, will be placed into the refrigerator. NOT THE FREEZER. We will leave all jars where they are for one full day.
Next day, we will take the worms out of the jars, and put them onto a sheet of waxed paper. We can't label the worms, but we should section off the paper and label it so we know which worm came from which environment.
On top of the worms' bodies, we should see a large blood vessel that pulses, which means it expands and contracts rhythmically. We will count the pulses, by watching the clock's second hand and counting how many "beats" we see in one minute.
We should notice that the worms from the refrigerator have fewer pulses because they were less active than the worms that were on the shelf. It takes more oxygen to be active than it does to be idle. Warm worms move around more than cool worms, so warm worms use more oxygen, and their pulses are faster.
We use more oxygen when we run than when we sit quietly. We can tell that by the fact that when we run, we breathe faster and harder, and our hearts (pulses) beat faster, than if we are quiet.
When bears hibernate (pronounced "HIGH-ber-nate") for the winter, their hearts slow so much that they hardly beat at all. They don't need much oxygen when all they do is to sleep.
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