Swimming Creatures Lesson 7: Sharks and Rays

4/22/2009
In this lesson we learned about Chondrichthyes, cartilaginous fish, such as sharks and rays. We learned that the scales of sharks and rays are like teeth and are called dermal denticles (skin teeth!). And we learned the differences between a shark and a ray, the differences between a sting ray and manta ray and how to tell the size of a shark by their teeth. Dylan is measuring the teeth in the book and did a good job recalling that every inch of tooth equals 10 feet of shark length. We learned how the ampullae of Lorenzini help a shark detect electrical signals given off by other animals in the water, which helps it hunt. Our experiment this lesson was to determine whether salt water or fresh water conducts electricity better.
Nathan and Dylan did the experiment together and they both hypothesized that the salt water would conduct electricity better (they both listened well during the reading).
Nathan used more salt than required in the directions and had some interesting reactions, besides discovering that the salt water does indeed conduct electricity better. The salt began to corrode the metal clips and turned the water around it black.
Jordan wasn't around to see their experiment was was clueless as to what would happen. He wasn't surprised to see the light not go on with the fresh water; but, was surprised the salt water conducted electricity enough to make the light bulb shine dimly. I reminded him that sharks can detect electrical signals in the water. He made the connection then. :-) He also noticed the reaction to the metal from the salt and thought that was cool. The homeschool mom in me wanted to rabbit trail and see if we can make electricity with a lemon. . . maybe another day!
We also learned some new words like agnatha and anadromous. And what a lamprey and a hagfish is and how they feed. And that a hagfish can tie itself in a knot because it has no backbone.
We drew a typical shark and ray in our notebooks talking about some of the characteristics of each. Then we note-booked on the difference between a shark and a ray. Then we did a note-booking page on lamprey and hagfish. Here are two of Nathan's notebooking pages:
"Did you know that shark's can smell fish from miles away because they have their ampullae of Lorenzini between their eye and the tip of the snout. And sharks have a great sense of hearing so it is easy to find a fish."
"Did you know that Manta Rays have hand like fins to guide plankton in it's mouth. And did you know that manta ray's weigh about 3,000 pounds and people ride on manta rays because manta rays do not sting."
Here are some more writings of what Nathan remembered from this lesson: "Did you know that lampreys suck on fish blood. In the picture above, lampreys are sucking on a tuna fish." "Did you know that Agnatha means without jaw and hagfish do not have a jaw. Did you know that when a hagfish is scared it will poop out 2 gallons of slime."
(Actually it vomits it up and is considered to be very repulsive by the fishermen who accidentally catch one of these fish). And I can see I need to remind him to use a question mark when he asks a question! I love his voice when he writes, it is similar to the friendly, personal style author Jeanie Fulbright writes in.
Here is a video we found on what a small amount of slime can grow!
Another interesting video we found:
Delightful Links:

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