Friday, August 16, 2013

Just Wondering: How Do Fish Breathe?

Seconda won a goldfish at the Howard County Fair last week. Mr. BibbleBubble is our first pet.

We set him up in big glass bowl with some of those glass vase filler things and put him on the counter. He's a charming little guy, I tell you, because he turned my staunchly No Pets Allowed heart into mush.

Mr. BibbleBubble has become quite the topic of conversation around here, so we were exactly do fish breathe? Here's the AP Biology explanation:

If your elementary schoolers are anything like mine, chances are that they are not quite ready for AP Biology. Big words and phrases like diffusion and concentration gradient are just not in their working vocabularies. Still, they are totally capable of understanding fish respiration, so we decided to figure out just what on Earth he was talking about.

First, we talked about cells being the basic parts of all living things. We didn't go into too much depth there, just noted that cells are surrounded by membranes, and membranes have holes in them that let only somethings in or out of the cell. We imagined putting salt and grapes in a jar, mixing them up, then pouring them into a colander set over a bowl. The grapes stay in the colander but the salt goes through to the bowl. (I should have said tomatoes, because who wants to eat salty grapes, really?)

As I was searching for more demonstrations, I came across a simple diffusion demo involving gummy bears. Terza was the only one with me at the time, so she got to describe it to her sisters. "This guy...he just took a gummy bear...and put it in water, justplainwater...and it GREW!"

"Well, how do you think that happened?" I asked.

Prima thought that since sugar dissolves in water, the sugar came out of the gummy bears allowing the water to go in. I asked, "How could we see if that's what happened? How could we see if the sugar left the gummy bear and went into the water?"

Seconda piped up, "Taste it!" (If there's tasting involved, she's all in.)

Terza decided she had a different idea. "I think the sugar stayed in and the gummy bear grew because the water just went in."

"How did the water get in?" I asked.

Just so I didn't forget that Terza thinks like most six-year old concrete-operational thinkers, she answered, "Well, the gummy bear has a face, so the water probably went in through its eyes and mouth."

"Hmm. Well, what if we took a gummy Easter egg and put it in the water? Would it grow?"


"How would the water get in? It doesn't have a face."

After a pause, Terza said, "Cracks!"


A conversation is all well and good, but an experience is even better. We set up our own growing gummy demo using dinosaur-shaped gummy vitamins. Here's the before, during, and after:




The girls tested Prima's idea that some of the sugar left the gummy dino and entered the water. It was inconclusive for sugar, but they did detect some of the artificial fruit flavor, and they didn't like it one bit. Next, they ate the gummies, and again, they were grossed out. I suspect they'll never look at Mr. BibbleBubble the same again!

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