Introduction to the Topic, Focus Words

1. READER'S THEATER

Characters: Yeast cell, Skin cell, Melanocyte (melanin-producing cell), Red blood cell, Endothelial cell, Dendritic cell

Trey is kneading bread dough. He has a tiny scratch on the skin of his thumb, too small to see. But it’s big enough for a yeast cell from the bread dough to get into.

Yeast cell: Wait, what happened? Where am I? One minute I’m living the good life in a batch of bread dough along with all my yeast pals and the next I’m… I dunno… Who are all these weird cells? Hey you, what is this place?

Skin cell: We’re skin cells. You’re inside the skin on Trey’s thumb. You’re down near the bottom of the outer layer of the skin, the epidermis. We don’t usually get visitors like you down here in the living part of the skin.

Yeast cell: The living part? Is there a nonliving part?

Skin cell: Well, yeah. Up there at the surface, those are dead skin cells that have moved up and hardened to make a tough layer that protects all of us here below. I’ll gradually move up there, and someday I’ll take my turn on the front lines. It’s worth it to keep the whole body going.

Yeast cell: That’s nuts. Why would you sacrifice yourself for all these other cells in this guy Trey’s body? What’s in it for you? With us baker’s yeast cells in the bread dough, it’s every cell for itself. We’re free and independent. You look like you’re stuck there with all those other cells, like a brick in a wall. What a pathetic, helpless existence.

Skin cell: You’re missing the point. It’s not a helpless existence. I help the other cells in the body and they help me. It’s a big collection of specialists who help each other out in all kinds of ways.

Yeast cell: Oh yeah? Like how?

Melanocyte: Excuse me, special delivery. Who ordered the melanin?

Yeast cell: The what?

Skin cell: Melanin. That’s the pigment that makes people’s skin dark and protects them from the sun’s ultraviolet radiation. Yeah, that’s for me.

Melanocyte: Okay, here you go, pal. If Trey goes out in the sunlight, I’ll make some extra for you. We gotta stop that ultraviolet radiation from damaging our DNA.

Skin cell: Okay, thanks buddy. I’ll keep blocking those rays.

Yeast cell: So that other cell helps you protect yourself and other cells farther inside from the sunlight?

Skin cell: Yes, that’s just one way we cooperate. We also—

Red blood cell: Hey there, oxygen anybody?

Skin cell: Ooo, yeah, I’ll take some! I just got a shipment of sugar from the digestive system a moment ago. I need that oxygen to help me get the energy out of the sugar.

Red blood cell: Sounds good—here’s your oxygen.

Endothelial cell: [in the blood vessel wall, talking to red blood cell] Okay, hold on. You gotta stay inside the blood vessel, but I can let you pass that oxygen on through.

Red blood cell: Sure, sure, I know the drill. I’ll just let that oxygen defuse on through, like this… Okay. Now, you got any carbon dioxide you want to get rid of?

Skin cell: You bet. Here: carbon dioxide, all ready to exhale. Thank all those cells in the lungs for me when you see them, will you?

Red blood cell: Sure, I’ll be back in the lungs in less than a minute. In fact, the cardiac muscle cells must be pulling together for another heartbeat right about now. I can feel the pulse coming, and here I goooooooooo! [The red blood cell is swept away down the blood vessel.]

Yeast cell: Did that blood cell just change color?

Endothelial cell: Oh yeah, they do that. The more oxygen they’re carrying, the redder the red blood cells are. They get kind of bluish purple as they unload oxygen and pick up carbon dioxide. Then they do a big gas exchange in the lungs, getting rid of waste carbon dioxide and taking on a fresh cargo of oxygen. They come away from the lungs bright red again for another trip around the body. Each of them leaves the heart and returns to it every 20 seconds or so! Always on the go, always in a hurry.

Skin cell: Yeah, those red cells get around. They’ve got all the gossip. One of them was just telling me about what happened in the liver this morning when Trey was playing soccer in his PE class. Trey was running around so much that his fat cells started shipping fatty acids to the liver to be converted into sugars. Those liver cells were crazy busy doing the conversion and sending the sugar to fuel Trey’s skeletal muscle cells as fast as they could. And out here in the skin, everybody was talking about how the blood vessels were widening and the sweat glands were pumping water into the air to cool things off…

Yeast cell: Whoa, whoa, too complicated! I manage all that kind of thing myself. I eat sugar, process it, get the energy and building materials I need, and get rid of waste. Done! I can do everything by myself.

Skin cell: Can you play soccer? Can you get up and go find sugar if it doesn’t come to you? You have sugar to eat because Trey put you in bread dough. But Trey doesn’t have to wait. He can move around and get food—or make it. His brain cells can work together to process his experiences, and learn and remember things. His bone cells make bones and his muscle cells move those bones around. He can go places and play sports and video games, read books and talk about them with his friends, all because we cells do our special jobs and work together for the whole organism.

Yeast cell: You don’t get it. The key to getting by is keeping things as simple as possible. Playing soccer? Learning things? You know, reckoning by sheer mass, most life on earth is made up of single celled organisms like myself, and I can tell you, we don’t waste a whole lot of time “learning things”!

Skin cell: Well if ignorance is bliss, you yeast cells must be in heaven. I know some nerve cells who would find your lack of intellectual initiative really disturbing. You just float around eating, burping, growing, and dividing when you get too big. Lazy!

Yeast cell: Hey, there’s a lot of complicated chemistry that goes into eating and burping! That’s enough trouble for me. But anyway, now that I’m here, I guess I might as well make myself at home. Yeah, this isn’t such a bad location. Trey eats, his digestive system breaks down the food and eventually ships sugar through the bloodstream to this neighborhood in the skin, and I’ll just enjoy the food without having to do anything for anybody else.

Skin cell: Hey, that’s not fair. You can’t just hang out here and take what the body has to offer without making a contribution.

Yeast cell: Oh I can’t, can’t I? Who’s going to stop me?

Dendritic cell: Yo, what’s going on here? Is this cell bothering you, Skinny?

Skin cell: Not much, but it does have kind of a rotten attitude.

Dendritic cell: [talking to yeast cell] Who are you, anyway?

Yeast cell: Hey, keep your pseudopods to yourself. Mind your own business. Who do you think you are?

Dendritic cell: My business is knowing who “I” am, and who everybody else is. My business is knowing which cells are and are not Trey, which cells are self and which are non-self. I’m one of the white blood cells that make up Trey’s immune system and protects him from germs. And you, buddy, smell funny to me. Not right, not right at all.

Yeast cell: What are you doing?!

Skin cell: Bye-bye! It was interesting meeting you.

Dendritic cell: [swallowing the yeast cell] GULP! Hmmm. Yep, that guy definitely tastes unfamiliar. Listen, I better head for the nearest lymph node while I break down our, um, visitor into tiny pieces. The white blood cells in the lymph node will be able to tell if any of those pieces are a match for any germs we need to worry about. If so, we’ll sound the alarm and go to battle stations.

Skin cell: It said it was just a baker’s yeast cell from some bread dough Trey was kneading. But what do I know? I try to keep invaders out of Trey, but germs are your specialty.

Dendritic cell: Better safe than sorry. It’s my job to be suspicious. You and some of the other skin cells should start dividing so you can patch up that scratch and keep any more potential germs from getting in here.

Skin cell: Okay, we’re on it. Give my regards to everybody in the lymph nodes! Go team Trey!

 

2. TURN AND TALK

• What are several kinds of human cells from the Reader's Theater and what do they do for the body?
• Do you know of any other kinds of cells in the human body? Give examples.
• Give some examples of multicellular organisms. Give some examples of single-celled organisms.
• Which do you think is a better strategy, single-celled or multicellular life? Explain your answer.

 

FOCUS WORDS

differentiate

inclusive

hierarchy

matrix

embedded