Notice:  As of December 14, 2016, the MindBites Website and Service will cease its operations.  Further information can be found here.  

Hi! We show you're using Internet Explorer 6. Unfortunately, IE6 is an older browser and everything at MindBites may not work for you. We recommend upgrading (for free) to the latest version of Internet Explorer from Microsoft or Firefox from Mozilla.
Click here to read more about IE6 and why it makes sense to upgrade.

Biology: Introduction to Gas Exchange of Animals


Like what you see? false to watch it online or download.

You Might Also Like

About this Lesson

  • Type: Video Tutorial
  • Length: 12:56
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 138 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Animal Systems and Homeostasis (63 lessons, $84.15)
Biology: Final Exam Test Prep and Review (42 lessons, $59.40)
Biology: Gas Exchange and Transport Systems (5 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

About this Author

2174 lessons

Founded in 1997, Thinkwell has succeeded in creating "next-generation" textbooks that help students learn and teachers teach. Capitalizing on the power of new technology, Thinkwell products prepare students more effectively for their coursework than any printed textbook can. Thinkwell has assembled a group of talented industry professionals who have shaped the company into the leading provider of technology-based textbooks. For more information about Thinkwell, please visit or visit Thinkwell's Video Lesson Store at

Thinkwell lessons feature a star-studded cast of outstanding university professors: Edward Burger (Pre-Algebra through...


Recent Reviews

Watching the video
~ Abdulaziz1

I can not watch the videos as it is written at the top of the page that is protected.Can somebody help me please, and thankyou.

Watching the video
~ Abdulaziz1

I can not watch the videos as it is written at the top of the page that is protected.Can somebody help me please, and thankyou.

I want to play a little game here. Ready? We're going to imagine ourselves a critter. You're a jellyfish. Are you happy, or are you not happy? You're a jellyfish. Well, you know, you're kind of cruising around the ocean, it's a nice place to be. But even more importantly, jellyfish have an easy life. In fact, all of the cnidarians have a pretty easy life. And why do they have an easy life, you might ask. Well, I've got to tell you, in terms of the phylogeny, in terms of the evolutionary history of these things, we see that they haven't changed a whole lot in 5 or 6 hundred million years, and the reason is because they've kept it simple. And what have they kept simple? What they have kept simple is the number of cells and tissues that they have. Remember what this is all about? This is all about maintaining stability. This is all about homeostasis. This is all about an organism becoming multi-cellular, and, in becoming multi-cellular, regulating those tissues talking to each other. Well, why is a jellyfish happy? It's very simple. A jellyfish is happy because he doesn't have a lot of cells--he, she, they!--because they're hermaphroditic. And here's the thing. If you were to look at a jellyfish--first I'll do my good artist jellyfish; there's my good artist jellyfish--but now, let's look at the cellular material in a jellyfish, or a hydra, or anything like that. They literally--a jellyfish literally has two cell layers. This could be a sea anemone or a hydra. And those two cell layers, all of them, are exposed to the environment. So, if I'm talking to a jellyfish about a topic like exchange of respiratory gases, the jellyfish is, like, "What's up with you? What do I care about the exchange of respiratory gases? All of my cells are in touch with my environment, and my environment is water." Granted, that may not be a lot of oxygen out there, but nevertheless, there's enough dissolved oxygen that I'm happy as a clam, except I'm a jellyfish. So you see, jellyfish have no problems like you and I do. And I've never seen a jellyfish that had to go in for therapy or any kind of respiratory work, or anything like that. And here's the thing. Jellyfish may not have that problem, but other things do. And why is that? Again, let's go back in time.
Remember that, as organisms evolved, what happened was you went from a very simple two-cell layer thick organism to one that was multiple-cell layers thick. And as those bodies closed up and multiple thicknesses of cells formed, the dilemma was, how do you get oxygen to those inside layers? How do you get CO2 out of those inside layers? How do you maintain homeostasis. Well, along came a gill one day. Now, it's not like one day, some wormy thing said "ugh" and grew a gill out of the side of its body or anything like that, but what started to happen was in their need to survive, certain pressures selected for certain traits. Now, one of the first creatures that came along, if we look back at our fossil evidence, one of the first multi-cellular, closed creatures that came along were worms. And, let's think about worms. And in fact, one worm comes to my mind--a worm called a polykete, which is, in essence, a marine worm, like an earthworm; a very close relative of the earthworm, but it's in the water. Now, let's think about the problem this thing has. It lives in the water, and it's a worm. Now, if you look at a worm, and it's multi-cellular and it's thick, but the only membrane it has to get to--inside that worm is where you want to get your gases. How are you going to get your gases in here when the only surface you have to allow for this kind of thing is this rather small surface area skin that the worm has. Now, what's interesting enough about all the evolution of respiratory membranes is they all had the same pressures on them. This worm had the same pressures on it that the very first amphibians had, that the very first fish had, that the very first mammals had, to get gas exchange. And I'll show you how he solves it in a second, but let's see what those pressures are.
The first pressure is you need to get oxygen across that. So it's got to be near an oxygen source. The second problem is it needs to be thin. The third problem is it has to be near a circulatory system. It's got to somehow get to fluids inside of this worm. So when the organisms eventually closed up, they had to have some kind of way to carry their sea water with them. We call that blood, but in essence, it's just glorified sea water. And not only that, not only does it have to be thin, near an oxygen source, near a circulatory system; two more things: It has to be wet. It has to be moist, which, for a marine worm, isn't a problem, that's the least of his problems. He lives in the water. And you need surface area. You need to have enormous amounts of surface in order for this diffusion to happen, and that wasn't enough. The more successful worms had more surface area. They all lived in the water, they had this nice thin layer, but they had more surface area. So let's take that worm, slice it down the middle, and look at a cross section. And what these worms had were these--this is a cross section; you guy's all okay with a cross section I hope? It simply means that we've cut the worm in half. It's like a giant worm, or length right across the middle, that's why it's called a cross section, and this used to be a worm coming up out of here, and we cut it. What I really want to show you here are these structures right here, which are called "parapodia." And parapodia not only increases--and so there would be parapodia off this segment, parapodia off this segment, and this one, and this one, and so on, and what's it doing? It's increasing the surface area. And not only is it increasing the surface area, it allows diffusion of gases. And not only does it allow diffusion of gases, but it allows diffusion of gases into a body fluid that has proteins in it that allow oxygen to diffuse readily, and CO2 to diffuse readily out. So life is good in the ocean, especially if you're a worm and, of course, if you're a jellyfish and everything in between. But then as life got more and more complex: fish--real thick, muscles, blood, bone. Now we come to the formation of gills, highly adapted respiratory pigments to carry the oxygen around, running through those gills so that when water goes in the fish's mouth and out through the operculum, it picks up all the dissolved oxygen that was in that water. But water, it's not always a picnic in there.
Let me show you a little something here. Now if we take a look at this graph, and you'll see that down along the bottom here is the temperature of water, and the key is that as water warms up, it loses its ability to hold oxygen. So warmer water holds less oxygen. So if you happen to be a fish that's just kind of like hanging out, and he can go at about 25 or so degrees, you'll notice that there's plenty of oxygen for this fish, but as the water gets warmer and warmer and warmer, that fish gets less and less oxygen available to it. So at about 25 degrees, that fish gets in trouble. On the other hand, that fish swimming around, it's even worse. Why? Because he's active. So, because he's swimming around and he's got a higher metabolic demand for oxygen, that fish is going to get into oxygen debt a lot sooner. So, water is a nice medium, and yeah, there's a lot of dissolved oxygen in there. But you know what? There's another medium that holds a lot more oxygen than water: air. That almost seems like a no-brainer, doesn't it? Do you realize that water has 10 milliliters of oxygen per liter. Air has twenty times that: 200 milliliters of oxygen per liter. So, why can't fish just flop around, and walk out on the land and be happy? Remember, thin, moist--fish's gills dry out. So when the very first creatures started to walk on land--and why did they walk on land? You know the story. The plants colonized the land first, and the crustaceans were down there in the tide pool saying "man, look at all that dinner out there." And crustaceans were kind of good for this, because they could live in those inter-tidal zones. Their gills were literally covered up by their carapace, and the crustaceans could actually leave the water for a little while and come back, and leave the water for a while and come back, and eventually, leave the water for a while, and now we call them "bugs," because they gave rise to all of the arthropods. Well, those guys could actually come out there and live with no problems because of some of the developments that they came up with. For example, this is a modern day insect. Two things about insects: number one, they have an open circulatory system--this is the great, great, great, great, great grandson of those first crustaceans--and in that open circulatory system, they actually have a blood substance running through their whole body that's pumped by a circulatory system up here. But what I want to talk about--look at a bug someday. They have holes in their side, and the holes in their side are called spiracles, and if I were to take a side view of this, let's see how these guys solve the problem of thin, moist, with lots of surface area, near an oxygen source, let's take a look at what they did. Let me cut open the bug and look inside from a side view. So, here's the bug's body, here's the spiracle, and there's the bug's body, and there's another spiracle, there's another spiracle--you get it. Here's what happens. The oxygen can go in this, And watch a big bug like a grasshopper some day, his body is constantly moving in and out. And why is it doing that? Because this spiracle branches into a series of tubes called tracheal tubes, and these tracheal tubes branch and branch and branch and branch. What am I doing here? Oh my, we could be talking about surface area, and don't forget how important surface area is--an increased surface area--and branch and branch and branch, and what do you know? It's being bathed by a fluid, and let's take a look at what we need. What did I say we needed? Well, we needed to be thin. One cell layer thick, is that thin enough for you? It needs to be moist. It's bathed in blood, is that wet enough for you? It needs to be near an oxygen source. Well, oxygen is coming to the source. So oxygen is cool. Not only does it need to be near an oxygen source, it needs to be near a circulatory system. And certainly, it needs to have lots of surface.
And now you start to see what started to happen as life moved to land. Homeostasis knows no boundary. No matter what pressures are put on, what will happen is nature will select those traits that will survive. And if you look at this, and what the bugs first did, and now we start thinking about what followed the bugs. Wow, the amphibians, and what did they do? They didn't have tracheal tubes, they were like fish, they had closed circulatory systems. How did they get around this? Perhaps they developed a bag-like structure inside of them with lots of surface area, maybe something we'll see later called the "lung."
Animal Systems and Homeostasis
Gas Exchange and Transport Systems
Introduction to the Gas Exchange of Animals Page [1 of 2]

Embed this video on your site

Copy and paste the following snippet: