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Biology: Plant Phylogeny: The Colonization of Land


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About this Lesson

  • Type: Video Tutorial
  • Length: 9:16
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 100 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: The Evolution of Life on Earth (34 lessons, $64.35)
Biology: The Colonization of Land by Plants (2 lessons, $2.97)

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.

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You know, plants have problems too. And plants, as they evolve, have the same problems that animals have. Remember, life started in the oceans, and plants, just like animals, started in the seas. And plants, just like animals, had to come up--had to evolve--and again, I keep saying, "come up." And they had to evolve--don't start calling me Mr. Lamarck here, all right? I'm not trying to say one day they went... and like grew roots. That's not what happened. But in order for them to survive they had to have certain abilities or they would have been selected against. So let me get away with this lazy way of saying, "They had to get."
So they had to come up with ways to survive on land, otherwise, forget it. You'd have a great ocean of life, but all those possibilities out there--and for plants, the possibilities weren't great, because let's face it, there was nothing up there but rocks. Because as plants, by their reproductive systems, spores, they would end up on land. Literally, there was nothing to fall into because there was no rotting plant material to grow, so they had it even tougher than animals. At least the animals, when they were down there in their tide pools checking stuff out up there, there were like plants to each, because obviously the plants had to colonize the land before the animals did. Just logic; common sense.
So what kind of problems would a plant have? The same problems an animal has--desiccation. You see, soon as you leave the water you dry out. So therefore, when we take a look at some of the structural adaptations and the reproductive adaptations that plants had to come up with we have to base it on the idea that what adaptations does a plant have in order to survive? And what I was just about to interrupt myself and say is, remember what we're talking about here. We're talking about gradual change and we're talking about natural selection. So let's say what would a plant need to do in order to survive? What adaptations would it need to have?
Well, what are you going to protect yourself from? How are you going to protect yourself? Well, you have to protect your body, just like an animal does. You have to come up with a way to transfer gametes--gametic transfer. You have to come up with all sorts of developmental issues. How are you going to have that baby plant develop? And so what a plant needed to do was in many ways similar to those very first animals that came out on land also.
So what kind of things did they develop? Well, you know enough about plants that we can talk about some of these structures. Let's talk about the plant body--part of it. Certainly they had to come up with anatomical changes. Number one, some of them had to develop roots. There's that "had to" word again, but certainly roots were a way to get to water. The first plants did not have roots. They were, again, like the algae that they evolved from. More on that in a second. You have to have a way to conduct water--vascular tissue. You had to have a way to keep from drying your leaves out. You had to have some kind of waxy covering. You had to get a way to suck water up out of the ground--stomates. You had to do reproductive things, too. You had to make reproductive changes, too, and that in itself, is incredibly fascinating, the reproductive changes that plants had to go through in order to evolve and survive on land. You know, the first plants probably were spore-producers, but they lived in the water, so you had to come up with a protein of some kind to cover your spores with and make them literally indestructible. Eventually, plants formed seeds and seed coats to enclose a sexually reproduced embryo in, so we had seed coats. Plants eventually had flowers. Why? Well, there was something else going on on land, too--animals. And so we saw a lot of things that happened between flowers and gamete transport that co-evolved with animals.
What a story this is. Co-evolution, the fact that flowers would evolve in plants as insects evolved on the planet, and more flowers would evolve, so more insects would evolve, so more flowers would evolve. This is great stuff here. Why? Because the gametic transport was often carried by water and wind, but man, along came the insects--boom! We had a great way to get the pollen transferred around. So same problems, logical problems. Let's start talking about how plants evolved.
You've heard me say a couple of times that plants probably evolved from algae. Our systematists have been working hard at this question. There's a lot of algae out there, and there's a group of algae called the charophytes that we think were probably the first algae, that primitive ancestral algae. Remember, we're talking phylogeny here, and we want to make a mono-phyletic, a one-branched tree that describes the way the plants evolved, so we need a common ancestor so that we can choose an out group with the most things in common with that ancestor. Remember, that's what phylogeny is all about. And we believe it's these charophytes. Why? Well, let me tell you some things they have in terms of homologies with these. First of all, a lot of it's biochemistry and molecular genetics, but it works for me. One of the commonalities that charophytes have with present day plants is they have a pigment called chlorophyll B and they have beta carotene. Other algae don't have these. Charophytes do, and guess what? So do land-dwelling plants.
Second thing--the chloroplast arrangement. Most algae don't have granna, don't have thylakoid membranes stacked. Remember that chloroplast? It has the granna, the thylakoid membranes for photosynthesis? Well, guess what? Charophytes have that; most algae don't, and of course, many of the land-dwelling plants of today have that.
Another thing that they have are some biochemical similarities. If you take a look at the cell wall of charophytes you'll find that their cell wall is very similar to the cell wall of land-dwelling plants, and none of the other algae are that similar, so certainly cell wall was one of the things we can talk about. And even to the point of the peroxisome enzymes. Remember, plants, animals, all cells, pretty much, eukaryotic cells, have peroxisomes, those organelles that contain enzymes, peroxidasis. Well, the peroxisomes of the charophytes are very similar to the peroxisomes of land-dwelling plants of today.
Some other generic things I want to tell you about, without going into a ton of detail, is they share similar mitotic processes. The mitotic process between the charophytes of today--remember, I'm talking about the charophytes of today, so we're assuming they would indeed have been the ancestor of these plants. The charophytes of today, their mitotic processes are similar to the modern plants. The way their sperm structure is--yes, plants have sperm, and yes, charophyte's sperm structure is similar to land-dwelling plant structure.
And last, but not least, and the big one we always bring up--DNA homology. Number six--I'll put it over here--DNA. The whole idea of the fact that their DNA is more similar to plants of today. Why are we talking about this? Well, the point here is this. As we start to try to understand plants, the simple saying still holds true. You'll never know where you are unless you know where you've been.
The Evolution of Life on Earth
The Colonization of Land by Plants
Plant Phylogeny: The Colonization of Land Page [1 of 2]

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