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Biology: Plant Dev: Cell Structure, Function


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About this Lesson

  • Type: Video Tutorial
  • Length: 11:07
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 120 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Plant Systems and Homeostasis (14 lessons, $24.75)
Biology: Plant Development (5 lessons, $11.88)

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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Recent Reviews

Layers of a plant
~ sdeniz

Explanation is simple and straight to the point.

Layers of a plant
~ sdeniz

Explanation is simple and straight to the point.

Don't forget--plants develop and have specialized structures just like animals. Too many of us look at plants and say, "Leafs, stem, roots, I'm out of here." But there's a lot more to plants. That's like looking at yourself in a mirror and saying, "Head, arms, legs, body, I'm out of here." There's a whole lot more to a plant than meets the eye. And plants, like animals, have embryological differentiation. They have organogenesis, just like animals, they have morphological changes just like animals. Here's the problem. The vocabulary is different. Being animals ourselves we identify more with ecto, meso, and endoderms than we do with words like procambium and this and that and the other thing. But that's okay. If you get the vocabulary down, there is a clear homology between plant and animal development in the sense that it starts with undifferentiated cells, it goes into layers that then will differentiate. There is homology there.
So let's take a deep breath and take a look at the plant developmental system and eventually arrive at what we're going to call the "primary plant body." There's the primary plant body and there's the secondary plant body. Everybody says, "Oh, we don't talk about that in humans," but in essence we do. We call it fetuses and adults. There's a good analogy for you. But in plants you have the same kind of thing. You have a primary plant body and in some cases you get secondary growth, and that's what you have to look forward to. That's what we're going to be talking about. But first, let's talk about those three tissues.
Now, remember what I said. If you know this you're going to be okay. Here is the plant embryo in three dimensions. We even have the outside green for you, even though inside of a seed it's not green. But you get the idea. Now, remember, there are three cylinders of tissue, and the three cylinders of tissue are going to have three different jobs. So if you picture these as cylinders now--one, two, three--we can start to get the idea of what each one will do, and you can get the idea that on the outside is going to be my covering materials, on the inside, or in the center, is going to be the kinds of tissues that are going to give rise to vascular materials, and then we're going to get structural things. So these are my three layers I want to tell you about.
Let's talk layers. Let's talk about ground meristem. This is the most numerous tissue inside of a developing plant. What the ground meristem is going to do is it's going to form living cells. These cells are going to be called "parenchyma." Actually, there's a few different cells that form. We'll start with this one--"parenchyma." So here's the thing. Parenchyma is living and these are generally thin cells. Now, you may want to link back to the discussion on how secondary cell walls form and the whole idea of the Golgi bodies laying down the vesicles, and then you get a lamella in between the two, and then you get a primary cell wall, and then you get secondary cell walls. These lack secondary cell walls, so they only have thin primary cell walls--parenchyma does. What these do, therefore--think--these must not be supportive because they're thin and weak and flexible. So what must they be used for? Aha! Storage. These are going to be big-time storage cells, and they're going to be photosynthetic. I always tell my students, "Remember, parenchyma and photosynthesis go together." So the point here is that parenchyma is one of the tissues that comes from ground meristem. Just like mesoderm or ectoderm gave rise to some particular kind of tissue, ground meristem is going to give rise to parenchyma. It's going to give rise to some other tissues, too.
Another one is called "sclerenchyma." The good news is it rhymes with "parenchyma" and that's good news because now you know they both have the same tissue derivative, ground meristem--or they both derive from ground meristem. This is dead cells. When I say they're dead cells, I don't mean they're dead like they never lived. They obviously had to go through some kind of mitotic division from the ground meristem. But when they become fully functional they're non-living. These are supportive. These are the ones that are going to give you support and they're going to have secondary walls. So these are the ones that are going to hold the plant up, whether you're a bean plant or a maple tree.
Now these have two types of cells in them--fiber cells. Fiber cells have--you guessed it--make fibers, and they are going to be the ones that are going to give you, if you think of any kind of seedling growing and it's fibrous inside but not hard and woody, kind of herbaceous. We call that "herbaceous." On the other hand, there are some called sclereids, which are going to give you a more stony or hard outer covering. In fact, these things produce a substance called "lignin," where lignin is a material in wood and it's hard and stony feeling. That's why you don't blow your nose in a hunk of wood instead of like the cellulose fibers of a napkin. Anyway, lignin is hard. You never thought of that before, did you?
The third kind of ground-meristem derivative is called collenchyma. We try to make it a little easy. All the "-enchymas" are going to be from ground meristem. Collenchyma also--flexible support. These have thicker primary walls, but no secondary wall. So look, we have gradations, from thin primary walls to thick primary walls to secondary walls. Thicker primary walls. And these are going to give you things like--I don't know if you know what a petiole is. If you've ever seen a branch and off the branch comes that, and then there's a leaf on that branch. That structure is called the petiole. The petiole would be collenchyma. It would have collenchyma in it. Celery, those things that are going to be containing the vascular bundles in that, are going to be collenchyma. The veins you get stuck in your teeth, that's going to be collenchyma. So remember when somebody gets a celery vein stuck in their teeth you can impress them by saying, "Wow, you have collenchyma, which is a ground meristem derivative, stuck in your teeth."
We said another one was procambium. Procambium is going to give rise to vascular tissue. Vascular tissue is the veins and arteries of a plant. There are no veins and arteries because they don't have a heart, but they do have xylem and phloem. Xylem consists of two cell types--let's get the vocabulary out of the way all at once. Tracheid cells and vessel elements. And when we talk about how plants move water, we're going to talk a lot about the difference between tracheids and vessel elements. Again, get the vocabulary out of the way. And what they do is--these are for water conduction, and these are dead. When they function, these are non-living. Of course, they were once alive. The other kind of vascular tissue--that's one--is phloem. Phloem is alive. Phloem literally pumps sap, if you will, a plant's blood, and sap is more than water. Sap is what contains sugar and it's the material that's made up in the leaves, so generally it goes downward to feed the rest of the plant. And what do we want to know about phloem? It's alive. Phloem is living, and there are two types of cells in phloem. Those two types of cells are called "sieve tubes," which are tube-like cells with sieve plates on the end, and then a companion cell that sits right next to it. So that's a sieve tube and a companion cell.
And then last but not least I want to tell you just very briefly about the third type of embryonic tissue--protoderm. It makes dermal tissue. Skin--it's going to make the skin of the plant. For example, the cuticle on the leaf--remember the waxy cuticle on the leaf? It's provided by the epidermal cells that were once protoderm. Root hairs. Root hairs are very cool. They are actually just cells. They're not hairs at all. They're just cells. So if this is like the side of the root right here, and this is at the cellular level, some of those root hair cells have these long extensions like that, and that's a root hair. And again, that's protodermal in origin.
So you see, it's not as bad as you thought it was going to be, now, is it? Three cylinders, one right into the other, the three embryonic tissues of a plant. Once we get our embryonic tissues established we can start talking about the primary plant body of the plant.
Plant Systems and Homeostasis
Plant Development
Plant Development: Cell Structure and Function Page [1 of 2]

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