Hi. It's Mr. Andersen and in this podcast I'm going to talk about plants.
More appropriately we're going to talk about land plants. And so they have a great diversity
on our planet. If it weren't for plants we'd literally would not be able to survive on
our planet. And so let's start with looking at their phylogeny. So here are all the eukaryotes
on our planet. So basically these are all things that have nucleus. And they're going
to have organelles. And so if we break off of this, this is a pretty ancient lineage.
In other words, plants have been separated for along time. Who are the things they are
more related to? Well red algae would be one right next door. But we're going to have green
plants right here. Most of these are all going to be protists. You can see us right here,
animals and then fungi right next to that. And so plants are important for the role they
play in our lives. If we zoom more into their phylogeny itself, there are going to be somethings
that you are familiar with. Like mosses and maybe liverworts and hornworts. But we're
also going to have seed plants all the way down here. You don't have to learn all of
these. These are simply the way that they're starting to be classified. But there are four
groups that you should be familiar with that I've chosen. And those are going to be the
bryophytes. So those are going to be like the mosses. The ferns. The gymnosperms. And
then the angiosperms. And the reason I've chosen those four is that they're monophyletic.
In other words they share a common ancestry with each other. So we know that they are
related. But they also show these four evolutionary steps in the movement of plants from water
to land. Alright. Let's talk about some of their characteristics. So they're eukaryotic.
We know that. They have a nucleus and organelles. They're also autotrophs. In other words they're
going to take energy from the sun and they're going to use chlorophyll A to make sugars
for themselves. And so they are self feeders. They all have cell walls. And that cell wall
is going to be made up of cellulose which is polysaccharide, but it's going to have
a lot of extra bonds on there that make it really really durable. Another chemical that
I could have written here is sporopollenin. They have this really resistant chemical that
can also protect their spores. They're terrestrial. In other words all of these plants are what
we call land plants. Sometimes we refer to those as embryophytes. But they all live on
land. And so things like seaweed aren't going to be technically plants. And things like
kelp are going to protists. And so they're not plants as well. And so all these things
on here live on land. The only exception to that would be like water lilies, which we
think moved on to land and then moved back into the water. All plants are also going
to show alternation of generation. That's part of their reproductive structure and I'll
show you that on the next slide. But the big thing, and it's where they actually get their
name is that they all have protected embryos, land plants. In other words this would be
a baby plant protected by material around the outside. And so all plants are going to
have one structure in their life when you have this little baby embryophyte. And that's
what's shared between all plants. Alternation of generation is a term that you should understand
especially when we're talking about plants. And basically what it means is that there
are two life cycles in plants. We have the haploid life cycle. Remember that's going
to be when you have one set of all the chromosomes. And then the diploid. Now botanists have given
specific names to these. And so the haploid portion we call the gametophyte. And then
the diploid portion we're going to call the sporophyte. In humans let's think about that.
What are the different diploid and haploid parts of our life cycle? Well the diploid
is going to be me. It's all the cells in my body. And then the haploid portion is only
going to be the gametes or the sex cells. But in plants lots of times that gametophyte
will actually be a part of the plant. Multicellular part of the plant. So let's look how this
plays out in ferns. So basically what you're going to have is meiosis which creates spores.
Since we've undergone meiosis, we've got some variability here. But we also now have reduced
our chromosome number down to n or haploid. So now we have mitotic growth of these. And
that's going to create the gametophyte portion. That's going to be this really small portion
below what you might think of as the fern. We then are going to have mitosis, fertilization.
That's going to create a sporophyte. And that sporophyte is going to be the diploid portion.
And then we have that cycle over and over again. Things like mosses, most of what you
see in a moss is going to be gametophyte. But as we move up towards things like a conifer
tree. Like a big tree, what you're mostly looking at, just like what you're looking
at in humans is going to be the sporophyte or the diploid portion. How do they make energy?
Well they're going to make energy through a process called photosynthesis. So their
taking energy from the sun. And they're converting that into sugars. Why are they doing that?
They're doing that so they can store the energy. They can build structures out of it. But they
can also use cellular respiration to release the energy in the form of ATP. In other words
they are self sufficient. And we are simply parasites on plants. As I mentioned before,
there are four big groups that you should understand when it comes to plants. And those
are also going to show you the four major steps that plants went through to dominate
our planet. And so basically we're going to start here deep in the ocean. Because that's
where plants started, as something similar to seaweed. And so basically what they were
able to do is move on to land. They were able to move material around. They then came up
with the seed. And then finally they cam up with the flower. And so the movement on to
land was the first step. Some of the organisms on our planet, the bryophytes which are like
the mosses, basically they're similar to what some of the first planets on our planet had.
They were definitely green. But they couldn't be very tall. Because in order to move water
around, it could only do it through diffusion. They didn't have vessels inside them that
could move the water. And so these are generally really really short. And they're also found
in areas where there's enough rain water on the bryophytes so that they can actually get
water that way. Next movement then is the vascular tissues show up. And so the bryophytes
are going to be from these vascular plants. They have true tissues. And so basically what
they're going to have are these xylem and phloem that can move material around. Once
we can move material, especially water from our roots to our shoots, then sizes got really
really big. We didn't have to live only in really really wet areas. And we didn't have
to be really low to the ground. And so the next big jump was the ferns. Next thing is
the evolution of the seed. The seed allowed them to protect that embryophyte. And it can
dry out totally. And then we can eventually start a new plant. Cycad is an example of
an gymnosperm. But so are all of these conifers over here. If we breakdown the word it is
naked seed. And so that's going to be this group. And then finally we have what are called
the angiosperms. And that's the evolution of the flower. What's the function of a flower?
The flower coevolved with insects and it gave them an ability to reproduce. So basically
what are these flowers doing? They're advertising to insects to come here. We've got some nectar.
And then when you go there you pick up a little pollen and you're going to move it somewhere
else. And this has allowed them to be incredibly successful. But even though you might not
be able to see a flower, almost every plant on our planet you can think of is going to
be an angiosperm. So let's think about grass. Well they're pollenated by the wind. And so
the wind is going to move their pollen and so they don't have to have a very fancy flower.
Because they're not advertising for insects. But that again is the evolution of plants.
Those four big groups again are the bryophytes, the ferns, the gymnosperms, an example would
be the conifer. Those were what were around when the dinosaurs were around. And then finally
we have the angiosperms. And so those are plants. I love plants. Because I eat them
or I eat things that eat plants. And I hope that's helpful.