Hi. It's Mr. Andersen and welcome to Biology Essentials video number 25. This
is on mechanisms of timing and control. And I'm going to talk about timing and control
in plants, in animals and even in bacteria. But I wanted to start by talking about something
that plagues you if you ever travel. And that is called jet lag. And the reason jet lag
is nasty is that you get used to a specific time. You set up what's called a circadian
rhythm according to the amount of light that you get. What's the time of the day. And when
you fly somewhere else, like this is across the international dateline, everything is
kind of out of whack. And it takes your body a little while to accommodate for that. But
we can. Because we can set up a new circadian rhythm. And so in this podcast I'm going to
talk about physiological events. And that's going to be events that occur within a specific
organism that allow us to do timing or control. And so first I'll start with plants. And two
big things that you should understand about plants are phototropism. That's how we grow
towards or away from light. And then photoperiodism. How do plants respond to changing amounts
of light throughout the seasons. Next I'm going to talk about animals and the importance
of circadian rhythms. But we'd also find circadian rhythms in a fungus or in a plant as well.
They're all tied to the time of the day. And then finally I'm going to talk about timing
and control in bacteria. And they use something called quorum sensing. A quorum is when you
have a group of people together to vote. And so bacteria, what we're figuring out can talk.
They can communicate between bacteria of the same species and even between interspecies.
And that's pretty crazy kind of stuff. And so let's get started. Let's start by talking
about phototropism. Phototropism is going to be growth towards light. We call that positive
phototropism. So if a plant were to grow, you can see it, light's over here. It's growing
towards it. And not only is this stem growing towards it, but you can see that all of the
leaves are oriented so they can pick up the maximum amount of light. Negative phototropism
would be growing in the other direction. And so immediately when you plant a seed, the
roots are going to show negative phototropism. They're actually going to grow down into the
dirt. Or away from that. And then we have gravitropism as well. Gravitropism would be
response to gravity. But how does a plant do that? It doesn't have muscles. It doesn't
have nerves. How does it grow towards the light? Or how does it grow away from the light?
Well they use a plant hormone called auxin to do that. Auxin is a series of plant hormones.
Plant hormones or hormones in general just are chemicals that move around an organism
and have specific effect. And so auxin, what auxin does, is it causes cells to lengthen.
What it really does is it loosens up the cell wall. And so when you loosen up the cell wall,
the cell wall, as water flows into the plant it actually makes it get larger. And so let's
say for example that I put the light or the sun over on this side. And that this represents
a stem of a plant. And I know this is kind of diagrammatic, but let's say this is a stem
of a plant. So it could b the stem of this plant right here. And let's say I put the
sun over on this side. Let's give it some eyes so it looks a little happier. So the
sun is over here. What auxin does is auxin will move inside the plant. Auxin will always
move away from the light in positive phototropism. So it's going to move away from the light
in this direction. Now what does that do to the cells? It causes the cells to get larger.
And so let me kind of clear this out of the way. So what happens to the cells where the
auxin is? Well the cells where the auxin is are going to get longer. And it's kind of
a continuum. These ones, not as long. These ones aren't going to change at all. I couldn't
quite get the animation right, but what is that really going to do? Well instead of just
making it taller on that side, since all these cells are connected, it's going to cause this
stem to actually grow towards the light. In other words since these are all attached here,
the whole thing is going to move in this direction and it's going to move towards the sun. And
so you could see that. Now if I were to clear this all off and let's say I put the sun on
the other side. So if the sun is over on this side, now the auxin would move in this direction
and then the stem in going to bend back like that. And so what that allows plants to do
is it's a physiological response to changes in the amount of light. It can grow towards
or away from the light. And they do that using auxin. Photoperiodism has photo in it as well.
So that means light. But what they're sensing is the amount of light throughout the day.
So timing it during the day. And we think that plants use something called a phytochrome.
A phytochrome is going to be a protein that's found inside plants. And when it absorbs light
it will change its confirmation. In other words, it usually has this red phytochrome
confirmation. But when it absorbs light it'll switch to a far red phytochrome. So it's actually
going to change its shape. And by the amount of phytochromes that have changed their shape,
they can tell what time of the day it is. Now why would you want to know what time of
the day it is? Or how much light there is in a day? Well that tells you what season
it is. And that's super important. I'll talk more about that in the next podcast. It determines
if you survive or not. And so what we could do is we could classify plants and the time
that they flower to the length of the day. And more importantly it's actually the length
of the night. And so poinsettias will actually flower around Christmas. And they flower when
the days are really really short. Or the nights are really really long. And they're sensing
that using these phytochromes. Or arabidopsis is a plant that we us a lot of the time in
studies in biology. It's actually going to require a long day. Lettuce is an example
of that. So it needs a really long day or a really short night to flower. Or a dandelion
doesn't care. Dandelions are going to flower all the time. And so it's independent on the
amount of light that they get. And so this allows plants to kind of respond, physiologically
respond, to their environment. Now plants will actually move their leaves during the
day. And that's called a circadian rhythm. But we have a circadian rhythm as well. In
other words as long as the light is out, our light is going to go through the eye and we're
going to sense that in something called the pineal gland. It's a small gland inside your
brain that looks kind of like a pinecone. But what it's going to do is it's going to
release a chemical into the brain called melatonin. Melatonin is going to set our clock or our
internal clock. And so if you look through, this is a, I grabbed this from wikipedia.
It's pretty cool. So in the morning, we'll have a high blood pressure, the sharp rise
in blood pressure rate before we get out. We stop making melatonin in the morning. Bowel
movements are likely at 8:30 in the morning. This is pretty funny. Best coordination is,
looks like at about 2:30 in the afternoon. Start making melatonin at night. So what does
this mean? We're set on a 24 hour schedule. And so our body according to the amount of
light sets itself on a schedule and so that's why jet lag is a problem if you move somewhere
else, we're already on a different schedule. And so now we have to wake up at this time
or we have to wake up at that time. And so it's hard for us to do that. But again, we
can set the amount of melatonin. It doesn't take us but a few days and we can kind of
set a new circadian rhythm. The first time I read about quorum sensing in bacteria, it
freaked me out. Because what it really is is a way that bacteria can communicate with
other members of their species or even members of another species. And so a quorum is a group
of individuals getting together. And bacteria, we found, can talk and communicate. And so
how does quorum sensing work? Well bacteria are going to give off what are called autoinducers.
In other words those are proteins that essentially just say I'm here. And if you are one bacteria
by itself, a lot of those are just going to kind of go unanswered. However, if there are
more bacteria and they give off their autoinducers, the chances that one of those will bounce
into another bacteria is going to be much greater. And if we even have more bacteria,
there's more autoinducers, and if we have more bacteria there are going to be even more
autoinducers. And so what does that mean? Bacteria can see how crowded it is. And if
they're all by themselves they're going to have one behavior. And if they're not they're
going to have a different behavior. And so it's a really complex way that bacteria can
actually communicate. And so what they can do is they can start giving off other proteins.
So this one picks up this autoinducer. It says, hey I'm crowded. It can send other proteins
out that are going to trigger a specific response. And so what do I mean by trigger a specific
response? Well for example, it could allow them to communicate and work together to solve
a problem. It could increase their virulence. In other words bacteria might grow to the
point where there are so many of them, now it's time to actually attack. Or they could
form biofilms. Or they could move really, really quickly. And so all quorum sensing
is a way to communicate bacteria to bacteria to say, hey this is how crowded it is. And
they can have different behaviors depending on that. And so it gives them real complex
behaviors. Behaviors that we never even envisioned years ago. And so that's how plants, animals
and bacteria respond to the timing and they can sense their environment. And I hope that's
helpful.