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Viruses AP Biology Topic 6.4 | A virus, its genetic material, its nucleic acid can either be DNA, RNA, like a single
strand of RNA, or it can be both. |
Viruses AP Biology Topic 6.4 | And sometimes it can even have double stranded RNA. |
Viruses AP Biology Topic 6.4 | It doesn't follow the same rules of like how eukaryotes have linear chromosomes and
prokaryotes have circular. |
Viruses AP Biology Topic 6.4 | It doesn't necessarily follow those rules. |
Viruses AP Biology Topic 6.4 | And instead of being surrounded by a cell membrane, it's surrounded by a protein coat. |
Viruses AP Biology Topic 6.4 | So this protein coat could have certain like glycoproteins on its surface. |
Viruses AP Biology Topic 6.4 | So when we talk about these proteins on the surface of a virus, this is one of the ways
that our immune systems can identify that this virus does not belong inside of our bodies. |
Viruses AP Biology Topic 6.4 | Now each of these protein coats, I believe on my next slide, so well, I guess I'll get
there. |
Viruses AP Biology Topic 6.4 | One thing that might occur in some viruses is they can pick up a like membranous or like
a lipid bilayer envelope from a host cell. |
Viruses AP Biology Topic 6.4 | So after they replicate and they are exiting a host cell, they can take some of that host's
cell membrane with them, kind of. |
Viruses AP Biology Topic 6.4 | So here's words for people who like to read. |
Viruses AP Biology Topic 6.4 | Now a DNA is called a, I mean a DNA, a virus is called a DNA virus or an RNA virus, depending
on the type of nucleic acid it has. |
Feedback Loops - AP Biology | in AP biology. |
Feedback Loops - AP Biology | In this video, we're going to review what feedback is, explain positive
and negative feedback mechanisms, as well as go over some examples of both and how they
affect or help maintain homeostasis. |
Feedback Loops - AP Biology | So feedback is used by organisms to maintain their internal
environments and respond to internal and external changes. |
Feedback Loops - AP Biology | We can also see feedback loops at
the cellular level, the organismal level, or at an environmental or population level. |
Feedback Loops - AP Biology | Feedback is a response within a molecule, cell, organism, even an ecosystem that influences
the continued activity or productivity of a system. |
Feedback Loops - AP Biology | Feedback loops help regulate homeostasis
or the internal balance all organisms need to survive. |
Feedback Loops - AP Biology | So the failure to maintain homeostasis
can cause disease or death, meaning that the failure to maintain feedback loops can also
lead to disease or death. |
Feedback Loops - AP Biology | Feedback loops are really important in biologic systems. |
Feedback Loops - AP Biology | I'm
going to review some of the types of them right now. |
Feedback Loops - AP Biology | There are both what we call negative
feedback loops and positive feedback loops. |
Feedback Loops - AP Biology | These don't mean something that are good or
bad. |
Feedback Loops - AP Biology | Rather, they refer to the inhibition or slowing down of a system versus the amplification
or the increase of a system. |
Feedback Loops - AP Biology | Negative feedback loops result in the inhibition or the slowing
down of a process, moving something back to that set point, that internal balance that
an organism wants to maintain. |
Feedback Loops - AP Biology | Positive feedback loops, on the other hand, amplify a signal
or some sort of output. |
Feedback Loops - AP Biology | Now, negative feedback loops, like I said, will work to maintain
homeostasis and go back toward a set point. |
Feedback Loops - AP Biology | Positive feedback loops are generally going
away from a set point, and they're working against what the normal system would normally
be. |
Feedback Loops - AP Biology | This isn't a bad thing, but generally it's not normal. |
Feedback Loops - AP Biology | In negative feedback loops,
these are more common within organisms and they maintain various body systems. |
Feedback Loops - AP Biology | Our temperature
regulation, our blood pressure regulation, our blood sugar regulation are all examples
of how negative feedback loops help us maintain our internal environments. |
Feedback Loops - AP Biology | You may see an
example of blood pressure or blood sugar regulation on an AP exam, so we're going to go over what
that could look like in just a moment. |
Feedback Loops - AP Biology | Positive feedback loops, though less common, are still
necessary in certain situations. |
Feedback Loops - AP Biology | Childbirth and having the contractions of the uterus
in order to deliver a child is obviously really important for mammals. |
Feedback Loops - AP Biology | Fruit ripening, producing
ethylene, for example, is another positive feedback loop that's necessary for the ripening
of apples on a tree. |
Feedback Loops - AP Biology | Lactation in mammals also is helped by positive feedback loops
in the release of oxytocin and blood clotting as well, which we'll go over as an example
in this video. |
Feedback Loops - AP Biology | A negative feedback loop, remember, is going back toward the set point. |
Feedback Loops - AP Biology | If we
start with a normal blood pressure and then an organism is exposed to stress, the blood
pressure would rise above normal. |
Feedback Loops - AP Biology | Now, the body receptors are going to detect change
and then decrease a heart rate and increase the blood vessel diameter. |
Feedback Loops - AP Biology | These effects will
then help decrease the blood pressure and bring the blood pressure back to normal, back
to that set point. |
Feedback Loops - AP Biology | This feedback loop would then stop here unless the body is exposed
to more stress. |
Feedback Loops - AP Biology | A positive feedback loop related to blood clotting kind of works in a different
way. |
Feedback Loops - AP Biology | If we have a break in a blood vessel wall from a cut or a laceration, platelets
are then going to adhere to the site and start to release chemical signals. |
Feedback Loops - AP Biology | Those chemicals
will then attract more platelets and platelets will adhere to the site and release more chemical
signals. |
Feedback Loops - AP Biology | This will continue to amplify the signal, which doesn't normally happen in
the body. |
Feedback Loops - AP Biology | And more and more platelets will come until finally we have what's called
a platelet plug that is formed at the site of the break. |
Feedback Loops - AP Biology | Then the cycle ends. |
Feedback Loops - AP Biology | We don't
have any more chemicals to attract more platelets because we don't need them anymore. |
Feedback Loops - AP Biology | Similar
with childbirth. |
Feedback Loops - AP Biology | Once the child is delivered, the contractions don't need to amplify because
the goal has been achieved. |
Feedback Loops - AP Biology | But this entire process was not what normally happens. |
Feedback Loops - AP Biology | It
goes away from homeostasis. |
Feedback Loops - AP Biology | Let's take a look at another positive feedback loop that
can happen within the environment. |
Feedback Loops - AP Biology | Now the positive feedback loop example I'm going to
use is called ice albedo. |
Feedback Loops - AP Biology | And albedo indicates what percentage of solar radiation or sunlight
is reflected by a surface. |
Feedback Loops - AP Biology | Generally ice is white and very reflective, but the ocean surface
is dark and absorbs heat faster. |
Feedback Loops - AP Biology | So when we have an environment where temperatures are
rising and we have ice melting, the ice or the white reflective surface is going away,
which is going to increase the water that's exposed and therefore absorb more heat in
the environment. |
Feedback Loops - AP Biology | That will then cause temperatures to rise and more ice to melt. |
Feedback Loops - AP Biology | The more ice
that melts, the more water that is exposed and you can see how this cycle is a positive
feedback loop. |
Feedback Loops - AP Biology | Now this isn't necessarily the same type of feedback that's going to
happen within an organism or a cell, but it is an example of positive feedback within
an ecosystem. |
Feedback Loops - AP Biology | So I want you thinking about this when we get to our unit on ecology. |
Feedback Loops - AP Biology | Feel
free to go back and watch this short video again. |
Feedback Loops - AP Biology | I hope you enjoyed our video on feedback
loops. |
Information Exchange | Hi. |
Information Exchange | It's Mr. Andersen and welcome to biology essentials video 40. |
Information Exchange | This is on information
exchange between organisms. |
Information Exchange | And so if you know anything about biology you know what
message these organisms are trying to send to us. |
Information Exchange | It's a go away from us kind of a message. |
Information Exchange | This is the poison arrow frog and we saw these when we were in Ecuador. |
Information Exchange | They produce this
coloration because they have skin that produces a toxin. |
Information Exchange | And so if you were to eat a poison
arrow frog and let's say you're a bird, you're going to associate that toxin with that color
and it's going to tell you to stay away. |
Information Exchange | Flamboyant cuttlefish is the same way. |
Information Exchange | It produces a
neurotoxin and it produces not only this coloration but it also can raise the musculature on it
and create these real wild looking pictures. |
Information Exchange | I mean just Google cuttlefish video and you're
going to find some crazy stuff. |
Information Exchange | And so again they have a toxin and it's a message they're
sending to other organisms. |
Information Exchange | Don't eat me or you'll die. |
Information Exchange | And so you're associating this
color with that. |
Information Exchange | This down here seems to be, this snake seems to be sending the same message. |
Information Exchange | But this one is actually using mimicry. |
Information Exchange | And so there's an old saying because a coral snake
looks like this and a milk snake does as well. |
Information Exchange | And the saying goes if red touches yellow
you're a dead fellow. |
Information Exchange | If red touches black you're okay Jack. |
Information Exchange | And so since the red is
touching the black here, this is just a harmless milk snake. |
Information Exchange | But if you're like me you're going
to stay away from anything that has coloration that looks like that. |
Information Exchange | Just because you've
been conditioned to do it. |
Information Exchange | And so in this podcast I'm going to talk about information
and how organisms use information to communicate. |
Information Exchange | Now in humans just talking is a great way
that we communicate and send information from one to another. |
Information Exchange | But again most organisms
don't have the ability to communicate verbally yet alone through podcasts. |
Information Exchange | And so I'm going
to talk about mechanisms by which they can communicate. |
Information Exchange | They will send signals. |
Information Exchange | Those
signals can be chemical. |
Information Exchange | Those signals can be visual, auditory. |
Information Exchange | And the example I'm going
to give you is how bees have learned to communicate using a waggle dance it's called. |
Information Exchange | That signal
is going to have a specific behavior. |
Information Exchange | And so especially in organisms that want to defend
a specific territory, they can actually mark that territory. |
Information Exchange | That signal is going to have
a desired consequence or desired effect in organisms which pick up on it. |
Information Exchange | The example
I'll talk about is wolves. |
Information Exchange | And then I want to delve a little bit more deeper and talk
about natural selection. |
Information Exchange | It's easy to say this is to observe a behavior. |
Information Exchange | But it's sometimes
harder to think about well how could this behavior have arisen? |