Hi. It's Mr. Andersen and welcome to Biology Essentials video number 19. This
is on response to external environments. Of all the animals that I love my favorite is
the water bear. Their name is tardigrade but we in general just call them water bears.
This is a picture of a couple of them under electron microscopy. They're about, the biggest ones
are maybe like 1.5 millimeters in length. So they're pretty small but they get their
name from the way that they walk. They kind of move back and forth almost like a bear.
They live everywhere on our planet. So you'd find them in the Himalayas. You'd find them
deep in the ocean. You find them everywhere. But what makes them interesting is that they're
able to survive incredible harsh environments. So they can survive near absolute zero, 304
degrees Fahrenheit. They can survive for decades without water. They seem to replace the water
inside them with some kind of a sugar. And recently they've been studied in space. So
they kept a population of water bears in space for 10 days just exposed to low earth orbit.
And not only did they survive, but they laid a number of eggs which also survived. And
so water bears are world record holders as far as surviving harsh environments. But a
lot of animals on our planet have to survive. An organism with changing environments. And
so they do that through two types of responses. First type is behavioral. So example of two
that I'll talk about are hibernation and migration. And those are response to changes in climate.
Not climate but in temperature. And then physiological are going to be changes within an organism
themselves. A couple I'll talk about in humans are shivering and sweating to keep ourselves
a little warmer and to keep ourselves cooler. And so behavioral response is an organism
or a group of organisms doing that. But physiological is going to be within that organism itself.
Okay. And so behavior responses, let me talk about a few. Let's say it gets cold. So let's
say it gets cold during the winter. What can you do? Well you can either stay or you
can go. And if you choose to stay, you're going to have to tough it out or you could
enter into something called hibernation. And so hibernation you're probably familiar with.
In true hibernation what you do is you lower your body temperature. You lower your metabolism.
And so a true hibernator, a great example, would be like a ground hog which is a type
of a marmot. And what they do is they'll actually crank their metabolism down so it's almost
the same as their environment. So right around freezing their body temperature is. Torpor
is a type of hibernation. It's essentially doing that on a daily scale. So lowering the
metabolism probably at night to survive that. And then it's kind of a continuum. And so
there's a continuum from torpor to hibernation. And so things that we think of as hibernators
are probably not true hibernators, like a bear, because a bear, even though they turn
their, they slow down their metabolism, crank down their body temperature a little bit,
they're easily aroused and it doesn't go near zero. And so there's this continuum from just
daily torpor to hibernation. But essentially what you're doing is cranking down your metabolism
so you're able to survive during the period of time where it's cold. Another way that
we can survive during a period of cold is to just leave. And so migration is an example
of that. So caribou will migrate to a calving area or to an area where they don't get such
harsh environment during the winter. But probably the most famous migrators of all are birds.
And of all of those the Bar-tailed Godwit is the record holder. They will migrate from
the northern hemisphere. During the summer they'll spend time there. Northern Asia. Some
of them all the way up in Alaska. And then they'll migrate all the way down to New Zealand
and Australia during what would be their summer there. And so instead of having to deal with
that harsh climate, they're simply moving. And so this is a group of individuals or a
population that is doing that. Now that can be innate. You could be born with it. Or it
could be something that you inherit. But one thing is that that's probably not fast enough.
In other words if it gets really cold or if it gets really hot, we also have to have physiological
responses. So physiological responses are changes within you. So a couple of examples
in humans could be shivering and sweating. This is during the Napoleon withdraw from
Russia. Thousands of people died from hypothermia. And so if you're an endotherm, warm-blooded
critter like we are, once your body temperature starts to drop off, then you can quickly die.
And so as a response for that we could get goose bumps. We could have our hair try to
stand up on end. We could have clothes for sure. But one thing that we start to do very
quickly when we get cold is we start to shiver. And the reason we do that, it's muscles, especially
muscles around the vital organs in our body will start to move very very quickly. And
the reason they're doing that is they're expending energy. They're generating ATP. But the other
thing that they're generating is heat. And that heat is being generated to keep that,
to keep us alive, keep us warm so we don't go hypothermic. On the other side, let's say
we get too hot. Then we'll start to sweat. And the reason that we sweat is that water
on our skin is quickly going to evaporate. And when it evaporates it's going to carry
heat with it. And so that's evaporative cooling. Now if you can't sweat, other organisms will
pant. Like a dog for example will pant. A funny story I remember reading about the marathon
is that they used to think that if you drank water during a marathon, it would slow you
down. Add weight to you. But if you're running a marathon you also have to get rid of the
heat. So this is Haile Gebrselassie. He's the world record holder in the marathon right
now. And they constantly are taking in water throughout the run. That's to replace water
that they've lost through sweating just to keep that core body temperature low. And so
these are physiological responses. And we constantly are doing this to maintain homeostasis.
But remember we can have behavioral responses. And all of these lead to the fitness of the
individual and are selected through natural selection. And so those are responses to environment
and I hope that's helpful.