Stimulus Any change in an organisms internal or external environment that causes the organism to react to the change Stimuli plural more than one stimulus Response The reaction of an organism to a stimulus ID: 934120
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Slide1
An Organism’s Responses to changes in their Environment
Slide2Stimulus
Any change in an organism’s
internal or external environment that causes the organism to react to the change.
Stimuli – plural (more than one stimulus)
Slide3Response
The reaction of an organism to a stimulus.
Slide4Examples of stimuli and their responses:
The dog is hungry, so it eats
some food from the bowl
A rabbit sees a wolf, so it
runs away to safety
Slide5Plants also respond to their environment.
When plants grow towards the sun, we call this reaction
phototropism
Slide6Plants respond to their environment in other ways too .
Plants roots grow down towards the water due to the effect of gravity
Slide7Two Types of Stimuli
Internal
External
Slide8Internal stimulus
A stimulus that comes from inside the organism.
When the body becomes too
warm due to exercise,
the skin responds by sweating. The
sweat evaporates and cools the body temperature down.
Slide9Internal Stimuli & Responses
Think of all the changing conditions that an organism might need to respond to.
Here’s just a few samples:
too hot
too cold
thirsty
hungry
tired
pain
sleepy
afraid
excited
And here are some
specific responses
to these
internal stimuli
.
kitten hides
Joe shivers
Joe drinks
H2O
Rex wags tail
owl grabs mouse
scream
yawn
lion rests
Joe sweats
Forget shivering…
Where’s my
hoodie
?!?
Slide10When
the finger senses
that something is dangerously hot, it pulls away.
External stimulus
A stimulus that comes from
outside
of the organism.
Slide11External Stimuli & Responses
External stimuli can
be more complicated. Let’s see how.
EXTERNAL STIMULUS RESPONSE
Bright sunlight
Squinting (ok, this one is pretty simple)
Shorter days, colder
temperatures
Trees drop their leaves in autumn
Increasingly hot weather
Dogs shed their thick
winter coats
in late spring
Sunlight, motion of the Sun.
Plants grow toward the Sun’s position.
Difficult survival conditions
coming up
Hibernation (chipmunks sleep
thru
cold months)
Migration (geese fly to
warm
weather &
easy food
)
Dormancy (grass turns brown in winter instead of
trying to grow & stay green)
There really are countless more examples, from as simple as an
itch on your arm to the complicated conditions that cause plants
to realize winter is over and spring back into life.
moonlight = external stimulus
howling
= response
Slide12When there is not enough light
to
see, the pupil of the eye enlarges to allow as much light in
as possible so you can see.
When the light
is
too
bright, the pupil
size becomes smaller to prevent too much light
from going in and temporarily blinding you.
pupil
Internal or External Stimulus?
External
Slide13When pollen
enters your nose,
the body responds by
sneezing.
External
Internal or External Stimulus?
Slide14When
growth hormones help you add more muscle & bone tissue during growth spurts
Internal
Internal or External Stimulus?
Slide15The End!!