Sharks Developed by Adam F Sprague

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SharksDeveloped by Adam F Sprague
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How does a shark work?
Sharks also have a very unique skin texture. They
don't have the large, prominent scales found in
bony fish. Instead they're covered with smaller,
tooth-like scales called denticles. These
tough, protective denticles are aligned so that
they channel water over the shark's body, minimiz
ing drag due to friction.
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Like bony fish, sharks breathe by extracting
dissolved oxygen from water. The water enters th
e mouth, passes through the gills
and is expelled through gill slits behind the
head. In bony fish, these slits are covered, but
in most sharks you can see them clearly.
As the water flows through the gill opening, it
passes tiny gill filaments. These filaments are
covered with microscopic blood
vessel capillaries, which have a lower oxygen
content than the water around them. This imbalan
ce causes oxygen in the water to diffuse into th
e shark's bloodstream, where it is distributed
throughout the body.
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Some sharks have a gill pump, a set of muscles
that suck in water and push it past the gills. T
his works something like our lungs --
the shark can continuously gather oxygen while it
is in a still position. Most sharks also extract
oxygen using ram ventilation, passing
water over the gills by moving forward. Some
highly-active sharks depend on ram ventilation a
lmost entirely, which means they stay in
motion most of the time!
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Nurse sharks, which hunt mostly at the ocean
bottom, have a gill pump that lets them breathe
without moving
through the water.
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A shark is more like an airplane. It doesn't have
a swim bladder, so it uses its forward movement
to control vertical position.
The tail is like the shark's propeller -- the
shark swings it back and forth to move forward.
In an airplane, this forward movement pushes air
around the wings. In a shark, this
forward movement pushes water around the fins.
In both cases, this movement of matter creates l
ift -- the fluid is different, but the principle
is exactly the same.
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Sharks have two sets of paired fins on the sides
of their body, in the same general position as t
he main wings and horizontal tail wings of a pla
ne. The shark can position these fins at
different angles, changing the path of the water
moving around them. When the shark tilts a fin u
p, the water flows so there is greater pressure
below the fin than above it. This creates upward
lift. When the shark tilts the fin down,
there is greater pressure above the fin than
below it. This pushes the shark downward.
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The shark also has one or two vertical dorsal
fins on its back and sometimes a vertical anal fi
n on its underside. These fins work like the ver
tical stabilizer wing on an airplane. They help
the shark keep its balance as it moves through t
he water and they can be moved from side to side
to turn the shark left and right.
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Silky sharks' long graceful bodies make them
excellent swimmers.
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The shark's nose is definitely one of its most
impressive (and prominent) features. As the shar
k moves, water flows through two forward facing
nostrils, positioned along the
sides of the snout. The water enters the nasal
passage and moves past folds of skin covered wit
h sensory cells. In some sharks, these sensitive
cells can detect even the slightest
traces of blood in the water. A great white
shark, for example, would be able to detect a si
ngle drop of blood in an Olympic-size
pool. Most sharks can detect blood and animal
odors from many miles away.
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Another amazing thing about a shark's sense of
smell is that it's directional. The twin nasal c
avities act something like your two ears Smell
coming from the left of the shark will
arrive at the left cavity just before it arrives
at the right cavity. In this way, a shark can fi
gure out where a smell is coming
from and head in that direction.
Sharks also have a very acute sense of hearing.
Research suggests they can hear low pitch sounds
well below the range of human hearing. Sharks m
ay track sounds over many miles, listening speci
fically for distress sounds from wounded prey.
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Extra Shark Senses
The ampullae of Lorenzini give the shark
electrosense. The ampullae consist of small clus
ters of electrically sensitive receptor cells po
sitioned under the skin in the shark's head. The
se cells are connected to pores
on the skin's surface via small jelly-filled
tubes. Scientists still don't yet understand eve
rything about these ampullary organs, but they d
o know the sensors let sharks "see" the weak ele
ctrical fields generated by living organisms. Th
e range of electrosense seems to be fairly limit
ed -- a few feet in front of the shark's nose
-- but this is enough to seek out fish and other
prey hiding on the ocean floor.
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Water flows through the lateral line systems.
Vibrations in the water stimulate sensory
cells in the main tube, alerting the shark to
prey and predators.
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Another unique sense organ is the shark's lateral
line. The lateral line is basically a set of tub
es just under the shark's skin. The two main tub
es run on both sides of the body, from the shark
's head all the way to its tail.
Water flows into these main tubes through pores
on the skin's surface. The insides of the main t
ubes are lined with hair-like protrusions, which
are connected to sensory cells. When something
comes near the shark, the water running through
the lateral line moves back and forth. This stim
ulates the sensory cells, alerting the
shark to any potential prey or predators in the
area.
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