gas exchange in fish Flashcards
what is the buccal cavity
the mouth
what is countercurrent flow
where two fluids flow in opposite directions
what are filaments
slender branches of tissue that make up the gill. often called primary lamellae
what are lamellae
sometimes called secondary lamellae. these are folds of the filament to increase surface area. also called gill plates
what is the operculum
a bony flap that protects and covers the gills
what is special about aquatic organism
they dont need to try and prevent water loss when getting oxygen from water
why is different about water compared to air
water is 1000 times denser than air and is 100x more viscous with a much lower oxygen content.
how does the respiratory sytem of a fish work
they move water in one direction (takes less energy)
how do bony fish exchange gases
with the water in which they live
what do fish have to absorb oxygen from the water and release carbon dioxide into the water
gills
is the oxygen concentration lower in water or in the air
the water
how many pairs of gills do bony fish have
5
what are the gills covered by
the operculum
what does each gill consist of
two rows of gill filaments (primary lamellae) attached to a bony arch
what do the surfaces of the thin filaments fold into
many secondary lamellae (gill plates)
what do the gill plates provide
a large surface area
where do the blood capillaries carry deoxygenated blood
close to the surface of the secondary lamellae where exchange takes place
how does the blood flow in a fish
blood flows along the gill arch and out the filaments to the secondary lamellae. the blood then flows through capillaries in the opposite direction to the flow of water over the lamellae
what does a countercurrent flow do
absorbs the maximum amount of oxygen from the water. countercurrent exchange removes up to 80% of the oxygen in the water by maintaining a steep gradient
how does a countercurrent flow system work in a fish
1) in countercurrent flow/exchange blood flows in the opposite direction to the flow of water.
2) this causes oxygen to diffuse down the oxygen concentration gradient from the water to the blood
3) this results in the oxygen concentration between the blood in the gills and the water being maintained across the entire legnth of the gill lamella
4) even when the concentration of oxygen in the water is low at the operculum cavity end of the lamella, blood has just entered the gill lamella, therefore is even lower in oxygen concentration
5) this means there is still a diffusion gradient allowing the diffusion of oxygen from the water into the blood
what happens if there is parallel (concurrent) flow of blood and water
the concentration of oxygen in the water and in the blood will equalise, therefore no more exchange of oxygen would take place.
what must the flow of water be like for countercurrent flow gas exchange
must be unidirectional and not tidal
why do the cells of bony fish have a high demand
bony fish are active animals
what does the scaly outer covering of bony fish not allow for
gas exchange.
what have bony fish evolved
a ventilatory system adapted to take in oxygen from the water and get rid of carbon dioxide from the water
in which direction does water flow over the gills
in one direction
what are some adaptations of the gills
- large surface area for diffusion
- good blood supply to maintain a steep concentration gradient for diffusion
- thin layers so diffusing substances have short distances to travel
what are the gills contained in and covered by
contained in a gill cavity and covered by a protective operculum which is active in maintaining a flow of water over the gills
why must fish be able to maintain a continuous flow of water over the gills even when they aren’t moving
to allow efficient gas exchange at all times
why does gas exchange need to be efficient
water is a medium where diffusion is slower than in air
what does the bony arch do
supports the structure of the gills
what is the main site of gas exchange in fish
gill filaments with their rich blood supply and large surface area. they occur in large stacks (gill plates)
what do the gills constantly need and why
a flow of water to keep the gills apart in order to expose the large surface area needed for gas exchange
what does afferent mean
describes things like nerves, blood vessels and arteries that lead towards or bring things (like blood) to an organ such as the heart or brain
what does efferent mean
used to describe parts that carry or lead away things from organs
what does an efferent blood vessel do
carries the blood leaving the gills in the opposite direction to the incoming water maintaining a steep concentration gradient
what happens when fish are swimming
they keep a current of water flowing over their gills by opening their mouth and operculum
what happens when fish stop moving
the flow of water stops
how can bony fish keep water flowing over the gills even when they aren’t moving
- they have a buccal-operculum pump, drawing water into the buccal cavity
- the buccal cavity can change volume
- the floor of the mouth moves downwards
- the mouth closes and the floor is raised again pushing water through the gills
- movements of the operculum are coordinated with the movements of the buccal cavity. as water is pushed from the buccal cavity the operculum moves outwards
- the reduces the pressure in the operculum cavity (the space under the operculum)
describe the mechanism of ventilation in fish
1) mouth opens (operculum is closed)
2) buccal cavity is lowered
3) increases the volume and decreases the pressure of the buccal cavity compared to outside
4) water rushes into the mouth down a pressure gradient
5) opercular cavity expands
6) the buccal cavity floor is raised
7) the pressure inside the buccal cavity is now higher than in the opercular cavity
8) water moves from buccal cavity over the gills into the opercular cavity
9) the mouth is now closed and the operculum opens
10) the sides of the opercular cavity move inwards increasing the pressure
11) water rushes out of the fish through the operculum
why do the tips of adjacent gill filaments overlap
to increase the resistance to the flow of water over the gill surfaces and slows down the movement of water. this gives more time for gaseous exchange to take place
what does a countercurrent exchange system ensure
stepps concentrations gradients are maintained so more gaseous exchange takes place. water moveing over the gills and the blood in the gill filaments flow in opposite directions
how much oxygen do bony fish remove from the water flowing over them
80%
