3.1.1 f gas exchange in fish and insects Flashcards
how do insects prevent water loss?
insects are covered in a cuticle which is a tough exoskeleton that is impermeable.
it prevents water loss but makes it impossible for oxygen and carbon dioxide to get through.
how do insects get oxygen?
small holes in the cuticle called spiracles where air enters and leaves.
maximises the efficiency of gas exchange but minimises water loss
what opens and closes the spiracles?
sphincters which close the spiracles as much as possible to minimise water loss.
what do the spiracles lead to?
the tracheae which are 1mm in diameter
what is the tracheae lined with?
spirals of chitin which keep them open if they are bent or pressed.
chitin is impermeable so little gas exchange happens in the tracheae
what is the cuticle made from?
chitin
what does the tracheae lead to?
tracheoles which are single, elongated cells which are NOT lined with chitin so they are freely permeable to to gases.
they are spread throughout the tissues of the insect.
what is at the end of the tracheoles?
tracheal fluid which limits the penetration of air for diffusion
what happens when the insect is active and the oxygen demand builds up?
there is a lactic acid build up in the tissues which results in water leaving the tracheoles by osmosis which then increases the surface area exposed for gas exchange
what do insects with a high energy demand do?
some insects have mechanical ventilation of the tracheal system where air is actively pumped by muscular pumping movements of the thorax and/or abdomen. the movements change the volume of the thorax, therefore changing the pressure either forcing air out or drawing air in.
some insects have a collapsible enlarged tracheae or air sacs which act as air reservoirs and are used to increase the amount of air travelling through the gas exchange system. they are usually inflated and deflated by ventilating movements of the thorax and abdomen.
discontinuous gas exchange cycles in insects
spiracles have three states; open, closed, fluttering.
when spiracles are closed, no gas moves in or out of the insect.
when spiracles flutter, they open and close rapidly which moves fresh air into the tracheae to renew the supply of oxygen while minimising water loss.
when carbon dioxide builds up, the spiracles open widely to diffuse it out rapidly.
adaptations of gills
large surface area, thin and good blood supply
the tips of adjacent gill filaments overlap which increases resistance to the flow of water over the gills and and slows down the movement of water so there is more time for gas exchange to take place.
where are gills contained in bony fish?
gill cavity and protected by operculum which is active in maintaining a flow of water over the gills
where is the main site of gas exchange in fish?
gill lamellae which have a rich blood supply and a large surface area
how does the ventilation of the gills work when the fish’s mouth is opened?
the mouth is opened and the floor of the buccal cavity is lowered so the volume of the buccal cavity is increased.
the pressure decreases and water is drawn into the buccal cavity.
at the same time, the opercular valve is shut and the opercular cavity where the gills are expands which lowers the pressure in the opercular cavity.
the floor of the buccal cavity moves up which increases the pressure so so water moves from the buccal cavity to the gills.
