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gas exchange system in insects (structure (system evolved so oxygen…
gas exchange system in insects
structure
tough exoskeleton - little or no gas exchange can take place through it
no blood pigments that can carry oxygen
system evolved so oxygen delivered directly to cells
most gas exchange occurs by diffusion
tracheal system supplies all oxygen needed by cells
rate of gas exchange controlled by opening and closing of spiracles in most insects
thorax and abdomen
spiracles - small openings
air enters and leaves through spiracles
water is lost through these as well
spiracle sphincters - closed as much as possible to minimise water loss
when inactive and low oxygen demands - spiracles are closed
when high oxygen demands or carbon dioxide levels raised e.g. insect flying - more spiracles open
tracheae
lead away from spiracles
largest tubes of gas exchange system - up to 1mm in diameter
carry air into the body
lined with spirals of chitin - keep them open
relatively impermeable to gases - little gas exchange takes place in tracheae
tracheoles
narrower tubes than tracheae
spread through tissues of the insect - run between individual cells
most gas exchange takes place here
large number of tracheoles gives large surface area for gas exchange
oxygen dissolves in moisture on walls of tracheoles
diffuses into surrounding cells
each tracheole is a single elongated cell - no chitin lining
freely permeable to gases
tracheal fluid
found towards end of tracheoles
limits penetration of air for diffusion
high oxygen demands - lactic acid build up in tissues means water moves out of tracheoles by osmosis
more surface are exposed for gas exchange
adaptations for increased gas exchange
some insects have high energy demands - e.g. locusts, grasshoppers, bees and flies
mechanical ventilation of tracheal system
air is actively pumped into system by muscular pumping movements of thorax and abdomen
movements change volume of body which changes pressure in trachea and tracheoles
air is drawn into trachea and tracheoles or forced out as pressure changes
collapsible enlarged tracheae or air sacs
act as air reservoirs
increase amount of air moved through gas exchange system
inflated and deflated by ventilating movements of thorax and abdomen