Transcript Gas exchange in insects

Gas Exchange in Insects
Instead of having lungs and a
circulatory system to carry O2 and CO2
like you and me, insects have a
tracheal system to carry air directly to
and from every cell in their body.
Gas exchange in insects – the
tracheal system
• Insects do not breathe through their mouths like
other animals.
• Instead, they breathe through tiny holes along the
sides of their body called spiracles.
• The spiracles connect to tubes called tracheae or
tracheal tubes and these branch into microscopic
tubes called tracheoles that reach right in amongst
their body cells.
• O2 and CO2 travel in air through this tracheal
system to and from the body cells by diffusion.
air sacs
air rich in O2
air rich in CO2
air
chitin bands in
tracheal tubes
The Tracheal System
• Spiracles – tiny holes along the sides of an
insect’s body (up to 10 pairs in total).
• These are the openings that let air in and out of the
tracheal system.
• Tiny hairs lining the spiracles trap dirt and dust,
preventing them from entering and blocking up the
fine tubes in tracheal system.
• Valves, controlled by tiny muscles, allow the insect
to open and close its spiracles to reduce water
loss. This has enabled insects to live successfully
on land, particularly in dry habitats.
The spiracles are lined with tiny hairs that trap dust and dirt
preventing them from entering the tracheal system.
The spiracle mechanism
• The spiracles can be opened and closed to
reduce water loss.
• This is done by contracting closer muscles
surrounding the spiracle.
• Relaxing the muscles opens the spiracles.
The Tracheal System
• Tracheae – tubes leading from the spiracles
and branching throughout the insects body.
• The tracheae or tracheal tubes are strengthened
and held open by bands of chitin. This ensures
that air can always pass freely through the
tracheal system.
• Tracheoles – microscopic tubes at the ends of
the tracheae that reach in amongst the body cells.
• Tracheoles are the gas exchange surfaces.
• They are thin-walled and do not have chitin bands.
This enables O2 and CO2 to diffuse easily through
the tracheoles to and from the body cells.
• The tracheoles have fluid at their ends to keep
them moist, as O2 and CO2 must dissolve in water
as they pass through the gas exchange surface.
• The millions of microscopic
tracheoles in an insects body
provide a very large surface
area for gas exchange.
• Air sacs – are present in the tracheal system of
some insects, particularly larger ones.
• As the insect moves, particularly during flight, its
body muscles squeeze on the air sacs making
them expand and contract. This increases air flow
through the tracheal system.
• Many insects also make pumping movements with
their abdomen to move air in and out of their
tracheal system.
• Pumping air through the tracheal system is called
ventilation and is the insect’s way of “breathing”.
• Ventilation helps to make gas exchange more
efficient and is particularly important for larger or
more active insects.
Air movement through the tracheal system
Air enters spiracles
and passes along
tracheae and tracheoles
O2 from the air dissolves
in fluid at the ends of the
tracheoles.
Dissolved O2 passes from a
high conc. in tracheole to a low
conc. in cells by diffusion.
Air rich in CO2 passes
out of the tracheal system
through the spiracles.
CO2 passes into the
air in the tracheae.
Dissolved CO2 passes
from a high conc. in cell
to a low conc. in tracheole
by diffusion.
Insects in different habitats
– dry climates
• Muscles controlling the spiracle valves
enable the insect to open and close them.
• In dry climates insects avoid losing
valuable body moisture by controlling the
size of their spiracle openings to match
their O2 requirements.
• During flight the spiracles are fully open
but at rest, with less oxygen demand, the
spiracles partially close.
Aquatic habitats
• Aquatic life poses particular challenges for this
primitive breathing system.
• Some insects, eg-mosquito larvae, obtain air
from above the water surface with a specialized
breathing tube called a siphon that connects to
their tracheal system.
• Other insects, like water boatmen and some
aquatic diving beetles, stay submerged for long
periods of time by trapping a bubble of air
against tiny hairs on their thorax and abdomen.
Gas exchange in aquatic insects
• Insects that are fully aquatic
eg – mayfly nymphs, have
tracheal gills that extract O2
from water by diffusion.
• Instead of spiracles, they
have gills which are leaf-like,
thin-walled extensions of the
body along the sides of the
abdomen.
Tracheal gills
Gas exchange in aquatic insects
• Tracheal gills do not contain
blood vessels like the gills of
fish, but contain fine tracheal
tubes which absorb O2 from
the water by diffusion.
• Some insects can move their
tracheal gills like paddles for
ventilation and can hold them
flat against their body to
protect them from damage.
Tracheal gills provide a very large surface area
for gas exchange. This is important because water
contains a much lower % of dissolved O2 than air.
Advantages of a tracheal system
• The tracheal system is a very efficient system for
gas exchange because:
- it is simple – air is delivered directly to all the
body cells without the need to carry O2 and CO2 in
the blood.
- it is internal so the tracheoles are protected from
damage and kept moist for gas exchange.
- the microscopic tracheoles provide a very large
surface area for gas exchange.
- ventilation enables air to be pumped through the
tracheal system to meet the needs of larger or
more active insects.
- valves in the spiracles allow the insect to control
the entry and exit of air to meet its needs and to
reduce water loss in dry habitats.
Limitations of a tracheal system
• The tracheal system limits the size that an insect
can grow to because:
- The diffusion of gases in a tracheal system,
even with ventilation, is effective over short
distances only so insects cannot be too large or
the gases would not reach all of their cells.
- The tracheal system has a large mass so if
insects get too large it becomes too heavy.
- Because insects rely solely on diffusion of air for
gas exchange and do not carry O2 and CO2 in
their blood, this restricts the size they can grow to.
Insect Gas Exchange websites
• http://www.szgdocent.org/resource/ff/farth2a.htm (exoskeletons)
• http://www.earthlife.net/insects/anatomy.html
(insect morphology and anatomy)
• http://everest.ento.vt.edu/~carroll/insect_video_d
issection.html (Cockroach dissection)
• http://www.agsci.ubc.ca/courses/agro/327/AGR
O327.lecture.07.pdf (spiracles and trachea)
• http://www.micd.com/gallery/oblique/insectspiracle.html
(spiracles)