Download 7.b. Insect Tracheoles

Insect Tracheoles
Introduction:
Insect Tracheole gas exchange systems are commonly studied as part of many animal diversity
courses because they are so dissimilar to any other animal system.
Gases are transported from spiracles (openings along the abdomen) by a series of branching
hollow tubes (trachea) to the tissues where oxygen is required and where carbon dioxide is
produced. The fine tubules that deliver oxygen to the tissues themselves are called tracheoles and
often have a film of moisture in their extremities. This system has its limitations because it is
essentially a one-way system and relies heavily on diffusion for gas movement (particularly if the
insect is at rest). Many insects employ pumping mechanisms when they are active and these
mostly involve the action of muscles in the abdomen.
Method
Cockroaches are suitable for this exercise as they
are large enough to handle easily. A freshly killed
cockroach is dissected by cutting along its sides
from the posterior end. Use a pointed pair of
scissors as shown by the two arrows on the
photograph at left.
When the two cuts have been made lift off the
ventral (front) surface (much like opening the cover
of a book) to expose the body contents.
The tissue you look for is muscle tissue. It is
recognised because it has a light pink ‘meaty’
appearance. There is a large amount of muscle
material in the region of the legs and wings in the
thorax.
Muscle tissue
Start here
Remember insects have 3 body parts;
head, thorax and abdomen. In the thorax
are the muscles that are responsible for
walking and flight.
Remove small portions of this muscle
tissue. Place on a slide in 0.9% salt solution
(or water). You might need to squash the
preparation slightly or else tease out the
muscle fibres with two needles before you
add the cover slip.
Images
Air bubble
inside
trachea
The four photographs on this page were taken at Low Power (x40) top right, or Medium Power
(x100) for the other photographs. They show larger trachea that branch into smaller and smaller
tubes that deliver oxygen to all tissues. Note the circular rings of chitin that supports the trachea
and keeps them open. The exoskeleton is made of this same material.
Air inside trachea
These four photographs show the smaller tracheoles. The top pictures were taken at Medium
Power (x100) and the bottom two were High Power (x400). Note how the trachea branch finely so
that no muscle cells are far from their supply of oxygen.