Lesson Plan For Primary School Science

Like all arthropods, German cockroach has a skeletal system on the outside of the body. According to Book Rags Website, the skeletal system is the framework of hard, articulated structures that provide physical support, attachment for muscles, and protection for the bodies of animals. It helps to support each organism and its limb in order to save from harm the internal organs. The attachment of muscle on skeletal system is essential to give functions in locomotion. Without this system, organisms would not move.

Lacking of internal skeletons, German cockroach wears its 'bone' on the outside in the form of an exoskeleton. This lifeless shell is placed atop the epidermis. “Exoskeleton is a chitin shell secreted by the mantle, a thin sheet of epithelial tissue that extends from the body wall.” (Boloman, Berg & Martin, 2005) It consists of three layers. The outermost layer is cuticle. “The cuticle is made up of a number of very thin laminations of chitin, arranged so that the fibers in each lamination run perpendicular to those above and below it, forming a cross-hatched pattern that gives great structural strength while allowing for flexibility”. (Starr, C., Evers & Starr, L., 2007) Everything that is visible on the outside of a cockroach which include the wings, skin, legs, and hairs. They are made of a single unbroken layer of cuticle.



The cuticle layer does not have cell on it. It is dead and unable to grow. The cuticle layer is made up of two parts. The waterproof epicuticle is placed in the outer part. It contains no chitin and is highly resistant to water solvents. Beneath this is the much thicker procuticle. It can be divided into two distinct layers. An outer exocuticle is laid below the epicuticle. An inner endocuticle which consists of a large number of layers of protein and chitin and chitin fibres laid down in a laminated pattern. Beneath the cuticle layer is the epidermis, which is made up of a layer of living cells that secrete the chitin making up the outer cuticle. Beneath this is the basal membrane that separates the epidermis from the internal body fluids and organs.



“Exoskeletons restrict the growth of the animal, thus it must shed its exoskeleton (or molt) to form a new one that has room for growth.” (Huber& Maler, 1990) In order to undergo the growth process, the exoskeleton of cockroaches will be molted periodically. When the cockroach is ready to molt, the exoskeleton will split down the back and force it to climb out from the old cuticle. “The exoskeleton of a newly molted roach is white and soft, and is incapable of supporting the cockroach weight--the roach depends on its blood pressure to keep the soft cuticle from collapsing.” (Raven & Johnson, 1998) It takes six or seven molts for a newly hatched cockroach to reach sexual maturity. Once it reaches the adult stage, it will not molt again. Unlike most insects, which have a waxy coating on their exoskeleton to prevent dehydration, the thin layer of grease that cover the cockroach makes itself looks dirty. However, in reality, cockroaches are clean animals and put a lot of good effort to keep their cuticle clean of foreign matter.

“Through the attachment of muscles to the part of exoskeleton, cockroach is allowed to receive some forces as the contraction of muscle occurs.” (Hickman, C. P., Robert, L.S., Larson, A., I’Anson, H. & Eisenhour, D. J., 2006) The joint of the muscles to the rigid chitin exoskeleton enable cockroach to move. These muscles usually occur in pairs that operate to each other such as the flexor and extensor muscle which control forward and backward movement. Both of the muscles are attached to the same points of its exoskeleton to ensure the each movement can be coordinated. The extensor tibiae muscle which causes the leg to extend, and the flexor tibiae muscle which causes the leg to flex. These muscles pull on tendons which are attached to the tibia on either side of the joint pivot. These tendons can be seen by removing the cuticle from one side of the leg in the joint region




Instead of this, the link of the muscle and skeletal system also allows cockroach to fly. The antagonistic movement of elevator and depressors muscle causes its wing to beat.


Cockroach becomes one of the insect that affects our quality of life. “Spray is natural or synthetic substances used by man to control pest organisms by disrupting some part of cockroaches’ life processes.” (Octopus, B., 2007) Literally, the term pesticide means to "kill pests." Spray contains chemicals that called acetylcholinesterase. Acetyl choline (ACh) is the nerve transmitter substance released by motor neurones to stimulate muscle contraction. The muscles relax (stops contracting) when the ACh is removed from the neuromuscular junction (NMJ) by the action of acetylcholinesterase. By inhibiting the cholinesterase the cockroach can no longer break down ACh in the NMJ and so its muscles lock up in a state of tetany (continuous contraction). It makes moving and flying impossible. Through controlling the muscle contraction within the skeletal system by chemical substance, cockroach can be easily killed. However, the chemical that released brings obvious disadvantage to our environment where it contributes a lot in air pollution.

Instead of this, many insects eat their cast cuticle (exuviae) after moulting. “Exuviate eating constitutes a meal, so the animal recycles its nitrogen content. Nitrogenous compounds (protein and chitin) are major components of the cuticle. The frequency of the behaviour decreased in newly emerged adults and varied between the sexes, males eating their exuviae less frequently than females.” (Mira, A., 2000) This may be due to the extra nitrogen endowment which females need for reproduction. Alex Mira stated that that over 58% of the nitrogen presents in the exuviae was recycled through the analysis of the frass produced after exuviae meals. This demonstrated that cockroaches digested nitrogenous compounds contained in the cuticle. Therefore, for those cockroaches which have approached directly to the spray may leave some of the chemical substance on their exoskeleton. They can be killed if eating their “skin” after molting due to the toxin substances left behind.