Question

cockroach digestive system in points for 3 marks

Answer 1

Feeding in Cockroach:

Cockroaches have adopted themselves to all types and sizes of diet. To handle the various types of food all the appendages of cockroach act synchro­nously. Out of all appendages only mouth parts are described here as feeding apparatus, followed by the process of feeding.

(a) Feeding Apparatus/Mouth Parts/ Trophi:

The mouth parts are composed of paired appendages like mandibles and maxillae and unpaired structures like labi­um, hypo-pharynx and labrum 
(b) Feeding Mechanism:
Cockroaches are not habitual predators. They generally take static matter as their food. They possess five types of receptors, viz., mechanoreceptors, photoreceptors, thermo-­receptors, chemoreceptors and hygroreceptors. Among these, photoreceptors locate food by forming images; chemoreceptors, present in antenna and other appendages, help in detecting chemical stimuli in the form of smell and taste.


Digestion in Cockroach:

Extracellular digestion is the characteristic like other developed animals. Digestion starts from the buccal cavity containing the mouth parts. The food is then subjected to a variety of biochemical reaction within a specialized digestive system.
Digestive System of Cockroach:

The digestive system, which is responsible for digestion and absorption of food materials, includes digestive canal or tract and diges­tive glands.

(a) Digestive Tract:

The tract is about 6.7 cm in length. It is divisible into three distinct regions:



Digestion Procedure in Cockroach:

Within the buccal cavity, the food comes in contact with saliva and passes through the oesophagus into the crop. Both peristalsis and antiperistalsis take place in the crop. Such activities of the crop are more intense in males than in females. The passage of food from the crop to the gizzard depends upon the ingested fluid.

From the crop, the food passes to the gizzard, where the cuticular teeth crushes the food and the hairy cushion permits only finer particles to enter the mid gut. The lining of mid gut and hepatic caeca act both as secretory and absorptive areas. Following enzymes are present in the secretion of these regions—amylase, maltase, invertase, lac­tase, β-glucosidase, protease and lipase.

The cellulase obtained in the mid gut is synthesised by the micro-organisms residing there. Most of the digested foods are absorbed only in the mid gut. Glucose is absorbed by the caeca.

After the absorption of digested food, the rest passes within the hind gut, where water and salts are absorbed. Residual matter is temporarily stored in the rectum and are periodically rejected through the anus. Food requires nearly 33 hours to travel the entire length of the alimentary canal.

It may be mentioned here that from the junction of gizzard and mid gut the epithelial cells constantly throw membranous struc­tures called peritrophic membrane of uncer­tain function. These membranous structures are toned up in the anterior region of the hind gut by the internal spines.

Electron microscopic studies have revealed that the peritrophic membranes are made up of several layers and resemble the structures present in saliva. Such similarity in structures indicates that probably peritrophic mem­branes from mid gut mix up with saliva at the time of regurgitation.

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