Study of Animal Type : Cockroach
Short Questions
1. What is the chemical nature of chitin in the cockroach exoskeleton?
Answer: Chitin is a carbohydrate (nitrogenous polysaccharide).
2. What type of mouthparts does a cockroach have?
Answer: Cockroaches have chewing and biting mouthparts.
3. How many pairs of spiracles are present in a cockroach?
Answer: Cockroaches have ten pairs of spiracles.
4. What is the function of the gizzard in a cockroach?
Answer: The gizzard grinds food with chitinous teeth and filters it with bristles.
5. What is the systematic position of cockroach at the phylum level?
Answer: Cockroach belongs to the phylum Arthropoda.
6. What is the haemocoel in a cockroach?
Answer: Haemocoel is the blood-filled body cavity in a cockroach.
7. What is the primary excretory organ of a cockroach?
Answer: Malpighian tubules are the primary excretory organs.
8. What is the brain of a cockroach called?
Answer: The brain is called the supra-oesophageal ganglion.
9. How many chambers are in the heart of a cockroach?
Answer: The cockroach heart has 13 chambers.
10. What is an ootheca in a cockroach?
Answer: Ootheca is a dark egg case containing 14-16 fertilized eggs.
11. What type of vision do cockroach compound eyes provide?
Answer: Cockroach compound eyes provide mosaic vision.
12. What is the role of hepatic caeca in digestion?
Answer: Hepatic caeca secrete digestive enzymes to aid digestion.
13. What type of circulatory system does a cockroach have?
Answer: Cockroaches have an open circulatory system.
14. What are anal cerci in a cockroach?
Answer: Anal cerci are sensory appendages on the tenth abdominal segment.
15. What is the developmental type of Periplaneta americana?
Answer: It undergoes paurometabolous development.
Long Questions
1. Describe the structure and function of the cockroach exoskeleton.
Answer: The cockroach exoskeleton is a hard, waxy, non-living structure made of chitin, a nitrogenous polysaccharide, covering each body segment with four sclerites (tergum, sternum, pleurons). It provides strength, elasticity, and a surface for muscle attachment, protecting the body. The exoskeleton requires moulting for growth due to its rigidity.
2. Explain the role of mouthparts in the cockroach digestive process.
Answer: Cockroach mouthparts, including labrum, mandibles, maxillae, labium, and hypopharynx, are adapted for chewing and biting. Mandibles crush food, maxillae and labium hold and manipulate it, while the hypopharynx mixes saliva for initial digestion. These structures ensure food is processed and directed into the alimentary canal efficiently.
3. How does the tracheal system facilitate respiration in cockroaches?
Answer: The tracheal system comprises spiracles, trachea, and tracheoles, allowing direct oxygen delivery to tissues without blood. Spiracles (10 pairs) permit air entry, trachea distribute it, and tracheoles facilitate gas exchange at fluid-filled tips. Muscle movements renew air, and fluid dynamics enhance oxygen intake during activity.
4. What is the significance of the gizzard in the cockroach digestive system?
Answer: The gizzard, or proventriculus, is a spherical organ in the foregut with six chitinous teeth and bristles. It mechanically grinds food and filters large particles, preparing it for enzymatic digestion in the midgut. Without the gizzard, digestion would be inefficient, impacting nutrient absorption.
5. Describe the structure of the cockroach compound eyes and their function.
Answer: Cockroach compound eyes, located laterally on the head, consist of ~2000 hexagonal ommatidia, each forming a small image. They produce mosaic vision, highly sensitive to motion but with low resolution, ideal for nocturnal environments. This vision helps detect predators and navigate surroundings.
6. How does the circulatory system of a cockroach function?
Answer: The cockroach has an open circulatory system with haemolymph flowing in a haemocoel, divided into pericardial, perivisceral, and perineural sinuses. The heart, with 13 chambers and ostia, pumps haemolymph to the dorsal aorta during systole, while alary muscles aid flow during diastole. This system distributes nutrients and wastes without capillaries.
7. Explain the role of Malpighian tubules in cockroach excretion.
Answer: Malpighian tubules, ~150 thread-like structures at the midegut-hindgut junction, extract nitrogenous wastes and water from haemolymph, converting them to uric acid. Their glandular epithelial cells with microvilli facilitate secretion and absorption, passing wastes to the ileum. This makes cockroaches uricotelic, conserving water.
8. Describe the nervous system organization in a cockroach.
Answer: The cockroach nervous system is ventral and ganglionated, comprising a central nervous system (CNS) with a nerve ring (supra- and sub-oesophageal ganglia) and ventral nerve cord (nine ganglia). The peripheral nervous system (PNS) innervates sensory and motor organs, while the autonomous nervous system (ANS) regulates visceral functions. This system coordinates sensory input and body responses.
9. How is fertilization achieved in cockroaches, and what is the role of the ootheca?
Answer: Fertilization in cockroaches is internal, with males transferring spermatophores to the female genital chamber, where sperms reach the spermatheca to fertilize eggs from the ovaries. The collateral glands secrete an ootheca, a protective egg case containing 14-16 eggs, deposited in humid crevices. The ootheca safeguards eggs during paurometabolous development.
10. Discuss the economic importance and control measures for cockroaches.
Answer: Cockroaches damage household items, contaminate food with pathogens (e.g., cholera, typhoid), but serve as prey in food chains and research subjects. Control measures include sanitation (cleaning, sealing crevices, maintaining drain traps) to eliminate habitats. Chemical controls like organophosphates, carbamates, pyrethroids, and boric acid effectively reduce populations.
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