Notes Class 11 Chapter 11 Biology Maharashtra Board

Study of Animal Type : Cockroach

Introduction

Cockroaches are ubiquitous insects belonging to the phylum Arthropoda, known for their adaptability and resilience. This chapter explores the biology of the cockroach (Periplaneta americana), covering its habit, habitat, morphology, anatomy, and interactions with humans, providing a comprehensive understanding for Class 11 students.

11.1 Habit and Habitat

• Distribution: Cockroaches are omnipresent, found worldwide, thriving in damp, moist places and crevices.
• Behavior: They are omnivorous (feed on plant and animal matter), nocturnal (active at night), and cursorial (fast runners).
• Common Species in India: Periplaneta americana, Blatta orientalis, Blatta germanica.

11.2 Systematic Position

• Kingdom: Animalia (no cell wall, heterotrophic nutrition)
• Phylum: Arthropoda (jointed appendages, segmented body, chitinous exoskeleton)
• Class: Insecta (two pairs of wings, three pairs of walking legs)
• Genus: Periplaneta (nocturnal, straight wings)
• Species: americana (origin in America)

11.3 External Morphology

Shape and Size

• Body Structure: Elongated, bilaterally symmetrical, dorso-ventrally flattened.
• Organization: Triploblastic, eucoelomate, segmented with a haemocoel (blood-filled body cavity).
• Coloration: Glistening brown or reddish-brown.

Body Division

• Regions: Head, thorax, abdomen.
• Connection: Head attached to thorax by a flexible neck (cervix), allowing mobility.

Exoskeleton

• Composition: Hard, waxy, non-living, formed by chitin (a nitrogenous polysaccharide).
• Function: Provides strength, elasticity, and surface for muscle attachment.
• Structure: Each segment covered by four sclerites: dorsal tergum, ventral sternum, two lateral pleurons.

Head

• Shape: Triangular or ovate, formed by fusion of six segments.
• Features:
  1. Antennae: Long, segmented, filamentous, lodged in antennal sockets; tactile and olfactory organs for locating food.
  2. Fenestrae (Ocellar Spots): White spots at antenna bases, sensory in function.
  3. Compound Eyes: Paired, kidney-shaped, lateral; composed of ~2000 ommatidia, producing mosaic vision with high motion sensitivity but low resolution.
  4. Mouthparts: Chewing and biting type, located in a pre-oral cavity, comprising:
     • Labrum (Upper Lip): Flap-like, holds food.
     • Mandibles (True Jaws): Hard, chitinous, serrated; cut and crush food.
     • Maxillae (Accessory Jaws): Paired, with cardo, stipes, galea, lacinia, and maxillary palps; hold food, aid mastication, clean antennae/legs.
     • Labium (Lower Lip): Second maxilla, with labial palps; pushes food, prevents loss during chewing.
     • Hypopharynx (Tongue): Cylindrical, with super-lingua plates; mixes saliva with food, aids feeding.

Thorax

• Segments: Prothorax (anterior), mesothorax (middle), metathorax (posterior).
• Appendages:
  • Legs: Three pairs, one per segment, ventrally located; each leg has five podomeres (coxa, trochanter, femur, tibia, tarsus). Tarsus has five tarsomeres, with the last bearing claws and a cushion-like arolium for clinging.
  • Wings: Two pairs, dorsally attached:
    • Forewings: Dark, opaque, leathery; protective.
    • Hindwings: Thin, membranous, transparent; used for flight, attached to metathorax.
  • Spiracles: Two pairs on thorax, part of the respiratory system.

Abdomen

• Segments: Ten segments, elongated.
• Sclerites: Each segment has a dorsal tergum and ventral sternum, connected laterally by pleura.
• Posterior Features: Eighth and ninth terga overlap the seventh; tenth tergum is notched, bearing anal cerci (sensory appendages). Males have anal styles on the ninth sternum.
• Sexual Dimorphism: Male abdomen is narrower and tapering; female abdomen is broader.

11.4 Body Cavity

• Type: True coelom, filled with haemolymph, termed haemocoel due to open circulation.
• Fat Bodies: Loose, whitish tissue masses in haemocoel, containing fat globules, proteins, and glycogen for storage.

11.5 Digestive System

Components

1. Mouthparts: As described, facilitate chewing and ingestion.
2. Alimentary Canal: 6-7 cm long tube with two openings, divided into:
   • Foregut (Stomodaeum):
     • Pharynx: Short, muscular, with taste sensillae.
     • Oesophagus: Narrow, leads to crop.
     • Crop: Pear-shaped, stores food.
     • Gizzard (Proventriculus): Spherical, with six chitinous teeth and bristles; grinds and filters food.
   • Midgut (Mesenteron):
     • Stomach (Ventriculus): Short, narrow, lined with glandular epithelium; digests and absorbs nutrients.
     • Hepatic Caeca: Thin, hollow tubules; secrete digestive enzymes.
   • Hindgut (Proctodaeum):
     • Ileum: Short, receives nitrogenous wastes via Malpighian tubules.
     • Colon: Wider, reabsorbs water.
     • Rectum: Spindle-shaped, with six rectal pads; expels waste via anus on the 10th segment.
3. Salivary Glands: Paired, with glandular lobes (secrete saliva) and reservoirs; ducts unite to form a common efferent salivary duct opening at the hypopharynx.

Function

• Feeding: Omnivorous; mouthparts chew food, which is mixed with saliva and pushed into the alimentary canal.
• Digestion: Occurs primarily in the midgut, with enzymes from hepatic caeca and stomach.
• Excretion: Undigested food expelled via anus.

11.6 Circulatory System

Type

• Open Circulation: Haemolymph flows freely in haemocoel, not confined to vessels.

Components

1. Haemolymph: Colourless, pigment-free, with plasma (water, solutes, nutrients, uric acid) and haemocytes.
2. Haemocoel: Divided into three sinuses by diaphragms:
   • Pericardial Sinus: Dorsal, contains heart.
   • Perivisceral Sinus: Middle, contains viscera.
   • Perineural Sinus: Ventral, contains nerve cord.
   • Diaphragms: Dorsal (with 12 pairs of alary muscles) and ventral; facilitate blood movement.
3. Dorsal Blood Vessel:
   • Heart: 2.5 cm, 13 chambers (10 abdominal, 3 thoracic), with 12 pairs of ostia (valved openings).
   • Dorsal Aorta: Thin-walled, extends to head, opens into haemocoel.

Circulation Mechanism

• Diastole: Alary muscles contract, flattening dorsal diaphragm; haemolymph enters heart via ostia.
• Systole: Heart contracts from posterior to anterior, pushing haemolymph to dorsal aorta and head; ostia close.
• Diastasis: Heart remains expanded.
• Flow: Haemolymph moves from pericardial to perivisceral and perineural sinuses via fenestrae (pores in diaphragms).

11.7 Respiratory System

Type

• Tracheal System: Network of air tubes for direct gas exchange between air and tissues.

Components

1. Spiracles: 10 pairs (2 thoracic, 8 abdominal), ventro-lateral, allow air entry/exit.
2. Trachea: Branched tubes (~1 mm thick) with chitinous spiral thickenings to prevent collapse.
3. Tracheoles: Fine, intracellular tubes, fluid-filled at blind ends; site of gas exchange.

Mechanism

• Gas Exchange: Oxygen enters via spiracles, travels through trachea and tracheoles, diffuses into tissues; carbon dioxide exits similarly.
• Fluid Dynamics: During high activity, tracheole fluid is partially absorbed, increasing oxygen intake.
• Ventilation: Thoracic and abdominal muscle movements renew air in the system.

11.8 Excretory System

Main Organ

• Malpighian Tubules: ~150 yellow, thread-like structures at the midgut-hindgut junction, freely hanging in haemocoel.
  • Structure: Single layer of glandular epithelial cells with microvilli; distal part secretory, proximal part absorptive.
  • Function: Extract water and nitrogenous wastes from haemolymph, convert to uric acid, pass to ileum.

Additional Excretory Structures

• Fat Bodies and Nephrocytes: Store nitrogenous wastes, released into haemocoel or during moulting.
• Uricose Glands (Males): Aid excretion.
• Cuticle: Some wastes deposited and shed during moulting.

Uricotelism

• Cockroaches excrete uric acid, making them uricotelic, conserving water in terrestrial environments.

11.9 Nervous System

Type

• Ventral, solid, ganglionated.

Components

1. Central Nervous System (CNS):
   • Nerve Ring:
     • Supra-oesophageal Ganglia (Brain): Above oesophagus, formed by fusion of protocerebrum, deutocerebrum, tritocerebrum.
     • Sub-oesophageal Ganglion: Below oesophagus, bilobed, formed by fusion of three ganglia pairs.
     • Circum-oesophageal Connectives: Link cerebral and sub-oesophageal ganglia.
   • Ventral Nerve Cord (VNC): Double cord from sub-oesophageal ganglion, with nine paired ganglia (3 thoracic, 6 abdominal; largest in 7th abdominal segment).
2. Peripheral Nervous System (PNS): Nerves from CNS ganglia innervate eyes, antennae, mouthparts, wings, legs, and visceral organs.
3. Autonomous Nervous System (ANS): Includes four ganglia (frontal, hypocerebral, ingluvial, ventricular) and retrocerebral complex, regulating visceral functions.

Sense Organs

• Compound Eyes: ~2000 ommatidia, provide mosaic vision, high motion sensitivity.
• Antennae: Tactile and olfactory.
• Anal Cerci: Detect vibrations/air movements.

11.10 Reproductive System

Type

• Dioecious: Separate male and female individuals.

Male Reproductive System

• Testes: Paired, in 4th-6th abdominal segments; produce sperms.
• Vasa Deferentia: Carry sperms to ejaculatory duct via seminal vesicles.
• Seminal Vesicles: Store sperms as spermatophores (sperm bundles).
• Ejaculatory Duct: Opens at male gonopore (ventral to anus).
• Mushroom/Utricular Gland: Accessory gland in 6th-7th segments.
• Phallomeres: Three asymmetrical chitinous structures (male gonapophyses) around gonopore.

Female Reproductive System

• Ovaries: Paired, in 2nd-6th abdominal segments; each with eight ovarioles containing ova.
• Oviducts: Lateral oviducts unite into a common oviduct (vagina), opening into the genital chamber (bursa copulatrix).
• Spermatheca: Stores sperms, in 6th segment, opens into genital chamber.
• Collateral Glands: Paired, secrete ootheca material.
• Gonapophyses: Six chitinous plates around genital pore.

Fertilization and Ootheca

• Copulation: Spermatophores transferred to female genital chamber via phallomeres.
• Fertilization: Internal; sperms from spermatheca fertilize eggs in the genital chamber.
• Ootheca: Egg case (8 mm, dark reddish-black) formed by collateral gland secretions, containing 14-16 eggs in two rows; deposited in humid crevices.
• Development: Paurometabolous (nymphal stages); nymphs resemble adults but are smaller and sexually immature. Moulting occurs ~13 times before adulthood. Embryonic period: ~58 days at 24°C, ~32 days at 30°C.

11.11 Interactions with Mankind

Negative Impacts

1. Damage: Destroy household items (clothes, shoes, paper) and food.
2. Contamination: Carry pathogens from sewers/gutters, causing diseases like cholera, diarrhoea, tuberculosis, typhoid.
3. Unhygienic: Contaminate food, imparting a foul smell.

Positive Roles

1. Food Chain: Prey for amphibians, birds, lizards, rodents; consumed by humans in some regions (South America, China, Myanmar).
2. Research: Used in laboratories for biological studies due to easy availability and minimal ecological impact.

Control Measures

1. Sanitation: Regular cleaning of kitchens, cupboards; sealing cracks/crevices; maintaining water-filled drain traps to prevent sewer migration.
2. Chemical Control: Use of organophosphates, carbamates, pyrethroids, boric acid-based pesticides.