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State Board · Class 11 · Biology

Lesson 11: Study of Animal Type - Cockroach

7 concepts · 56 practice questions with answers · Free to read

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Classification and external features

Link to Std 9–10

Std 9–10 introduced insects generally; here we study the complete system-wise structure of one animal, the cockroach (Periplaneta americana).

From daily life

A cockroach scurrying when the kitchen light is switched on is the best example of an insect's body plan.

Simple definition

Cockroach (Periplaneta americana): Kingdom Animalia, phylum Arthropoda, class Insecta. Flattened, bilaterally symmetrical, segmented body; chitinous exoskeleton; three regions: head, thorax, abdomen.

Cockroach: external structureHeadThoraxAbdomenAnal cerciTegmina = forewingsSystematic positionKingdomAnimaliaPhylumArthropodaClassInsectaGenusPeriplanetaSpeciesamericanaHabit: everywhere; damp crevices; omnivorous, nocturnalBody: bilateral, flattened; segmentedExoskeleton: chitin; sclerites = tergum, sternum, 2 pleuraDivisions: head, thorax (3), abdomen (10)Thorax: 3 pairs legs + 2 pairs wingsSpiracles: 10 pairs (2 thoracic + 8 abdominal)Body cavity = haemocoel (haemolymph)Species: Periplaneta, Blatta orientalis, B. germanica

In the figure : External parts and systematic position of a cockroach.

Rule 1 : Classification and habits — Arthropoda: jointed appendages, segmented body, chitinous exoskeleton. Insecta: 3 pairs of walking legs and 2 pairs of wings. Cockroaches live everywhere, in damp crevices; omnivorous, nocturnal, cursorial. Three common Indian species: Periplaneta americana, Blatta orientalis, B. germanica.

  • Easy : Arthropoda = jointed legs.
  • Medium : Insecta = 6 legs + wings.
  • Exam-type (CET) : Americana = originates in the Americas.

Rule 2 : External morphology — Exoskeleton of chitin (nitrogenous polysaccharide); each segment has 4 sclerites: tergum (back), sternum (belly), 2 pleura (sides). Colour glistening brown. Body cavity = haemocoel (haemolymph). Head = fusion of 6 segments; thorax 3 segments (3 pairs of legs, 2 pairs of wings); abdomen 10 segments; 10 pairs of spiracles.

  • Easy : Tergum = back; sternum = belly; pleura = sides.
  • Medium : Chitin = hard, flexible, muscle attachment.
  • Exam-type (CET) : Spiracles 10: 2 thoracic + 8 abdominal.
Remember

Cockroach = H-T-A: Head 6, Thorax 3, Abdomen 10.

Common mistake and CET trap

‘Cockroach blood is red’ is wrong (colourless). Trap: ‘wings are on the legs’ is wrong (dorsal on the thorax).

Shortcut

Memory clue : "Insect = 6 legs (Hexapod)".

Spot the difference

RegionSegmentsAppendages
Head6 (fused)Antennae, eyes, mouth parts
Thorax33 leg pairs, 2 wing pairs
Abdomen10Anal cerci

Practice questions

Easy
  1. 1Phylum of cockroach?
  2. 2Exoskeleton is made of?
  3. 3Name four sclerites.
Medium
  1. 4Body cavity name?
  2. 5Number of legs?
  3. 6How many spiracles?
Challenging
  1. 7Why nocturnal?
  2. 8Three Indian species.
Show answers (try them yourself first)
  1. 1Arthropoda.
  2. 2Chitin.
  3. 3Tergum, sternum, two pleura.
  4. 4Haemocoel.
  5. 56 (3 pairs).
  6. 610 pairs.
  7. 7Active at night.
  8. 8P. americana, B. orientalis, B. germanica.

Mouth parts, thorax and abdomen

From daily life

Imagine tongs, scissors and a paw in one – cockroach mouth parts are such chewing tools.

Simple definition

Mouth parts (chewing): labrum, mandibles, maxillae, labium, hypopharynx. Thorax: pro-, meso-, metathorax; 5-segmented legs; two pairs of wings. Abdomen: 10 segments.

Mouth parts and legMouth parts (chewing)LabrumMandibleHypoph.MaxillaeLabium (lower lip)Palps = tactile/sensoryLeg (5 segments)CoxaTrochanterFemurTibiaTarsus (5)Tarsus: claws + arolium (clinging)Antennae: touch + smell; fenestrae at baseCompound eyes: ommatidia (~2000); mosaic vision, motion-sensitiveForewings (tegmina) protect | hindwings membranous, for flightAbdomen: 10 segments; anal cerci on the 10th tergumMale: anal styles, narrower | female: broaderHead = fusion of 6 segments; flexible cervix (neck)

In the figure : Mouth parts, the 5 leg segments and features of head, thorax, abdomen.

Rule 1 : Head and mouth parts — Triangular head on a flexible cervix. Antennae: touch + smell. Fenestrae: white ocellar spots at their base. Compound eyes: kidney-shaped; ommatidia (about 2000); mosaic vision. Labrum (upper lip), mandibles (true jaws; crush), maxillae (hold food; palps tactile), labium (lower lip), hypopharynx (tongue; salivary duct).

  • Easy : Mandible = true jaws; maxilla = accessory.
  • Medium : Ommatidium = unit of the eye.
  • Exam-type (CET) : Saliva mixes at the hypopharynx.

Rule 2 : Thorax and abdomen — Thorax: 3 segments, one pair of legs each: coxa, trochanter, femur, tibia, tarsus (tarsus has 5 subsegments; claws + arolium at the end). Wings: forewings (tegmina) thick, protective; hindwings thin, membranous, for flight. Abdomen: 10 segments; anal cerci on the 10th tergum; male has anal styles and is narrower; female broader.

  • Easy : Leg order: C-T-F-T-T (coxa → tarsus).
  • Medium : Hindwings = the ‘true’ wings (for flight).
  • Exam-type (CET) : Male has anal styles on the 9th sternum.
Remember

Leg: Coxa, Trochanter, Femur, Tibia, Tarsus (‘Can The Fat Tiger Talk?’).

Common mistake and CET trap

‘Mandibles have palps’ is wrong (maxillae/labium). Trap: ‘forewings are for flight’ is wrong.

Shortcut

Memory clue : "Can The Fat Tiger Talk? = Coxa, Trochanter, Femur, Tibia, Tarsus".

Spot the difference

PointForewingHindwing
NatureThick, opaqueThin, transparent
RoleProtectionFlight

Practice questions

Easy
  1. 1Function of antennae?
  2. 2What is an ommatidium?
  3. 3Job of mandibles?
Medium
  1. 4What is the labium?
  2. 5Other name of hypopharynx?
  3. 6Five parts of a leg.
Challenging
  1. 7What are tegmina?
  2. 8Male vs female difference.
Show answers (try them yourself first)
  1. 1Touch and smell.
  2. 2Unit of a compound eye.
  3. 3Cut and crush food.
  4. 4Lower lip (second maxilla).
  5. 5Tongue (lingua).
  6. 6Coxa, trochanter, femur, tibia, tarsus.
  7. 7Thick forewings.
  8. 8Male narrower with anal styles; female broader.

Digestive system

From daily life

Food is chewed, stored, ground and then digested – the cockroach follows the same sequence.

Simple definition

Alimentary canal (6–7 cm): foregut (pharynx, oesophagus, crop, gizzard), midgut (stomach, hepatic caeca), hindgut (ileum, colon, rectum) + one pair of salivary glands.

Digestive systemAlimentary canal (6–7 cm)Foregut (stomodaeum)Midgut (mesenteron)Hindgut (proctodaeum)PharynxOesoph.CropGizzardCrop: temporary storeGizzard: 6 teeth + bristlesStomachHepatic caecadigestion + absorptionIleumColonRectumRectum: 6 pads → water uptakeAnus: on 10th segmentMalpighian tubules: open into ileum at midgut–hindgut junction (~150)Salivary glandsOne pair: 2 glandular lobes + 1 reservoir; common ductEfferent salivary duct opens at the base of hypopharynxDiet: omnivorous; cannibalism (eats young cockroaches)Path: mouth → pharynx → oesophagus → crop → gizzard→ stomach (+ caeca) → ileum → colon → rectum → anusForegut and hindgut are chitin-lined

In the figure : Digestive system: three regions and glands.

Rule 1 : Foregut and midgut — Foregut: pharynx (taste sensillae), oesophagus, crop (temporary store), gizzard/proventriculus (6 chitinous teeth + bristles; crush and filter). Midgut: stomach (ventriculus), glandular lining – digestion and absorption; hepatic caeca – secrete enzymes.

  • Easy : Crop = store; gizzard = grinder.
  • Medium : Foregut ends at the gizzard.
  • Exam-type (CET) : Digestion is mainly in the stomach.

Rule 2 : Hindgut and salivary glands — Ileum (short; Malpighian tubules open here; sphincter) → colon (reabsorbs water) → rectum (6 rectal pads; absorb water) → anus (10th segment). Salivary glands: each with 2 glandular lobes + 1 reservoir; ducts unite into an efferent duct opening at the base of the hypopharynx. Omnivorous; cannibalism occurs.

  • Easy : Rectal pads conserve water.
  • Medium : Ileum + colon + rectum = hindgut.
  • Exam-type (CET) : Saliva mixes with food near the hypopharynx.
Remember

Path: mouth → pharynx → oesophagus → crop → gizzard → stomach → ileum → colon → rectum → anus.

Common mistake and CET trap

‘Digestion in the gizzard’ is wrong (crushing). Trap: ‘hepatic caeca near the heart’ is wrong (midgut).

Shortcut

Memory clue : "C-G-S: Crop stores, Gizzard grinds, Stomach digests".

Spot the difference

PartFunction
CropStores food
GizzardCrushes, filters
Hepatic caecaSecrete enzymes
RectumAbsorbs water

Practice questions

Easy
  1. 1Three regions of alimentary canal.
  2. 2Function of crop?
  3. 3What does gizzard contain?
Medium
  1. 4Function of hepatic caeca?
  2. 5Where do Malpighian tubules open?
  3. 6Why rectal pads?
Challenging
  1. 7Where does the salivary duct open?
  2. 8Where is the anus?
Show answers (try them yourself first)
  1. 1Foregut, midgut, hindgut.
  2. 2Temporary storage of food.
  3. 36 chitinous teeth and bristles.
  4. 4Secrete digestive enzymes.
  5. 5Into the ileum.
  6. 6Water absorption.
  7. 7Base of hypopharynx.
  8. 8Ventral side of the 10th segment.

Circulatory system

From daily life

Water flowing freely in a room rather than in closed pipes – cockroach blood flows in a cavity: open circulation.

Simple definition

Open circulation: colourless haemolymph, dorsal blood vessel (heart + aorta) and haemocoel (3 sinuses).

Cockroach circulationOpen circulation: haemocoel + haemolymph (colourless)Pericardial sinus (dorsal, small): dorsal vesselPerivisceral sinus (middle, largest): gut, fat body, reproductive organsPerineural sinus (ventral, small): ventral nerve cordDorsal diaphragm (12 pairs of alary muscles)Ventral diaphragmHeart : 13 chambers (10 abdominal + 3 thoracic)posterior → anterior; dorsal aorta in head; ostia (first 12 chambers) with valvesDiastole: alary muscles contract → blood enters heart via ostiaSystole: wave front-ward → blood to aorta, ostia closedHaemolymph: plasma + 7 haemocyte types; no pigment, no O₂ transport

In the figure : Three sinuses and the 13-chambered heart.

Rule 1 : Haemolymph and haemocoel — Haemolymph: plasma + 7 types of haemocytes; no pigment → colourless; nutrients and uric acid. Haemocoel is divided by two diaphragms (dorsal, ventral) into 3 sinuses: pericardial (top; heart), perivisceral (middle, largest; gut, fat body, reproductive organs), perineural (bottom; nerve cord). Dorsal diaphragm has 12 pairs of alary muscles.

  • Easy : Haemolymph does not carry gases.
  • Medium : Perivisceral is the largest.
  • Exam-type (CET) : Alary muscles are fan-shaped triangles.

Rule 2 : Heart and circulation — Heart 2.5 cm, muscular tube; closed behind, open in front; 13 chambers (10 abdominal + 3 thoracic); ostia on the first 12 chambers (with valves; blood only inward). Continues as dorsal aorta opening into the haemocoel in the head. Diastole: alary muscles contract → blood enters via ostia. Systole: wave from behind forward → blood to aorta; ostia closed. Third phase: diastasis.

  • Easy : Ostia = inlet doors.
  • Medium : Systole = blood forward; diastole = into the heart.
  • Exam-type (CET) : Heart 13 chambers; ostia on 12.
Remember

3 sinuses: P-P-P (pericardial, perivisceral, perineural) top to bottom.

Common mistake and CET trap

‘Cockroach blood is red’ is wrong. Trap: ‘ostia let blood out’ is wrong (inward).

Shortcut

Memory clue : "Dorsal = Pericardial (Pump); Middle = Perivisceral (Pack); Ventral = Perineural (Nerve)".

Spot the difference

SinusPositionMain content
PericardialDorsalHeart
PerivisceralMiddleGut, fat body
PerineuralVentralNerve cord

Practice questions

Easy
  1. 1What is open circulation?
  2. 2Why is haemolymph colourless?
  3. 3Three sinuses.
Medium
  1. 4Chambers in the heart?
  2. 5What are ostia?
  3. 6Where are alary muscles?
Challenging
  1. 7Ostia during systole?
  2. 8Cockroach vs human circulation.
Show answers (try them yourself first)
  1. 1Blood flows in a cavity, not closed vessels.
  2. 2No respiratory pigment.
  3. 3Pericardial, perivisceral, perineural.
  4. 413.
  5. 5Valved slits at the sides of the heart.
  6. 6On the dorsal diaphragm; 12 pairs.
  7. 7Remain closed.
  8. 8Open (haemocoel) / closed (vessels).

Respiratory and excretory systems

From daily life

A cockroach needs no blood to breathe; air tubes carry air straight to the cells, like a pipe taking water directly into a house.

Simple definition

Tracheal system: spiracles → trachea → tracheoles. Malpighian tubules (~150) = main excretory organs; uricotelic (uric acid).

Respiration and excretionTracheal systemCuticleSpiracleTracheaTracheolesTrachea: chitin rings (don't collapse)Tracheole: no lining, fluid-filled tips; gas exchangeMalpighian tubulesGut (midgut | ileum)~150wastes from haemolymph → uric acid → ileumSpiracles: 10 pairs; muscle movements renew airBlood does not carry gases; air reaches tissues directlyUricotelic: excretes uric acid (saves water)Others: fat body, nephrocytes, uricose gland (male)Some waste deposits on cuticle, shed in moultingMalpighian: distal secretory, proximal absorptive

In the figure : Tracheal system and Malpighian tubules.

Rule 1 : Tracheal system — Ten pairs of spiracles (2 thoracic + 8 abdominal) open into air sacs; trachea = branching tubes (~1 mm; spiral/annular chitin thickening prevents collapse); tracheoles = fine, unlined, intracellular, fluid-filled at the blind end; gas exchange. Muscle movements renew the air. Blood does not carry gases.

  • Easy : Spiracle → trachea → tracheole → cell.
  • Medium : Tracheoles have no chitin lining.
  • Exam-type (CET) : Muscle movements renew the air.

Rule 2 : Excretion — Malpighian tubules at the midgut–hindgut junction; yellow, thread-like, hanging in the haemocoel; single glandular layer; distal part secretory, proximal absorptive; extract water and nitrogenous waste, make uric acid and pass it into the ileum. Others: fat bodies, nephrocytes, uricose gland (male only). Some waste is deposited on the cuticle and shed at moulting.

  • Easy : Uricotelic = uric acid; needs little water.
  • Medium : Malpighian tubules = the cockroach ‘kidney’.
  • Exam-type (CET) : Uricose gland is only in males.
Remember

Spiracle → trachea → tracheole; Malpighian = uric acid.

Common mistake and CET trap

‘Cockroach is ammonotelic’ is wrong (uricotelic). Trap: ‘tracheole has chitin’ is wrong.

Shortcut

Memory clue : "Malpighian = Mini kidney; Uric = water saving".

Spot the difference

StructureFunction
SpiracleAir entry
TracheaCarries air
TracheoleGas exchange
Malpighian tubuleExcretion

Practice questions

Easy
  1. 1Number of spiracles?
  2. 2Why chitin in trachea?
  3. 3Why fluid in tracheoles?
Medium
  1. 4Main excretory organ?
  2. 5Number of Malpighian tubules?
  3. 6What is uricotelic?
Challenging
  1. 7What are nephrocytes?
  2. 8Does blood carry gases?
Show answers (try them yourself first)
  1. 110 pairs (2 + 8).
  2. 2To prevent collapse.
  3. 3Medium for gas exchange.
  4. 4Malpighian tubules.
  5. 5About 150.
  6. 6Excretes uric acid.
  7. 7Cells storing waste.
  8. 8No; air reaches cells via tracheae.

Nervous system and sense organs

From daily life

A cockroach bolts at once because the ganglia of its ventral nerve cord pass signals instantly.

Simple definition

The cockroach nervous system is ventral, solid, ganglionated: CNS (nerve ring + ventral nerve cord), PNS and ANS.

Nervous systemNervous system (ventral)BrainSub-oes.3 thoracic ganglia6 abdominal ganglia6th is largestSupra-oes. = brainCircum-oes. connectivesThree divisionsCNSnerve ring + ventral nerve cordPNSnerves from gangliaANS4 ganglia + retrocerebralANS ganglia: frontal, hypocerebral,ingluvial (crop), ventricular (gizzard)Sense organsAntennaetouch, smellCompound eyesvision (mosaic)Palpstouch, tasteAnal cercisense dangerPharynxtaste (sensillae)Cockroach nervous system: ventral, solid, ganglionated

In the figure : Nerve ring, ventral nerve cord and sense organs.

Rule 1 : CNS, PNS, ANS — Nerve ring: supra-oesophageal ganglia (= ‘brain’; proto-, deuto- and tritocerebrum), circum-oesophageal connectives, sub-oesophageal ganglion. Ventral nerve cord: 9 pairs of ganglia – 3 thoracic (large) + 6 abdominal; the 6th abdominal ganglion is the largest, in the 7th segment. PNS: nerves from ganglia (eyes, antennae, mouth parts, wings, legs). ANS: frontal, hypocerebral, ingluvial (crop), ventricular (gizzard) + retrocerebral complex.

  • Easy : Brain = supra-oesophageal ganglia.
  • Medium : VNC is ventral (unlike the dorsal cord in humans).
  • Exam-type (CET) : Ingluvial on crop; ventricular on gizzard.

Rule 2 : Sense organs — Antennae: touch and smell. Compound eyes: ~2000 ommatidia; mosaic image – low resolution but high motion sensitivity. Maxillary/labial palps: touch and taste. Anal cerci: sense danger from behind. Pharynx: taste sensillae.

  • Easy : Mosaic vision = low resolution, high sensitivity.
  • Medium : Palps = touch + taste.
  • Exam-type (CET) : Cerci help it escape quickly.
Remember

Brain above, nerve cord below; ganglia: 3 thoracic + 6 abdominal.

Common mistake and CET trap

‘Nerve cord is dorsal’ is wrong. Trap: ‘20 ommatidia’ is wrong (~2000).

Shortcut

Memory clue : "VNC = Ventral Nerve Cord = belly side".

Spot the difference

Sense organFunction
AntennaeTouch, smell
Compound eyeVision
PalpsTouch, taste
Anal cerciDanger

Practice questions

Easy
  1. 1Parts of nerve ring.
  2. 2Ganglia in the ventral nerve cord?
  3. 3Largest ganglion?
Medium
  1. 4ANS ganglia.
  2. 5How does a compound eye see?
  3. 6What do anal cerci do?
Challenging
  1. 7Describe the nervous system.
  2. 8Function of palps?
Show answers (try them yourself first)
  1. 1Supra-oes. ganglia, connectives, sub-oes. ganglion.
  2. 29 pairs (3 + 6).
  3. 3Sixth abdominal ganglion.
  4. 4Frontal, hypocerebral, ingluvial, ventricular.
  5. 5Ommatidia build a mosaic image.
  6. 6Sense danger.
  7. 7Ventral, solid, ganglionated.
  8. 8Touch and taste.

Reproduction, development and interactions with humans

From daily life

Cockroaches multiply fast: a female drops many egg cases (oothecae) from which nymphs hatch.

Simple definition

Cockroaches are dioecious. Ootheca = egg case. Development is paurometabolous: egg → nymph → adult. Both harmful and useful.

Reproduction and developmentPaurometabolous developmentOotheca14–16 eggsNymphwing pads onlymoults ×13Adultwinged24°C: ~58 days30°C: ~32 daysInstar = stage between moultsReproduction: dioecious♂ testes (4–6 seg) → vas deferens → seminal vesicle → spermatophores utricular gland; phallomeres = external genitalia♀ 2 ovaries × 8 ovarioles (2–6 seg) → oviduct → vagina → genital chamber spermatheca (6th seg), collaterial glands → ootheca; internal fertilisationInteraction with humansHarm: spoil clothes, paper, food; spread cholera, typhoid, TB, diarrhoea germsBenefit: food-chain link; lab animal; bio-indicator of poor hygieneControl: sanitation, seal cracks, keep drain traps filledChemical: organophosphates, carbamates, pyrethroids, boric acid

In the figure : Life cycle, reproductive organs and interactions with humans.

Rule 1 : Reproduction and development — Male: testes (4–6 segments) → vas deferens → seminal vesicle → ejaculatory duct; sperms in spermatophores; utricular gland; phallomeres. Female: 2 ovaries × 8 ovarioles (2–6 segments) → oviduct → vagina → genital chamber; spermatheca (6th segment); collaterial glands. Internal fertilisation; collaterial secretion forms the ootheca (14–16 eggs, 8 mm); a female drops 9–10 oothecae. Nymph wingless (wing pads); about 13 moults; ~58 days at 24 °C, ~32 days at 30 °C.

  • Easy : Ootheca = egg case.
  • Medium : Paurometabolous = no pupa; nymph resembles adult.
  • Exam-type (CET) : Instar = stage between two moults.

Rule 2 : Interactions with humans and control — Harm: damage clothes, paper, food; contaminate food; spread cholera, diarrhoea, TB, typhoid germs from sewers. Benefit: link in the food chain (preyed on by amphibians, birds, lizards); experimental animal; bio-indicators of poor hygiene. Control: sanitation, sealing cracks, keeping drain traps filled with water; chemical – organophosphates, carbamates, pyrethroids, boric acid.

  • Easy : Cockroach = bio-indicator of poor hygiene.
  • Medium : A dry drain trap lets cockroaches in.
  • Exam-type (CET) : Boric acid = simple chemical control.
Remember

Egg → nymph → adult; ootheca 14–16 eggs; moults ≈ 13.

Common mistake and CET trap

‘Cockroach has a pupa stage’ is wrong. Trap: ‘ootheca holds 140 eggs’ is wrong (14–16).

Shortcut

Memory clue : "Ootheca = oval egg-oven; paurometabolous = partial change (no pupa)".

Spot the difference

PointMaleFemale
GonadTestesOvaries
StorageSeminal vesicleSpermatheca
ExternalPhallomeresGonapophyses

Practice questions

Easy
  1. 1What is dioecious?
  2. 2What is a spermatophore?
  3. 3What is an ootheca?
Medium
  1. 4What is paurometabolous?
  2. 5Number of moults?
  3. 6Where is spermatheca?
Challenging
  1. 7Two uses of cockroach.
  2. 8Two ways to control.
Show answers (try them yourself first)
  1. 1Separate sexes.
  2. 2Packet/bundle of sperms.
  3. 3Case of 14–16 eggs.
  4. 4Nymph stage; no pupa.
  5. 5About 13.
  6. 6In the 6th segment of the female.
  7. 7Food chain; laboratory animal; bio-indicator.
  8. 8Sanitation; boric acid / pyrethroids.

Quick revision of the whole lesson

ConceptKey fact
ClassificationArthropoda → Insecta; Periplaneta americana
BodyHead 6, thorax 3, abdomen 10
DigestionForegut-midgut-hindgut; crop, gizzard
BloodOpen; 13 chambers; 3 sinuses
Resp. / excretionTracheae; Malpighian; uric acid
NervesVentral cord; 9 ganglia
ReproductionOotheca 14–16; nymph; moult ~13

🎯 Most important points for the exam

  • Classification and external features.
  • Mouth parts and leg.
  • Order of the digestive tract.
  • Heart, sinuses and circulation.
  • Tracheal system and Malpighian tubules.
  • Reproduction, ootheca and paurometabolous development.
Study mantra

Understand the concept → draw the figure → memorise the key points → solve questions yourself.