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Structural Organisation in Animals and Plants - Morphology and Anatomy of Cockroach

Grade 11ICSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The scientific name of the common cockroach is Periplaneta americanaPeriplaneta \ americana. It belongs to Phylum Arthropoda and Class Insecta.

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The body is divided into three distinct regions: Head, Thorax, and Abdomen. The entire body is covered by a hard chitinous exoskeleton composed of hardened plates called sclerites (tergitestergites dorsally and sternitessternites ventrally).

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The head is formed by the fusion of 66 segments and bears a pair of compound eyes and long filiform antennae. Mouthparts are of the biting and chewing type, consisting of a labrum, two mandibles, two maxillae, a labium, and a tongue-like hypopharynx.

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The thorax consists of three parts: prothorax, mesothorax, and metathorax. It bears three pairs of jointed legs and two pairs of wings. The first pair (tegmina) arises from the mesothorax and is opaque, while the second pair (hindwings) arises from the metathorax and is used for flight.

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The digestive system consists of the foregut (mouth, pharynx, oesophagus, crop, and gizzard), midgut (mesenteron), and hindgut (ileum, colon, and rectum). The gizzard has 66 highly chitinous teeth for grinding food.

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The circulatory system is of the 'open type'. The heart is an elongated muscular tube lying along the mid-dorsal line of the thorax and abdomen, consisting of 1313 funnel-shaped chambers.

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Respiration occurs through a network of trachea that open through 1010 pairs of small holes called spiracles. Excretion is performed by 100−150100-150 yellow thin filamentous Malpighian tubules which convert nitrogenous waste into uric acid (uricotelismuricotelism).

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Cockroaches are dioecious. Males possess anal styles (on the 9th9^{th} sternite), which are absent in females. Both sexes possess a pair of jointed filamentous structures called anal cerci on the 10th10^{th} segment.

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Development is paurometabolous, meaning development through a nymphal stage. Nymphs moult about 1313 times to reach the adult form.

📐Formulae

Total segments in Head=6 (fused)\text{Total segments in Head} = 6 \text{ (fused)}

Total segments in Abdomen=10\text{Total segments in Abdomen} = 10

Number of Heart Chambers=13\text{Number of Heart Chambers} = 13

Pairs of Spiracles=10 (2 thoracic + 8 abdominal)\text{Pairs of Spiracles} = 10 \text{ (2 thoracic + 8 abdominal)}

Number of Hepatic Caeca=6−8\text{Number of Hepatic Caeca} = 6 - 8

Number of Malpighian Tubules=100−150\text{Number of Malpighian Tubules} = 100 - 150

💡Examples

Problem 1:

Determine the sexual dimorphism features in Periplaneta americanaPeriplaneta \ americana. How can you distinguish a male from a female externally?

Solution:

Check for the presence of anal styles. If the specimen has both anal cerci and anal styles, it is a male. If it only has anal cerci, it is a female.

Explanation:

In males, the 9th9^{th} sternite bears a pair of short, thread-like anal styles which are absent in females. Both sexes possess anal cerci on the 10th10^{th} segment.

Problem 2:

A student observes a structure in the cockroach's gut containing 66 chitinous teeth. Identify the structure and its function.

Solution:

The structure is the Gizzard (or Proventriculus). Its function is the mechanical grinding of food particles.

Explanation:

The gizzard has an outer layer of thick circular muscles and a thick inner cuticle forming 66 highly chitinous plates (teeth) used for crushing food.

Problem 3:

Calculate the total number of appendages found on the thorax of a cockroach.

Solution:

3 pairs of legs+2 pairs of wings=10 total appendages3 \text{ pairs of legs} + 2 \text{ pairs of wings} = 10 \text{ total appendages}

Explanation:

Each of the three thoracic segments (pro, meso, meta) bears a pair of walking legs. The mesothorax and metathorax each bear a pair of wings.

Morphology and Anatomy of Cockroach Revision - Class 11 Biology ICSE