Ch 4Organ and Organ Systems in Animals — Class 11 Zoology, concept-first.

Every animal body, however small or large, is built the same fundamental way: cells group into tissues, tissues combine into organs, and organs in turn associate into organ systems.

Lampito mauritii, commonly called the earthworm, is a terrestrial invertebrate belonging to Phylum Annelida, Class Clitellata, Order Opisthopora.

Lampito mauritii has a long, narrow, cylindrical body that is bilaterally symmetrical, typically 80 to 210 mm long and 3.5 to 5 mm wide, light brown in colour with a purplish tinge towards the front c…

The earthworm's body wall lies just beneath a thin, moist cuticle and consists of an epidermis (with supporting, gland, basal and sensory cells), an outer layer of circular muscle, an inner layer of l…

The earthworm's alimentary canal runs as a single straight tube from the mouth to the anus, so digestion proceeds through clearly zoned regions rather than looping organs.

The earthworm has no lungs, gills or any other dedicated breathing organ. Instead, respiration is entirely cutaneous - gas exchange happens across the thin, permanently moist body wall.

Lampito mauritii has a closed type of blood vascular system, meaning the blood always travels inside distinct vessels rather than pooling freely in body cavities.

The earthworm's nervous system is centred on a bilobed mass of nerve tissue on the dorsal side of the pharynx in segment 3, functionally equivalent to a brain and called the supra-pharyngeal ganglion.…

Excretion in the earthworm is carried out by numerous small, coiled, paired tubules called nephridia, distributed segmentally along almost the whole body.

Earthworms are hermaphrodites (monoecious animals), meaning each individual carries both male and female reproductive organs, yet they still cross-fertilize rather than self-fertilize because the two…

Fertilization and the earliest development of Lampito mauritii both occur inside the protective cocoon secreted by the clitellum; the cocoon is deposited in the soil and hatches after an incubation pe…

Periplaneta americana, the American cockroach, is a cosmopolitan, largely nocturnal insect belonging to Phylum Arthropoda, Class Insecta, Order Orthoptera, and shows all the fundamental features of it…

The adult cockroach is 2-4 cm long and about 1 cm wide, with a body that is flattened dorso-ventrally, bilaterally symmetrical, segmented, and organised into three regions - head, thorax and abdomen -…

Digestion in the cockroach takes place along an alimentary canal divided into three functional regions - foregut, midgut and hindgut.

The cockroach's respiratory system is unusually well developed for a terrestrial insect and works independently of the blood.

Periplaneta has an open type of circulatory system, in which the blood vessels are poorly developed and simply empty into a large body cavity called the haemocoel, so the colourless haemolymph (plasma…

The cockroach's nervous system is built around a nerve ring encircling the oesophagus in the head, formed by the supra-oesophageal ganglion (the "brain," mainly a sensory and endocrine centre) linked…

The cockroach's principal excretory organs are its Malpighian tubules, 100-150 thin, long, yellow, filamentous structures attached at the junction of the midgut and hindgut and arranged in 6-9 bundles…

Periplaneta is dioecious, with well-developed and clearly distinct male and female reproductive systems.

Rana hexadactyla, the common Indian green frog, belongs to Phylum Chordata, Class Amphibia, Order Anura - the largest amphibian order, containing frogs and toads.

The frog's body is streamlined for swimming, flattened dorso-ventrally, and divided into just two regions - head and trunk - with no neck and no tail in the adult.

Food captured on the large, sticky, bilobed tongue - which is attached at the front and free at the back, so it can be flicked out and instantly withdrawn - passes into the buccal cavity, whose upper…

Frogs use two entirely different sets of respiratory organs depending on where they are. In water, gas exchange happens across the skin (cutaneous respiration): dissolved oxygen simply diffuses in thr…

The frog's blood-vascular system has a heart of three chambers - two thin-walled anterior auricles (atria) and one thick-walled posterior ventricle - enclosed in a double-walled pericardium, plus a la…

The frog's nervous system is organised into a central nervous system (brain and spinal cord), a peripheral nervous system of 10 pairs of cranial nerves and 10 pairs of spinal nerves, and an autonomic…

The frog's excretory system removes nitrogenous waste and manages the body's salt and water balance through a pair of dark red, flattened, mesonephric kidneys lying on either side of the vertebral col…

Sexes are separate in the frog. In the male, a pair of testes is attached to the kidney and the dorsal body wall by folds of peritoneum called the mesorchium; fine vasa efferentia carry sperm from eac…

After external fertilization, frog eggs hatch within a few days into tadpoles that live at first on their own stored yolk.

Columba livia, the common rock pigeon, is a member of Phylum Chordata, Class Aves, Order Columbiformes, found throughout India among the more than 500 pigeon species worldwide.

The pigeon's body is compact, boat-shaped and streamlined for flight, and is divided into head, neck, trunk and tail.

The pigeon's skeleton is strong but built to be as light as possible: many of its long bones are hollow and filled with air rather than marrow, a feature called pneumaticity, which substantially reduc…

The pigeon's exoskeleton, derived from the epidermis, appears as horny claws (used for walking and perching), scales on the legs and feet, a horny toothless beak (used for feeding, fighting and preeni…

Flight is produced by the coordinated action of several paired muscles collectively called the flight muscles, of which the pectoral muscles are by far the largest and most important, both arising fro…

Because pigeons have no teeth, swallowed grain is first softened rather than chewed: it passes through the toothless beak, buccal cavity (where a narrow horny tongue and numerous mucus glands help lub…