Structural Organisation in AnimalsNEET Zoology · Class 11 · NCERT Chapter 7

You can expect 1 question from this chapter in NEET 2027. The most reliable scoring areas are: the four types of animal tissue and their subtypes, the distinguishing features of each epithelial subtype, the three model organisms (earthworm, cockroach, frog) with their circulatory system type, excretory organs and respiratory organs, and Malpighian tubules in cockroaches.

The four animal tissue types are: (1) Epithelial tissue: covers body surfaces and lines organs. Forms the first barrier between the body and the environment. (2) Connective tissue: connects and supports other tissues. Includes loose, dense, cartilage, bone and blood. (3) Muscular tissue: produces movement. Includes skeletal, smooth and cardiac muscle. (4) Neural tissue: receives stimuli and transmits impulses. Made of neurons and neuroglia.

Simple epithelium is a single layer of cells. It is found where absorption and filtration happen, like the lining of the intestine and kidney tubules. Types include squamous, cuboidal and columnar. Compound epithelium has two or more cell layers. It protects against wear and tear, like in the skin (stratified squamous), the lining of the oral cavity, and the urethra. It is not good for absorption.

The earthworm (Pheretima) has a closed circulatory system. Blood stays inside blood vessels at all times. The main vessel is the dorsal blood vessel (pumps blood forward). Four to five pairs of hearts (muscular tubes in segments 7 to 11) pump blood. The cockroach (Periplaneta) has an open circulatory system. Blood (called haemolymph) flows freely through body cavities called sinuses, not through veins. The heart is a muscular tube in the abdomen that pumps haemolymph forward. There is no separate respiratory pigment.

Malpighian tubules are the excretory organs of the cockroach (and other insects). They are thin, yellow tubules that arise from the junction of the midgut and hindgut (about 100 to 150 in Periplaneta). They absorb nitrogenous waste from the blood and pass it into the hindgut. The final waste is uric acid, so cockroaches are uricotelic. Earthworms use nephridia for excretion; frogs use kidneys (mesonephros).

The clitellum is a thick, glandular band on segments 14 to 16 of the earthworm Pheretima. It appears as a distinct ring around the body. During reproduction, the clitellum secretes a cocoon that receives eggs and sperm and protects the developing embryos. It is a NEET-common identifier because it tells you which segments contain the clitellum and that earthworms are hermaphrodites (both male and female organs in the same individual).

Cockroaches breathe through a tracheal system. Air enters through spiracles (10 pairs: 2 on the thorax, 8 on the abdomen). The spiracles open into tracheae, which branch into finer tracheoles. Oxygen diffuses directly from tracheoles to body cells. There is no respiratory pigment and no use of blood for oxygen transport. This is very different from earthworms (breathe through moist skin) and frogs (breathe through skin, lungs and buccal cavity).