Structural Organisation in Animals: NEET PYQ, 2018–2026

Answer: (A)

Connective tissues differ in how their fibres are arranged. Dense regular tissue has collagen fibres lined up in parallel, which gives strength against a pull applied along one axis. Tendons (muscle to bone) and ligaments (bone to bone) are built this way. Loose and dense irregular tissues have fibres in no fixed direction, and adipose tissue is mainly for fat storage.

Answer: (A)

The frog's vertebral column has presacral vertebrae, one sacral vertebra, and a posterior rod formed by fusion of the post-sacral vertebrae. That rod is the urostyle. The student should locate it by position: it lies just behind the sacrum at the posterior end of the column, and it reflects the tail skeleton lost in the adult.

Answer: (A)

Insects excrete nitrogen as uric acid, produced by Malpighian tubules and passed into the hindgut. Uric acid is poorly soluble, so it can leave as a paste with very little water. This is an adaptation for water conservation in terrestrial animals such as cockroaches, unlike the urea or ammonia excretion common in other groups.

Answer: (A)

The eyes of a frog are bulged and covered by a nictitating membrane that protects them while the animal is in water. On either side of the eyes lies the membranous tympanum, which receives sound signals.

Answer: (A)

Principle: insects are uricotelic and excrete through Malpighian tubules, which are slender blind tubules projecting into the haemocoel at the midgut-hindgut junction. They pick up nitrogenous wastes from the haemolymph and pass them to the hindgut. Apply: identify the excretory organ by its function (removing waste from haemolymph, releasing it into the gut), and then remember that cockroach has Malpighian tubules, not nephridia or green glands.

Answer: (B)

Gas exchange needs a very short diffusion path. Simple squamous epithelium is one cell thick, which satisfies this, and the alveolar lining is therefore the squamous type. Thick stratified, tall columnar and cuboidal types are all adapted for protection, transport or secretion rather than rapid diffusion. The correct answer combines the tissue type with the reason, which is the thinness of the barrier.

Answer: (A)

In frogs, the rectum, the ureters or urinary bladder, and the genital ducts all open into the cloaca, which in turn opens outside through the cloacal aperture. Recognising a common chamber for three systems is the key idea.

Answer: (A)

Principle: connective tissues differ in the type and arrangement of their fibres. Reticular connective tissue has reticular fibres, a fine form of collagen organised as a network. This forms the internal framework of lymphoid organs and bone marrow. Dense regular tissue has parallel thick collagen bundles, areolar tissue has loose fibres in a variety of cell types, and adipose tissue is specialised for fat storage. Matching fibre pattern to function identifies reticular tissue.

Answer: (C)

Frogs lack ribs and a diaphragm, so their breathing relies on pressure changes in the buccal cavity. With the nostrils open and the glottis closed, lowering the buccal floor draws air in through the nostrils. Then the nostrils close, the glottis opens, and the floor is raised, which pushes the air into the lungs. Expelled air leaves through elastic recoil of the lungs and body wall. Since the mechanism depends on the timing of nostrils and glottis, a student must know the sequence rather than only the presence of a respiratory organ.

Answer: (A)

Cardiac muscle tissue is a contractile tissue present only in the heart. Its cells are branched and striated, joined by cell junctions (intercalated discs) at some fusion points that allow the cells to contract as a unit. Its contraction is involuntary.