Structural Organisation in Animals

The official NEET UG 2026 syllabus contains the known Unit 2 phrase involving "an insect(Frog)". The official NEET UG 2026 FAQ resolves the wording and states that it should be read as an insect and a frog. Current NCERT Chapter 7 provides the current structural-organisation and frog teaching context, while NCERT Exemplar Chapter 7 explicitly retains cockroach-focused questions alongside frog and animal-tissue questions. Cockroach is therefore used as the NCERT teaching-context insect specimen, while the official NTA syllabus wording itself is recorded as "an insect and a frog".

Specialised cells form tissues; tissues combine into organs; organs coordinate in organ systems. This page teaches structure-function relationships rather than definition-only lists.

Epithelia are closely packed cell sheets covering surfaces or lining cavities/ducts.

• Simple squamous: thin, flat cells suited to diffusion and delicate lining.
• Cuboidal: cube-like cells commonly suited to secretion/absorption in ducts and tubules.
• Columnar: tall cells commonly involved in secretion/absorption.
• Ciliated: cilia move material along an epithelial surface.
• Compound/stratified: multiple layers provide protection.

Connective tissues have cells embedded in an extracellular matrix whose composition varies with function.

• Areolar: loose packing/support between tissues.
• Adipose: fat storage, cushioning and insulation relationships.
• Dense connective: fibre-rich tissue supporting strong attachment/tension resistance.
• Cartilage: firm flexible matrix with chondrocytes in lacunae.
• Bone: mineralised rigid matrix for support/protection.
• Blood: fluid connective tissue; plasma is the matrix and formed elements circulate within it.

Skeletal muscle has long cylindrical striated, multinucleate fibres under voluntary control and drives body/skeletal movement. Smooth muscle has spindle-shaped non-striated cells under involuntary control and drives visceral-wall movement. Cardiac muscle has branched striated cells with intercellular junction specialisation under involuntary rhythmic control and drives heart-wall contraction.

Neural tissue contains neurons specialised for excitability/conduction plus supporting glial cells. Detailed impulse physiology belongs to the Neural Control and Coordination page.

External organisation: cockroach has a segmented body divided into head, thorax and abdomen and covered by a chitinous exoskeleton. The thorax bears three pairs of legs. Adult wings are associated with the thoracic region, and antennae are prominent sensory structures.

Digestive system: mouth/foregut leads to crop, gizzard/proventriculus, midgut and hindgut. Crop stores food temporarily; gizzard contributes mechanical processing; midgut is associated with digestion/absorption and gastric/hepatic caeca; Malpighian tubules arise near the midgut-hindgut junction and function in excretion.

Circulation: cockroach has an open circulatory system. Haemolymph occupies the haemocoel and is moved by a dorsal heart/vessel system rather than remaining in a closed vessel network throughout.

Respiration: spiracles open into tracheae that branch into finer tubes and deliver gases close to tissues, so gas transport is not dependent on a vertebrate-style haemoglobin circulation.

Nervous system: cephalic ganglia and segmentally arranged ganglia connected by a ventral nerve cord form the main organisation.

Reproduction: sexes are separate. Male and female systems contain paired gonads, ducts and accessory structures; treatment is kept brief as required by current scope.

External organisation: frog has an amphibian body with head and trunk, moist glandular skin and paired limbs adapted for terrestrial movement and swimming. External structures include nostrils and tympanum at textbook depth.

Digestive system: mouth/buccal cavity leads to pharynx, oesophagus, stomach, small intestine, rectum and cloaca. Liver and pancreas supply digestive secretions.

Circulation: frog has a closed circulatory system and a three-chambered heart with two atria and one ventricle. Pulmonary/skin and systemic flows are coordinated but not completely separated as in a four-chambered mammalian heart.

Respiration: gas exchange can occur through skin, buccopharyngeal lining and lungs, with relative contribution depending on physiological/environmental context.

Nervous system: brain and spinal cord form the central nervous system with peripheral nerves connecting the body.

Reproduction: sexes are separate; gonads and ducts form the reproductive systems. Fertilisation is external in the standard NCERT frog account.