Structural Organisation in Animals · Class 11 NEET Notes

• The NMC syllabus covers this unit in one line: animal tissues, then the morphology, anatomy and functions of the systems of an insect (Frog), as a brief account only.
• So tissues come first and are named on their own. That matches the papers: roughly half the questions from this chapter are tissue questions.
• Frog is named explicitly, so it is certainly examinable.
• Earthworm does not appear at all in the current list.
• The phrase an insect (Frog) is a drafting error, since a frog is not an insect. That stray word is exactly why most teachers keep cockroach in.

• Tissue: a group of similar cells with intercellular substance, doing one job.
• Organ: different tissues arranged in a definite pattern, such as the stomach.
• Organ system: two or more organs working on one function.
• The heart is quoted in the textbook as containing all four tissue types.

• Epithelium covers and lines. Every epithelium sits on a basement membrane.
• Its cells are packed with very little material between them, which is the opposite of connective tissue.
• Name the shape and you have named the function.

• Simple squamous: thin and flat, for diffusion. Alveoli and blood vessel walls.
• Simple cuboidal: cube shaped, for secretion and absorption. Kidney tubules, gland ducts.
• Simple columnar: tall with elongated nuclei. Stomach and intestine.
• Ciliated: carries cilia that move particles in one direction.
• Glandular: modified to secrete. Goblet cells are unicellular, salivary glands multicellular.
• Compound: two or more layers, mainly protective. Skin, buccal cavity, pharynx.

• The most abundant and widely distributed tissue.
• Everything about it is decided by the matrix the cells sit in.
• The more matrix, and the harder it is, the more specialised the tissue.

• Areolar: fills spaces inside organs. Contains fibroblasts, macrophages and mast cells.
• Adipose: stores fat, mainly beneath the skin.
• Dense regular: fibres in one direction. Tendon joins muscle to bone, ligament bone to bone.
• Cartilage: solid but pliable, cells sit in spaces called lacunae. The pinna and nose tip are elastic cartilage.
• Bone: hard matrix rich in calcium salts.
• Blood: the only fluid connective tissue. Its matrix is plasma.

• Three types. Questions are almost always a matter of matching a property to the right one.

• Skeletal: cylindrical and unbranched, many nuclei at the edge, voluntary, and it tires.
• Smooth: spindle shaped with a single central nucleus, involuntary. Stomach, intestine, vessels.
• Cardiac: branched and striated with intercalated discs, involuntary, and it never tires.

• Short section, and the facts asked from it are few and predictable.

• Neurons are excitable: they respond to stimuli and conduct the impulse.
• Neuroglia are support cells, and they make up more than half the volume of neural tissue.
• Neural tissue does not divide, so damaged neurons are generally not replaced.

• The one animal the syllabus names, so treat this as compulsory.
• Body: head and trunk only. There is no neck and no tail in the adult.
• Skin is moist and smooth, because it is also a respiratory surface.
• Respiration: lungs on land, and cutaneous through the skin both in and out of water.
• Excretion: ureotelic, through a pair of mesonephric kidneys.
• Nervous system: 10 pairs of cranial nerves.
• Reproduction: external fertilisation in water, 2500 to 3000 eggs at a time.

• Circulation is closed, with a three-chambered heart plus a sinus venosus and conus arteriosus.
• There are hepatic and renal portal systems.
• The heart keeps beating after removal because it is myogenic. The beat starts in the cardiac muscle itself, not in a nerve.

• Not named in the syllabus, but the phrase an insect points straight at it.
• It also has a long history in the papers, so it is worth keeping.

Gathered in one place rather than scattered through the notes. Cover the gold band and test yourself.