Structural Organisation In Animals: Complete Chapter Notes For Class 11 NEET by PW

Remembering the different animal tissues, their types, locations and functions can become confusing when several tissues have similar features or closely related roles. For NEET preparation, you also need to distinguish their structural characteristics and connect each tissue with the function it performs.

The PW Structural Organisation In Animals Complete Chapter One-Shot Revision Video For Class 11 NEET brings these concepts together for quick chapter revision. It covers the major animal tissues and their structural organisation, helping you revise important characteristics, functions and examples before attempting NEET questions.

From Cells To Organisms

Unicellular organisms such as Amoeba and bacteria perform respiration, nutrition, digestion, excretion, and reproduction through a single cell. They do not show division of labour.

During evolution, cells joined to form multicellular organisms. Different groups of cells then performed different functions. This produced the following organisational hierarchy:

Cells to Tissues to Organs to Organ Systems to Organism

• Tissue: A group of similar cells with a common function.

• Organ: Different tissues working together for a specific function.

• Organ System: A group of organs performing related functions.

A tissue is a group of similar cells with a common embryonic origin, along with their intercellular substance, performing a specific function. Similar cells need not be identical. Blood is a tissue even though red blood cells, white blood cells, and platelets differ in structure.

Tissue properties depend on both the cells and the intercellular substance. Plasma makes blood fluid, while collagen and calcium salts make bone hard and strong.

Embryonic Layers

The three primary embryonic layers are:

• Ectoderm: Forms epithelial and neural tissues.

• Endoderm: Forms epithelial tissue, especially the lining of the buccal cavity, stomach, and alimentary canal.

• Mesoderm: Forms epithelial, connective, and muscular tissues, bone, blood, cartilage, and muscles.

(*Memory Tip: Remember Ectoderm, Mesoderm, and Endoderm as the three foundational layers from which body tissues develop.)*

Four Major Animal Tissues

Epithelial Tissue

Epithelial tissue covers external surfaces and lines internal cavities, organs, ducts, tubes, and blood vessels. Its cells are tightly packed and rest on a non-cellular basement membrane. Connective tissue generally lies below it.

The epithelium is avascular, meaning it has no blood vessels. Nutrients and oxygen reach its cells by diffusion from the underlying connective tissue.

Simple And Compound Epithelium

Types of simple epithelium include:

• Simple Squamous Epithelium: Thin, flat cells suited for diffusion. Found in alveoli and blood vessel walls.

• Simple Cuboidal Epithelium: Cube-shaped cells involved in secretion and absorption. Found in glandular ducts and nephron tubules.

• Simple Columnar Epithelium: Tall cells involved in secretion and absorption. Found in the stomach and intestine.

Microvilli form a brush border and increase surface area for absorption. Cilia move substances across epithelial surfaces. Brush-bordered epithelium occurs in the proximal convoluted tubule and intestinal villi, while ciliated epithelium occurs in the trachea, bronchioles, and fallopian tubes.

Cilia cause movement, whereas microvilli increase absorption.

Glandular Epithelium

Glandular epithelium is specialised for secretion.

• Unicellular Gland: Made of one cell, such as a goblet cell.

• Multicellular Gland: Made of many cells, such as salivary and sweat glands.

• Exocrine Gland: Has ducts and releases secretions through them.

• Endocrine Gland: Is ductless and releases hormones into the blood.

• Mixed Gland: Has both exocrine and endocrine functions. The pancreas releases digestive enzymes, insulin, and glucagon.

Compound epithelium may be keratinised or non-keratinised. Keratinised epithelium forms the skin and protects dry surfaces from friction and water loss. Non-keratinised epithelium lines moist surfaces such as the buccal cavity, pharynx, and vaginal cavity.

Transitional epithelium lines the urinary bladder. Its cells become thinner when the bladder is full and thicker when it is empty.

Cell Junctions

• Tight Junctions: Prevent leakage between cells.

• Adhering Junctions: Hold adjacent cells together.

• Gap Junctions: Allow communication and movement of ions and small substances between cells.

Connective Tissue

Connective tissue links and supports other tissues. It has widely spaced cells and an abundant intercellular matrix. Unlike epithelium, it generally contains blood vessels.

Major types include:

• Loose Connective Tissue: Includes areolar and adipose tissue.

• Dense Connective Tissue: Includes regular and irregular connective tissue.

• Specialised Connective Tissue: Includes cartilage, bone, and blood.

Areolar tissue supports epithelium and contains fibroblasts, macrophages, and mast cells. Fibroblasts produce collagen fibres for strength and elastin fibres for flexibility. Macrophages remove microbes and debris, while mast cells release histamine, serotonin, and heparin during injury responses.

Adipose tissue contains adipocytes that store fat, provide insulation, cushion organs, and 

protect internal structures.

Dense regular connective tissue has parallel fibres. Ligaments connect bone to bone, while tendons connect bone to muscle. Dense irregular connective tissue has fibres arranged in many directions and provides strength to skin. 

Cartilage is solid but pliable. Its cells, called chondrocytes, lie in lacunae.

Bone is hard and non-pliable because its matrix contains calcium salts and collagen fibres. Osteocytes lie in lacunae and are arranged around Haversian canals in concentric lamellae. Blood is a fluid connective tissue in which plasma acts as the matrix and red blood cells, white blood cells, and platelets act as cellular components.

Muscular Tissue

Muscular tissue produces movement and locomotion.

Smooth muscle cells are fusiform, or tapered at both ends and thicker in the middle. Cardiac cells are connected by intercalated discs, which help coordinate heartbeat.

Nervous Tissue

Nervous tissue controls and coordinates responses. It contains:

• Neurons: Excitable cells that generate and transmit electrical disturbances.

• Neuroglial Cells: Provide nutrition, protection, support, and waste removal.

Schwann cells form myelin, microglia remove waste, and astrocytes support neural structures. A neural impulse is a propagating electrical disturbance moving across the plasma membrane of a neuron.

Cockroach: Key Features And Organ Systems

The cockroach belongs to phylum Arthropoda and class Insecta. It is an omnivorous, nocturnal pest and can carry diseases. Its body has a chitinous exoskeleton and three regions: head, thorax, and abdomen.

It has three pairs of walking legs, two pairs of wings, one pair of antennae, and compound eyes. The forewings are leathery tegmina, while the hindwings are transparent and used mainly for 

flight.

The head has six fused segments and biting-chewing mouthparts, including mandibles, maxillae, labrum, labium, and hypopharynx. The thorax has three segments. The abdomen has ten segments.

• Tergites: Dorsal plates.

• Sternites: Ventral plates.

• Pleurites: Lateral plates.

• Anal Cerci: Present in both sexes.

• Anal Styles: Present only in males.

The digestive tract includes the foregut, midgut, and hindgut. The crop stores food temporarily, while the gizzard grinds it. Hepatic caeca assist digestion. Malpighian tubules remove nitrogenous waste.

Cockroaches have an open circulatory system, haemolymph, a 13-chambered heart, and 12 pairs of alary muscles. Respiration occurs through spiracles, tracheae, and tracheoles. They are uricotelic and excrete uric acid.

They are dioecious, show internal fertilisation, and produce an ootheca. Development is paurometabolous, with nymphal stages and gradual changes. Only adults have wings.

Frog: Key Features And Organ Systems

Frogs belong to class Amphibia and live in both water and on land. They are cold-blooded and use aestivation during extreme summer and hibernation during winter.

Their moist skin supports cutaneous respiration. Adult frogs use skin, buccopharyngeal lining, and lungs for respiration, while tadpoles use gills. Frogs have a closed circulatory system and a three-chambered heart. Their red blood cells are nucleated.

Frogs possess paired kidneys and are ureotelic. Urine passes through the ureters into the cloaca. The digestive, excretory, and reproductive systems open into the cloaca.

The frog nervous system includes the brain, spinal cord, peripheral nerves, and autonomic nervous system. The brain has forebrain, midbrain, and hindbrain regions. Frogs do not possess a pons.

Frogs are dioecious and show external fertilisation in water. The male holds the female during amplexus. The female releases thousands of ova, which develop into tadpoles. Thyroxine is essential for tadpole metamorphosis into an adult frog.

Structural Organisation In Animals requires you to connect the structure of a tissue with its function, location and identifying features. Revise the major tissue types and their examples carefully, especially the points that help distinguish similar tissues. The PW Structural Organisation In Animals Complete Chapter One-Shot Revision Video For Class 11 NEET can help you revise the complete chapter before practising questions. 

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