Structural Organisation in Animals: Class 11 CBSE Notes

Key Terms and Definitions

Tissue

A group of similar cells along with intercellular substances that perform a specific function.

Epithelial Tissue

A sheet of cells that covers a body surface or lines a body cavity. It has a free surface and a basal surface.

Connective Tissue

Tissue that connects, supports, binds, or separates other tissues or organs. It is characterized by cells scattered in an extracellular matrix.

Haemolymph

The circulatory fluid in invertebrates with an open circulatory system, equivalent to blood in vertebrates.

Malpighian Tubules

The main excretory organs in insects, consisting of fine tubules that open into the alimentary canal.

Neuron

The structural and functional unit of the nervous system, specialized to transmit electrical and chemical signals.

Organ

A structure composed of two or more different types of tissues that work together to perform a specific function.

Organ System

A group of organs that work together to perform major functions or meet physiological needs of the body.

The Four Primary Animal Tissues

All complex animals are made up of four basic types of tissues, each with a specific function. Understanding these is fundamental to understanding animal anatomy and physiology.

1. Epithelial Tissue: This tissue provides covering and lining for parts of the body. The cells are compactly packed with little intercellular matrix. There are two main types: Simple epithelium (single layer of cells) and Compound epithelium (multiple layers). Simple epithelium is further divided into squamous (flattened), cuboidal (cube-like), and columnar (tall and slender). Their shapes are directly related to their function, e.g., squamous for diffusion boundaries, and columnar for secretion and absorption.

1. Connective Tissue: This is the most abundant and widely distributed tissue. Its main function is linking and supporting other tissues. It includes a wide range of types from soft connective tissues to specialized ones like cartilage, bone, adipose, and blood. A key feature is the presence of a substantial extracellular matrix in which the cells are embedded.

1. Muscular Tissue: This tissue is responsible for movement. Muscle cells, or fibers, can contract and relax. There are three types: Skeletal muscle (voluntary, attached to bones), Smooth muscle (involuntary, found in internal organs), and Cardiac muscle (involuntary, found only in the heart).

1. Neural Tissue: This tissue exerts the greatest control over the body’s responsiveness to changing conditions. It comprises neurons, the excitable cells that transmit signals, and neuroglia, which support and protect the neurons. This tissue forms the brain, spinal cord, and nerves.

Comparison of Muscle Tissues

Must-Remember Key Points

• Cell Junctions: Tight junctions prevent leaking, Adhering junctions cement cells together, and Gap junctions facilitate communication between cells.
• Blood as Connective Tissue: Blood is considered a fluid connective tissue because it has a fluid matrix (plasma) and originates from mesoderm.
• Cockroach Respiration: Respiration in cockroaches is via a tracheal system. Air enters through 10 pairs of spiracles (2 thoracic, 8 abdominal) and reaches tissues through a network of tracheae and tracheoles. It does not involve blood.
• Cockroach Excretion: Excretion is performed by Malpighian tubules, which are located at the junction of the midgut and hindgut. They absorb nitrogenous wastes from the haemolymph and convert them into uric acid (uricotelism).
• Cartilage vs. Bone: Cartilage is pliable (e.g., chondroitin salts), while bone is hard and non-pliable (e.g., calcium salts). Osteocytes are bone cells found in lacunae; chondrocytes are cartilage cells.
• Simple vs. Compound Epithelium: Simple epithelium (one layer) is for absorption, secretion, and filtration. Compound epithelium (multiple layers) has a protective function.
• Areolar Tissue: Often called the 'packaging tissue', it is a loose connective tissue found beneath the skin, providing support for epithelium and containing fibroblasts, macrophages, and mast cells.
• Neuron Structure: A neuron consists of a cell body (cyton), dendrites (receive signals), and an axon (transmits signals away from the cell body).

Anatomy of a Cockroach (Periplaneta americana)

Exam Traps and Scoring Tips

Focus on Diagrams and Functions: Examiners frequently ask questions based on diagrams of tissues or the cockroach's organ systems. Practice drawing and labeling the alimentary canal of the cockroach, the structure of a neuron, and different epithelial tissues. When describing a tissue, always link its structure to its specific function and location in the body (e.g., 'Simple squamous epithelium, composed of flattened cells, is found in the alveoli of lungs and lining of blood vessels to facilitate diffusion'). This structure-function-location link fetches full marks.

Quick Revision Check

• What is the function of intercalated discs in cardiac muscle? Intercalated discs are communication junctions that allow cardiac muscle cells to contract as a single, coordinated unit.
• Why is blood considered a connective tissue? Because it has an extracellular matrix (plasma) and connects different body systems by transporting nutrients, gases, wastes, and hormones.
• Name the grinding organ in a cockroach's digestive system. The gizzard, or proventriculus, located in the foregut.
• What are the three main components of connective tissue? Cells (e.g., fibroblasts, macrophages), fibers (collagen, elastin), and ground substance (matrix).

Frequently Asked Questions