Structural Organisation in Animals
Structural Organisation in Animals explains how cells combine to form tissues, tissues form organs, and organs work together by forming organ systems in multicellular animals. This organisation helps animals perform various life processes efficiently and maintain proper functions of the body. Understanding the structural organisation of animals is important for studying their anatomy, physiology, and adaptations.
This Story also Contains
- Important Topics of Structural Organisation in Animals
- Importance of Structural Organisation in Animals
- Structural Organisation in Animals
- Morphology and Anatomy of the Earthworm
- Structure and Anatomy of the Cockroach
- Structure and Anatomy of the Frog
- Recommended Video on Structural Organisation in Animals
This chapter covers the four basic types of animal tissues: epithelial, connective, muscular, and nervous tissues. It also explains the morphology and anatomy of important animals such as the earthworm, cockroach, and frog. All these topics help students understand the relationship between structure and function in animals and are an important part of Class 11 Biology.
Important Topics of Structural Organisation in Animals
This chapter discusses some important concepts concerning the structure and function of animal tissues, organs, and body systems. It further encompasses the comparative anatomy of a few organisms for studying evolutionary adaptations. The following are the topics to understand:
Animal tissues: Epithelial, connective, muscular, and nervous tissues
Morphology and anatomy of the earthworm (Pheretima posthuma)
Structure and anatomy of the cockroach (Periplaneta americana)
External and internal features of the frog (Rana tigrina)
Importance of Structural Organisation in Animals
Studying structural organisation helps us understand how different tissues, organs, and organ systems work together to carry out essential life processes. Understanding this chapter is important for studying physiology, evolution, medicine, veterinary science, and animal classification.
Structural Organisation in Animals
While all animals are multicellular, the arrangement and functional organisation of their cells differ between groups. Depending on the degree of complexity in cellular arrangements and functions, animals show four main levels of structural organisation:
Cells of these organisms can either be loose groups, tissues, organs, or highly organised organ systems. These levels show body design evolutionary progress.
| Level of Organisation | Description | Example Organism(s) |
|---|---|---|
| Cellular Level | Cells are loosely arranged with minimal coordination No true tissues are formed. | Sponges (Porifera) |
| Tissue Level | Similar cells are grouped to form functional tissues Division of labour begins. | Coelenterates (e.g., Hydra) |
| Organ Level | Different tissues combine to form specific organs with defined functions. | Platyhelminthes (Flatworms) |
| Organ-System Level | Organs work together as part of systems for complex body functions. | Annelids, Arthropods, Vertebrates |
Classification of Tissues
Tissues are classified into four types. All of them, along with their feature and level of organisation, are discussed below:
| Component | Key Features | Examples/Types |
|---|---|---|
| Epithelial Tissue |
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| Connective Tissue |
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| Muscular Tissue |
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| Nervous Tissue |
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| Organ Level of Organisation |
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| Organ System Level of Organisation |
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Morphology and Anatomy of the Earthworm
Earthworms are invertebrates of the phylum Annelida found in damp soil. The species, Pheretima posthuma, is widely used for study purposes in India. Earthworms contribute significantly to soil fertility and are referred to as 'friends of farmers' because their burrowing activities and their mode of feeding enrich the soil. Some important Morphological Characters are discussed below:
- The body is cylindrical, bilaterally symmetrical, long, and segmented.
- The back is darker and has a median dorsal line.
- Segmentation: The body is divided into approximately 100-120 segments or metameres.
- Clitellum: A well-developed glandular band found between segments 14 to 16, which plays a role in reproduction.
- Does not have eyes, yet reacts to light, touch, and chemicals with the help of sensory cells.
- Setae: Small chitinous bristles found on all segments except the first, last, and clitellum segments, which are used for locomotion.
Anatomy of the Earthworm
The anatomical features are discussed below in the table:
| System | Description |
|---|---|
| Digestive System | Complete and straight Consists of the mouth, pharynx, oesophagus, gizzard, intestine, and anus. |
| Circulatory System | Closed type with blood vessels and capillaries, blood is red due to haemoglobin dissolved in plasma. |
| Respiratory System | Gaseous exchange occurs through the moist body surface. |
| Excretory System | Excretion through nephridia is present in almost all segments. |
| Nervous System | A nerve ring and a paired ventral nerve cord with segmental ganglia. |
| Reproductive System | Hermaphroditic cross-fertilisation occurs. Testes in the 10th & 11th segments, ovaries in the 13th segment. |
Structure and Anatomy of the Cockroach
Cockroaches are of the phylum Arthropoda and class Insecta. The Indian cockroach is Periplaneta americana. They are nocturnal, omnivorous, and swift insects that typically live in dark and moist areas. Their bodies are externally protected with a hard exoskeleton made of chitin, which is used for protection as well as for muscle attachment.
Cockroaches have bilateral symmetry and a segmented body that is separated into the head, thorax, and abdomen. They possess well-developed sensory organs such as compound eyes, antennae, and cerci that enable them to react rapidly to changes in their environment. Because of their strong adaptability and reproductive nature, cockroaches are regarded as hardy survivors and have been on Earth for more than 300 million years.
Key Morphological Characteristics:
Body dorsoventrally flattened, elongated, and segmented; bilaterally symmetrical.
Size: About 34–53 mm long and reddish-brown.
Composed of three segments: Head, Thorax, and Abdomen.
Triangular head with a pair of compound eyes, antennae, and chewing-type mouthparts.
The thorax has three segments: prothorax, mesothorax, and metathorax, each with a pair of walking legs.
Wings: Two pairs of forewings (tegmina) are leathery; hindwings are membranous and employed for flying.
The abdomen is 10-segmented. Both sexes possess cerci (sensory organs), and males possess styles.
Anatomy of the Cockroach
The anatomical features are discussed below in the table:
| System | Description |
|---|---|
| Digestive System | Includes foregut (pharynx, oesophagus, crop, gizzard), midgut, and hindgut. Digestive glands include salivary glands. |
| Circulatory System | Open circulatory system with colourless haemolymph that lacks respiratory pigments. The heart is tubular with 13 chambers. |
| Respiratory System | Network of tracheae opening outside through spiracles, oxygen is directly delivered to tissues. |
| Excretory System | Uses Malpighian tubules for the removal of nitrogenous wastes. |
| Nervous System | Consists of a nerve ring and paired ventral nerve cords with segmental ganglia. |
| Reproductive System | Sexually dimorphic internal fertilisation. Males have testes, Females have ovaries and produce egg cases called oothecae. |
Structure and Anatomy of the Frog
Frogs are amphibians of the phylum Chordata, class Amphibia. Rana tigrina (previously renamed Hoplobatrachus tigerinus) is the species generally used in India. Frogs are cold-blooded, have moist skin, and can survive on land as well as in water. They are carnivorous and help regulate insects in their food cycle.
Key Morphological Characteristics:
- The body is streamlined, bilaterally symmetrical, and consists of two halves: head and trunk (no tail or neck).
- Skin is glandular and moist, assisting in cutaneous respiration; no scales.
- Eyes are bulging and shielded by nictitating membranes.
- The tympanum (eardrum) found behind the eyes is utilised for hearing.
- Forelimbs are short (for support), and hindlimbs are muscular and lengthy (modified for swimming and jumping).
- Feet are webbed, aiding in swimming.
- Sexes are distinct; males possess vocal sacs and nuptial pads to facilitate mating.
Anatomy of the Frog
The anatomical features are discussed below in the table:
| System | Description |
|---|---|
| Digestive System | The digestive system consists of the mouth, buccal cavity, pharynx, oesophagus, stomach, intestine, rectum, and cloaca. |
| Circulatory System | A closed-type heart is three-chambered (two atria and one ventricle) Blood is red with nucleated RBCs. |
| Respiratory System | Respiration occurs through the lungs, skin, and buccal cavity. |
| Excretory System | Excretion via a pair of kidneys that open into the cloaca through the ureters. |
| Nervous System | The central nervous system includes the brain and spinal cord; the peripheral and autonomic systems are present. |
| Reproductive System | Sexes separate males have testes, females have ovaries. Fertilisation is external, and development is indirect via the tadpole stage. |
Comparative Study of Earthworm, Cockroach, and Frog
Feature | Earthworm | Cockroach | Frog |
Phylum | Annelida | Arthropoda | Chordata |
Circulation | Closed | Open | Closed |
Respiration | Skin | Tracheae | Skin and lungs |
Excretion | Nephridia | Malpighian tubules | Kidneys |
Fertilisation | Cross-fertilisation | Internal | External |
Recommended Video on Structural Organisation in Animals
Frequently Asked Questions (FAQs)
The animal cell is divided into several structures such as the nucleus, cytoplasm, and cell organelles. This means each of them performs a different role that essentially supports the life processes of the cell. Consequently, understanding this kind of organization helps one understand bigger biological concepts.
Around 2-3 questions can be expected from this chapter in NEET, about the structural and functional organization of tissues and organs in animals.
It describes the hierarchical arrangement of cells into tissues, tissues into organs, and organs into systems which together serve to perform the physiological functions of an animal.
Yes, this topic carries significant weightage in NEET 2024 and is a must-do-and-know for the study of the anatomy and physiology of animals. A very important topic that is a must-prep for biology aspirants.
Cells, tissues, organs, and organ systems are the four layers of hierarchical organisation in every animal. The complexity of each level of the hierarchy increases, and all organ systems work together to build an organism. (See the "Cellular Basics" chapter for more information on cells and tissues.)
Tissues are classified as follows:
Nervous tissue
Connective tissue
Epithelial tissue
Muscular tissue
An organ is a collection of tissues; an organ system is a collection of organs that work together to fulfill one or more functions. Every organ is made up of at least one sort of tissue. An organ system is a collection of organs that operate together to accomplish a common goal. Organ systems include the excretory system, reproductive system, endocrine system, circulatory system, and respiratory system.
An organism's smallest structural and functional unit is the cell. The basic job of cell components is to carry out numerous living tasks.
A gland that produces and releases substances such as perspiration, tears, saliva, milk, and digestive fluids through a duct or aperture to the surface of the body. Sweat glands, lacrimal glands, salivary glands, mammary glands, and digestive glands in the stomach, pancreas, and intestines are examples of exocrine glands.
