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NCERT Notes of Class 11 Biology Chapter 7 Structural Organisation in Animals

Last Updated : 05 Apr, 2024
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Notes on NCERT for Class 11 Biology Chapter 7 Structural Organisation in Animals: Structural organization in animals refers to the arrangement of cells, tissues, organs, and organ systems that work together through the division of labour and ensure the survival of the whole body. In this article, you will find the structural organisation in animals class 11 notes for self-study. Also, NCERT Solutions for Class 11 Biology Chapter 7 Structural Organisation in Animals are available.

Here, we will study the morphology and anatomy of frogs. Morphology is the study of the external form and appearance of different parts of the body. Anatomy refers to the study of the morphology of internal organs of the body.

Structural Organisation in Animals Class 11 Notes

In a unicellular organism, the single cell performs all the functions like respiration, digestion, etc. In multi-cellular organisms, different groups of cells work together in an organized manner to carry out the basic functions of the body. The​ ​structural organization in ​animals is the same at the basic level, that is:

Cell→Tissue→Organ→Organ System

​​Organs of all animals at the higher level consist of one or more types of tissues, for example, the human heart consists of all four basic types of tissue that are epithelial, connective, muscular, and neural. The complexity of organs and organ systems follows a particular pattern. This pattern is known as the evolutionary trend.

Organ and Organ System

Cell forms the basic functional and structural unit of all animals. A group of cells, together with intercellular substances carrying a specific function, are called tissues. Tissues are organized together in a definite pattern to form an Organ – for example, Heart, Kidney, Stomach, etc. ​When two or more organs interact physically and chemically to perform a common function, they constitute Organ System. Examples are the Respiratory system, cardiovascular system, etc. Such an organization is necessary to ensure that millions of cells in an organism work together in an efficient and coordinated manner.

Also Read: Organ and Organ System


Frogs can live on both land and in freshwater. They belong to the class Amphibia of phylum Chordata. The Indian bullfrog, ​​Rana tigrina, is ​the most common frog found in India. Frogs are cold-blooded animals, as their body temperature varies with the temperature of the environment. Frogs use a protective coloration technique known as mimicry​ in order to camouflage​. To protect themselves from extreme heat in summer and extreme cold in winter, frogs undergo summer sleep (aestivation) and winter sleep (hibernation), respectively.

Also Read: Difference Between Cold Blooded And Warm-Blooded Animals

Morphology of Frog

The morphology of frogs is given below:

Skin of Frog

The body of a frog is covered with skin. The dorsal side of the body is olive green in color with irregular dark spots. The ventral side is uniformly pale yellow. Mucous glands are present in the skin,​ which makes the skin moist, smooth, and slippery. Frogs absorb water through their skin but never drink it.

Body of Frog

The body of the frog is divided into the head and trunk. A neck and tail are absent. Eyes are bulged and covered with a protective membrane while in water, known as a nictitating membrane.​ The ear (membranous tympanum) ​receives sound signals.

Limbs of Frog

Hind limbs are larger and more muscular than forelimbs. Hind limbs end in five digits, and forelimbs end in 4 digits. To help in swimming, feet have webbed digits.

Frogs exhibit sexual dimorphism. Male frogs can be distinguished from female frogs by sound-producing vocal sacs and a copulatory pad on the first digit of the fore limb.

Morphology of Frog

Diagram of Frog

Anatomy of Frog

The body cavity of the frog consists of different organ systems like the respiratory, digestive, excretory, circulatory system, etc., that are well developed in structure and function.

Anatomy of Frog

Digestive System

The digestive system of frogs consists of an alimentary canal and digestive glands. The alimentary canal is short as frogs are carnivores and therefore, the length of the intestine is reduced. Food, after being captured by the bilobed tongue (mouth), enters the buccal cavity. It leads to the esophagus, a short tube that opens into the stomach. Gastric juice and HCL are secreted​ by the walls of the stomach, which helps in the digestion of food.

Partially digested food (chyme) goes from the stomach into the duodenum (Ist part of the small intestine). The common bile duct in the duodenum receives bile from the gall bladder to emulsify fat and pancreatic juice from the pancreas to digest carbohydrates and proteins. The final digestion of the food takes place in the small intestine. Digested food is absorbed by numerous finger-like folds in the inner wall of the intestine called villi and microvilli. The undigested solid ​waste moves into the rectum and passes out through the cloaca.

Respiratory System

Respiration in frogs occurs by two different methods – on land, and in water method. In water, respiration is a cutaneous type​, the dissolved oxygen in water is exchanged through the skin by diffusion. On land, respiration takes place through the buccal cavity, skin, and lungs (pulmonary respiration). Air enters the buccal cavity through the nostrils and then into the lungs. During aestivation and hibernation, respiration takes place through the skin.

Circulatory system

Frogs have a well-developed closed-type circulatory system and lymphatic system. The blood-vascular system involves the heart, blood vessels, and blood. The lymphatic system consists of lymph, lymph channels, and lymph nodes. The heart is a muscular structure covered by a membrane called the pericardium. It has three chambers, two atria, and one ventricle, and ​carries out blood circulation through pumping action.

The right atrium receives blood through the vena cava. The ventricle opens into the conus arteriosus present on the ventral side of the heart. Arteries carry the blood from the heart to all parts of the body (Arterial system). Veins carry the blood from the different body parts to the heart (venous system). Special venous connections between the liver and intestine ( hepatic portal), as well as the kidney and lower parts of the body (renal portal), are present in frogs.

Blood is composed of plasma and blood cells. Blood cells are RBC, WBC, and platelets. Blood carries nutrients, water, and gasses to the respective sites during circulation. Lymph lacks protein and RBC.

Excretory System

Frog has a well-developed excretory system, which consists of a pair of kidneys, ureters, cloaca, and urinary bladder. Each kidney is composed of several uriniferous tubules or nephrons, that form the structural and functional unit of the kidney. In male frogs, from the kidney emerges two ureters that act as a urogenital duct, which opens into the cloaca. In female frogs, the ureter and oviduct open separately into the cloaca. Frogs are ureotelic animals ( excrete urea). Excretory waste, after being carried by the blood into the kidney, is separated and excreted.

​​Nervous System

In frogs, control and coordination are carried out by both the neural system and Endocrine glands. Endocrine glands secret hormones that carry out the chemical coordination of various organs of the body. The prominent endocrine glands in frogs are the pituitary, thyroid, thymus, pineal body, pancreatic, adrenals, and gonads.

The nervous system is divided into a central neural system (brain and spinal cord), a peripheral neural system (cranial and spinal nerves ), and an automatic neural system (sympathetic and parasympathetic). From the brain arises ten pairs of cranial nerves. The brain is divided into fore brain, mid brain, and hind brain. The forebrain consists of the olfactory lobe, cerebral hemispheres, and unpaired diencephalon. The midbrain is by a pair of optic lobes. Hind-brain consists of the cerebellum and medulla oblongata.

Frog has different types of sense organs like an organ of touch (sensory papillae), taste (taste ​buds), smell (nasal epithelium), vision (eyes), and hearing (tympanum with internal ears). Eyes and external ears are well-developed structures, while the remaining are cellular aggregations around nerve endings.

Reproductive System

The male reproductive organ consists of a pair of testes. From the testes arises 10-12 ​vasa efferentia, which enters the kidney on their side and opens into Bidder’s canal.​ ​It finally communicates with the urogenital duct that opens ​into the cloaca. The cloaca’s function is to pass fecal matter, urine, and sperm to the exterior.​

The female reproductive organs consist of a pair of ovaries. A couple of oviducts arising from the ovaries open into the cloaca separately. A female lays 2500-3000 ova at a time. Fertilization and maturation ​are external and take place in water. The development involves metamorphosing a tadpole (larval stage) ​into an adult.

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FAQs on Structural Organisation in Animals

​Define Epithelia.

Epithelia is a thin tissue ​​​that covers the body surface and its cavities, ducts, and tubes.​ It forms the lining of the digestive, respiratory, and excretory tracts.

Define Tissue.

A group of cells, along with intercellular substances​ performing a specific function is defined as tissue.

What are the Different Types of Animal Tissues?

Animal tissues include epithelial, connective, muscular, and nervous tissues, each with specific functions in the body.

What is the Structural Organisation of Animals?

The structural organization of animals ranges from cells forming tissues, tissues forming organs, and organs working together in organ systems to support life functions. The flowchart is given here – Cell→​Tissue→Organ→Organ System.

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