Chapter 7 - Structural Organisation in Animals

Structural Organisation in Animals explains how cells, tissues, organs and organ systems divide biological work in a multicellular animal. In the current rationalised NCERT Class 11 Biology textbook, Chapter 7 uses the frog as the representative vertebrate and examines its external morphology and internal organ systems.

Teachoo provides chapter-wise notes, labelled frog diagrams, NCERT exercise solutions, important questions and MCQs for school examinations and NEET. The explanations connect each anatomical feature with its function and with the frog’s amphibious way of life.

The chapter first establishes the organisational sequence of cell → tissue → organ → organ system. A tissue is a group of similar cells together with intercellular substances performing a specific function. Different tissues combine in particular proportions to form organs, and physically or chemically coordinated organs form systems. This division of labour enables a complex organism to function efficiently.

The frog belongs to class Amphibia of phylum Chordata and can live both on land and in freshwater. It is poikilothermic, meaning its body temperature changes with environmental temperature. Students learn how camouflage, aestivation and hibernation help the frog survive seasonal and environmental challenges.

The external morphology of the frog includes its moist, mucus-covered skin, head and trunk, nostrils, bulging eyes, nictitating membranes, tympanum and limbs. The longer, muscular and webbed hind limbs support swimming and jumping. Sexual dimorphism allows male and female frogs to be distinguished by features such as vocal sacs and copulatory pads in males.

The anatomy section studies the frog’s major organ systems:

• Digestive system

• Respiratory system

• Blood vascular and lymphatic systems

• Excretory system

• Nervous system and sense organs

• Male and female reproductive systems

The frog is carnivorous and has a relatively short alimentary canal. Food passes from the mouth through the buccal cavity, pharynx, oesophagus, stomach, intestine, rectum and cloaca. The liver, gall bladder and pancreas contribute digestive secretions.

Respiration changes with habitat and condition. In water, gaseous exchange occurs mainly through moist skin. On land, the buccal cavity, skin and lungs contribute. During aestivation and hibernation, cutaneous respiration is especially important.

The frog has a closed vascular system and a three-chambered heart with two atria and one ventricle. Its circulation includes special hepatic and renal portal systems. Frog red blood cells are nucleated, an important difference from mature human red blood cells.

The excretory system contains kidneys, ureters, urinary bladder and cloaca. Frogs are ureotelic because urea is their main nitrogenous waste. Students also compare male and female urinogenital arrangements and study the organisation of the brain, nerves and reproductive organs.

Teachoo’s Chapter 7 category helps students prepare:

• Frog morphology and adaptations

• Aestivation, hibernation and camouflage

• Digestive and respiratory pathways

• Three-chambered heart and portal circulation

• Excretory and urinogenital systems

• Nervous-system organisation

• Male and female reproductive diagrams

• Sexual dimorphism

• NCERT solutions, labelled diagrams and NEET MCQs

For revision, redraw the external and internal frog diagrams and trace one system at a time. Connect structure to habitat: moist skin supports cutaneous respiration, webbed feet support swimming, and seasonal dormancy supports survival during extreme conditions. This makes the chapter a coherent study of vertebrate adaptation rather than a list of organs.