CBSE Class 11 Biology Revision Notes Chapter 7 Structural Organisation in Animals

Structural Organisation in Animals explains how tissues, organs and organ systems divide work in multicellular animals. In CBSE Class 11 Biology, this chapter focuses on organ systems and frog morphology and anatomy.

Structural Organisation in Animals studies how cells form tissues, tissues form organs and organs work together as organ systems. This organisation helps multicellular animals perform digestion, respiration, circulation, excretion, control and reproduction efficiently.

Use CBSE Class 11 Biology Revision Notes Chapter 7 for 2026–27 to revise organ and organ system, animal tissues, frog morphology and frog anatomy. The chapter uses Rana tigrina to explain major vertebrate organ systems.

Key Takeaways

• Tissue: A group of similar cells with intercellular substances performing a specific function.
• Four basic tissues: Epithelial, connective, muscular and neural tissues form complex animal bodies.
• Frog: Rana tigrina is the common Indian frog studied as a vertebrate example.
• Organ systems: Frog has digestive, respiratory, circulatory, excretory, nervous and reproductive systems.

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Structural Organisation in Animals Class 11 Biology Notes: Chapter Overview

In unicellular organisms, one cell performs all life functions. In multicellular animals, different groups of cells perform different functions.

Cells, tissues, organs and organ systems show division of labour. This helps the body work as one coordinated unit.

Organ and Organ System in Class 11 Biology Chapter 7 Notes

An organ is made of one or more types of tissues. An organ system is formed when two or more organs work together for a common function.

The heart contains all four basic tissue types: epithelial, connective, muscular and neural. This shows how different tissues support one organ.

Evolutionary Trend in Organ Systems

Organ systems show an evolutionary trend. This means their structure becomes more organised and specialised across animal groups.

For example, simple animals have fewer specialised systems, while vertebrates like frogs have well-developed organ systems for digestion, circulation, respiration and reproduction.

Animal Tissues in Structural Organisation in Animals Class 11 Notes

All complex animals have four basic types of tissues. These are epithelial tissue, connective tissue, muscular tissue and neural tissue.

Epithelial Tissue in CBSE Class 11 Biology Notes Chapter 7

Epithelial tissue forms coverings and linings. It has tightly packed cells with very little intercellular matrix.

Epithelial tissue lines body cavities, ducts, tubes and external surfaces.

Types of Epithelial Tissue

Cell Junctions in Epithelial Tissue

These junctions help epithelial cells work as a continuous protective and functional layer.

Connective Tissue in Biology Notes for Chapter 7 Structural Organisation in Animals Class 11

Connective tissue is the most abundant tissue in complex animals. It connects, supports and protects organs and tissues.

The matrix determines the function of connective tissue.

Types of Connective Tissue

Loose Connective Tissue

Areolar tissue supports epithelium and helps repair tissues after injury.

Adipose tissue stores fat and reduces heat loss from the body.

Dense Connective Tissue

Tendons are tough and less flexible. Ligaments are elastic and allow movement at joints.

Specialised Connective Tissue

Bone protects organs and supports the body. Cartilage occurs in the nose tip, outer ear and between some bones. Blood transports gases, nutrients, hormones and wastes.

Muscular Tissue in Class 11 Biology Chapter 7 Notes

Muscular tissue helps in movement by contraction and relaxation.

Muscle fibres contract when stimulated and relax after contraction.

Types of Muscular Tissue

Skeletal muscles help in body movement. Smooth muscles work in internal organs. Cardiac muscles contract rhythmically throughout life.

Neural Tissue in Structural Organisation in Animals Class 11 Biology Notes

Neural tissue is specialised for receiving and conducting impulses.

Structure of a Neuron

When a neuron is stimulated, an electrical impulse travels along its plasma membrane. This impulse can stimulate or inhibit another neuron.

Frog in CBSE Class 11 Biology Revision Notes Chapter 7

Frogs belong to class Amphibia of phylum Chordata. They can live both on land and in freshwater.

Frogs are poikilotherms because their body temperature changes with the temperature of the surroundings.

Frog Morphology in Structural Organisation in Animals Class 11 Notes

Morphology refers to the study of external features. In frog, the body is divided into head and trunk.

Frogs never drink water. They absorb water through the skin.

Sexual Dimorphism in Frog

Sexual dimorphism means visible differences between male and female frogs.

The nictitating membrane protects the eyes when the frog is in water.

Frog Anatomy in Class 11 Biology Chapter 7 Notes

Anatomy studies internal organs. Frog has well-developed digestive, respiratory, circulatory, excretory, nervous and reproductive systems.

Digestive System of Frog

The digestive system of frog consists of the alimentary canal and digestive glands. Frog has a short alimentary canal because it is carnivorous.

The bilobed tongue helps frog capture food.

Digestive Glands in Frog

Partially digested food in the stomach is called chyme. Chyme passes into the duodenum, where bile and pancreatic juice act on it.

Villi and microvilli in the intestine absorb digested food.

Respiratory System of Frog

Frog respires through skin, buccal cavity and lungs. The mode of respiration depends on habitat and activity.

In water, dissolved oxygen diffuses through the moist skin. On land, air enters through nostrils into the buccal cavity and then moves to lungs.

The lungs are elongated, pink, sac-like structures present in the upper trunk region.

Circulatory System of Frog

Frog has a well-developed closed circulatory system and a lymphatic system.

RBCs of frog are nucleated and contain haemoglobin.

Main Parts of Frog Heart

The hepatic portal system connects the liver and intestine. The renal portal system connects the kidney with lower body parts.

Excretory System of Frog

The excretory system removes nitrogenous wastes from the body. Frog is ureotelic because it excretes urea.

Each kidney has many structural and functional units called uriniferous tubules or nephrons.

In male frogs, ureters also act as urinogenital ducts. In female frogs, ureters and oviducts open separately into the cloaca.

Nervous System of Frog

The nervous system of frog controls and coordinates body activities.

Frog has ten pairs of cranial nerves arising from the brain.

Brain of Frog

The brain is enclosed in the cranium. The medulla oblongata continues into the spinal cord through the foramen magnum.

Sense Organs in Frog

External ear is absent in frogs. Tympanum is visible externally.

Reproductive System of Frog

Frogs have separate male and female reproductive systems. Fertilisation is external and takes place in water.

Male Reproductive System

The cloaca passes faecal matter, urine and sperms to the exterior.

Female Reproductive System

Development includes a larval stage called tadpole. Tadpole undergoes metamorphosis and becomes an adult frog.

Importance of Frogs

Frogs are useful for humans and ecosystems.

In some countries, muscular legs of frogs are used as food.

Quick Comparison of Four Animal Tissues

Frog Organ Systems at a Glance

Important Terms from Structural Organisation in Animals Class 11 Biology Notes

NCERT-Based Exam Points

• A tissue is a group of similar cells with intercellular substances performing a specific function.
• Complex animals have four basic tissues: epithelial, connective, muscular and neural.
• Organs are formed by tissues arranged in a definite pattern.
• Organ systems are formed when organs work together.
• Heart contains all four tissue types.
• Rana tigrina is the common Indian frog.
• Frog belongs to class Amphibia and phylum Chordata.
• Frog is poikilothermic.
• Frog shows camouflage and mimicry.
• Aestivation is summer sleep.
• Hibernation is winter sleep.
• Frog body has head and trunk.
• Neck and tail are absent in frog.
• Frog skin is smooth, moist and slippery.
• Frog absorbs water through skin.
• Male frogs have vocal sacs and copulatory pads.
• Frog has a short alimentary canal because it is carnivorous.
• Bile emulsifies fats.
• Pancreatic juice digests carbohydrates and proteins.
• Frog respires through skin in water.
• Frog respires through lungs on land.
• Frog has a three-chambered heart.
• Frog RBCs are nucleated.
• Frog is ureotelic.
• Frog has ten pairs of cranial nerves.
• Fertilisation in frog is external.
• Tadpole undergoes metamorphosis to become adult frog.

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