Structural Organisation in Animals

Introduction

Unicellular vs Multicellular: Unicellular organisms perform all functions in one cell. Multicellular organisms use groups of cells for different functions.
Definition of Tissue: Group of similar cells performing a specific function.
Basic Tissues: Epithelial, connective, muscular, and neural tissues.
Organ Systems: Two or more organs performing common functions form systems (e.g. digestive, respiratory systems).

Organ Formation: Basic tissues organize to form organs; organs form organ systems.
Example: The heart consists of epithelial, connective, muscular, and neural tissues.
Evolutionary Trend: Complexity in organs and systems shows trends which will be studied in detail in later classes.

Habitat: Live on land and in freshwater; belong to Amphibia class of Chordata.
Species: Rana tigrina is common in India.
Body Temperature: Cold-blooded (poikilotherms); temperature varies with the environment.
Camouflage: Ability to change color, called mimicry.
Aestivation and Hibernation: Frogs shelter in burrows during extreme heat and cold.

Skin: Smooth, slippery with mucus; dorsal side olive green with spots, ventral side pale yellow.
Body Structure: Divided into head and trunk; has no neck or tail; nostrils, nictitating membrane on eyes, tympanum for hearing.
Limbs: Forelimbs with four digits, hind limbs with five digits, webbed for swimming.
Sexual Dimorphism: Males have vocal sacs, copulatory pad.

Digestive System: Short alimentary canal; mouth, buccal cavity, oesophagus, stomach, intestine, rectum, cloaca; liver, pancreas.
Respiratory System: Skin (cutaneous respiration), lungs (pulmonary respiration), buccal cavity.
Circulatory System: Closed system with heart (three chambers), arteries, veins, lymphatic system; hepatic and renal portal systems.
Excretory System: Kidneys, ureters, cloaca, urinary bladder; excretes urea.
Nervous System: Central, peripheral, autonomic nervous systems; brain with fore-brain, mid-brain, hind-brain.
Sense Organs: Touch, taste, smell, vision, hearing; eyes and internal ears well-organized.
Reproductive System: Males have testes, females have ovaries; external fertilization.
Ecological Role: Control insect population, maintain ecological balance.

Division of Labour: Cells, tissues, organs, organ systems contribute to survival.
Tissue Functions: Epithelia line surfaces, connect at junctions.
Indian Bullfrog (Rana tigrina): Covered by skin with mucous glands; can respire through skin and lungs; closed circulatory system; nucleated RBCs.
Reproduction: Females lay 2500-3000 eggs; external fertilization and development into tadpoles.