Structural organisation

• In multicellular animals, all functions like digestion, respiration, and reproduction are performed by different groups of cells in a well-organised manner
• Simple organisms like Hydra are made of different types of cells with thousands of cells in each type
• The human body is composed of billions of cells to perform various functions
• Tissues are groups of similar cells along with intercellular substances that perform specific functions in multicellular animals
• Complex animals consist of only four basic types of tissues: epithelial, connective, muscular, and neural
• Organs are made of one or more types of tissues and associate to form organ systems in multicellular organisms
• The complexity in organ and organ systems displays an evolutionary trend
• The body of a frog is divisible into head and trunk, with a neck and tail absent
• Frogs exhibit sexual dimorphism with male frogs having sound-producing vocal sacs and a copulatory pad on the first digit of the forelimbs
• The digestive system of frogs consists of the alimentary canal, digestive glands, mouth, oesophagus, stomach, intestine, rectum, and cloaca
• Frogs respire through cutaneous respiration in water and through the buccal cavity, skin, and lungs on land
• The circulatory system of frogs is a well-developed closed type with a heart, blood vessels, and blood
• The excretory system of frogs consists of kidneys, ureters, cloaca, and urinary bladder, with frogs being ureotelic animals
• Frogs have a well-developed system for control and coordination involving neural system and endocrine glands
• The nervous system of frogs is organised into central, peripheral, and autonomic systems with ten pairs of cranial nerves
• Frogs have different types of sense organs including organs of touch, taste, smell, vision, and hearing
• Male frogs have a pair of testes and female frogs have a pair of ovaries, with fertilisation being external and development involving a larval stage called tadpole
• Frogs are beneficial for mankind as they eat insects, protect crops, and maintain ecological balance in the ecosystem