Class 11 Biology Structural Organisation In Animals Morphology & Anatomy of Frog

Morphology & Anatomy of Frog

  • Frogs can live both on land and in freshwater and belong to class Amphibia of phylum Chordata.
  • The most common species of frog found in India is Rana tigrina.
  • They are called cold blooded or poikilotherms and go for summer sleep.
  • They have the ability to camouflage.
  • During extreme hot, frogs take shelter in deep burrows to protect them from extreme heat and cold called as summer sleep or aestivation
  • Winter sleep is called as hibernation.


  • The skin absorbs water, which is smooth and slippery due to the presence of mucus and maintains a moist condition.
  • Dorsal side is olive green in color and ventral side is uniformly pale yellow.
  • Body is divisible into head and trunk.
  • The body of frogs has pair nostrils, bulged eyes covered by nictitating membrane, a membranous tympanum (ear), forelimbs and hind limbs, webbed digit in feet.
  • Frogs exhibit sexual dimorphism, with vocal sacs and copulatory pad on the first digit of the fore limbs in males.


Fig. Morphology of frog


  • The digestive system consists of short alimentary canal and digestive glands, with the mouth opening into the buccal cavity that leads to the oesophagus through pharynx.
  • Oesophagus is a short tube that opens into the stomach which in turn continues as the intestine, rectum and finally opens outside by the cloaca.
  • Liver secretes bile; pancreas secretes pancreatic juice containing digestive enzymes.
  • Food is captured by the bilobed tongue and digested by HCl and gastric juices in stomach from where partially digested food called chyme passes to the duodenum, which receives bile for fat emulsification and pancreatic juice to digest complex molecules and final digestion takes place in the intestine, from where the digested food is absorbed by the numerous finger-like folds in the inner wall of intestine called villi and microvilli.
  • Respiration can take place though both skin, lungs and buccal cavity.
  • In water, dissolved oxygen in the water is exchanged through the skin by diffusion and in land air enters through the nostrils into the buccal cavity and then to lungs.
  • The blood vascular system involves heart, blood vessels and blood and the lymphatic system consists of lymph, lymph channels and lymph nodes.
  • Heart consists of three chambers, two atria and one ventricle and is covered by a membrane called pericardium.
  • A triangular structure called sinus venosus joins the right atrium, which receives blood through the major veins called vena cava and the ventricle opens into a saclike conus arteriosus on the ventral side of the heart.
  • Special venous connection between liver and intestine is called hepatic portal system as well as the kidney and lower parts of the body is called renal portal system.
  • The blood is composed of plasma and nucleated RBC (red blood cells) or erythrocytes, WBC (white blood cells) or leucocytes and platelets.
  • The excretory system consists of a pair of kidneys, ureters, cloaca and urinary bladder and each kidney is composed of several structural and functional units called uriniferous tubules or nephrons.
  • The frog excretes urea and thus is a ureotelic animal.
  • Frogs have both neural system and endocrine glands like pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals and gonads.
  • Nervous system is divided into
  • a central nervous system (brain and spinal cord),
  • a peripheral nervous system (cranial and spinal nerves)
  • an autonomic nervous system (sympathetic and parasympathetic).
  • There are ten pairs of cranial nerves arising from the brain and the brain is enclosed in a bony structure called brain box.
  • The brain is divided into
  • fore-brain- includes olfactory lobes, paired cerebral hemispheres and unpaired diencephalon
  • mid-brain- a pair of optic lobes is present.
  • hind-brain- consists of cerebellum and medulla oblongata, medulla passes out through the foramen magnum and continues into spinal cord.
  • The sensors organs present are
  • touch (sensory papillae),
  • taste (taste buds),
  • smell (nasal epithelium),
  • vision (eyes)
  • hearing (tympanum with internal ears).
  • Male reproductive organs consist of a pair of yellowish ovoid testes adhered to the upper part of kidneys by a double fold of peritoneum called mesorchium, vasa efferentia enter the kidneys on their side and open into Bidder’s canal, which finally communicates with the urinogenital duct that opens into the small, median chamber cloaca.
  • The female reproductive organs include a pair of ovaries with a pair of oviduct opening into the cloaca separately.
  • Fertilisation is external, development involves a larval stage called tadpole, which undergoes metamorphosis to form the adult.


Fig. Anatomy of frog


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