NEET Physics: Waves – NCERT Masterclass & 100 MCQ Quiz

STRUCTURAL ORGANISATION IN ANIMALS

NCERT Masterclass: Anatomy & Morphology of Frog (Rana tigrina)

1. Morphology of Frog

Frogs are amphibians that live in fresh water and on land. The most common species in India is Rana tigrina.

• Poikilotherms: They are cold-blooded (body temperature varies with the environment).
• Camouflage: They show ability to change color to hide from enemies (mimicry). They undergo summer sleep (Aestivation) and winter sleep (Hibernation) to protect themselves from extreme cold and heat.
• Body Division: Divided into Head and Trunk. Neck and tail are completely absent.
• Skin: Always maintained in a moist condition (mucous). Dorsal side is olive green with dark irregular spots, ventral side is pale yellow. Frogs never drink water; they absorb it through the skin.
• Sensory organs: Eyes are bulged and covered by a nictitating membrane (protects them in water). On either side of eyes, a membranous tympanum (ear) receives sound signals.

🔥 Sexual Dimorphism in Frogs:
Male frogs can be easily distinguished from female frogs by the presence of sound producing vocal sacs and a copulatory pad on the first digit of the forelimbs. Both of these are absent in female frogs.

2. Digestive System

The alimentary canal is incredibly short because frogs are carnivores (length of intestine is reduced).

• Path: Mouth $\rightarrow$ Buccal cavity $\rightarrow$ Pharynx $\rightarrow$ Oesophagus $\rightarrow$ Stomach $\rightarrow$ Intestine $\rightarrow$ Rectum $\rightarrow$ Cloaca.
• Liver secretes bile (stored in gall bladder). Pancreas produces pancreatic juice containing digestive enzymes.
• Food is captured by the bilobed tongue. Digestion occurs by action of HCl and gastric juices secreted from stomach walls.
• Digested food is absorbed by the numerous finger-like folds in the inner wall of intestine called villi and microvilli.

3. Respiratory System

• In Water / During Hibernation & Aestivation: Skin acts as the aquatic respiratory organ (Cutaneous respiration). Dissolved oxygen in water is exchanged through skin by diffusion.
• On Land: Buccal cavity, skin, and lungs act as respiratory organs. Respiration by lungs is called Pulmonary respiration. Lungs are a pair of elongated, pink coloured, sac-like structures present in the upper part of the trunk region (thorax).

4. Circulatory System

Frogs have a well-developed closed type circulatory system and a lymphatic system.

• Heart: 3-chambered (two atria and one ventricle). Covered by a membrane called pericardium.
• A triangular structure called Sinus venosus joins the right atrium (receives blood from major veins called vena cava). The ventricle opens into a sac-like Conus arteriosus on the ventral side of the heart.
• Portal Systems: Frogs uniquely possess a Hepatic portal system (venous connection between liver and intestine) and a Renal portal system (venous connection between kidney and lower parts of body).
• Blood: Composed of plasma and cells. RBCs (erythrocytes) are nucleated and oval, containing haemoglobin.

5. Excretory & Nervous System

Excretion: Elimination of nitrogenous wastes is carried out by a well-developed excretory system consisting of a pair of kidneys, ureters, cloaca, and urinary bladder. Frogs excrete urea and thus are ureotelic animals.

Control & Coordination:

• Central Nervous System (Brain and Spinal Cord). Brain is enclosed in a bony structure called the brain box (cranium).
• Brain is divided into: Fore-brain (olfactory lobes, paired cerebral hemispheres, unpaired diencephalon), Mid-brain (a pair of optic lobes), and Hind-brain (cerebellum and medulla oblongata).
• The Medulla oblongata passes out through the foramen magnum and continues into the spinal cord.
• Frog has 10 pairs of cranial nerves.

6. Reproductive System

Male Reproductive System: Consists of a pair of yellowish ovoid testes attached to the upper part of kidneys by a double fold of peritoneum called mesorchium.
Vasa efferentia (10-12 in number) arise from testes, enter the kidneys and open into Bidder's canal. It finally communicates with the urinogenital duct that comes out of the kidneys and opens into the cloaca.

• Female Reproductive System: Ovaries are situated near kidneys, but there is NO functional connection with kidneys. A pair of oviducts open into the cloaca separately.
• A mature female can lay 2500 to 3000 ova at a time.
• Fertilization: External, takes place in water.
• Development: Involves a larval stage called tadpole, which undergoes metamorphosis to form the adult frog.

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🚀 NEET FROG ANATOMY MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Frog Morphology, Digestion, Circulation, and Reproduction.

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