Frog — Revision Notes

⚡ 30-Second Revision

Classification: — Phylum Chordata, Subphylum Vertebrata, Class Amphibia, Order Anura.
Species: — *Rana tigrina* (Indian Bullfrog).
Skin: — Moist, smooth, slippery; cutaneous respiration.
Respiration: — Cutaneous (skin), Buccopharyngeal (mouth lining), Pulmonary (lungs).
Heart: — 3-chambered (2 atria, 1 ventricle); Incomplete double circulation.
Excretion: — Ureotelic (urea); Mesonephric kidneys, cloaca.
Reproduction: — External fertilization; Sexual dimorphism (male: nuptial pads, vocal sacs).
Life Cycle: — Egg $ightarrow$ Tadpole (gills, herbivorous) $ightarrow$ Metamorphosis (thyroxine) $ightarrow$ Adult (lungs, carnivorous).
Dormancy: — Hibernation (winter), Aestivation (summer) - reduced metabolic rate.

2-Minute Revision

Frogs, specifically *Rana tigrina*, are amphibians known for their dual life. Their smooth, moist skin is vital for cutaneous respiration, supplementing buccopharyngeal and pulmonary breathing. The heart is three-chambered, leading to incomplete double circulation, a key feature to remember.

Digestion is carnivorous, with a short alimentary canal. Excretion is ureotelic, with kidneys filtering waste into ureters that, in males, also carry sperm (urinogenital ducts) to the cloaca. Reproduction involves external fertilization during amplexus, where males use nuptial pads.

The life cycle is marked by metamorphosis from an aquatic, gill-breathing, herbivorous tadpole to a terrestrial, lung-breathing, carnivorous adult, a process controlled by thyroid hormones. Frogs are ectothermic and survive extreme conditions through hibernation (winter) and aestivation (summer), characterized by a significantly reduced metabolic rate.

They serve as important bioindicators due to their environmental sensitivity.

5-Minute Revision

Let's quickly review the essential facts about frogs for NEET. We're focusing on *Rana tigrina*. Morphologically, remember their smooth, moist skin for camouflage and respiration, prominent eyes with nictitating membranes, and a large mouth with a sticky, bilobed tongue. Males are distinguished by vocal sacs and nuptial pads on their forelimbs during breeding. Their powerful hind limbs are webbed for swimming and jumping.

Internally, the digestive system is adapted for carnivory, featuring a short alimentary canal from mouth to cloaca, aided by the liver and pancreas. Respiration is diverse: cutaneous (skin, especially underwater/dormancy), buccopharyngeal (mouth lining, on land at rest), and pulmonary (lungs, on land). The circulatory system is closed, with a three-chambered heart (two atria, one ventricle) resulting in incomplete double circulation. Don't forget the hepatic and renal portal systems.

Excretion is via mesonephric kidneys, producing urea (ureotelic). Ureters carry urine to the cloaca; in males, they also transport sperm. The nervous system includes a brain, spinal cord, and 10 pairs of cranial nerves. Sensory organs include eyes, tympanum (ear), and olfactory receptors.

Reproduction is sexual, with external fertilization. Males clasp females in amplexus, releasing sperm as females lay eggs in water. The eggs hatch into tadpoles, which are aquatic, gill-breathing, and herbivorous.

They undergo metamorphosis, a thyroid hormone-regulated process, to become adult frogs. Finally, remember their ectothermic nature and survival strategies: hibernation (winter sleep) and aestivation (summer sleep), both involving a drastic reduction in metabolic rate to conserve energy.

Frogs are crucial bioindicators, reflecting environmental health.

Prelims Revision Notes

Frog (Rana tigrina) - NEET Revision Notes

1. Classification:

Phylum: Chordata
Subphylum: Vertebrata
Class: Amphibia
Order: Anura
Species: *Rana tigrina* (Indian Bullfrog)

2. Morphology:

Skin: — Smooth, moist, slippery (mucus glands). Highly vascularized for cutaneous respiration. Chromatophores for camouflage.
Head: — Broad, triangular. Bulging eyes with nictitating membrane. Tympanum (eardrum) behind eyes. External nares (nostrils). Large mouth with bilobed, sticky tongue (anteriorly attached).
Limbs: — Forelimbs (4 digits), Hindlimbs (5 webbed digits for swimming/jumping).
Sexual Dimorphism (Males): — Smaller size, Nuptial pads (copulatory pads) on first digit of forelimb during breeding, Vocal sacs (resonators) for croaking.

3. Anatomy & Physiology:

Digestive System (Carnivorous):

* Alimentary Canal: Mouth $ightarrow$ Buccal cavity $ightarrow$ Pharynx $ightarrow$ Oesophagus $ightarrow$ Stomach $ightarrow$ Small intestine $ightarrow$ Large intestine $ightarrow$ Cloaca. * Glands: Liver (bile), Pancreas (pancreatic juice).

Respiratory System (3 types):

* Cutaneous: Through moist skin (primary underwater/dormancy). * Buccopharyngeal: Through lining of mouth/pharynx (on land, at rest). * Pulmonary: Through simple sac-like lungs (on land).

Circulatory System (Closed, Incomplete Double):

* Heart: 3-chambered (2 atria, 1 ventricle). Some mixing of oxygenated/deoxygenated blood. * Blood: Plasma, nucleated RBCs, WBCs, platelets. * Portal Systems: Hepatic portal system, Renal portal system.

Excretory System (Ureotelic):

* Kidneys: Paired, dark red, mesonephric. * Ureters: Carry urine to cloaca. In males, also carry sperm (urinogenital ducts). * Urinary Bladder: Stores urine temporarily. * Cloaca: Common chamber for urine, faeces, gametes.

Nervous System: — CNS (brain, spinal cord), PNS (10 pairs cranial nerves, 10 pairs spinal nerves), ANS.
Sensory Organs: — Eyes, tympanum (hearing), olfactory (smell), taste buds, tactile receptors.
Reproductive System:

* Male: Testes (sperm), Vasa efferentia (sperm to kidneys), Urinogenital ducts (ureters). * Female: Ovaries (ova), Oviducts (collect eggs, secrete jelly). * Fertilization: External (in water) during amplexus.

4. Life Cycle:

Eggs (frogspawn) $ightarrow$ Tadpole (aquatic, gills, tail, herbivorous) $ightarrow$ Metamorphosis (thyroid hormones) $ightarrow$ Adult Frog (terrestrial/semi-aquatic, lungs, no tail, carnivorous).

5. Adaptations:

Ectothermic: — Cold-blooded.
Dormancy: — Hibernation (winter sleep), Aestivation (summer sleep) - both involve reduced metabolic rate.
Bioindicators: — Sensitive to environmental changes.

Vyyuha Quick Recall

Frogs Respirate Cutaneously, Buccopharyngeally, Pulmonarily. Heart is Three-chambered. Males have Nuptial pads and Vocal sacs. Metamorphosis is Thyroxine-driven.