Biology: Class 11 — Chapter 7: Structural Organisation in Animals

• Scientific Name: Rana tigrina (Common Indian bullfrog).
• Classification: Class Amphibia, Phylum Chordata. Can live on both land and freshwater.
• Thermoregulation: Poikilothermic (cold-blooded); body temperature fluctuates with environmental temperature.
• Adaptations:
  • Camouflage (mimicry): Ability to change skin colour to blend with surroundings and hide from enemies.
  • Aestivation: Summer sleep to survive extreme heat.
  • Hibernation: Winter sleep to survive extreme cold.

• Skin: Smooth, slippery (due to mucus secretion), and kept moist. Dorsal side is olive green with dark irregular spots; ventral side is pale yellow. Water is absorbed through the skin (frogs never drink water).
• Body Divisions: Divided into head and trunk. Neck and tail are completely absent.
• Sensory Structures:
  • A pair of nostrils above the mouth.
  • Bulged eyes covered by a transparent nictitating membrane for protection underwater.
  • A membranous tympanum (ear) on either side of the eyes to receive sound signals.
• Limbs:
  • Forelimbs: End in 4 digits; help in swimming, walking, leaping, and burrowing.
  • Hind limbs: Larger, muscular, and end in 5 webbed digits that facilitate swimming.
• Sexual Dimorphism: Male frogs are distinguished by the presence of sound-producing vocal sacs and a copulatory pad on the first digit of the forelimbs (both absent in females).

Consists of a short alimentary canal (due to carnivorous diet) and digestive glands.

1. Ingestion: Food is captured using a bilobed tongue.
2. Pathway: Mouth → Buccal cavity → Pharynx → Oesophagus → Stomach → Intestine → Rectum → Cloaca.
3. Digestion in Stomach: Gastric juices and hydrochloric acid ($HCl$) break down food into semi-digested chyme.
4. Duodenum & Glands: Receives bile (secreted by liver, stored in gall bladder) to emulsify fats, and pancreatic juice (from pancreas) to digest carbohydrates and proteins.
5. Absorption: Occurs in the intestine via finger-like folds called villi and microvilli.
6. Egestion: Undigested solid waste passes through the rectum and out via the cloaca.

• Cutaneous Respiration (In Water): Skin acts as the respiratory organ. Dissolved oxygen is exchanged via simple diffusion.
• Pulmonary Respiration (On Land): Performed by a pair of elongated, pink, sac-like lungs in the thorax. Air enters through nostrils into the buccal cavity and then to the lungs.
• Aestivation & Hibernation: Gaseous exchange occurs exclusively through the skin.

Well-developed closed circulatory system and a lymphatic system.

• Heart Structure: Three-chambered (two atria and one ventricle), covered by the pericardium.
  • Sinus venosus: A triangular structure joining the right atrium; receives deoxygenated blood via the vena cava.
  • Conus arteriosus: A sac-like structure on the ventral side of the heart where the ventricle opens.
• Portal Systems:
  • Hepatic portal system: Venous connection between liver and intestine.
  • Renal portal system: Venous connection between kidneys and lower parts of the body.
• Blood Composition: Plasma and blood cells.
  • RBCs (Erythrocytes): Nucleated and contain red-coloured haemoglobin.
  • WBCs (Leucocytes) and Platelets.
• Lymph: Differs from blood; lacks RBCs and certain proteins.

• Components: A pair of kidneys, ureters, cloaca, and urinary bladder.
• Kidneys: Compact, dark red, bean-like structures containing structural units called uriniferous tubules or nephrons.
• Ureters:
  • In males: Act as a urinogenital duct opening directly into the cloaca.
  • In females: Open separately into the cloaca alongside the oviducts.
• Excretion Type: Ureotelic (excretes urea, which is filtered from the blood by the kidneys).

• Endocrine System: Chemical coordination via hormones from glands: pituitary, thyroid, parathyroid, thymus, pineal body, pancreatic islets, adrenals, and gonads.
• Nervous System:
  • Central Nervous System (CNS): Brain (enclosed in a bony cranium) and spinal cord.
  • Peripheral Nervous System (PNS): 10 pairs of cranial nerves and spinal nerves.
  • Autonomic Nervous System (ANS): Sympathetic and parasympathetic systems.
• Brain Divisions:
  • Fore-brain: Olfactory lobes, paired cerebral hemispheres, and unpaired diencephalon.
  • Mid-brain: Characterised by a pair of optic lobes.
  • Hind-brain: Cerebellum and medulla oblongata (passes through the foramen magnum to continue as the spinal cord).
• Sense Organs: Sensory papillae (touch), taste buds (taste), nasal epithelium (smell), simple eyes (vision), and tympanum with internal ears (hearing and balancing/equilibrium).

• Male Reproductive System:
  • A pair of yellowish ovoid testes adhered to the upper kidneys by a double fold of peritoneum called mesorchium.
  • 10-12 vasa efferentia arise from testes, enter kidneys, and open into Bidder's canal.
  • Communicates with the urinogenital duct to open into the cloaca.
• Female Reproductive System:
  • A pair of ovaries situated near the kidneys (no functional connection with kidneys).
  • A pair of oviducts opening separately into the cloaca.
  • A mature female lays 2500 to 3000 ova at a time.
• Fertilisation & Development:
  • Fertilisation is external and occurs in water.
  • Development is indirect, involving a larval stage called a tadpole, which undergoes metamorphosis to become an adult.