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2.3 Structural Organisation in Animals: The Frog
Morphology of the Frog
Body:
Divisible into head and trunk; neck and tail are absent.
Skin:
Moist, smooth, and slippery; dorsal side is olive green, ventral side is pale yellow.
Limbs:
Short forelimbs (4 digits) and muscular hind limbs (5 webbed digits).
Sexual Dimorphism:
Males have vocal sacs and a copulatory pad on the first digit of the forelimbs.
Digestive System
Alimentary Canal:
Mouth -> Buccal Cavity -> Pharynx -> Oesophagus -> Stomach -> Intestine -> Rectum -> Cloaca.
Digestive Glands:
Liver:
Secretes bile.
Pancreas:
Produces pancreatic juice.
Digestion:
Occurs in the stomach and intestine; absorption through villi and microvilli.
Respiratory System
Cutaneous Respiration:
Through the skin in water.
Pulmonary Respiration:
Through the lungs on land.
Buccal Respiration:
Through the buccal cavity on land.
Circulatory System
Heart:
Three-chambered (two atria, one ventricle).
Blood:
Plasma, RBCs (nucleated), WBCs, platelets.
Circulation:
Incomplete double circulation (mixed blood in the ventricle).
Excretory System
Organs:
Kidneys, ureters, cloaca, urinary bladder.
Excretion:
Ureotelic (excretes urea).
Pathway:
Kidneys -> Ureters -> Cloaca.
Nervous System
Central Nervous System (CNS):
Brain and spinal cord.
Peripheral Nervous System (PNS):
Cranial and spinal nerves.
Autonomic Nervous System (ANS):
Sympathetic and parasympathetic.
Reproductive System
Male:
Testes -> Vasa efferentia -> Bidder's canal -> Urinogenital duct -> Cloaca.
Female:
Ovaries -> Oviducts -> Cloaca.
Fertilization:
External, in water.
Development:
Indirect, with a tadpole larval stage.