Structural Organisation in Animals

[Image of Frog Digestive System Diagram]

Description of the Diagram:

• Alimentary Canal: A short tube (as frogs are carnivores) consisting of the mouth, buccal cavity, pharynx, oesophagus, stomach, intestine, rectum, and cloaca.
• Mouth: Opens into the buccal cavity.
• Oesophagus: A short tube that connects the pharynx to the stomach.
• Stomach: Muscular bag where food digestion occurs (gastric juice and HCl).
• Intestine: Divided into the small intestine (duodenum and ileum) and large intestine (rectum).
• Cloaca: The common chamber where the digestive, excretory, and reproductive tracts open to the exterior.
• Digestive Glands:
  • Liver: Secretes bile (stored in the gall bladder).
  • Pancreas: Secretes pancreatic juice containing digestive enzymes.

The function of ureters differs between male and female frogs:

• In Male Frogs: The ureters act as a Urinogenital Duct. They carry both urine (excretory waste) from the kidneys and sperm (reproductive cells) from the testes to the cloaca.
• In Female Frogs: The ureters carry only urine from the kidneys to the cloaca. The oviducts (carrying eggs) open separately into the cloaca.

Feature	Simple Epithelium	Compound Epithelium
Layers	Single layer of cells.	Multi-layered cells.
Function	Absorption, secretion, filtration.	Protection against stress (mechanical/chemical).
Example	Alveoli, Nephrons.	Skin, Buccal cavity lining.

Feature	Cardiac Muscle	Striated (Skeletal) Muscle
Location	Heart walls only.	Attached to bones.
Control	Involuntary.	Voluntary.
Structure	Branched, uninucleate, intercalated discs.	Cylindrical, unbranched, multinucleate.

Blood is a fluid connective tissue composed of plasma and formed elements. The cellular components (formed elements) are:

• Erythrocytes (Red Blood Cells – RBCs): Carry oxygen via hemoglobin. Biconcave and enucleated in mammals; oval and nucleated in frogs.
• Leucocytes (White Blood Cells – WBCs): Part of the immune system. Includes Granulocytes (Neutrophils, Eosinophils, Basophils) and Agranulocytes (Lymphocytes, Monocytes).
• Thrombocytes (Platelets): Cell fragments involved in blood clotting (coagulation).

Frogs respire in three different ways depending on their habitat:

1. Cutaneous Respiration (Skin): In water and during hibernation/aestivation, the frog breathes through its moist, vascular skin. Dissolved oxygen diffuses directly into the blood.
2. Buccal Respiration: On land, the mouth cavity floor is raised and lowered, forcing air in and out through the nostrils. The lining of the buccal cavity is moist and vascular for gas exchange.
3. Pulmonary Respiration (Lungs): On land, air enters the lungs via the nostrils and buccal cavity. The lungs are a pair of elongated, pink, sac-like structures in the thorax.

Feature	Dense Regular	Dense Irregular
Fiber Arrangement	Collagen fibers are present in rows between many parallel bundles of fibers.	Fibroblasts and many fibers (mostly collagen) are oriented differently (randomly).
Examples	Tendons (muscle to bone), Ligaments (bone to bone).	Skin (dermis).

[Image of Male Reproductive System of Frog]

• Testes: A pair of yellowish, ovoid testes are found attached to the upper part of the kidneys by a double fold of peritoneum called Mesorchium.
• Vasa Efferentia: 10-12 in number, arising from the testes. They enter the kidneys and open into Bidder’s canal.
• Urinogenital Duct: The vasa efferentia communicate with the urinogenital duct, which comes out of the kidneys and opens into the cloaca.
• Cloaca: A small median chamber used to pass faecal matter, urine, and sperms to the exterior.