Biology

Study Material for Medical Entrance Exam

Tetrapoda: 
>>    Mostly terrestrial, aquatic or amphibious
>>   Two pairs of pentadactyl limbs present
>>    Lungs are the chief respiratory organs
>>    It includes the classes Amphibia, Reptilia, Aves and Mammalia

Class Amphibia: 
>>   Earliest group of tetrapods and lead dual mode
>>    Evolved during devonian period and flourished during carboniferous period
>>    Osteolepid fishes are ancestors of amphibians
>>    Body divisions are head & trunk
>>   Skin soft without exoskeleton
>>    Two pairs of pentadactyl limbs without claws present
>>    Skull dicondylic
>>   Vertebrae procoelous (anurans), amphicoelous(apodans)and opisthocoelous (many urodeles)
>>    Sternum developed for the first time in this group
>>    Mouth large, teeth are homodont, acrodont, polyphyodont
>>    Respiration mostly through skin (cutaneous),buccal cavity(buccal respiration) or lungs (pulmonary respiration)
>>    Heart three chambered with sinus venosus on dorsal side and truncus arteriosus on ventral side.
>>    Incomplete double circulation
>>   Hepatic and renal portal systems are well developed
>>    Kidneys mesonephric; ureotelic
>>    Brain covered by outer duramater and inner piamater
>>    10 pairs of cranial nerves
>>    Middle ear has single ossicle called columella auris which is modified hyomandibular
>>    Tympanum, lacrimal and harderian glands appeared for the first time.
>>   Eggs are mesolecithal and teloleci thal
>>    Development mostly indirect
>>    Amphibia includes 3 orders
>>   Order Apoda/Gymnophiona-caecilians or blind worms. Eg. Ichthyo phis, Uraeotyphlus, Gegenophis, Typhlonectes
>>   Order Urodela/Caudata-Salam and ers and newts, Eg. Salamandra, Nect urus, Mud puppy Tylototriton (Him alayan newt), Ambystoma (tiger salamander), Amphiuma(congoeel), Cryptobranchus
>>   Order Anura/Salientia-frogs and to ads Eg.Bufo melanosticus (Indian toad) Rana (frog)Rhacophorus (Flying frog) Hyla(Tree frog) Alytes (Mid wife toad)Ascaphus

FROG 
order : Anura 
Family : Ranidae
>>  Freshwater in habitat
>>  Carnivores
>>  Poikilothermic anamniotes
>>   Frogs exhibit hibernation (winter sleep) and aestivation (summer sleep)
>>   Change the skin colour to match their surroundings which is called camouflage Rana tigrina
>>  Skin smooth,moist and scaleless
>>   Body divided into head and trunk
>>   Neck and tail are absent
>>   Eyes with immovable upper eyelid and the movable lower eyelid is drawn over the eye ball as nictitating membrane.
>>   Tympanum present behind and below each eye
>>   Forelimbs with four fingers, hindlimbs with five toes.
>>   Webbed feet help in swimming
>>  Sexual dimorphism: Male frogs have sound amplifying vocal sacs and a copulatory or
>>   amplexusory pad on the first digit of each fore limb.

Digestive system 
>>   Alimentary canal shorter as frog is carnivorous
>>   Mouth opens into large buccopharyngeal cavity
>>   Teeth present along the margin of upper jaw only called maxillary teeth
>>   Vomerine teeth are present on the roof of buccal cavity.
>>   Maxillary teeth are homodont, acrodont and polyphyodont
>>   Tongue bifid and useful for capturing the prey
>>   Buccopharyngeal cavity opens into oesophagus through gullet.
>>   Oesophagus is short and leads into stomach
>>   sphincter present between oesophagus and stomach whereas pyloric sphincter present between stomach and dueodenum
>>   Dueodenum and ileum are anterior and posterior parts of small intestine.
>>   Rectum forms the large intestine which opens into cloacal chamber
>>   Cloacal chamber also receives ureters, urinary bladder and opens out by cloacal aperture.
>>   Villi in small intestine are foldings of columnar epitherlium which increase the area of absorption.
>>   Dueodenum and ileum are anterior posterior parts of small intestine.
>>   Rectum forms the large intestine which opens into cloacal chamber
>>   Cloacal chamber also receives urete rs and urinary bladder and opens out by cloacal aperture
>>   Villi in small intestine are floldings of columnar epithelium which incre ase the area of absorption.
>>   Liver bilobed with gall bladder to store the bile juice
>>   Bile duct is formed by the union of hepatic ducts and cystic duct
>>   Panecreas is an irregular gland present between stomach and dueodenum
>>  Pancreatic ducts join the bile duct forming hepatopancreatic duct which opens into dueodenum.
>>   Bile helps in emulsifiation of fats and converts the acidic food to alkaline medium
>>  Digestion occurs by the action of pancreatic juice and intestinal juice (succus entericus)

Respiratory system:
>>  Respiraton occurs by 3 methods.
>>  Cutaneous respiration- occurs thro ugh moist, vascular skin and is the most important method of respiration
>>  Buccopharyngeal respiration-occurs through moist vascular lining of buccopharyngeal cavity
>>  Pulmonary respiration-occurs thro ugh lungs and buccopharyngeal cavity acts as force pump.
>> Floor of the buccal cavity is raised and lowered by the contractions of petrohyal and sternohyal muscles respiration.
>> Glottis opens into laryngotracheal chamber which is connected to lungs by short bronchi
>>  Vocalcords are present in laryngotracheal chamber
>>   Laryngotracheal chamber is supported by ring like cricoid and two crescentic arytenoid cartilages.

Circulatory system:
>>   Heart-3 chambered with two atria and single ventricle and covered by double layer pericardium
>>   Sinus venosus opens into right atrium whereas common pulmonary vein opens into left atrium.
>>   Atrioventricular aperture is the common opening through which the two atria open into ventricle.
>>  Atrioventricular aperture is guarded by 2 pairs of atrioventricular valves.
>>   Atrioventricular valves are attached to the wall of ventricle by chordae tendinae.
>>  Columnae carneae are the ridges of the thick muscular walls of ventricle.
>>   Conus arteriosus arises from the right side of ventricle.
>>  Pylangium and synangium are proximal and distal parts of conus arteriosus
>>   2 sets of semilunarvalves are present, one set at the origin of conus arteriosus and second set
>>   between pylangium and synangium.
>>   Longitudinal spiral valve divides the conus arteriosus into dorsal, left cavum pulmocutaneum and ventral, right cavum aorticum

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