Question

Consider the following four statements (A-D) related to the common frog Rana tigrina, and select the correct option stating which ones are true (T) and which ones are false (F) . Statements :
(A) On dry land it would die due to lack of $O_2$ if its mouth is forcibly kept closed for a few days
(B) it has four-chambered heart
(C) On dry land it turns uricotelic from ureotelic
(D) Its life-history is carried out in pond water

• A. (A)-T ,(B) - F, (C)- F, (D)- T
• B. (A)-T ,(B) - T, (C)- F, (D)- F
• C. (A)-F ,(B) - F, (C)- T, (D)- T
• D. (A)-F ,(B) - T, (C)- T, (D)- F

Answer 1

Answer: (A)

Frog respires in three different manners; cutaneous or skin respiration; buccopharyngeal respiration; pulmonary or lung respiration. The skin of frog provides an extensive surface for the exchange of gases. It is thin, richly supplied with blood and kept moist by the mucus and water. The cutaneous respiration is always carried out. During hibernation (winter sleep) and aestivation (summer sleep) it is the only method of respiration in frog. Buccopharyngeal respiration occurs when the animal is on the land or partially immersed in water. There are present two external nares situated at the tip of the snout. Each external naris (nostril) leads into a nasal chamber which opens into the buccopharyngeal cavity. During this mode of respiration the mouth remains permanently closed while the nostrils remain open. The floor of the buccal cavity is alternately raised and lowered, so that air is drawn into and expelled out of the buccal cavity repeatedly through the open nostrils. During buccal respiration, the glottis remains closed so that no air enters or leaves the lungs into buccal cavity. Pulmonary respiration is less frequent than the cutaneous and buccopharyngeal respiration. As lungs are poorly developed in frog, the inadequate supply of $O_2$ obtained through lungs is supplemented through moist skin and buccal cavity. Hence, first statement is false. Heart of frog has three chambers, two atria and one ventricle. Hence, second statement is false. The frog excretes urea and thus is a ureotelic animal. The elimination of nitrogenous wastes is carried out by a well developed excretory system. The excretory system consists of a pair of kidneys, ureters, cloaca and urinary bladder. Frog do not change into uricotelic animal in any condition. Hence, third statement is false. In frog, fertilization is external and takes place in water. Within two weeks, fertilized eggs or zygotes develop into free-swimming aquatic larvae, called tadpoles, which undergo metamorphosis to become adult terrestrial frogs.