Elimination of Nitrogenous Waste Products in Tadpole and Adult Frog

The elimination of nitrogenous waste products is an important process in living organisms as it helps maintain the overall balance of their internal environment. In the case of tadpoles and adult frogs, nitrogenous waste products are eliminated primarily as ammonia in tadpoles and urea in adult frogs.

Ammonia in Tadpole
During the early stages of their life cycle, tadpoles live in aquatic environments such as ponds or streams. They obtain oxygen through gills and excrete waste products, including nitrogenous waste, mainly in the form of ammonia. Ammonia is highly toxic and requires a large amount of water to dilute its concentration. As tadpoles are constantly surrounded by water, they are able to eliminate ammonia easily. Ammonia diffuses out of the tadpole's body through the gills and into the surrounding water.

Urea in Adult Frog
As tadpoles undergo metamorphosis and develop into adult frogs, they transition from an aquatic to a semi-aquatic or terrestrial lifestyle. Adult frogs have lungs for respiration and their skin also plays a role in gas exchange. In order to conserve water and prevent dehydration, adult frogs need to eliminate nitrogenous waste in a less toxic form that requires less water for dilution. Therefore, adult frogs convert ammonia into urea, which is less toxic and more water-soluble than ammonia. Urea is transported to the kidneys for filtration and elimination from the body.

Reasoning behind the Answer
Based on the differences in the habitat and lifestyle of tadpoles and adult frogs, the elimination of nitrogenous waste products in these two stages of their life cycle differs. Tadpoles living in aquatic environments eliminate nitrogenous waste mainly as ammonia, which can be easily diluted and eliminated in water. Adult frogs, on the other hand, living in a semi-aquatic or terrestrial environment, convert ammonia into urea, which is less toxic and requires less water for elimination. Therefore, option B, which states that ammonia is eliminated in tadpoles and urea in adult frogs, is the correct answer.