Quiz 42: Animal Reproductive Systems


As the proteins present in our body break, they produce toxic ammonia. This ammonia will be converted to urea, in all mammals. The urea produced can be eliminated from the body when it is dissolved in water present in the urine. In a similar way, in birds and reptiles, the ammonia produced will be converted as uric acid. This solid substance will be excreted when it dissolves with little amount of water. The amount of water required to excrete 1 gram of urea is twenty to thirty times more than that is required to eliminate 1 gram of uric acid. This indicates that mammals require more amount of water, than birds and reptiles do. Thus, water is the deciding factor for species richness of mammals, birds, and reptiles. For mammals to be more in number there should be good amount of water in their surroundings. But, birds and reptiles can survive well even when there is very little amount of water. For example, lizards can live long even without water. They have the ability to absorb moisture from the solid food they eat. In order to test our hypothesis, let us examine the area in which there is very less amount of water. If we count the numbers of each species surviving in that area, then we can observe the numbers of mammals to be very less, than birds and reptiles. This shows the importance of water for the survival of mammals. Unless the toxic ammonia is converted to urea, no mammal can survive on the land. Thus, the species richness is related to the amount of water required for the conversion of toxic ammonia into urea and uric acid.

Freshwater fish continually gains water by the process of osmosis (particularly diffusion) that occurs through the skin of fish. The excess of water that enters the body is excreted in the form of dilute urine. Freshwater fish is an example of osmoregulator. Hence, the correct option is (c) 'osmosis'. Freshwater fish does not drink water. It absorbs the water through its skin by the process of diffusion. Hence, option (a) 'drinking' is incorrect. Freshwater fish balances the solutes by the food intake and absorbs the water by diffusion. Hence, option (b) 'eating food' is incorrect. Ions are transported in the freshwater fish through the gills. Hence, option (d) 'transport across the gills' is incorrect.

Kangaroo rat are found in the desert areas. These animals are adapted to live in their habitat. They can live without drinking water for their lifetime and can absorb the moisture from the food they eat. Kangaroo rat have a nephron in which loop of Henle is longer than in humans. The main function of the loop of Henle is to concentrate the urine by absorbing more water. This helps the kangaroo rat to excrete a very concentrated urine. Excreting a very concentrated urine helps the kangaroo rat to conserve water. Hence, longer loop of Henle helps kangaroo rat to preserve water.

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