UPSC Civil Services 2018 Prelims General Studies Paper I

As per NIOS biology page 159&176: Thorn is not a 'leaf modification, it is an 'aerial modification of stem'. "Spine" is a leaf modification to protect the plant and help in reducing transpiration. So by elimination Answer should 'B'. However, Goh Cheng Leong Page 136 mentioned that "Desert plants have few or no leaves, and the foliage is either waxy, leathery, hairy or needle shaped to reduce water loss through transpiration. Some of them are entirely leafless, with pricks or thrones." So accordingly Answer should be D. Thus, experts were divided between A or d. UPSC has kept 'd' as the official answer.