They are modified into spines because every leaf has stomata (plural of stoma) that are kind of pores which let the plant release extra water but because cacti lives in desert,it needs to store...
A normal leaf is assigned some specific functions i.e. Photosynthesis and transpiration. When a leaf is performing some functions other than these two then it needs to have some structural changes in...
None of the two. They are just a way the cacti protects its self from parasites and damage.
They are in fact modified leaves. The function of leaves has been taken over by the stem of the cacti that...