Nicotiana sylvestris flowers only during long days and N.tabacum flowers only during short days. If raised…
Nicotiana sylvestris flowers only during long days and N.tabacum flowers only during short days. If raised in the laboratory under different photoperiods, they can be indued to flower at the same time and can be cross-fertilized to produce self-fertile offspring. What is the best reason considering $N$. sylvestris and N.tabocum to be separate species ?
they cannot interbreed in nature
they are reproductively distinct
they are physiologically distinct
they arc morphologically distinct
Solution
According to biological species concept, a species is a natural inbreeding group which may have essentially similar morphological traits but they are genetically distinct and reproductively isolated from others. As under laboratory conditions, N. tabacum and $\mathrm{N}$. sylvestris cannot produce selffertile offspring, so they are not reproductively isolated. They are considered as separate species because since their flowering periods are different so cross pollination is not possible between them naturally. This makes them different species.
Caution
Students are generally intimidated by such long questions. However, in most cases. such type of questions are framed to test the presence of mind and witty nature. These questions are easy to answer and the actual question is asked in last 2 lines only, rest form the story around it. As in this case, 'What is the best reason for considering $N$. sylvestris and $N$. tabacum to be separate species' is the question in focus and the options given defines the universal term 'species.'