Biochemical recognition systems within the stigma of a flowering plant prevent the pollen from a different species from developing a pollen tube and fertilizing its eggs. This is an example of what kind of reproductive isolation?

A. post-zygotic, temporal separation

Bpre-zygotic, lock and key

C. pre-zygotic, behavioral isolation

D. post-zygotic, ecological separation

E. pre-zygotic, temporal separation

B. pre-zygotic, lock and key

Explanation:

When pollens from the different species fall on the stigma of a flower from some other species, the chemicals released from the stigma do not allow the pollens to germinate. The pollen tube is not formed to carry the male gametes to the egg cell for fertilization. Since this process does not allow the formation of zygote between the male and female gamete of two different species, it is a pre-zygotic isolating mechanism.

Here, the pollens and stigma of different plant species are not compatible with each other and the structural incompatibility of the reproductive structures prevents fertilization. This represents the lock and key mechanism of reproductive isolation.

The correct answer is - option B. pre-zygotic, lock and key.

Explanation:

Reproductive isolation is the method or process that involves preventing the particular species from mating and producing offspring in nature. Prezygotic isolation keeps the fertilization to occur that is the reason it termed as the pre-zygotic isolation or barrier.

Lock and key isolation system is a hypothesis that suggests that reproduction isolation can be increased due to the species-specific morphological compatibility of male and female reproductive parts like presented in the question.

Thus, the correct answer is - option B.