Answer:
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.
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Getting and using energy Reproducing and Maintaining structure
