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 separationb. pre-zygotic, lock and keyc. pre-zygotic, behavioral isolationd. post-zygotic, ecological separatione. pre-zygotic, temporal separation

prezygotic, lock and key

Explanation:

Prezygotic isolation mechanisms are the ones that operate before zygote is formed. When the pollen of a different species lands on the stigma, the chemicals secreted by stigma do not allow pollen germination. Without pollen germination, the pollen tube is not formed and fertilization does not occur. This represents the prezygotic isolating mechanism.

Since the mechanism is based on the incompatibility of the reproductive parts of plants where pollen and stigma of different species do not fit each other, it is a lock and key mechanism of reproductive isolation.

equal distribution i think.