Final answer:
Fertilization in pine trees occurs approximately 12 months after pollination, when the pollen tube fuses with the egg nucleus, leading to the formation of a zygote. It's part of a lengthy reproductive process that reflects seasonal cycles and can take up to two years from pollination to seed development.
Step-by-step explanation:
In pine trees, fertilization is a process that can often take a considerable amount of time after pollination. Specifically, it occurs approximately 12 months later. At the time of pollination, the female part of the plant, the cone, has only a megaspore which will develop into the female gametophyte. As the pollen grains reach the female cone, they germinate and the pollen tube starts to slowly grow towards the egg which is encased within the female gametophyte. This process is not quick and reflects an adaptation to the longer seasonal cycles of the pine trees' environments.
The diploid zygote, which kicks off the next generation of pine trees, forms when one of the sperm nuclei from the pollen tube fuses with the egg nucleus of the mature female gametophyte during fertilization. The resulting zygote then develops into an embryo, which is enclosed in the seed and takes up to two years after pollination to fully develop. Therefore, the correct answer to when fertilization occurs after pollination in a pine is option d, 12+ months.