Which structure is responsible for fertilization in gymnosperms?

The correct answer is the ovule, as it plays a critical role in the fertilization process in gymnosperms. In these plants, fertilization occurs when a pollen grain—essentially the male gamete—lands on the ovule, which is located within the female cone. The ovule contains the female gametophyte and can develop into a seed once fertilization occurs. This process is essential for the reproduction of gymnosperms, enabling the development of seeds that will eventually grow into new plants.

Other structures mentioned do not directly participate in fertilization. For instance, the pollen grain is necessary for delivering sperm cells but is not where fertilization occurs. A sorus is a cluster of sporangia found on ferns and is unrelated to gymnosperms. A frond refers to the leaf-like structure of ferns and is also not involved in the fertilization process. Thus, the ovule is specifically designated for fertilization in gymnosperms, outlining its importance in the reproductive cycle of these plants.