Final answer:
Double fertilization is a process unique to angiosperms, which involves one sperm fertilizing the egg while another fertilizes two polar nuclei to form the endosperm. It doesn't occur in bryophytes, cryptogams, or gymnosperms.
Step-by-step explanation:
Double fertilization is a unique feature found in angiosperms only, which are also known as flowering plants. This reproductive process involves two separate fertilization events within the plant's life cycle. One sperm from the pollen fertilizes the egg, forming a diploid zygote, while the other sperm fertilizes the two polar nuclei, creating a triploid cell that develops into the endosperm, which serves as a food storage tissue for the developing embryo. This ensures that the embryo will have the necessary nutrients for its early growth. The occurrence of double fertilization is significant because it is not seen in other groups such as bryophytes, cryptogams, or gymnosperms, thus the correct answer to the student's question is a) angiosperms only.
Angiosperms are divided into monocots and eudicots based on the number of cotyledons they have, and they exhibit a life cycle predominantly in the sporophyte stage. This group includes a wide variety of plants including grasses, herbs, shrubs, and most deciduous trees.