Final answer:
The assertion that fern gametophytes are one cell thick except in the middle where the reproductive structures like archegonia and antheridia are located is true. They are heart-shaped and essential for the reproductive cycle of ferns.
Step-by-step explanation:
The statement that fern gametophytes are one cell thick except towards the middle is true. Most fern gametophytes are small, photosynthetic, and typically heart-shaped. They are indeed one cell layer thick but may be slightly thicker in the center where reproductive structures like archegonia and antheridia are present.
These structures are essential for sexual reproduction in ferns, housing the egg and sperm cells, respectively. Fern gametophytes are attached to the substrate through rhizoids and play a crucial role in the fern life cycle by producing haploid gametes which lead to the development of a diploid sporophyte generation after fertilization. Thus, the centrality of the gametophyte increases in thickness due to the presence of reproductive organs.