USA Biology Olympiad (USABO) Practice Exam

In the fern life cycle, which generation is dominant?

1. Haploid Gametophyte

2. Diploid Sporophyte

3. Diploid Gametophyte

4. Haploid Sporophyte

The correct answer is: Diploid Sporophyte

In the fern life cycle, the dominant generation is the diploid sporophyte. This is significant because ferns, which are classified as vascular plants, primarily exhibit this stage throughout their life. The sporophyte is the larger, more complex, and long-lived phase in ferns, characterized by the presence of true roots, stems, and leaves. During this stage, the sporophyte produces spores through meiosis in specialized structures called sporangia, located on the undersides of fronds (the leaves). These spores are haploid and will eventually germinate to form the gametophyte generation. However, the gametophyte is typically small, independent, and short-lived compared to the robust sporophyte. In ferns, this shift towards a dominant diploid phase is a crucial adaptation that allows for greater resilience and reproductive success in varying environmental conditions. The sporophyte's complexity also facilitates efficient photosynthesis and nutrient transport, enabling these plants to thrive in diverse habitats. This distinction between the generations highlights the evolutionary significance of the sporophyte in the plant life cycle.