The dominant phase in the life cycle of a fern is the?

Step 1: Analyze the question The question asks which phase is dominant (the larger, more conspicuous, longer-living stage) in the life cycle of a fern.

Step 2: The concept: Alternation of generations Plants alternate between two phases:

• Sporophyte (diploid, 2n): produces spores by meiosis
• Gametophyte (haploid, n): produces gametes by mitosis

Which phase dominates depends on the plant group:

| Plant group | Dominant phase | |---|---| | Mosses/liverworts (bryophytes) | Gametophyte | | Ferns (pteridophytes) | Sporophyte | | Conifers and flowering plants | Sporophyte |

Step 3: Apply it to ferns

• The fern plant you see, with its green fronds, rhizome and roots, is the sporophyte. It is large, leafy, independent and long-lived.
• Sori on the underside of the fronds contain sporangia, which release spores.
• A spore germinates into a prothallus, which is the gametophyte. It is tiny, heart-shaped, short-lived and easily overlooked. It bears the antheridia (male) and archegonia (female).
• After fertilization, the zygote grows into a new sporophyte.

Step 4: Evaluate the options

• A. Prothallus: this is the gametophyte, so it is small and not dominant. ✗
• B. Sporophyte: the large, conspicuous fern plant. ✓
• C. Antheridium: just the male sex organ on the prothallus. ✗
• D. Gametophyte: this is the reduced, short-lived phase in ferns. ✗

Answer: B. Sporophyte

Exam tip: Remember that "only mosses are gametophyte-dominant." For every other plant group (ferns, conifers, flowering plants), the sporophyte dominates. Also note that A (prothallus) and D (gametophyte) are the same thing, so they cannot both be correct. That is a clue that neither is the answer.