Questions: Alternation of Generations and Land Plant Diversity

Question 1

When you look at a patch of moss, the green leafy plants you see are:

• A. Diploid sporophytes
• B. Haploid gametophytes
• C. Spores
• D. Seeds

Answer: (B)

In bryophytes the gametophyte is the dominant, long-lived, photosynthetic stage. The sporophyte grows out of it as a stalk topped by a capsule and depends on the gametophyte for nutrition.

Question 2

In land plants, gametes are produced by meiosis.

• T. True
• F. False

Answer: False

Meiosis in plants produces spores. Each spore divides by mitosis to form a gametophyte, and the gametophyte produces eggs and sperm by mitosis. This is the main difference from the animal life cycle, where meiosis produces gametes directly.

Question 3

Why are mosses and ferns usually found in moist places, even though a fern sporophyte has vascular tissue?

Model answer: In both groups the sperm have flagella and must swim through a film of water to reach the egg on the gametophyte. Without water, fertilization cannot happen, so these plants depend on moist conditions to reproduce.

Seed plants freed themselves from this need. Their sperm are delivered by pollen grains and pollen tubes, so fertilization does not require free water.

Question 4

Which trend describes the evolution of the gametophyte from bryophytes to ferns to seed plants?

• A. It became larger and more independent
• B. It stayed the same size throughout
• C. It became smaller and, in seed plants, was retained inside sporophyte tissue
• D. It disappeared completely from seed plants

Answer: (C)

Bryophyte gametophytes are the main plant body. Fern gametophytes are small but free-living. Seed plant gametophytes are usually microscopic: the male gametophyte is the pollen grain, and the female gametophyte develops inside the ovule.