Question 1

What are the three main groups of nonvascular plants?

Accepted Answer

Nonvascular plants include mosses, liverworts, and hornworts, collectively called bryophytes. These small, herbaceous plants lack extensive vascular tissue and true roots, leaves, or stems. Many species are aquatic, and all rely on diffusion through cells to distribute nutrients and water, limiting their size and keeping them low-growing.

Question 2

How do nonvascular plants reproduce without seeds?

Accepted Answer

Nonvascular plants reproduce using spores produced by the diploid sporophyte. These spores grow via mitosis to form the haploid gametophyte. Once mature, gametophytes generate male sperm or female eggs in structures called antheridia or archegonia. In the presence of water, sperm swim to fertilize eggs, forming a new sporophyte.

Question 3

Why do nonvascular plants require water for fertilization?

Accepted Answer

Male gametes in nonvascular plants are self-motile and must actively swim through water to reach female gametes. Unlike seed plants that use pollen, bryophytes depend on water—even small amounts like morning dew—to disperse sperm. This water dependency restricts nonvascular plants to moist habitats and makes reproduction more successful when plants grow close together.

Question 4

What is alternation of generations in bryophytes?

Accepted Answer

Bryophytes alternate between haploid gametophyte and diploid sporophyte stages during their life cycle. Unlike other plants, bryophytes are dominated by the gametophyte stage, which is typically larger and longer-lived than the sporophyte. The sporophyte depends on the gametophyte for nourishment and protection, remaining attached to it after fertilization.

Question 5

How do nonvascular plants transport nutrients and water without vascular tissue?

Accepted Answer

Nonvascular plants lack extensive vascular tissue and rely on diffusion through cells to distribute nutrients and water. This passive transport mechanism limits their ability to grow large or reach significant heights. Because they cannot efficiently transport resources over distance, bryophytes remain small and low-growing, restricting them to moist environments where resources are readily available.

Question 6

Why were nonvascular plants important in Earth's terrestrial history?

Accepted Answer

Nonvascular plants were once primary colonizers of the terrestrial landscape before seed plants became dominant. Today, most plants on Earth grow from seeds, yet bryophytes continue to thrive in moist habitats worldwide due to their many adaptations. Their historical significance reflects their role in establishing early plant communities on land.

Question 7

What structural limitations prevent nonvascular plants from growing large?

Accepted Answer

Nonvascular plants lack true roots, leaves, and stems, and possess no extensive vascular tissue for efficient resource transport. Without these structures, they cannot develop the internal support systems or transport mechanisms needed for large size. Consequently, bryophytes remain small and low-growing, dependent on diffusion for nutrient and water distribution.

Plantes sans graines non vascularisées

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