Lecture Notes: Plant Diversity - Bryophytes

Introduction

• Focus on plant diversity, starting with bryophytes.
• Videos for each plant diversity subsection.
• Refresher on alternation of generations included in each video.

Characteristics of Bryophytes

• Simplest plants in study of plant diversity.
• Lack of vascular tissue (xylem and phloem).
  • Cannot grow large.
• Absence of a cuticle.
  • Cannot prevent drying out.
  • Found in moist, damp, shaded areas.
  • Example: Moss.
• Reliance on water for reproduction.
  • Not ideal for dry terrestrial environments.
• Lack of true roots, stems, or leaves.
  • Possess rhizoids instead of roots (anchors plant to surfaces).

Alternation of Generations

• Plants exist in two generations: reproductive and adult growing stages.
• Key Terms:
  • Meiosis: Process of halving chromosome number to produce gametes.
  • Mitosis: Cell division maintaining chromosome number for growth.
  • Haploid (n): Half the number of chromosomes.
  • Diploid (2n): Full set of chromosomes.
• Generations:
  • Sporophyte: Produces spores, diploid, visible structure (mature plant).
  • Gametophyte: Produces gametes, haploid, often reduced in size.

Bryophyte Life Cycle

• Begin with a spore (haploid), grows into protonema.
• Protonema: Early plant structure, grows rhizoids.
• Gametophytes emerge, make gametes (eggs and sperm).
• Mosses primarily in gametophyte generation.
  • Male and female gametophytes grow adjacent to each other.
• Antheridium: Male reproductive structure, produces sperm.
• Archegonium: Female reproductive structure, contains eggs.
• Water facilitates sperm movement to fertilize eggs.

Post-Fertilization

• Transition to sporophyte generation (diploid).
• Zygote: Formed by fusion of sperm (n) and egg (n), diploid.
• Zygote grows into sporophyte, visible as stalk with capsule on female gametophyte.

Sporophyte Development

• Sporangium: Capsule where spores are produced.
  • Spores produced via meiosis, released to begin new cycle.

Unique Bryophyte Feature

• Sporophyte grows out of gametophyte, unusual compared to other plants.

Key Terminology Recap

• Vascular Tissue: Absent in bryophytes.
• Alternation of Generations: Life cycle involves two phases.
• Meiosis vs. Mitosis: Meiosis for reproduction, mitosis for growth.
• Sporangium: Produces spores.
• Antheridium/Archegonium: Male/female reproductive structures.
• Zygote: Result of fertilization, grows into sporophyte.

Conclusion

• Overview of bryophytes and their life cycle.
• Unique reproductive strategies and growth characteristics.