Lecture on Plant Diversity: Bryophytes

Introduction

• Focus on bryophytes as part of plant diversity.
• Subsequent videos will cover other subsections.
• Refresher on alternation of generations included in each video.

Characteristics of Bryophytes

• Simplest plants in the study of plant diversity.
• Lack of Vascular Tissue
  • Do not have xylem or phloem.
  • Cannot grow very large.
• No Cuticle
  • Cannot prevent desiccation.
  • Typically found in moist, damp, and shaded areas.
• Water-Dependent Reproduction
  • Not ideal for terrestrial environments due to dryness.
  • Require water for reproduction.
• No True Roots, Stems, or Leaves
  • Structures resemble roots or leaves but are not true forms.
  • Have rhizoids instead of roots, similar to those in fungi.

Alternation of Generations

• Plants alternate between two generations: sporophyte and gametophyte.
• Terms to Understand
  • Meiosis: Reduces chromosome number by half, produces gametes.
  • Mitosis: Cell division maintaining chromosome number, for growth.
  • Haploid (n): Single set of chromosomes.
  • Diploid (2n): Two sets of chromosomes.

Life Cycle of Bryophytes

• Start with adult structures: megasporophyte (female) and microsporophyte (male).
• Sporophyte Stage
  • Produces spores through meiosis.
  • Spores develop into gametophytes.
• Gametophyte Stage
  • Produces gametes.
  • In mosses, spend most time in gametophyte stage.
• Reproductive Structures
  • Antheridium (male): Produces sperm.
  • Archegonium (female): Produces eggs.

Moss Reproduction Cycle

• Gametophyte Generation
  • Starts with the release of spores.
  • Develops into protonema, then grows rhizoids.
  • Male and female gametophytes grow next to each other.
  • Fertilization
    • Water facilitates sperm reaching eggs.
    • Results in sporophyte growth from the gametophyte.
• Sporophyte Generation
  • Sporophyte grows out of gametophyte.
  • Sporangium develops spores for the next cycle.

Terminology Recap

• Vascular Tissue: Absent in bryophytes.
• Alternation of Generations: Plants exist as sporophyte or gametophyte.
• Meiosis and Mitosis: Chromosomal changes for reproduction and growth, respectively.
• Sporangium: Structure where spores are produced.
• Antheridium and Archegonium: Male and female reproductive organs, respectively.
• Zygote: Result of sperm and egg fusion.

Conclusion

• Overview of bryophyte characteristics and life cycle.
• Explanation of unusual reproduction cycle in bryophytes, particularly mosses.
• Clarity on concepts such as sporophyte growing out of gametophyte.