Overview
This lecture covers the characteristics and life cycle of tracheophytes (ferns), emphasizing alternation of generations and key plant reproductive terminology.
Characteristics of Tracheophytes (Ferns)
- Tracheophytes (ferns) are more advanced than bryophytes because they have vascular tissue (xylem and phloem).
- Vascular tissue allows ferns to grow larger and stronger than mosses.
- Ferns possess a cuticle to prevent drying out, but it is thin, so they prefer shady, moist habitats.
- They reproduce using water, have true leaves and stems, but still use rhizoids for anchoring like roots.
Alternation of Generations
- Plants alternate between two generations: sporophyte (makes spores) and gametophyte (makes gametes).
- Sporophyte is typically the visible plant in ferns and is diploid (2n, full set of chromosomes).
- Gametophyte is usually smaller and produces sperm and egg cells (haploid, n).
Key Cellular Processes
- Meiosis reduces chromosome number by half to create gametes (from 2n to n).
- Mitosis creates new cells while maintaining chromosome number.
Fern Life Cycle
- Mature fern sporophyte (2n) forms sori (clusters) on leaf undersides, containing sporangia.
- Sporangia undergo meiosis to produce haploid spores (n).
- Spores grow into a gametophyte called a prothallus, a small heart-shaped structure.
- Male (antheridium) and female (archegonium) reproductive organs develop on the same prothallus but in separate places.
- Water enables sperm from antheridium to swim to eggs in archegonium for fertilization, forming a diploid zygote (2n).
- The zygote grows via mitosis into a new sporophyte, completing the cycle.
Key Terms & Definitions
- Tracheophyte — vascular plant with xylem and phloem tissue.
- Sporophyte — diploid generation producing spores.
- Gametophyte — haploid generation producing gametes.
- Meiosis — cell division halving chromosome number to create gametes.
- Mitosis — cell division maintaining chromosome number for growth.
- Diploid (2n) — cell with a full chromosome set.
- Haploid (n) — cell with half the full chromosome set.
- Sorus (pl. sori) — cluster on a fern leaf containing sporangia.
- Sporangium — spore-producing structure inside sori.
- Prothallus — heart-shaped fern gametophyte.
- Antheridium — male gamete-producing organ.
- Archegonium — female gamete-producing organ.
- Rhizoid — root-like structure for anchoring.
Action Items / Next Steps
- Review the alternation of generations diagram focusing on fern life cycle.
- Prepare for questions on differences between sporophyte and gametophyte generations.
- Ensure understanding of key terminology for upcoming quizzes.