Exam (elaborations) BIOLOGY 1301 Lab #7 - Seedless Vascular Plants

Lab #7 Seedless Vascular Plants Introduction In today’s lab, we will study seedless vascular plants. This plant group evolved by the late Devonian period and was the prominent group during the Carboniferous period of the Paleozoic era. They formed the first forests about 385 million years ago. These forests are the main source of fossil fuels we use today. Critical innovations that lead to the success of seedless vascular plants were the vascular tissue and wind-blown spores. The vascular tissue is made up of xylem (which conducts water) and phloem (which conducts organic material). Unlike seedless non-vascular plants, seedless vascular plants have true leaves (meaning leaves with veins), stems and roots. Seedless vascular plants include two phyla: Phylum Lycophyta (club mosses) and phylum Pteridophyta (Ferns). Seedless vascular plants exhibit alternation of generations with a dominant sporophyte plant alternating with a haploid gametophyte plant. The sporophyte is well adapted to life on land and bears the sporangia (spore bearing structures). The cells in the sporangia undergo meiosis to form haploid spores. In most seedless vascular plants, sporangia are borne adjacent to specialized leaves called the sporophylls. The sporophylls with sporangia sometimes aggregate into structures called strobili. The strobili can bear spores of the same kind (homosporous) or of different kinds (heterosporous). The spores germinate to form the haploid gametophyte. In seedless vascular plants, the gametophyte is small but photosynthetic; it bears gametangia – antheridia and archegonia that produce sperm and eggs, respectively. During fertilization, the sperm swim to the egg resulting in a diploid zygote. The zygote then develops into a young sporophytic plant which eventually grows into a dominant and independent sporophyte.