18 1 Onto Land cont 18 1 Onto Land cont The third event was the evolution of seeds The fourth event was the evolution of the flower Alternation of Generation The plant life cycle differs from the life cycle of animals Plants undergo alternation of generation meaning that there are two forms of a plant The spore bearing sporophyte is diploid The gamete producing gametophyte is haploid Alternation of Generation cont Alternation of Generation cont The production of haploid spores by plants occurs as a result of meiosis Spores undergo mitosis to produce the plant gametophyte The zygote formed by fertilization also undergoes mitosis to form the sporophyte The Dominant Generation The dominant generation of a plant is the form that we recognize as the plant For non vascular plants the gametophyte is the dominant generation For vascular plants the sporophyte is the dominant generation During the evolution of land plants the sporophyte developed vascular tissue and became the larger dominant generation of plants 1 The Dominant Generation cont 18 2 Diversity of Plants Non vascular plants those lacking vascular tissue were the first land plants to evolve Vascular plants evolved from non vascular plants Nonvascular Plants Nonvascular Plants cont The nonvascular plants include the bryophytes liverworts and true mosses Bryophytes lack true roots stems leaves and have a dominant gametophyte Bryophytes are found in every environment Vascular Plants cont Vascular Plants Vascular plants generally have true roots stems leaves Vascular plants have vascular tissue consisting of the xylem and phloem The xylem can be reinforced with lignin 2 Seedless Vascular Plants Seedless vascular plants include the club mosses horsetails and ferns Club mosses are found in temperate forests Horsetails are taller stems with whorls of slender green branches During the Carboniferous period these plants were as tall as trees These compressed remains of these plants are what formed coal Ferns Ferns are a widespread group of plants with large leaves called fronds The fern gametophyte is dependent upon water to achieve fertilization so ferns are found in moist environments Some ferns produce rhizomes which allow them to scavenge water and survive in drier areas Ferns cont General Biology of Ferns There are several commercial uses for ferns and fern tissues Ferns are ornamental plants The wood of tropical ferns can be used as a building material because it resists decay and insect damage Some ferns can be used as food Some ferns have medicinal value Seed Plants Seed Plants cont Seed plants are the most common plants Recall that seeds have three major parts The embryo The stored food supply The seed coat Seed plants have two types of spores and two types of gametophytes Male Female 3 Seed Plants cont In seed plants the gametophytes are microscopic in size The desiccation tolerant pollen grains are the male spermproducing gametophyte Pollination occurs when the pollen grain fertilizes the female gametophyte Seed Plants cont The female gametophyte develops within an ovule which develops into the seed In gymnosperms the ovule is not completely enclosed by sporophyte tissue at pollination In angiosperms the ovule is completely enclosed by sporophyte tissue the ovary at pollination Gymnosperms Seed Plants cont The ovules and seeds of gymnosperms are exposed on a modified leaf called the scale Gymnosperm means naked seed Cycads and conifers are gymnosperms Conifers Angiosperms Conifers are plants that produce cones The angiosperms covered seeds are the flowering plants The needles of conifers have adaptations that resist water loss allowing these plants to grow in frozen soils where water may be limiting Angiosperms are also found in nearly all climates and can vary greatly in size from species to species Conifers also produce resins to protect the tree from insect or fungal attack 4 The Flower Flowers have several common structures The sepals which form the calyx protect the flower bud before it opens The Flower cont The carpels have three major regions The ovary female reproductive structure contains the ovules The style elevates the stigma The stigma collects pollen The petals which form the corolla help to attract pollinators The stamen male reproductive structure consists of the filament and a pollen producing anther The Flower cont The ovary also produces nectar in some flowers to attract pollinators Flowering Plant Life Cycle The flower anther produces male microspores which divide mitotically to form pollen The pollen is released from the anther Within the ovule female megaspores undergo mitosis to produce the egg Flowering Plant Life Cycle cont During pollination a pollen grain is transported to the stigma The pollen tube germinates and extends a pollen tube to the ovule The pollen tube delivers two sperm to the egg to carry out double fertilization Flowering Plant Life Cycle cont The sperm are involved in two fusion events One sperm fuses with an egg to form a diploid zygote One sperm fuses with two other ovule cells to form the triploid endosperm The ovule develops into the seed bearing the embryo and the stored nutrients 5 Flowering Plant Life Cycle cont Flowering Plant Life Cycle cont In some angiosperms the embryo uses the seed endosperm as nourishment during germination In other angiosperms the endosperm is absorbed into the cotyledon seed leaves A fruit is derived from an ovary and in some species parts of the flower Adaptations and Uses of Angiosperms 18 3 The Fungi Angiosperms have a variety of mechanisms that facilitate the distribution of pollen and seeds Like plants and animals fungi are generally multicellular eukaryotes Pollination can be accomplished by wind water insects or animals However fungi have several unique characteristics that differentiate them from these two types of organisms The structure of the flower is specific to the mode of pollination The fruit serves two primary purposes The fruit protects the seeds The fruit aids in the dispersal of the seeds 18 3 The Fungi cont DNA sequence data has indicated that fungi are more closely related to animals General Biology of a Fungus Fungi are composed of thin filaments of cells called hyphae The hyphae are typically organized into a mass called a mycelium The mycelium penetrates soil wood or other media to acquire nutrients Most fungi are saprotrophic degrading the remains of other organisms in the soil 6 General Biology of a Fungus cont Black Bread