18.1 Onto Land Plants are a diverse group of eukaryotic organisms. Plants are classified into four groups. –Mosses, hornworts, and liverworts –Ferns and the fern allies –Gymnosperms (conifers) –Angiosperms (flowering plants)
18.1 Onto Land (cont.) These plant groups can be associated with four evolutionary events that helped adapt plants to existence on land. The first is the nourishment of the multicellular embryo within the body of the female plant. The second event was the evolution of vascular tissue to distribute water, nutrients, and carbohydrates through the plant.
18.1 Onto Land (cont.) The third event was the evolution of seeds. The fourth event was the evolution of the flower.
18.1 Onto Land (cont.)
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.) 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.
Alternation of Generation (cont.)
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.
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 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.
Nonvascular 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.
Vascular Plants (cont.)
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.
General Biology of Bacteria 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 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
Seed Plants (cont.)
In seed plants the gametophytes are microscopic in size. The desiccation-tolerant pollen grains are the male, sperm-producing 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.
Seed Plants (cont.)
Gymnosperms 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 Conifers are plants that produce cones. The needles of conifers have adaptations that resist water loss, allowing these plants to grow in frozen soils where water may be limiting. Conifers also produce resins to protect the tree from insect or fungal attack.
Angiosperms The angiosperms (“covered seeds”) are the flowering plants. Angiosperms are also found in nearly all climates and can vary greatly in size from species to species.
The Flower Flowers have several common structures. The sepals, which form the calyx, protect the flower bud before it opens. 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 carpels have three major regions. –The ovary (female reproductive structure) contains the ovules. –The style elevates the stigma. –The stigma collects pollen. The ovary also produces nectar in some flowers to attract pollinators.
The Flower (cont.)
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.
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.
Flowering Plant Life Cycle (cont.)
Adaptations and Uses of Angiosperms Angiosperms have a variety of mechanisms that facilitate the distribution of pollen and seeds. Pollination can be accomplished by wind, water, insects, or animals. 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 Like plants and animals, fungi are generally multicellular eukaryotes. However fungi have several unique characteristics that differentiate them from these two types of organisms. DNA sequence data has indicated that fungi are more closely related to animals.
18.3 The Fungi (cont.)
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.
General Biology of a Fungus (cont.)
Black Bread Mold The hyphae of some fungi, like black bread mold, grow horizontally and vertically to anchor the fungi and acquire nutrients. The mycelia are also involved in fungal reproduction.
Black Bread Mold (cont.) The hyphae can also develop stalks bearing sporangia for spore production. During asexual reproduction, the fungal spores are distributed and divide mitotically to produce new hyphae. The sexual reproduction of fungi involves the conjugation of mycelia between fungi.
Black Bread Mold (cont.) The mycelia of sexually-reproducing fungi must be of different mating types. –One is the positive (+) mycelium. –One is the negative (-) mycelium. The hyphal tips of these fungi fuse to form a zygospore. The zygospore germinates to form sporangiophores.
Black Bread Mold (cont.) Meiosis occurs in the sporangiophores to produce spores of each mating type. The spores are distributed and divide mitotically to produce new hyphae. Except for the zygospore, all stages of the fungal life cycle are haploid.
Black Bread Mold (cont.)
Mushroom A mushroom is the fruiting body of a fungi. The fruiting body is also spore producing. The mushroom forms when a positive and negative hyphae fuse but the nuclei do not fuse. This dikaryotic nuclei forms the stalk and cap of the mushroom.
Mushroom (cont.) Club-like, spore-producing structures develop within the gills of the cap. The spores are distributed by the wind. In some instances, the fungal mycelium forms a ring as it explores the soil.
Mutualistic Relationships In a mutualistic relationship, two different species contribute positively to each other’s growth. Lichens are a mutualistic relationship between a fungi and a cyanobacteria or algae. Lichens are important because they are colonizers of disturbed soils.
Mutualistic Relationships (cont.)
There are three varieties of lichens. – Compact crustose, seen on rocks and bark – Fruticose, which are shrublike – Foliose, which are leaflike. Lichens have three cell layers. –An upper and lower fungal cell layer –A middle algal or cyanobacteria layer Lichens generally reproduce asexually.
Mutualistic Relationships (cont.) Mycorrhizal fungi form mutualistic relationships with plant roots. Mycorrhizal fungi live within plant roots are growing on the surface of roots. These fungi help roots obtain water and nutrients by increasing the absorptive surface area.
Mutualistic Relationships (cont.)
Fungi as Disease-Causing Organisms Certain fungi can cause disease in plants and animals, acting as pathogens.
Fungi and Plant Diseases Fungal pathogens of plants usually enter through wounds or the stomata. Some fungal diseases impact agricultural production. –Rice blast disease –Corn smut –Rusts –Leaf curl
Fungi and Plant Diseases (cont.)
Fungi and Human Diseases Mycoses are diseases caused by fungi. Mycoses have three levels of infection. – Cutaneous mycoses only affect the epidermal layers. – Subcutaneous mycoses affect deeper skin layers. – Systemic mycoses spread throughout the body.
Fungi and Human Diseases (cont.) The widest array of fungal diseases are caused by Candida albicans. –Yeast infections –Oral thrush
Fungi and Human Diseases (cont.) Fungi from the genus Tinea contribute to the ringworm and athlete’s foot. Histoplasma capsulatum is a soil fungi that causes “fungal flu”.