Transcript Chapter 23
Chapter 23 Introduction to Plants I. Establishment of Plants on land • Plants probably evolved from multicellular aquatic green algae that could not survive on land A. Absorb Nutrients • On land, most plants take nutrients from the soil with their roots • The first plants had no roots and probably formed symbiotic relationships with fungi to get nutrients from rocky surfaces B. Prevent water loss • A watertight covering called the cuticle reduced water loss • The cuticle is a waxy layer that covers the nonwoody parts of a plant that are above ground • Pores called stomata allow oxygen gas (O2) and carbon dioxide (CO2) to pass through the cuticle C. Reproduce without water • Aquatic algae reproduce sexually when sperm swim through water to fertilize eggs • The sperm of plants must be able to move without water • Pollen is a structure that encloses sperm to prevent them from drying out - pollen allows sperm to be carried by wind or animals rather than by water II. Vascular Tissue, Seeds, and Flowers A. Advantages of conducting tissue • The vascular system allowed for plants to grow larger and more complex • The vascular system is composed of welldeveloped vascular tissues that distribute materials more efficiently • Specialized cells in vascular tissue are connected end to end and transport water and nutrients within a plant • Plants with a vascular system are called vascular plants • Plants without a vascular system are called nonvascular plants - three groups of plants today are nonvascular B. Advantages of seeds • Seeds contain the embryo of a plant • Seed plants are vascular plants that produce seeds - make up largest part of plant population • Seeds offer a plants offspring several survival advantages 1. Protection • A seed coat protects the seed from drying out and from mechanical injury or disease 2. Nourishment • Most seeds have a supply of nutrients stored in them 3. Plant dispersal • Can be carried away from the parent plant by wind, water, or animals • Prevents competition for water, nutrients, light, and living space between plants 4. Delayed growth • Seeds can wait to sprout until conditions are most favorable C. Advantages of Flowers • The flower is a reproductive structure that produces pollen and seeds • Flowers attract animals which can carry pollen directly from one flower to another III. Plant Life Cycle • In algae, the zygote is the only diploid (2n) cell - zygotes undergo meiosis right after fertilization so bodies of these algae are haploid (n) • In plants, meiosis is delayed after fertilization resulting in an alternation of generations between haploid and diploid plants • Summary: - haploid plants (gametophytes) make haploid gametes by mitosis - diploid plants (sporophytes) make haploid spores by meiosis • In nonvascular plants, the gametophyte (n) generation is dominant • In vascular plants, the sporophyte (2n) generation is dominant IV. The Vascular-Plant Sporophyte A. Vascular System • The sporophytes of vascular plants have a vascular system with two types of vascular tissue 1. Phloem • Relatively soft-walled cells that transport organic nutrients 2. Xylem • Hard-walled cells that transport water and mineral nutrients • The thick walls of cells in the xylem help support the plant body - allows the plant to grow to great heights B. Distinctive body form • The part of a plant that grows mostly upward is called the shoot • The part of a plant that grows mostly downward is called the root • Meristems are zones of actively dividing plant cells that produce plant growth V. Kinds of Plants A. Nonvascular Plants • Do not have a vascular system for transporting water and nutrients • Lack true roots, stems, and leaves 1. Key Features of Nonvascular Plants a. Small size • Water and nutrients are transported short distances by osmosis and diffusion - this greatly limits the size of nonvascular plants b. Larger gametophyte • Hairlike projections called rhizoids anchor the gametophytes to the surfaces on which they grow • Sporophytes grow on the gametophytes and depend on them for nutrients c. Require water for sexual reproduction • Eggs and sperm form in separate structures usually on separate plants • Nonvascular plants must be covered by a film of water for sperm to swim to neighboring individuals to fertilize their eggs 2. Kinds of nonvascular plants a. Mosses • “leafy” green plant parts are gametophytes • Most sporophytes grow from the tip of the gametophyte • Most have a cuticle, stomata, and some simple conducting cells that carry water short distances b. Liverworts • The gametophytes are flattened and have lobes • The sporophytes are very small and consist of a short stalk topped by a spore capsule • Do not have cuticles, stomata, or conducting cells c. Hornworts • Gametophytes are green and flattened • Sporophytes are green and hornlike • Have cuticles and stomata but no conducting cells B. Seedless Vascular Plants 1. Key features of seedless vascular plants • Larger and more complex than nonvascular plants a. Vascular system • Contains both a xylem and phloem • Develop true roots, stems, and leaves b. Larger sporophyte • Sporophytes are larger than the gametophytes • Large spores are easier to disperse • Water is needed for fertilization of eggs by sperm swimming to them c. Drought-resistant spores • Spores have thickened walls that are resistant to drying 2. Kinds of seedless vascular plants a. Ferns • Have a rhizome, or underground stem, that is anchored by roots • Leaves are called fronds • Spores are produced in sporangia that grow in clumps on the lower sides of fronds • Gametophytes are flattened, heart-shaped, green plants b. Club mosses • Have roots, stems, and leaves that branch from a rhizome • Spores develop in sporangia that form on specialized leaves • Some of these specialized leaves cluster together to form a structure called a cone c. Horsetails • Have roots, stems, and leaves that branch from a rhizome • Stems are hollow and have joints • Spores form in cones located at the tips of stems d. Whisk ferns • Highly branched stems • No leaves or roots • Spores produced in sporangia that form at the tips of short branches C. Gymnosperms • Seed plants whose seeds do not develop within a sealed container (a fruit) 1. Key features of gymnosperms a. Seeds • Protect plant embryos, provide them with nutrients, and permit them to survive unfavorable conditions b. Greatly reduced gametophytes • Two types of gametophytes (male and female) form within the tissues of sporophytes • Grains of pollen are male gametophytes and develop in male cones • Female gametophytes form within structures that become seeds and develop in female cones c. Wind pollination • Water is not required for fertilization allowing sexual reproduction in dry conditions 2. Kinds of gymnosperms a. Conifers • Leaves are either needle-like or reduced to tiny scales • Berrylike structures are the female cones b. Cycads • Short stems and palmlike leaves - cones that produce pollen and those that produce seeds develop on different plants c. Ginkgo • Fan-shaped leaves • Male and female gametophytes develop on separate trees • Female seeds do not develop within a cone d. Gnetophytes • Diverse group of trees, shrubs, and vines • Produce pollen and seeds in cones that resemble flowers D. Angiosperms • Produce seeds that develop enclosed within a specialized structure called a fruit 1. Key features of angiosperms a. Flowers • Male and female gametophytes develop within flowers • Promotes pollination and fertilization more efficiently than do cones by attracting insects and animals b. Fruits • Promote seed dispersal as they are eaten by animals and dispersed as they pass undigested from the animals bodies c. Endosperm • A supply of stored food that is absorbed by the embryo before the seeds mature 2. Kinds of angiosperms a. Monocots • Flowering plants that produce seeds with one seed leaf • Long, narrow leaves with parallel veins • Flowers in multiples of 3 b. Dicots • Flowering plants that produce seeds with two seed leaves • Leaves have branching veins • Flowers are in multiples of two, four, or five VI. Plants as Food • Plant parts contain organic nutrients (carbohydrates, fats, and proteins) and minerals (calcium, magnesium, and iron) A. Fruits and Vegetables • To a botanist, a fruit is the part of a plant that contains seeds • A vegetative part is any nonreproductive part of a plant B. Root Crops • Crops that grow underground i.e. potatoes, carrots, radishes, turnups, beets, and cassava • These vegetables are enlarged roots that store starch C. Legumes • Produce protein-rich seeds in long pods i.e. peas, peanuts, beans, and alfalfa VII. Cereals • Cereals are grasses that produce a dry fruit called a grain i.e. wheat, corn, and rice • A grain is covered by a dry, papery husk called the bran which includes the wall of the ovary and the seed coat • Rich in carbohydrates and contain protein, vitamins, and dietary fiber VIII. Nonfood uses of plants A. Wood B. Medicines • People have always used substances obtained from plants to treat a variety of ailments 1. Foxglove • Yields digitalis, a drug used to stabilize irregular heartbeats and to treat cardiac disorders 2. Rosy periwinkle • Original source of two cancer-treatment drugs – vinblastine and vincristine C. Fibers • Strands of cellulose in plant cell walls are ideal for making paper, cloth, and rope