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Biology A Guide to the Natural World Chapter 24 • Lecture Outline Plants: The Diversity of Life 4 Fifth Edition David Krogh © 2011 Pearson Education, Inc. 24.1 The Roles and Characteristics of Plants © 2011 Pearson Education, Inc. Roles of Plants • The photosynthesis that plants perform indirectly feeds many life-forms. • The oxygen plants produce as a by-product of photosynthesis is vital to many organisms • Many plant products are important to human beings. © 2011 Pearson Education, Inc. Characteristics of Plants • With a few exceptions, all plants • Are multicelled • Fixed in one spot • Carry out photosynthesis. • All plant cells have a cell wall and most contain organelles called chloroplasts, which are the sites of photosynthesis. © 2011 Pearson Education, Inc. Characteristics of Plants cell wall (made of lignin and cellulose) cell membrane nucleus central vacuole (contains mostly water) chloroplast (site of photosynthesis) © 2011 Pearson Education, Inc. Figure 24.3 Characteristics of Plants • Plants reproduce through an alternation of generations: a life cycle in which successive plant generations produce either spores (the sporophyte generation) or gametes (the gametophyte generation). • Within a given species, these two generations can differ greatly in size and structure. © 2011 Pearson Education, Inc. (a) Human reproduction meiosis egg multicellular diploid adults sperm 1n fertilization 2n mitosis and development zygote (b) Plant alternation of generations multicellular gametophyte spores meiosis gametes 1n fertilization 2n multicellular sporophyte zygote haploid (1n) diploid (2n) © 2011 Pearson Education, Inc. Figure 24.4 24.2 Types of Plants © 2011 Pearson Education, Inc. Types of Plants • The four principal categories of plants are: • • • • Bryophytes (mosses) seedless vascular plants (ferns) Gymnosperms (coniferous trees) Angiosperms (a wide array of plants) © 2011 Pearson Education, Inc. Types of Plants flowering mosses ferns conifers plants (a) Moss (b) Ferns (c) Conifers (d) Flowering plants flowers seeds vascular tissue multicellularity green algae (ancestors) © 2011 Pearson Education, Inc. Figure 24.6 Bryophytes • Bryophytes are close living relatives of the earliest plants that made the transition from living in water to living on land. • They lack a fluid transport or vascular system and thus tend to be low lying. • Tend to inhabit damp environments and their sperm get to eggs primarily by swimming through water © 2011 Pearson Education, Inc. Bryophytes © 2011 Pearson Education, Inc. Figure 24.7 Seedless Vascular Plants • Seedless vascular plants have a vascular system but do not produce seeds in reproduction. • Their sperm must move through water to fertilize eggs. © 2011 Pearson Education, Inc. Seedless Vascular Plants © 2011 Pearson Education, Inc. Figure 24.8 Gymnosperms • Gymnosperms are seed-bearing plants with seeds that are not encased in tissue called fruit. • There are only about 1000 gymnosperm species, but their presence is considerable, particularly in northern latitudes, where gymnosperm trees, such as pine and spruce, often dominate landscapes. © 2011 Pearson Education, Inc. Gymnosperms © 2011 Pearson Education, Inc. Figure 24.9 Gymnosperm Reproduction • Gymnosperms produce seeds in carrying out reproduction. • Seeds are reproductive structures that include a plant embryo, its food supply, and a tough, protective casing. © 2011 Pearson Education, Inc. Gymnosperms wing protective seed coat seed embryo nutritional tissue © 2011 Pearson Education, Inc. Figure 24.10 male cone 1. Wind carries pollen to female cone. pollen female cone 2. Sperm within the pollen fertilizes one egg within the cone. mature tree seedling 3. Embryo begins to develop within seed. seed 5. New pine tree begins to grow. 4. Seed germinates. © 2011 Pearson Education, Inc. Figure 24.11 Angiosperms • Angiosperms, or flowering plants, produce seeds that are incased in fruit. • Angiosperms are easily the most dominant group of plants on Earth, with some 260,000 species having been identified to date. © 2011 Pearson Education, Inc. Angiosperms • Angiosperm species include not only plants with flowers, such as roses, but almost all trees except for the conifers, all important food crops, cactus, shrubs, and common grass. © 2011 Pearson Education, Inc. Angiosperms © 2011 Pearson Education, Inc. Figure 24.12 24.3 Angiosperm–Animal Interactions © 2011 Pearson Education, Inc. Angiosperm–Animal Interactions • Angiosperm pollen grains generally are transferred from one plant to another by animals, such as insects and birds. © 2011 Pearson Education, Inc. Angiosperm–Animal Interactions • To induce animals to carry out this pollination, angiosperm flowers produce nectar and have developed attractive colorations and fragrances. © 2011 Pearson Education, Inc. Angiosperm–Animal Interactions © 2011 Pearson Education, Inc. Figure 24.13 Endosperm • Angiosperm seeds contain tissue called endosperm, which functions as food for the growing embryo. • Endosperm supplies much of the food that human beings eat. Rice and wheat grains consist largely of endosperm. © 2011 Pearson Education, Inc. Endosperm wheat endosperm seed coat (bran) embryo (wheat germ) © 2011 Pearson Education, Inc. Figure 24.15 Fruit • Angiosperm seeds are unique in the plant world due to being wrapped in a layer of tissue called fruit. • Fruit that is edible functions in angiosperm seed dispersal because animals will eat and digest the fruit but then excrete the tough seeds inside, often in a different location. © 2011 Pearson Education, Inc. Seed Carriers © 2011 Pearson Education, Inc. Figure 24.16 24.4 Responding to External Signals © 2011 Pearson Education, Inc. Gravitropism • With gravitropism, plants are able to sense their orientation with respect to the Earth and direct the growth of their roots and shoots accordingly—roots into the Earth, shoots toward the sky. © 2011 Pearson Education, Inc. Phototropism • Plants will bend toward a source of light to gain additional access through the process of phototropism, meaning a curvature of shoots in response to light. © 2011 Pearson Education, Inc. Thigmotropism • Thigmotropism is defined as the growth of a plant in response to touch. • Some plants can climb upward on other objects by making contact with them and then encircling them in growth to gain additional access to light. © 2011 Pearson Education, Inc. Differential Growth • Gravitropism, phototropism, and thigmotropism are made possible by differential growth on one side of a root or stem. © 2011 Pearson Education, Inc. Responding to Seasons • In temperate climates, deciduous trees exhibit a coordinated, seasonal loss of leaves and enter into a state of dormancy, existing on stored nutrient reserves in colder months. • Dormancy evolved in deciduous trees because any photosynthesis they could perform in winter would not offset the water loss and leaf damage that would result from leaf retentention © 2011 Pearson Education, Inc. Responding to Seasons • Plants can sense the passage of seasons and time their metabolic and reproductive activities accordingly. • One mechanism that assists in this process is photoperiodism, which is the ability of a plant to respond to changes it is experiencing in the daily duration of darkness relative to light. © 2011 Pearson Education, Inc. Responding to Seasons • Some plants that exhibit photoperiodism are long-night plants, meaning those whose flowering comes only with an increased amount of darkness—in late summer or early fall. © 2011 Pearson Education, Inc. Responding to Seasons • Others are short-night plants, meaning those whose flowering comes only with a decreased amount of darkness—in early to midsummer. © 2011 Pearson Education, Inc.