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BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor CHAPTER 31 Plant Structure, Reproduction, and Development From PowerPoint® Lectures for Biology: Concepts & Connections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A Gentle Giant • This giant sequoia, the General Sherman, is the largest plant on Earth – It is 84 m (275 ft) tall – Its trunk is 10m in diameter Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The General Sherman has been growing for about 2,500 years Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Growth rings mark each year in a tree's life – Rings vary in thickness depending on weather conditions during the growing season Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Humans depend on plant products – Lumber – Fabric – Paper – Food – Industrial chemicals Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Plants are vital to Earth's well-being – They provide food for land animals – They offer shelter and breeding areas for animals, fungi, and microorganisms – Their roots prevent soil erosion – Photosynthesis in plant leaves helps reduce carbon dioxide and adds oxygen to the air Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.1 Talking About Science: Plant scientist Katherine Esau was a preeminent student of plant structure and function • Katherine Esau was one of the twentieth century's most prolific plant scientists • Her early research on sugar beets led to important discoveries about – phloem – viral infections of plant tissue Figure 31.1A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Dr. Esau later used an electron microscope to continue studying the relationship between plant structure and function • She discovered that plant viruses are transmitted through plant tissues via plasmodesmata Figure 31.1B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings PLANT STRUCTURE AND FUNCTION 31.2 The two main groups of angiosperms are the monocots and the dicots • Angiosperms, or flowering plants, are the most familiar and diverse plants • There are two main types of angiosperms – Monocots include orchids, bamboos, palms, lilies, grains, and other grasses – Dicots include shrubs, ornamental plants, most trees, and many food crops Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Monocots and dicots differ in seed leaf number and in the structure of roots, stems, leaves, and flowers SEED LEAVES LEAF VEINS STEMS FLOWERS ROOTS MONOCOTS One cotyledon Main veins usually parallel Vascular bundles in complex arrangement Floral parts usually in multiples of three Fibrous root system DICOTS Two cotyledons Main veins usually branched Vascular bundles arranged in ring Floral parts usually in Taproot multiples of four or five usually present Figure 31.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.3 The plant body consists of roots and shoots • Root system – Provides anchorage – Absorbs and transports minerals and water – Stores food • Root hairs increase the surface area for absorption Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Shoot system – Consists of stems, leaves, and flowers in angiosperms – Stems are located above the ground and support the leaves and flowers – Leaves are the main sites of photosynthesis in most plants Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Terminal bud Blade Leaf Flower Petiole Axillary bud Stem SHOOT SYSTEM Node Internode Taproot ROOT SYSTEM Root hairs Figure 31.3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The terminal bud is located at the tip of a stem – It is the growth point of the stem • Axillary buds can give rise to branches • In apical dominance, the terminal bud produces hormones that inhibit the growth of axillary buds – This results in a taller plant that has greater exposure to light Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.4 Many plants have modified roots and shoots • Roots and stems are adapted for a variety of functions – Storing food – Asexual reproduction – Protection • Plant breeders have improved the yields of root crops by selecting varieties, such as the sugar beet plant, with very large taproots Figure 31.4A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Modified stems include STRAWBERRY PLANT – runners, for asexual reproduction Runner POTATO PLANT – rhizomes, for plant growth and food storage – tubers, for food storage in the form of starch Rhizome IRIS PLANT Rhizome Tuber Taproot Root Figure 31.4B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Modified leaves include tendrils and spines – Tendrils help plants to climb – Spines may protect the plant from plant-eating animals Figure 31.4C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.5 Plant cells and tissues are diverse in structure and function Figure 31.5A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • There are five major types of plant cells – Parenchyma – Collenchyma – Sclerenchyma – Water-conducting cells – Food-conducting cells Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Parenchyma cells function in food storage, photosynthesis, and aerobic respiration Primary wall (thin) Pit Figure 31.5B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Collenchyma cells provide support in parts of the plant that are still growing Primary wall (thick) Figure 31.5C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Sclerenchyma cells provide a rigid scaffold that supports the plant – Fiber cells Pits Secondary wall Fiber cells Primary wall FIBER Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 31.5D – Sclereids (stone cells) Secondary wall Primary wall Sclereid cells Pits SCLEREID Figure 31.5D continued Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Water-conducting cells convey water from the roots to the stems and leaves – Chains of tracheids or vessel elements form a system of tubes for water transport Pits Tracheids Vessel element Pits Openings in end wall Figure 31.5E Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Food-conducting cells function in the transport of sugars, other compounds, and some mineral ions – Sieve-tube members are arranged end-to-end, forming tubes – Their end walls are perforated with plasmodesmata, forming sieve plates – At least one companion cell flanks each sievetube member Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sieve plate Companion cell Cytoplasm Primary wall Figure 31.5F Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Complex tissues are composed of more than one type of plant cell • Vascular tissues are complex tissues that conduct water and food – Xylem contains water-conducting cells that convey water and dissolved minerals – Phloem contains sieve-tube members that transport sugars Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.6 Three tissue systems make up the plant body • Roots, stems, and leaves are made of three tissue systems Leaf Stem – The epidermis – The vascular tissue system – The ground tissue system Root Epidermis Ground tissue system Vascular tissue system Figure 31.6A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The epidermis covers and protects the plant – The cuticle is a waxy coating secreted by epidermal cells that helps the plant retain water • The vascular tissue contains xylem and phloem – It provides support and transports water and nutrients Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The ground tissue system functions mainly in storage and photosynthesis – It consists of parenchyma cells and supportive collenchyma and sclerenchyma cells Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The ground tissue system of the root forms the cortex – The cortex consists mostly of parenchyma tissue • The selective barrier forming the innermost layer of the cortex is the endodermis Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings VASCULAR TISSUE SYSTEM Xylem Phloem Epidermis GROUND TISSUE SYSTEM Cortex Endodermis Figure 31.6B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • These microscopic cross sections of a dicot and a monocot indicate several differences in their tissue systems Figure 31.6C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The three tissue systems in dicot leaves – The epidermis consist of pores called stomata (singular, stoma) flanked by regulatory guard cells Figure 31.6D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – The ground tissue system of a leaf is called mesophyll and is the site of photosynthesis Figure 31.6D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings – The vascular tissue consists of a network of veins composed of xylem and phloem Figure 31.6D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings PLANT GROWTH 31.7 Primary growth lengthens roots and shoots • Most plants exhibit indeterminate growth – They continue to grow as long as they live • In contrast, animals are characterized by determinate growth – They cease growing after reaching a certain size Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Annuals complete their life cycle in a single year or growing season – Examples: wheat, corn, rice, and most wildflowers • Biennials complete their life cycle in two years, with flowering occurring in the second year – Examples: beets and carrots • Perennials live and reproduce for many years – Examples: trees, shrubs, and some grasses Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Growth in all plants originates in tissues called meristems – Meristems are areas of unspecialized, dividing cells • Apical meristems are located at the tips of roots and in the terminal buds and axillary buds of shoots – They initiate primary growth, lengthwise growth by the production of new cells – Roots and stems lengthen further as cells elongate and differentiate Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Terminal bud Axillary buds Arrows = direction of growth Root tips Figure 31.7A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cortex Epidermis DIFFERENTIATION Vascular cylinder CELL DIVISION ELONGATION Root hair Cellulose fibers Apical meristem region Root cap Figure 31.7B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Leaves Apical meristem Axillary bud meristems 1 2 Figure 31.7C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.8 Secondary growth increases the girth of woody plants • An increase in a plant's girth results from secondary growth • Secondary growth involves cell division in two cylindrical meristems – Vascular cambium – Cork cambium Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Vascular cambium thickens a stem by adding layers of secondary xylem, or wood, next to its inner surface – It also produces the secondary phloem, which is a tissue of the bark • Cork cambium produces protective cork cells located in the bark Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 31.8A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Everything external to the vascular cambium is considered bark – Secondary phloem – Cork cambium – Protective cork cells • Heartwood in the center of the trunk consists of older, clogged layers of secondary xylem • Sapwood consists of younger, secondary xylem that still conducts water Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • A woody log is the result of several years of secondary growth Sapwood Rings Wood rays Heartwood Sapwood Vascular cambium Secondary phloem Bark Cork cambium Cork Heartwood Figure 31.8B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings PLANT REPRODUCTION 31.9 Overview: The sexual life cycle of a flowering plant • The angiosperm flower is a reproductive shoot consisting of Anther Carpel Stigma Ovary – sepals – petals Stamen – stamen Ovule – carpels Sepal Petal Figure 31.9A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Sepals are usually green and resemble leaves in appearance – Sepals enclose and protect the flower bud before the flower opens • Petals are often bright and colorful – They attract insects (pollinators) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Stamens are the male reproductive organs of plants – Pollen grains develop in anthers, at the tips of stamens • Carpels are the female reproductive organs of plants – The ovary at the base of the carpel houses the ovule Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • The life cycle of an angiosperm involves several stages Ovary, containing ovule Embryo Fruit, containing seed Seed Mature plant with flowers, where fertilization occurs Seedling Germinating seed Figure 31.9B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.10 The development of pollen and ovules culminates in fertilization • The plant life cycle alternates between diploid (2n) and haploid (n) generations • Double fertilization is unique to plants Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 31.10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.11 The ovule develops into a seed • After fertilization, the ovule becomes a seed – The fertilized egg within the seed divides to become an embryo – The other fertilized cell develops into the endosperm, which stores food for the embryo • A resistant seed coat protects the embryo and endosperm Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Triploid cell OVULE Zygote Two cells Cotyledons Endosperm Seed coat Shoot Embryo Root SEED Figure 31.11A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Seed dormancy is an important evolutionary adaptation in which growth and development are suspended temporarily – It allows time for a plant to disperse its seeds – It increases the chance that a new generation of plants will begin growing only when environmental conditions favor survival Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Comparison between dicot and monocot seeds Seed coat Embryonic shoot Embryonic leaves Embryonic root Cotyledons COMMON BEAN (DICOT) Fruit tissue Cotyledon Seed coat Endosperm Embryonic leaf Embryonic shoot Sheath Embryonic root CORN (MONOCOT) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 31.11B 31.12 The ovary develops into a fruit • The ovary develops into a fruit which helps protect and disperse the seeds Figure 31.12A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • There is a correspondence between flower and fruit in a pea plant – The wall of the ovary becomes the pod – The ovules develop into the seeds Upper part of carpel Ovule Seed Ovary wall Sepal Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pod (opened) Figure 31.12B – The small, threadlike structure at the end of the pod is what remains of the upper part of the flower's carpel – The sepals of the flower stay attached to the base of the green pod Upper part of carpel Ovule Seed Ovary wall Sepal Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Pod (opened) Figure 31.12B • Simple fruits develop from a flower with a single carpel and ovary – Apples, pea pods, cherries • Aggregate fruits develop from a flower with many carpels – Raspberries • Multiple fruits develop from a group of flowers clustered tightly together – Pineapples Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 31.12C 31.13 Seed germination continues the life cycle • A seed starts to germinate when it takes up water, expands, and bursts its seed coat • Metabolic changes cause the embryo to resume growth and absorb nutrients from the endosperm • An embryonic root emerges, and a shoot pushes upward and expands its leaves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Pea germination (a dicot) Foliage leaves Embryonic shoot Cotyledons Embryonic root • Corn germination (a monocot) Foliage leaves Protective sheath enclosing shoot Embryonic root Cotyledon Figure 31.13A, B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.14 Asexual reproduction produces plant clones • Many plants can reproduce asexually via bulbs, sprouts, or runners • Asexual reproduction often involves fragmentation – Fragmentation is the separation of parts from the parent plant and regeneration of those parts into whole plants Figure 31.14A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Sprouts from the roots of a coast redwood tree may eventually take the place of its parent in the forest Figure 31.14B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • These creosote bushes came from generations of vegetative reproduction by roots Figure 31.14C Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Most grasses can propagate asexually by sprouting shoots and roots from runners Figure 31.14D Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 31.15 Connection: Vegetative reproduction is a mainstay of modern agriculture • Propagating plants from cuttings or bits of tissue can increase agricultural productivity – But it can also reduce genetic diversity Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Test-tube cloning is the growth of a plantlet from a few meristem cells cultured on a chemical medium – A single plant can be cloned into thousands of copies that will continue to grow when planted in soil – Orchids and certain pine trees used in mass plantings are propagated this way Figure 31.15A Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Protoplast fusion is the fusion of plant cells that have had their cell walls removed by treatment with enzymes – Plant species unable to interbreed in nature can be fused in the laboratory – This produces a hybrid plant with a desirable combination of traits Figure 31.15B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • "GM" (genetically modified) plants are created when foreign genes are incorporated into a single parenchyma cell – The cell is then cultured until it develops into a new plantlet • The commercial adoption of GM crops has been rapid – However, many people are concerned about the potential environmental risks associated with their use Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings • Monocultures are large areas of land planted with a single crop • Gene-cloning techniques and monocultures have led to crop plants with little genetic diversity – This increases the likelihood that a small number of diseases could devastate large crop areas Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings