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Chapter 31 Plant Structure, Reproduction, and Development PowerPoint Lectures for Biology: Concepts and Connections, Fifth Edition – Campbell, Reece, Taylor, and Simon Lectures by Chris Romero Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Gentle Giant • The General Sherman giant sequoia is the largest plant on Earth – 2,500 years old – 84-m tall – 1,400-ton trunk – A gymnosperm, bearing seeds in cones • Angiosperms, bearing seeds in flowers, make up more than 90% of the plant kingdom Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings TALKING ABOUT SCIENCE 31.1 Plant scientist Natasha Raikhel studies the Arabidopsis plant as a model biological system • Natasha Raikhel is one of America's most prominent plant biologists • Dr. Raikhel uses Arabidopsis (mustard plant) to study – Biological systems – Structure–function relationship in plants Copyright © 2005 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 • Cotyledons are seed (embryonic) leaves • Monocots – One cotyledon – Main veins usually parallel – Vascular bundles in complex arrangement – Floral parts usually in multiples of three – Fibrous root system Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Dicots – Two cotyledons – Main veins usually branched – Vascular bundles arranged in ring – Floral parts usually in multiples of four or five – Taproot usually present Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-02 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 multiples of four or five Taproot usually present 31.3 A typical plant body consists of roots and shoots • A plant is adapted to draw resources from two different environments • Root system – Anchors plant in the soil – Absorbs and transports minerals and water • Root hairs increase absorptive surface – Stores food Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Shoot system – Obtains CO2 and light from air – Stem, with nodes and internodes, supports leaves and flowers – Leaves are main photosynthetic organs – Flowers are reproductive organs • Terminal and axillary buds • Apical dominance is an evolutionary adaptation that increases the plant's exposure to light Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-03 Terminal bud Blade Leaf Petiole Axillary bud Shoot system Flower Stem Node Internode Taproot Root system Root hair Root hairs Epidermal cell 31.4 Many plants have modified roots, stems, and leaves • Roots, stems, and leaves are adapted for a variety of functions – Modified roots store sugar – Modified stems • Stolons enable a plant to reproduce asexually • Rhizomes store food and can form new plants • Tubers are structures specialized for storage Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-04b Strawberry plant Potato plant Stolon (runner) Taproot Ginger plant Rhizome Rhizome Root Tuber – Modified leaves • Store food or water • Function in protection of plant • Aid in climbing (tendrils) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 31.5 Plant cells and tissues are diverse in structure and function • Most plant cells have three unique structures – Chloroplasts, the sites of photosynthesis – A central vacuole containing fluid – A cell wall that surrounds the plasma membrane Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-05a Chloroplast Nucleus Central vacuole Cell walls Primary cell wall Secondary Middle cell wall lamella Endoplasmic reticulum Mitochondrion Golgi apparatus Cell walls of adjoining cells Ribosomes Plasma membrane Microtubules Plasmodesmata Pit Plasma membrane • Plants have five major types of cells – Parenchyma: perform most of the plant's metabolic functions – Collenchyma: provide support – Sclerenchyma: form a rigid skeleton that supports the plant; the main component of wood • Fibers: long cells arranged in bundles • Sclereids: shorter, have very hard secondary walls Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-05b LM 270 Primary cell wall (thin) Pit Starch-storing vesicles LE 31-05c LM 270 Primary cell wall (thick) LE 31-05d Sclereid cells Secondary cell wall Pits Secondary cell wall Fiber Pits Primary cell wall Sclereid LM 200 Primary cell wall LM 266 Fiber cells • Water-conducting cells in angiosperms – Tracheids and vessel elements – Hollow tubes of dead cell walls • Food-conducting cells – Sieve-tube members separated by sieve plates – Companion cells • Vascular tissue – Xylem: conveys water and minerals – Phloem: transports sugars Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-05e Pits Vessel element Openings in end wall Tracheids Pits Colorized SEM 150 LE 31-05f Sieve plate Companion cell Cytoplasm LM 45 Primary cell wall 31.6 Three tissue systems make up the plant body • A tissue system consists of one or more tissues organized into a functional unit • Dermal tissue system forms outer protective covering of the plant – Epidermis – Cuticle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Vascular tissue system – Contains xylem and phloem – Provides long-distance transport and support • Ground tissue system – Most of the bulk of young plants – Pith: internal to vascular tissue – Cortex: external to vascular tissue Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arrangement of tissue systems in root – Vascular cylinder is in center • Xylem radiates out • Phloem fills in spaces – Ground tissue system consists entirely of cortex • Endodermis is one-cell-thick innermost layer Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arrangement of tissue systems in stem – Vascular tissue in vascular bundles • Dicot: arranged in a ring • Monocot: scattered throughout ground tissue – Ground tissue • Dicot: has both cortex and pith regions • Monocot: Not divided into regions Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Arrangement of tissue systems in leaf – Epidermis interrupted by stomata flanked by guard cells – Mesophyll ground tissue sandwiched between lower and upper epidermis – Vascular system made up of network of veins Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-06 Dicot leaf Vein Cuticle Upper epidermis Xylem Phloem Mesophyll Guard cells Lower epidermis Stoma Sheath Dicot stem Monocot stem Vascular bundle Vascular bundle Cortex Pith Epidermis Epidermis Xylem Phloem Vascular cylinder Epidermis Key Dermal tissue system Ground tissue system Cortex Endodermis Dicot root Vascular tissue system PLANT GROWTH 31.7 Primary growth lengthens roots and shoots • Plants undergo indeterminate growth but are not immortal • Flowering plants are categorized based on length of life cycle – Annuals: complete life cycle in a single year or less – Biennials: complete life cycle in two years – Perennials: live and reproduce for many years Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Primary growth enables a plant to grow in length – Apical meristems are unspecialized cells that continue to give rise to new cells • Located in the tips of roots and the terminal and axillary buds of shoots • Covered by a protective root cap that is sloughed off during growth Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-07a Terminal bud Axillary buds Arrows = direction of growth Root tips • Primary growth occurs behind the root tip in three zones – Zone of cell division – Zone of elongation – Zone of maturation Video: Root Growth in a Radish Seed (time lapse) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-07b Vascular cylinder Root hair Cortex Epidermis Zone of maturation Zone of elongation Cellulose fibers Apical meristem region Zone of cell division Key Dermal tissue system Ground tissue system Vascular tissue system Root cap LE 31-07c Leaves Axillary bud meristems LM 103 Apical meristem 31.8 Secondary growth increases the girth of woody plants • Secondary growth is produced by lateral meristems, two cylinders of dividing cells – Vascular cambium • Lies between primary xylem and primary phloem • Thickens a stem by adding secondary xylem and phloem on both sides – Cork cambium • Makes cork, a new outer layer of epidermis Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Bark comprises everything external to the vascular cambium – Layers sloughed off as secondary xylem expands outward • Wood is made of secondary xylem – Heartwood: older layers of secondary growth in center of tree that no longer function in transport – Sapwood: younger secondary xylem that conducts xylem sap – Wood rays: parenchyma cells that transport water to outer living tissue Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-08a Year 2 Late Summer Year 1 Late Summer Year 1 Early Spring Key Dermal tissue system Ground tissue system Vascular tissue system Shed epidermis Primary xylem Vascular cambium Primary phloem Epidermis Cortex Secondary xylem (wood) Cork Cork cambium Secondary phloem Bark Secondary xylem (2 years’ growth) LE 31-08b Sapwood Rings Wood rays Heartwood Sapwood Vascular cambium Bark Heartwood Secondary phloem Cork cambium Cork REPRODUCTION OF FLOWERING PLANTS 31.9 Overview: The sexual life cycle of a flowering plant • The angiosperm flower consists of four types of modified leaves – Sepals enclose and protect bud – Petals advertise flower to pollinators – Stamen: male reproductive organ • Pollen grains develop in anther at tip of filament Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Carpel: female reproductive organ • Stigma, at tip of style, receives pollen grains • Ovary at base of carpel houses ovules – Contain developing egg and supporting structures Video: Flower Blooming (time lapse) Video: Time Lapse of Flowering Plant Life Cycle Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-09a Stigma Carpel Stamen Style Anther Ovary Petal Filament Ovule Sepal • Life cycle of an angiosperm – Fertilization occurs in ovule – Ovule develops into seed containing embryo – Ovary develops into fruit – Seed germinates – Embryo develops into seedling – Seedling grows into mature plant Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-09b Ovary, containing ovule Embryo Fruit (mature ovary), containing seed Seed Mature plant with flowers, where fertilization occurs Seedling Germinating seed 31.10 The development of pollen and ovules culminates in fertilization • The plant life cycle includes alternation of haploid and diploid generations – Diploid sporophyte produces haploid spores by meiosis – Spores divide by mitosis, becoming microscopic, multicellular, haploid gametophytes Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – Gametophyte produces gametes by mitosis – Fertilization produces diploid zygote – Zygote divides by mitosis and develops into a new sporophyte Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Development of male gametophyte – Cell in anthers develops into four haploid spores – Spores form haploid tube cell and generative cell – Wall forms around the cells, resulting in twocell pollen grain (male gametophyte) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Development of female gametophyte – Ovary contains central cell surrounded by smaller cells – Central cell produces four haploid spores – Three spores degenerate – Surviving spore enlarges and develops into embryo sac (female gametophyte) • Contains large central cell and the haploid egg, ready to be fertilized Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Double fertilization, a hallmark of angiosperms – Pollination – Pollen grain germinates on stigma • Tube cell gives rise to pollen tube, which grows downward to ovary • Generative cell forms two sperm – Pollen tube discharges two sperm in ovary • One fertilizes egg, forming zygote • One contributes haploid nucleus to diploid central cell of embryo sac, giving rise to endosperm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-10-3 Development of male gametophyte (pollen grain) Development of female gametophyte (embryo sac) Anther Ovule Ovary Cell within anther Meiosis Meiosis Surviving cell (haploid spore) Four haploid spores Pollen germinates Single spore Mitosis Wall forms Mitosis (of each spore) Pollination Two cells Pollen grain released from anther Embryo sac Egg cell Two sperm in pollen tube Pollen tube enters embryo sac Two sperm discharged Double fertilization occurs Triploid (3n) endosperm nucleus Diploid (2n) zygote (egg plus sperm) Animation: Plant Fertilization Video: Bat Pollinating Agave Plant Video: Bee Pollinating Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 31.11 The ovule develops into a seed • Ovule contains triploid central cell and zygote • Central cell develops into endosperm that nourishes seedling • Zygote divides and becomes embryo • Result of embryonic development is a seed – Develops hard seed coat – Undergoes seed dormancy – Contains embryonic root, shoot, and leaf; cotyledon(s); and endosperm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-11a Triploid cell Ovule Zygote Cotyledons Endosperm Seed coat Two cells Shoot Embryo Root Seed LE 31-11b Embryonic leaves Embryonic shoot Embryonic root Cotyledons Seed coat Common bean (dicot) Fruit tissue Cotyledon Seed coat Endosperm Embryonic leaf Embryonic Shoot Sheath Embryonic root Corn (monocot) Animation: Seed Development Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 31.12 The ovary develops into a fruit • A fruit is a specialized vessel that houses and protects seeds and helps them disperse • Changes leading to fruit formation – Soon after pollination, flower drops petals – Ovary expands, walls thicken, forming fruit Animation: Fruit Development Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-12b Upper part of carpel Ovule Seed Ovary wall Sepal Pod (opened) • Fruits are highly varied – Simple fruit: derived from a flower with a single carpel (peach, pea, nut) – Aggregate fruit: results from a single flower with multiple carpels (raspberry) – Multiple fruit: develops from tightly clustered separate flowers (pineapple) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 31.13 Seed germination continues the life cycle • Germination resumes growth and development that was suspended during seed dormancy – Seed takes up water and starts to expand – Embryo resumes growth and absorbs nutrients from the endosperm Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings – In dicots, the root emerges first, followed by the shoot, which is covered by a protective hook – In monocots, a protective sheath surrounding the shoot breaks the soil – Cotyledons remain in soil Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings LE 31-13a Foliage leaves Embryonic shoot Embryonic root Cotyledons LE 31-13b Foliage leaves Protective sheath enclosing shoot Embryonic root Cotyledon 31.14 Asexual reproduction produces plant clones • Asexual or vegetative reproduction is an extension of an angiosperm's indeterminate grown – Fragmentation: separation of a parent into parts that develop into whole plants (garlic) – Sprouting from roots (redwood trees) – Asexual reproduction from roots (creosote bushes) – Sprouting shoots or roots from runners (dune grass) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CONNECTION 31.15 Asexual reproduction is a mainstay of modern agriculture • Plants can be propagated asexually from cuttings or bits of tissue – Can increase productivity – Can reduce genetic diversity • Most crops today are grown in monocultures Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings