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Chapter 28 The Life of a Flowering Plant Power. Point® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc.
Biology and Society: Plants and Human Civilization • Human progress has always depended upon expanding our use of plants for – Food – Fuel – Clothing – Countless other trappings of modern life • Wheat accounts for about 20% of all calories consumed worldwide. © 2010 Pearson Education, Inc.
Figure 28. 00
• Throughout much of prehistory, humans were nomadic hunter/gatherers, moving and foraging with the changing seasons. • About 10, 000 years ago a major shift occurred. – People in several parts of the world began to domesticate wild plants. – Surplus food was produced. – Year-round farming villages were formed. © 2010 Pearson Education, Inc.
• During the latter half of the 20 th century, a “green revolution” led to an international effort to improve wheat and other staple crops. • Through repeated selective breeding – Wheat yield more than doubled from 1940 to 1980 – The cost of wheat production was cut in half © 2010 Pearson Education, Inc.
• Plants are vital to the well-being of Earth’s biosphere, providing – Shelter – Food – Breeding areas for – Animals – Fungi – Microorganisms © 2010 Pearson Education, Inc.
• Angiosperms – Make up over 90% of the plant kingdom – Are the focus of this unit © 2010 Pearson Education, Inc.
THE STRUCTURE AND FUNCTION OF A FLOWERING PLANT • Angiosperms – Have dominated the land for over 100 million years – Account for about 250, 000 species alive today © 2010 Pearson Education, Inc.
• Most of our foods come from a hundred or so domesticated species of flowering plants including – Roots such as beets and carrots – Fruits of trees and vines such as apples, nuts, berries, and squash – Fruits and seeds of legumes, such as peas, peanuts, and beans – Fruits of grasses, which are grains such as wheat, rice, and corn © 2010 Pearson Education, Inc.
Monocots and Dicots • On the basis of several structural features, angiosperms are classified into two groups: – Monocots – Dicots • The names of the groups refer to cotyledons, or seed leaves found in the embryo. • Most angiosperms are dicots. • The largest group of dicots are eudicots. © 2010 Pearson Education, Inc.
Table 28. 1
Plant Organs: Roots, Stems, and Leaves • Plants have – Organs composed of different tissues – Tissues composed of cells of different types © 2010 Pearson Education, Inc.
• The evolution of plants onto land required – Structures for absorbing water and minerals from the soil – A large light-collecting surface – The ability to take in carbon dioxide from the air for photosynthesis – Adaptations for surviving dry conditions © 2010 Pearson Education, Inc.
• In a land plant, these vital functions are performed by: – roots (below ground) – shoots (above ground), including – Stems – Leaves – Flowers © 2010 Pearson Education, Inc.
Terminal bud Blade Leaf Petiole Flower Axillary bud Shoot system Stem Node Internode Taproot Root system Root hairs Figure 28. 1
Roots • A plant’s roots – Anchor it in the soil – Store food – Absorb and transport minerals and water • All of a plant’s roots make up its root system. © 2010 Pearson Education, Inc.
• Root hairs – Are tiny projections near the root tips – Increase the surface area of the root © 2010 Pearson Education, Inc.
• Large taproots in plants such as carrots, turnips, sugar beets, and sweet potatoes store food in the form of carbohydrates such as starch. © 2010 Pearson Education, Inc.
• Other types of modified roots include buttress roots, aerial roots that – Look like buttresses – Support the tall trunks of the trees that produce them © 2010 Pearson Education, Inc.
(a) The root of a sugar beet stores carbohydrates. (b) The buttress roots of this Indonesian Paldoa tree help support the trunk. Figure 28. 2
Stems • The shoot system of a plant is made up of – Stems – Leaves – Structures for reproduction (flowers) • Stems generally – Grow above the ground – Support the leaves and flowers © 2010 Pearson Education, Inc.
• A stem has – Nodes, the points at which leaves are attached – Internodes, the portions of the stem between nodes © 2010 Pearson Education, Inc.
• When a plant stem is growing in length, the terminal bud, at the apex (tip) of the stem has – Developing leaves – A compact series of nodes and internodes • The axillary buds, embryonic shoots in each of the angles formed by a leaf and the stem, usually remain dormant. © 2010 Pearson Education, Inc.
• In many plants, the terminal bud produces hormones that inhibit growth of the axillary buds, a phenomenon called apical dominance. • Removing the terminal bud can make a plant bushier. © 2010 Pearson Education, Inc.
Terminal bud removed Figure 28. 3
• Stems take many forms. – Strawberry plants have horizontal stems, or runners, that – Grow along the ground surface – Serve as a form of asexual reproduction – Iris or ginger plants have horizontal underground stems called rhizomes. – A potato plant has rhizomes ending in tubers. © 2010 Pearson Education, Inc.
Taproot Runner Rhizome Tuber at end of rhizome (a) Strawberry plants Root (b) Ginger plant (c) Potato plant Figure 28. 4
Leaves • Leaves are the primary sites of photosynthesis in most plants and consist of – A flattened blade – A stalk, or petiole, which joins the leaf to the stem • Leaves are highly varied in their – Arrangements – Shapes © 2010 Pearson Education, Inc.
LEAF ARRANGEMENT Simple Compound Doubly Compound Leaflet Petiole Axillary bud A single individual blade One blade consisting of many leaflets (which lack axillary buds) Petiole Axillary bud Each leaflet divided into smaller leaflets Figure 28. 5
• Leaves can be modified as – A tendril that helps plants climb up their supports – Spines of a cactus that may protect the plant from predatory animals © 2010 Pearson Education, Inc.
(a) Tendrils of a gourd plant Tendril (b) Spines of a cactus Figure 28. 6
Plant Tissues and Tissue Systems • Tissues – Are a group of cells with a common structure or function – Form organs of plants • A tissue system consists of one or more tissues organized into a functional unit within a plant. © 2010 Pearson Education, Inc.
• Plants have two types of vascular tissues. – Phloem transports sugars from leaves or storage tissues to other parts of the plant. – Xylem conveys water and dissolved minerals upward from the roots to the stems and leaves. © 2010 Pearson Education, Inc.
• Plant organs – Include roots, stems, and leaves – Are made up of three tissue systems: – The dermal tissue system – The vascular tissue system – The ground tissue system © 2010 Pearson Education, Inc.
• Each tissue system is – Continuous throughout the entire plant body – Arranged differently in leaves, stems, and root Video: Root Growth in a Radish Seed (time lapse) © 2010 Pearson Education, Inc.
Leaf Eudicot Stem Monocot Root Key Dermal tissue system Vascular tissue system Ground tissue system Figure 28. 7
• The dermal tissue system – Covers and protects leaves, stems, and roots – Helps prevent water loss with a waxy coating called the cuticle produced by epidermal cells • The vascular tissue system – Provides support and long-distance transport – Includes xylem and phloem © 2010 Pearson Education, Inc.
• The ground tissue system functions in – Photosynthesis – Storage – Support © 2010 Pearson Education, Inc.
• A cross section of a eudicot root illustrates the three tissue systems. – In the center of the root, the vascular tissue system forms a cylinder, with – Xylem cells that radiate from the center – Phloem cells that fill in the wedges between the spokes © 2010 Pearson Education, Inc.
– The ground tissue system forms the cortex, where cells – Store food – Take up water and minerals – The innermost layer of cortex is the endodermis, a thin cylinder one cell thick that is a selective barrier that regulates the passage of substances between the cortex and the vascular tissue. © 2010 Pearson Education, Inc.
Xylem Phloem LM Epidermis Cortex Endodermis Figure 28. 8
• All plant stems have vascular tissue systems arranged in numerous vascular bundles. – The location and arrangement of these bundles differ between monocots and eudicots. – In eudicots the pith – Fills the center of the stem – Is often important in food storage © 2010 Pearson Education, Inc.
• The three tissue systems occur in eudicot leaves. – The epidermis contains stomata, tiny pores between two specialized guard cells that regulate the size of the stomata. – The ground tissue system of a leaf contains the mesophyll, the main site of photosynthesis. – The leaf’s vascular tissue system is made up of a network of veins. © 2010 Pearson Education, Inc.
Cuticle Upper epidermis Mesophyll Lower epidermis Guard cells Vein Xylem Phloem Stoma Key Dermal tissue system Vascular tissue system Ground tissue system Figure 28. 9
Plant Cells • Most plant cells have three unique structures: – Chloroplasts, the sites of photosynthesis – A large central vacuole containing fluid that helps maintain the cell’s firmness (turgor) – A supportive cell wall that – Surrounds the plasma membrane – Consists largely of the carbohydrate cellulose © 2010 Pearson Education, Inc.
Chloroplast Nucleus Central vacuole Cell wall Primary cell wall Endoplasmic reticulum Secondary cell wall Mitochondrion Golgi apparatus Cell walls of adjoining cells Ribosomes Plasma membrane Microtubules Plasmodesmata Plasma membrane Figure 28. 10
• Parenchyma cells – Are the most abundant type of cell in most plants – Perform a variety of functions, such as – Food storage – Photosynthesis © 2010 Pearson Education, Inc.
LM Primary wall (thin) Parenchyma cells LM Primary wall (thick) Collenchyma cells LM Secondary wall Sclerenchyma cells Primary wall Figure 28. 11 a
• Collenchyma cells – Resemble parenchyma cells in lacking secondary walls but have unevenly thickened primary walls – Provide support in parts of the plant that are actively growing © 2010 Pearson Education, Inc.
LM Primary wall (thick) Collenchyma cells Figure 28. 11 ac
• Sclerenchyma cells – Have thick secondary cell walls usually strengthened with lignin, the main chemical in wood – Provide support to the plant © 2010 Pearson Education, Inc.
LM Secondary wall Primary wall Sclerenchyma cells Figure 28. 11 ae
LM Sclerenchyma cells Figure 28. 11 af
• Angiosperms have two types of water-conducting cells: – Tracheids, long, thin cells with tapered ends – Vessel elements, wider and shorter cells that are less tapered • Water-conducting cells are – Dead, with only their cell walls remaining – Arranged in chains of hollow tubes with overlapping ends © 2010 Pearson Education, Inc.
Vessel element Tracheids Openings in end wall Water-conducting cells Colorized SEM Secondary wall with lignin Plasmodesmata LM Primary wall Food-conducting cells Figure 28. 11 b
• Food-conducting cells are – Arranged end to end, forming tubes – Remain alive at maturity © 2010 Pearson Education, Inc.
PLANT GROWTH • Most animals have determinate growth, ending growth after reaching a certain size. • Most plants have indeterminate growth, the ability to grow throughout life. © 2010 Pearson Education, Inc.
• The life span of plants varies greatly. – Annuals live for only a year. – Biennials – Live for two years – Typically reproduce in their second year – Perennials may live for many years. © 2010 Pearson Education, Inc.
PLANT LIFE SPANS Annuals (live for just one growing season) Rice Biennials (live for two growing seasons) Wild chervil (also called cow parsley) Perennials (live for many growing seasons) Japanese cherry tree Figure 28. 12
Primary Growth: Lengthening • Growth in all plants is made possible by tissues called meristems, undifferentiated (unspecialized) cells that divide frequently, generating new cells and tissues. • Apical meristems – Occur at the tips of roots and shoots – Enable primary growth, growth in length © 2010 Pearson Education, Inc.
Terminal bud Axillary buds Key Direction of growth Root tips Figure 28. 13
• A growing root – Is pushed through the soil by primary growth – Contains a root cap that protects the actively dividing cells • Primary growth in a root is achieved by – Cell division – Cell elongation, mainly by taking up water © 2010 Pearson Education, Inc.
Vascular system Cortex Epidermis Root hair Zone of differentiation Key Dermal tissue system Vascular tissue system Ground tissue system Zone of elongation Apical meristem region Zone of cell division LM Root cap Figure 28. 14
Secondary Growth: Thickening • The stems and roots of many plant species also thicken by a process called secondary growth. • The vascular cambium is a cylinder of actively dividing cells between the primary xylem and primary phloem. • Secondary growth adds cells on either side of the vascular cambium. © 2010 Pearson Education, Inc.
Figure 28. 15
Key Dermal tissue system Vascular tissue system Ground tissue system Year 1 Early Spring Year 2 Late Summer Shed epidermis wth Primary xylem Epidermis Vascular cambium Primary phloem wth Grow Cortex Gro Secondary xylem (wood) Cork Bark Secondary xylem (2 years’ growth) Cork cambium Secondary phloem Figure 28. 16 -3
• Annual growth rings result from the layering of secondary xylem. • The layers are visible as rings because of uneven activity of the vascular cambium during the year. © 2010 Pearson Education, Inc.
Annual rings Heartwood Sapwood Vascular cambium Bark Secondary phloem Cork cambium Cork Figure 28. 17
The Process of Science: What Happened to the Lost Colony of Roanoke? • In 1587, 121 English settlers landed on Roanoke Island in present day North Carolina. • Three years later they were gone and the settlement was deserted. • Observation: A large number of very old bald cypress trees around Roanoke Island could provide a reliable record of the climate over the last 800 years. © 2010 Pearson Education, Inc.
• Question: Could the tree ring data provide insight into the colony’s mysterious disappearance? • Hypothesis: The loss of the colony corresponded to a period of drought. • Prediction: Tree ring data would show abnormal growth during the years after settlement. • Experiment: Dozens of trees that covered the period 1185 to 1984 were analyzed. © 2010 Pearson Education, Inc.
Canada Cape May United States Ch e s a p e ak Mexico Virginia e Bay Roanoke Island North Carolina Cape Fear ATLANTIC OCEAN N Figure 28. 18
• Results: – The colonists arrived at the start of the worst three-year drought in the southeastern United States during the past 800 years. – The drought and its effects on the colonists’ vital crops could have forced them to abandon the settlement. © 2010 Pearson Education, Inc.
• When secondary growth begins – The epidermis is sloughed off – It is replaced with a new outer layer called cork, produced by cork cambium • Mature cork cells – Are dead – Have thick, waxy walls, which protect the underlying tissues of the stem © 2010 Pearson Education, Inc.
• Bark consists of everything external to the vascular cambium: – The secondary phloem – Cork cambium – Cork © 2010 Pearson Education, Inc.
THE LIFE CYCLE OF A FLOWERING PLANT • Many flowering plants can reproduce sexually and asexually. • Asexual reproduction allows a single plant to produce many offspring quickly and efficiently. © 2010 Pearson Education, Inc.
Garlic Holly trees Creosote bushes Figure 28. 19
Garlic Figure 28. 19 a
Holly trees Figure 28. 19 b
Creosote bushes Figure 28. 19 c
• Sexual reproduction in plants involves fertilization, the union of gametes from two parents to produce genetically distinct offspring. © 2010 Pearson Education, Inc.
The Flower • In angiosperms, the structure specific to sexual reproduction is the flower. • The main parts of a flower are modified leaves: – Sepals – Petals – Stamens – Carpels Blast Animation: Flower Structure © 2010 Pearson Education, Inc.
Petal Stamen Anther Stigma Carpel Style Ovary Filament Ovule Sepal Figure 28. 20
• The flower’s reproductive organs are the stamen and the carpel. • A stamen consists of a stalk tipped by an anther, where meiosis occurs and pollen grains develop. Video: Flower Blooming (time lapse) © 2010 Pearson Education, Inc.
• A carpel has a long slender neck (the style) with a sticky stigma where pollen grains land. • The base of the carpel is the ovary. • Within the ovary are ovules, each containing: – One developing egg – The cells that support it • The term pistil is sometimes used to refer to a single carpel or a group of fused carpels. © 2010 Pearson Education, Inc.
Overview of the Flowering Plant Life Cycle • The plant life cycle alternates between – Haploid generation – Diploid generation • The diploid plant body is the sporophyte. • The haploid plant is the gametophyte. © 2010 Pearson Education, Inc.
• The sexual life cycle of an angiosperm involve – Fertilization – The ovule of a flower maturing into a seed containing the embryo – The ovary developing into a fruit – The seed germinating in a suitable habitat – The embryo developing into a seedling – The seedling growing into a mature plant Video: Flowering Plant Life Cycle (time lapse) © 2010 Pearson Education, Inc.
Embryo Seed Fruit (mature ovary) containing seed Ovary, containing ovule Germinating seed Mature plant with flowers, where fertilization occurs Seedling Figure 28. 21 -4
Pollination and Fertilization • Fertilization requires gametes, which are produced by gametophytes. – The male gametophyte is the pollen grain, which produces sperm. – The female gametophyte is a multicellular structure called the embryo sac, which produces the egg. © 2010 Pearson Education, Inc.
Development of male gametophyte (pollen grain) Haploid nuclei of two cells Anther Meiosis Cell within anther Mitosis Four haploid spores Two haploid nuclei of large, central cell Ovule Ovary Meiosis Pollen grain (will be released from anther) Mitosis Embryo sac Development of female gametophyte (embryo sac) Surviving cell (haploid spore) Egg cell (with haploid nucleus) Figure 28. 22 -6
• The first step leading to fertilization is pollination, the delivery of pollen grains from anther to stigma. • Many angiosperms are dependent on animals to transfer their pollen. Video: Bat Pollinating Agave Plant Animation: Plant Fertilization Blast Animation: Pollination and Fertilization © 2010 Pearson Education, Inc.
Pollen grain Pollination Germination of pollen grain Delivery of two haploid sperm (n) to ovule Stigma Pollen tube Triploid (3 n) endosperm nucleus Ovule Embryo sac Double fertilization Haploid egg cell (n) Two sperm about to be discharged into ovule Diploid (2 n) zygote Figure 28. 23
• Double fertilization occurs as – One sperm fertilizes the egg, forming the diploid zygote – The other sperm – Contributes its haploid nucleus to the large diploid central cell of the embryo sac – Produces a triploid cell that will give rise to the food-storing tissue called endosperm. © 2010 Pearson Education, Inc.
Seed Formation • After fertilization, the ovule, containing the zygote and the triploid central cell, begins developing into a seed. © 2010 Pearson Education, Inc.
• The zygote – Divides via mitosis – Forms a ball of cells that becomes the embryo • The triploid cell – Divides via mitosis – Develops into the endosperm © 2010 Pearson Education, Inc.
• The result of embryonic development in the ovule is a mature seed, a plant embryo and endosperm packaged within a tough protective covering called a seed coat. Animation: Seed Development © 2010 Pearson Education, Inc.
Triploid nucleus of large, central cell Ovule Zygote Cotyledons Endosperm Two cells Seed coat Shoot Embryo Root Seed Figure 28. 24
Fruit Formation • A fruit is a mature ovary that acts as a vessel – Housing and protecting seeds – Helping disperse seeds from the parent plant • Pea pods are a type of fruit. Animation: Fruit Development Video: Bee Pollinating © 2010 Pearson Education, Inc.
Figure 28. 25
• Mature fruits can be either – Fleshy or – Dry © 2010 Pearson Education, Inc.
Fleshy fruits Figure 28. 26 a
Dry fruits Figure 28. 26 b
Seed Germination • Germination of a seed usually begins when the seed takes up water. • The hydrated seed expands and bursts its seed coat. © 2010 Pearson Education, Inc.
Foliage leaves Cotyledon Embryonic shoot Cotyledon Embryonic root Seed coat Figure 28. 27
Foliage leaves Cotyledon Embryonic shoot Cotyledon Embryonic root Seed coat Figure 28. 27 a
Figure 28. 27 b
Evolution Connection: The Problem of the Disappearing Bees • Flowering plants and land animals have had mutually beneficial relationships throughout their evolutionary history. – Angiosperms depend on insects, birds, or mammals for – Pollination – Seed dispersal – Most land animals depend on angiosperms for food and shelter. © 2010 Pearson Education, Inc.
• In late 2006, U. S. beekeepers noticed a sudden and drastic die off in their bee colonies. • The next year, similar problems were reported in Europe. • Bees pollinate about $15 billion worth of crops each year, which is about one-third of our food supply. • The cause of the disorder is still unclear. © 2010 Pearson Education, Inc.
Figure 28. 28
Figure 28. UN 01
Terminal bud (grows stem) Flower (reproductive organ) Stem (supports leaves and flowers) Axillary bud (produces a branch) Shoot system (photosynthetic center) Internode Node Blade Petiole Leaf (main photosynthetic organ) Root system (anchors, absorbs nutrients, and stores food) Root hairs (microscopic; increase surface area for absorption) Figure 28. UN 02
THE THREE TISSUES OF PLANT ORGANS Dermal Tissue System • Functions in protection • Includes the epidermis, an outer layer that covers and protects the plant • Stomata (each surrounded by two guard cells) are pores that regulate gas exchange between the cells of the leaf and the environment Vascular Tissue System • Functions in support and transport • Xylem: transports water and dissolved minerals • Phloem: transports sugar Ground Tissue System • Functions mainly in storage • Includes leaf mesophyll, where most photosynthesis occurs Figure 28. UN 03
Pollen (n) Ovary Embryo sac (n) Ovule FERTILIZATION within ovule Fruit (from ovary) Mature plant (2 n) Seed (from ovule) Embryo (2 n) Germinating seed (2 n) Figure 28. UN 04