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Chapter 22
Lecture OutlineSee PowerPoint Image Slidesfor all figures and tables pre-inserted intoPowerPoint without notes.
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What is a plant?
Eukaryotic Multicellular Contains chlorophyll a and b Carries on photosynthesis Has cellulose cell walls Lives in a variety of terrestrial habitats
– And a few shallow aquatic habits Exhibits alternation of generations
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Plant Diversity
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Alternation of Generations A life cycle that involves two generations
– Sporophyte generation Diploid Undergoes meiosis to generate haploid spores Spores germinate and divide by mitosis to give rise to
the gametophyte generation.– Gametophyte generation
Multicellular haploid generation Undergoes mitosis to produce haploid gametes Gametes unite to form a zygote. Zygote divides by mitosis to form the sporophyte
generation.
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Alternation of Generations
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The Evolution of Plants
Photosynthetic algae are thought to be the ancestors of plants.– Green algae have the same types of chlorophyll.– There is extensive DNA homology between plants
and green algae. The evolution of plants shows two trends.
– Toward greater specialization for living in a dry environment
– Toward a more prominent sporophyte generation
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The Evolution of Plants
Primitive plants– Lack vascular tissue to carry water– Have flagellated sperm; no seeds– Have to live in moist habitats– Have dominant gametophyte generation
More advanced plants– Have specialized cells that transport water– Have seeds that do not require water for distribution– Have dominant sporophyte generation
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The Taxonomy of Plants
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Nonvascular Plants Include
– Mosses, hornworts, liverworts Known as the bryophytes Common features
– Lack vascular tissue Use diffusion and osmosis to obtain water and nutrients
– Do not have true roots or leaves– Gametophyte is dominant– Sperm swim to egg
Must have water to reproduce sexually– Are small and confined to moist habitats
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Moss Life Cycle
http://www.youtube.com/watch?v=jcWYAnmm-QE
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Kinds of Nonvascular Plants
Mosses– Grow as a carpet of
many individual gametophyte plants
– Each individual is less than 5 cm tall.
Liverworts and hornworts
– Form flat sheets only a few cells thick
– Each cell contains one large chloroplast.
Non-vascular plants
http://www.youtube.com/watch?v=kBPLKUTtXBM
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The Significance of Vascular Tissue Vascular tissue is an adaptation to living in dry
environments.– Allows plants to transport water and nutrients throughout
the plant– Associated with the development of
Leaves for photosynthesis Roots for absorbing water and minerals
– Vascular tissue allowed for an increase in plant size– Accompanied by the appearance of a waterproof coating on
the plant surfaces Two types of vascular tissue
– Xylem– Phloem
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Xylem
A series of dead, hollow cells that form tubes– Vessel elements
Form long tubes with cells end-to-end– Tracheids
Tapered cells with holes Overlap to form a sieve-like tube
The walls of these cells are strengthened by cellulose and lignin.
Transports water and minerals from the soil to the leaves
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Xylem
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Phloem
Carries organic molecules produced in the leaves to the rest of the plant
– Sugar– Amino acids
Consists of two types of cells– Sieve-tube elements
Lack a nucleus and organelles, but have cytoplasm Have holes in the end walls for the transport of material
– Companion cells Actively transport sugars and amino acids out of the leaf cells
and into the sieve-tube elements
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Phloem
Video Xylem and phloem
http://www.youtube.com/watch?v=J1PqUB7Tu3Y
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The Development of Roots, Stems, and Leaves The appearance of
vascular tissue allowed for the development of specialized plant parts.
Roots are specialized for absorption.
Stems are specialized for transport.
Leaves are specialized for photosynthesis.
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Roots
Underground parts of a plant that – Anchor in the soil– Absorb water and nutrients
Move the nutrients into the vascular system Grow from the tips
– Explore new areas of soil for water and nutrients– Root tips have root hairs that increase their absorptive
surface. Can be important storage sites
– Many plants store carbohydrates in their roots during growing season to be used during the winter.
– Carrots, turnips, radishes, maple trees, rhubarb, grasses
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Kinds of Roots
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Stems
Above-ground structures that – Support the leaves– Transport raw material from the roots to the leaves– Transport manufactured material from the leaves to other
parts of the plant Vary greatly in diameter and length
– Tree trunks are large and support branches.– Dandelion stems are short.– Some stems are underground.
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Stems
The structure of cell walls allows the stem to support the leaves.– Cell walls are made of cellulose interwoven into a
box. When cells are full of water, the cell walls will not
stretch. This makes the cells turgid, stiff and able to support
weight.– Woody plants have especially thick cell walls.
These have lignin in them. Allows woody plants to grow tall and withstand wind
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Stems
Stems contain a lot of vascular tissue.
Stems also– Store food
Sugar cane Yams Potatoes
– Photosynthesize– Have waterproof layers
Can be waxy or woody
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Leaves
Specialized for photosynthesis– Have large surface area to collect sunlight– Relatively thin to allow light penetration– Have bundles of vascular tissue to transport
Water and minerals needed for photosynthesis into the leaf
The sugar that is made out of the leaf– Thick cell walls for support– Are arranged to minimize shading of lower leaves
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The Structure of a Leaf
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Leaves
Specialized for photosynthesis– Covered by a waxy coating to minimize water loss
Water evaporates from leaves through transpiration.– Pulls water and nutrients up from the roots– Transpiration must be regulated so plant doesn’t
lose too much water.– Water and oxygen exit, and carbon dioxide enters,
through stomata.
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Stomates
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Seedless Vascular Plants
Include– Whisk ferns– Horsetails– Club mosses– Ferns
Have vascular tissue– Are not limited to aquatic environments
Do not have seeds– Have flagellated sperm– Must have moist conditions to reproduce
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Fern Life Cycle
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Kinds of Seedless Vascular Plants
Ferns– Most common seedless
vascular plant Whisk ferns
– Lack roots and leaves– Anchored by an
underground stem Modifications of the
stem serve the functions of roots and leaves.
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Kinds of Vascular Seedless Plants
Horsetails– Low-growing plants with jointed
stems– Most photosynthesis occurs in
the stems.– Have silicon dioxide in their cell
walls Called (and used as)
scouring brushes by pioneers
Club mosses– Usually evergreen– Low-growing, branching plants– Some are called ground pines.
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Seed-producing Vascular Plants
A seed is a specialized structure that contains – An embryo – Stored food– A protective outer coating (seed coat) that prevents drying
Seeds allow plants to live in dry habitats.– Aid in dispersal
Gymnosperms and angiosperms produce seeds. Accompanied by the development of pollen
– Encased sperm (male gametophyte generation)– Allows plants to reproduce without water
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Gymnosperms
Means “naked seed” Woody, perennial
plants Produce seeds that are
not enclosed (naked)– Produce seeds in cones
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The Pine Life Cycle
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Kinds of Gymnosperms
Cycads– Wood plants with a ring of fern-like leaves at the
top– Live in tropical regions
Ginkgo– Ginkgo biloba is the only living species– A tree with fan-shaped leaves
Used in many herbal medicines
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Kinds of Gymnosperms
Conifers– Trees and shrubs that bear cones– Have needle-shaped leaves– Called evergreens because they do not lose their
leaves Do shed needles throughout the year
– Used in the production of lumber
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Several Gymnosperms
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Angiosperms
Produce flowers Have vascular tissue, seeds and pollen Have seeds enclosed in a fruit
– A modification of the ovary wall
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Flower Structure
Composed of highly modified leaves– Petals are usually colorful.– Sepals surround petals– Petals and sepals are arranged in whorls.
Specialized for sexual reproduction Female parts in the center
– Pistil (stigma, style and ovary) Ovary produces eggs
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Flower Structure
Male parts surround the pistil.– Stamens (filament and anther)
Anther produces sperm.
Perfect flowers have both pistils and stamens.
Imperfect flowers have either pistils or stamens.
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Flower Structure
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The Life Cycle of a Flowering Plant
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Pollination Strategies
Wind– Plants with inconspicuous flowers are usually
wind-pollinated.– Produce large numbers of flowers and pollen– Many species are wind-pollinated.
Grasses and sedges Aspens, birches and oaks
– Responsible for hay fever Some people have allergic reactions to pollen.
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Strategies for Pollination
Animals– Plants with showy flowers are usually animal-
pollinated. These flowers usually produce nectar. Also smell good to attract animals
– Flowers attract insects, birds and small mammals.– The animals feed on the nectar and pick up the
pollen. Then move to another plant for more nectar, transferring
the pollen
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Wind- and Insect-pollinated Flowers
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Fruit
A modification of the ovary that contains seeds Involved in dispersal of seeds Many fruits are nutritive to animals.
– The animals eat the fruit and ingest the seeds.– The seeds pass through the digestive tract unharmed and
get “planted” in the animals’ feces. Other fruits burst open and release light seeds that
are dispersed by wind. Other fruits have sticky surfaces that cling to animals
that pass by.
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Types of Fruits
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Angiosperm Diversity
Classified as either monocots or dicots– Refers to the number of cotyledons found in the
seeds of the species Monocots have one cotyledon (peanut). Dicots have two cotyledons (lima bean).
– Cotyledons (seed leaves) store food for the growing embryo.
They emerge as the first leaves.
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Embryos in Dicots and Monocots
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Monocots vs. Dicots
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Angiosperm Diversity
Monocots– Yuccas and palms are woody.– The rest are herbaceous.
Wheat, rice, corn, sweet potatoes, onions, bananas
Dicots– Mints, carrots, cabbages, mustards, tomatoes and
potatoes are herbaceous dicots.– Aspen and sagebrush are woody dicots.
These are deciduous.
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Deciduous Trees Lose their leaves once
a year– Occurs in the fall before
they go dormant The bark of the tree is
the phloem.– Produce a new layer of
xylem and phloem each year
– Therefore, the trunk increases in diameter each year.
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Growth of Woody Plants
Woody plants have the ability to grow continuously for many years.– They get taller and grow in diameter each year.
Growth occurs at the tips of the roots and stems.
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Growth of Woody Plants
Grow in diameter by adding new xylem and phloem to the outside of the stem– Vascular cambium is made of xylem in the middle
and phloem around the perimeter (bark) Between the xylem and phloem is the cambium.
– The cambium is responsible for lateral growth. Cambium cells go thought mitosis, making two cells. One cell remains cambium; the other cell forms vascular
tissue.– As the xylem accumulates, it becomes wood.
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A Cross Section of Woody Stem
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Plant Responses to their Environment
Plants are constantly changing in response to changes in their environment.– They produce flowers at certain times of year.– Grow toward the light– Can mount an attack against a competitor
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Tropisms
Growth toward or away from a stimulus Phototropism
– Growing toward light– Involves a hormone called auxin
The tip of the stem produces auxin– Transported into the stem on the shaded side– Stimulates cells on that side to divide and elongate– Causes the stem to bend toward the light
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Phototropism
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Tropisms
Thigmotropism– Climbing vines can wrap around an object using
tendrils.– Tendrils wave about and when they touch an
object, they wrap around it.– Once attached, the tendrils harden.– Sweet peas, grape vines and ivy exhibit
thigmotropism.
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Thigmotropism
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Seasonal Responses Plants can measure the length of the day.
– In response to day length, plants make hormones that trigger development of fruit or flowers.
– In deciduous trees, shortening days triggers leaves to fall off.
Plants can sense changes in temperature.– In dormant plants, warming of the soil triggers above
ground growth. Plants can sense the amount of water.
– During dry seasons, certain plants will lose their leaves and go dormant.
– When it begins to rain, these plants begin to grow and flower.
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Response to Injury
Plants are attacked by pathogens and herbivores.
Plants can fight infection and repair damage by forming scar tissue.
Plants defend themselves against predation.– By producing toxins that interfere with herbivores’
metabolism– Once leaves are eaten, the new leaves produce
even more toxin.
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Coevolution of Plants and Animals Plants evolved before animals.
– Insects and amphibians followed terrestrial plants. Symbiotic relationships evolved between plants and
animals.– Many flowering plants are pollinated by insects and birds.
These flowers are brightly colored, have nectar and have odor.– Grasses and grazers have coevolved.
Grass has silicon that wears down grazers’ teeth. Grazers have very long teeth that take a long time to wear down.
– Many angiosperms produce nutritive fruit. Animals eat the fruit and distribute the seeds.