Chapter 22
Lecture Outline
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22-1
What is a plant?
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Eukaryotic
Multicellular
Contains chlorophyll a and b
Carries on photosynthesis
Has cellulose cell walls
Lives in a variety of terrestrial habitats
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22-2
And a few shallow aquatic habits
Exhibits alternation of generations
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Plant Diversity
22-3
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Alternation of Generations
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A life cycle that involves two generations
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Sporophyte generation
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Gametophyte generation
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Diploid
Undergoes meiosis to generate haploid spores
Spores germinate and divide by mitosis to give rise to
the 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
22-5
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The Evolution of Plants
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Photosynthetic algae are thought to be the
ancestors of plants.
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The evolution of plants shows two trends.
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Green algae have the same types of chlorophyll.
There is extensive DNA homology between plants
and green algae.
Toward greater specialization for living in a dry
environment
Toward a more prominent sporophyte generation
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The Evolution of Plants
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Primitive plants
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More advanced plants
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Lack vascular tissue to carry water
Have flagellated sperm; no seeds
Have to live in moist habitats
Have dominant gametophyte generation
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
22-8
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Nonvascular Plants
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Include
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Mosses, hornworts, liverworts
Known as the bryophytes
Common features
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Lack vascular tissue
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Do not have true roots or leaves
Gametophyte is dominant
Sperm swim to egg
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22-9
Use diffusion and osmosis to obtain water and nutrients
Must have water to reproduce sexually
Are small and confined to moist habitats
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Moss Life Cycle
22-10
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22-11
http://www.youtube.com/watch?v=jcWYAnm
m-QE
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Kinds of Nonvascular Plants
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Mosses
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Liverworts and
hornworts
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Grow as a carpet of
many individual
gametophyte plants
Each individual is less
than 5 cm tall.
Form flat sheets only a
few cells thick
Each cell contains one
large chloroplast.
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Non-vascular plants
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22-13
http://www.youtube.com/watch?v=kBPLKUTt
XBM
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The Significance of Vascular
Tissue
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Vascular tissue is an adaptation to living in dry
environments.
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Allows plants to transport water and nutrients throughout
the plant
Associated with the development of
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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
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Leaves for photosynthesis
Roots for absorbing water and minerals
Xylem
Phloem
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Xylem
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A series of dead, hollow cells that form tubes
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Vessel elements
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Tracheids
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Form long tubes with cells end-to-end
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
22-16
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Phloem
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Carries organic molecules produced in the
leaves to the rest of the plant
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Sugar
Amino acids
Consists of two types of cells
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Sieve-tube elements
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Companion cells
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22-17
Lack a nucleus and organelles, but have cytoplasm
Have holes in the end walls for the transport of material
Actively transport sugars and amino acids out of the leaf cells
and into the sieve-tube elements
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Phloem
22-18
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Video Xylem and phloem
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22-19
http://www.youtube.com/watch?v=J1PqUB7T
u3Y
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The Development of Roots,
Stems, and Leaves
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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
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Underground parts of a plant that
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Anchor in the soil
Absorb water and nutrients
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Grow from the tips
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Explore new areas of soil for water and nutrients
Root tips have root hairs that increase their absorptive
surface.
Can be important storage sites
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Move the nutrients into the vascular system
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
22-22
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Stems
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Above-ground structures that
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Vary greatly in diameter and length
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Support the leaves
Transport raw material from the roots to the leaves
Transport manufactured material from the leaves to other
parts of the plant
Tree trunks are large and support branches.
Dandelion stems are short.
Some stems are underground.
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Stems
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The structure of cell walls allows the stem to
support the leaves.
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Cell walls are made of cellulose interwoven into a
box.
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Woody plants have especially thick cell walls.
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When cells are full of water, the cell walls will not
stretch.
This makes the cells turgid, stiff and able to support
weight.
These have lignin in them.
Allows woody plants to grow tall and withstand wind
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Stems
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Stems contain a lot of
vascular tissue.
Stems also
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Store food
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Photosynthesize
Have waterproof layers
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22-25
Sugar cane
Yams
Potatoes
Can be waxy or woody
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Leaves
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Specialized for photosynthesis
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Have large surface area to collect sunlight
Relatively thin to allow light penetration
Have bundles of vascular tissue to transport
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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
22-27
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Leaves
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Specialized for photosynthesis
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Covered by a waxy coating to minimize water loss
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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
22-29
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Seedless Vascular Plants
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Include
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Have vascular tissue
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Are not limited to aquatic environments
Do not have seeds
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Whisk ferns
Horsetails
Club mosses
Ferns
Have flagellated sperm
Must have moist conditions to reproduce
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Fern Life Cycle
22-31
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Kinds of Seedless Vascular Plants
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Ferns
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Most common seedless
vascular plant
Whisk ferns
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Lack roots and leaves
Anchored by an
underground stem
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Modifications of the
stem serve the
functions of roots and
leaves.
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Kinds of Vascular Seedless Plants
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Horsetails
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Club mosses
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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
Usually evergreen
Low-growing, branching plants
Some are called ground pines.
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Seed-producing Vascular Plants
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A seed is a specialized structure that contains
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Seeds allow plants to live in dry habitats.
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Aid in dispersal
Gymnosperms and angiosperms produce seeds.
Accompanied by the development of pollen
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An embryo
Stored food
A protective outer coating (seed coat) that prevents drying
Encased sperm (male gametophyte generation)
Allows plants to reproduce without water
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Gymnosperms
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Means “naked seed”
Woody, perennial
plants
Produce seeds that are
not enclosed (naked)
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Produce seeds in cones
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The Pine Life Cycle
22-36
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Kinds of Gymnosperms
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Cycads
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Wood plants with a ring of fern-like leaves at the
top
Live in tropical regions
Ginkgo
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Ginkgo biloba is the only living species
A tree with fan-shaped leaves
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22-37
Used in many herbal medicines
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Kinds of Gymnosperms
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Conifers
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Trees and shrubs that bear cones
Have needle-shaped leaves
Called evergreens because they do not lose their
leaves
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Do shed needles throughout the year
Used in the production of lumber
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Several Gymnosperms
22-39
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Angiosperms
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Produce flowers
Have vascular tissue, seeds and pollen
Have seeds enclosed in a fruit
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A modification of the ovary wall
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Flower Structure
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Composed of highly modified leaves
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Petals are usually colorful.
Sepals surround petals
Petals and sepals are arranged in whorls.
Specialized for sexual reproduction
Female parts in the center
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Pistil (stigma, style and ovary)
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Ovary produces eggs
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Flower Structure
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Male parts surround the pistil.
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Stamens (filament and anther)
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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
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Wind
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Plants with inconspicuous flowers are usually
wind-pollinated.
Produce large numbers of flowers and pollen
Many species are wind-pollinated.
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Responsible for hay fever
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Grasses and sedges
Aspens, birches and oaks
Some people have allergic reactions to pollen.
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Strategies for Pollination
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Animals
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Plants with showy flowers are usually animalpollinated.
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Flowers attract insects, birds and small mammals.
The animals feed on the nectar and pick up the
pollen.
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These flowers usually produce nectar.
Also smell good to attract animals
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
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A modification of the ovary that contains seeds
Involved in dispersal of seeds
Many fruits are nutritive to animals.
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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
22-49
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Angiosperm Diversity
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Classified as either monocots or dicots
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Refers to the number of cotyledons found in the
seeds of the species
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Cotyledons (seed leaves) store food for the
growing embryo.
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Monocots have one cotyledon (peanut).
Dicots have two cotyledons (lima bean).
They emerge as the first leaves.
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Embryos in Dicots and Monocots
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Monocots vs. Dicots
22-52
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Angiosperm Diversity
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Monocots
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Yuccas and palms are woody.
The rest are herbaceous.
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Dicots
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Mints, carrots, cabbages, mustards, tomatoes and
potatoes are herbaceous dicots.
Aspen and sagebrush are woody dicots.
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Wheat, rice, corn, sweet potatoes, onions, bananas
These are deciduous.
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Deciduous Trees
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Lose their leaves once
a year
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The bark of the tree is
the phloem.
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Occurs in the fall before
they go dormant
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
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Woody plants have the ability to grow
continuously for many years.
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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
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Grow in diameter by adding new xylem and
phloem to the outside of the stem
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Vascular cambium is made of xylem in the middle
and phloem around the perimeter (bark)
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The cambium is responsible for lateral growth.
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Between the xylem and phloem is the cambium.
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
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Plants are constantly changing in response
to changes in their environment.
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They produce flowers at certain times of year.
Grow toward the light
Can mount an attack against a competitor
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Tropisms
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Growth toward or away from a stimulus
Phototropism
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Growing toward light
Involves a hormone called auxin
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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
22-60
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Tropisms
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Thigmotropism
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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
22-62
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Seasonal Responses
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Plants can measure the length of the day.
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Plants can sense changes in temperature.
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In dormant plants, warming of the soil triggers above ground
growth.
Plants can sense the amount of water.
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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.
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
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Plants are attacked by pathogens and
herbivores.
Plants can fight infection and repair damage
by forming scar tissue.
Plants defend themselves against predation.
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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
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Plants evolved before animals.
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Insects and amphibians followed terrestrial plants.
Symbiotic relationships evolved between plants and
animals.
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Many flowering plants are pollinated by insects and birds.
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Grasses and grazers have coevolved.
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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.
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These flowers are brightly colored, have nectar and have odor.
Animals eat the fruit and distribute the seeds.
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