Download Fruit and Seed dispersal

Angiosperms: Phylum Anthophyta,
the flowering plants
1. 
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6. 
Overview of seed plant evolution
Traits of flowering plants
The angiosperm life cycle
Seed (fruit) dispersal (continued)
Seed morphology and germination
Hormones (Auxin) briefly (we’ll come
back to this)
Fruit adaptations that enhance seed dispersal: Red berries are animal
dispersed, while dandelion fruits are wind-dispersed (right).
The seeds of many plants have elaiosomes—
fleshy attachments which attract ants. Ants carry
the seeds back to their nests, eat the elaiosome,
and often discard the seed. (One example is our
native wild ginger, Asarum caudatum)
Fruit and Seed dispersal
•  Fruits protect seeds during development and
sometimes aid in their dispersal
•  Fleshy fruits or seeds are adapted to animal
dispersal
•  Dry fruits can be adapted to air or water dispersal,
animal dispersal, or to release the seeds at maturity
•  Seeds themselves often have their own dispersaladapted morphology, and adaptations for survival
and germination
Some fruits, such as these burrs, hitch a ride
on the fur of animals
Don’t forget: many plants also reproduce asexually. Two examples: the
maternity plant (Kalanchoe, left), aspen (Populus) groves (right)
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Seed adaptations for survival and
germination
Figure 38. 8 Review: Three types of seed structure
•  Many seeds exhibit dormancy, a temporary condition of
low metabolism and no growth or development. Some
seeds can survive like this for decades or more. What are
the potential benefits of dormancy?
•  Dormancy in some seeds is simply broken by favorable
environmental conditions, but others only germinate after
specific cues
•  What would you expect the cues to be for seeds living in
deserts, fire-prone habitats (such as California chaparral),
or at high latitudes? How about for seeds borne in berries
eaten by mammals?
The four steps of seed germination: 1. imbibition of water,
2. enzyme digestion of stored food, 3. embryo begins growth and radicle is
pushed through the seed coat, and 4. shoot tip grows toward soil surface.
Figure 38.10 Two ways that young shoots break through the soil surface.
Germination of a barley seed is shown below.
Figure 38.7 The development of a dicot plant embryo
Hormones
One bad apple…
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A word about Auxin:
Auxin is a term used for any
chemical substance that promotes
the elongation of coleoptiles (though
they have multiple functions in
monocots and eudicots)
The natural Auxin occuring in most
plants is IAA - indoleacetic acid
How do plants grow toward the
light? (phototropism)
Plants exhibit phototropism and
gravitropism
•  Phototropism: in response to light (shoots)
•  Gravitropism: in response to gravity
(pressure really) – roots
•  Thigmotropism: in response to mechanical
pressure/touch (vines)
Auxin causes cell elongation along the
dark side of the shoot, causing the
shoot to bend towards light
It also works in conjunction with other
hormones….for example in fruit
ripening
A word about Auxin:
Thigmotropism: pressure/mechanical
Auxin is a term used for any
chemical substance that promotes
the elongation of coleoptiles (though
they have multiple functions in
monocots and eudicots)
The natural Auxin occuring in most
plants is IAA - indoleacetic acid
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What auxin does in plants
Structure and Growth
•  Promotes shoot elongation
•  Suppresses shoot branching (apical
dominance)
•  Inhibits root elongation
•  Promotes root branching
•  Promotes growth of fruit
Figure 35.2 Morphology of a flowering plant: an overview
Plant systems
•  The plant body has a hierarchy of organs,
tissues, and cells, like multicellular animals
–  Have organs composed of different tissues, which are
in turn composed of cells
•  The basic morphology of vascular plants
–  Reflects their evolutionary history as terrestrial
organisms that draw nutrients from two very different
environments: below-ground and above-ground
Roots
•  A root
–  Is an organ that anchors the vascular plant
–  Absorbs minerals and water
–  Often stores organic nutrients
•  In most plants
–  The absorption of water and
minerals occurs near the root
tips, where vast numbers of
tiny root hairs increase the
surface area of the root
•  Three basic
organs
evolved: roots,
stems, and
leaves
•  They are
organized into
a root
system and a
shoot system
Roots cont.
•  Gymnosperms and eudicots: taproots with
lateral roots
•  Seedless vascular and monocots: fibrous
root system: spread out
•  Many plants have modified roots:
adventitious roots arise above ground from
stems and even leaves
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Many plants have modified roots
(a) Prop roots
(d) Buttress roots
(b) Storage roots
(c) “Strangling” aerial
roots
Stems (shoot system)
•  Nodes: point of leaf attachment
•  Internodes: segments between nodes
•  Axillary buds can form new shoots or
branches
•  Terminal buds can lead to apical
dominance (grow up!)
(e) Pneumatophores
Figure 35.4 Modified shoots: Stolons, strawberry (top left); rhizomes, iris (top
right); tubers, potato (bottom left); bulb, onion (bottom right)
Leaves
Leaf types
•  Main photosynthetic organ - but in many,
the stems can dominate too.
•  Blade and petiole (monocots don’t have
petioles - base of the leaf forms a sheath
around leaf.
•  Leaf types:
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Figure 35.5 Simple versus compound leaves
Leaf types
Figure 35.6 Modified leaves: Tendrils, pea plant (top left); spines, cacti (top
right); succulent (bottom left); brightly-colored leaves, poinsettia (bottom right)
Figure 35.19 Leaf anatomy
Note: “Cuticle” = waxy or fatty layer on
outer wall of epidermal cells
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The plant body – organs: root and shoots
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Root system and shoot system are designed to
draw ‘nutrients’ from two very different habitats
Many are modified to accommodate specific
conditions or strategies
Leaf types can be confusing (like fruits), but
you need to know them
Leaf anatomy includes many different kinds of
cells: living to dead. Pallisade parenchyma
and spongy parenchyma can help determine
orientation of leaf and stomata.
Some leaf morphologies are adapted for
specific conditions: oleanders and water
conservation
Figure 35.7 The three tissue systems
The plant cell—tissue systems,
tissues, and cells
A review of the tissue systems and cells –
this is really here for you to read and
review…
Pay attention to the ‘new context’ – we’ll
look at monocots vrs. eudicots
Figure 35.7 The three tissue systems
Tissue
Systems
Tissues/cells
Ground
Parenchyma
Collenchyma
Sclerenchyma
Vascular
Xylem
Figure 35.18 Primary tissues, and their functions, in young stems
Sclerenchyma tissue: support of
mature plant parts
Xylem tissue: water & mineral
transport; Phloem tissue:
“food” (sugar) transport
(a.k.a. “pith ray”)
Collenchyma tissue: support of
young, growing parts
Parenchyma tissue:
photosynthesis, storage, and/or
secretion
Phloem
The three tissue systems
Dermal
Epidermis
Epidermal tissue: protection,
control of water loss, and a variety
of other functions
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Figure 35.16 Organization of primary tissues in young stems. Note difference
from root: vascular tissue is arranged in bundles, with ground tissue in center.
Also note difference in arrangement of bundles between dicot and monocot.
Figure 35.15 Organization of tissue systems and tissues in young roots
“Epidermis:” Dermal system, epidermal
tissue
“Cortex:” Ground system, parenchyma
tissue
“Stele:” Vascular system, xylem & phloem
tissues
Figure 35.13 Organization of primary tissues in young roots. Note the
difference between the monocot and the dicot in the arrangement of the xylem
& phloem in the stele.
Tissue Systems
Tissues
(& cell types)
Ground
Parenchyma
(parenchyma cells, transfer cells)
Collenchyma
(collenchyma cells)
Sclerenchyma
(fibers & sclereids)
Vascular
Xylem
(tracheids or vessel members, also some
parenchyma cells, fibers, & sclereids )
Phloem
(sieve cells or sieve-tube members, also specialized
parenchyma cells called companion or albuminous
cells, some fibers & sclereids)
Dermal
Epidermis
(ground cells, guard cells, trichomes, and others,
also some fibers & sclereids)
Figure 35.19 Leaf anatomy
Three tissue systems of plants
•  Dermal tissue - outer protective covering
Note: “Cuticle” = waxy or fatty layer on
outer wall of epidermal cells
–  Epidermis/periderm analogous to skin
–  Cuticle - waxy coating to preserve water
•  Vascular tissue - transport system
–  Xylem: carries water and nutrients from roots to
leaves. Support and food storage too.
–  Phloem: transport organic nutrients (sugar),
amino acids, lipids, hormones etc.
•  Ground tissue - “everything else”.
–  Pith (internal to vascular), Cortex
–  Function in storage, photosynthesis, & support
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•  Primary Tissues are arranged in a ‘ring’ in
eudicot stems, and are scattered in
monocot stems
•  The stele, within the root, contains xylem
that is more centralized in eudicots and
more scattered in monocots
•  You remember all those cell types
Plant Growth
1.  Meristems and overview of plant growth
Remember: A major
adaptation of land
plants is the meristem
—a region of
perpetual cell division
that allows the plant
to grow rapidly
2.  Apical meristems and primary growth
There are two types of
meristems: Apical and
lateral.
3.  Lateral meristems and secondary growth
Apical meristems
lengthen the plant
(“primary growth”).
Roots and shoots
Figure 35.10 Locations of major meristems
Lateral meristems
thicken the plant with
bark and wood
(“secondary growth”).
Figure 35.11 Illustration of primary and secondary growth: Morphology of a
winter twig
Plant Growth
1.  Meristems and overview of plant growth
2.  Apical meristems and primary growth
3.  Lateral meristems and secondary growth
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Figure 35.12 Primary growth of a root. Notice that the apical meristem
produces three primary meristems, which produce the three primary tissue
systems (dermal, ground, and vascular).
Figure 35.13 Organization of primary tissues in young roots. Note the
difference between the monocot and the dicot in the arrangement of the xylem
& phloem in the stele.
Figure 35.14 The formation of lateral roots. Lateral roots arise from the
pericycle—the outermost cell layer of the stele.
Figure 35.12 Primary growth of a root. Notice that the apical meristem
produces three primary meristems, which produce the three primary tissue
systems (dermal, ground, and vascular).
Figure 35.15 The terminal bud and primary growth of a shoot. Just like in the
root, the apical meristem produces three primary meristems, which develop
into the three tissue systems.
Figure 35.16 Organization of primary tissues in young stems. Note difference
from root: vascular tissue is arranged in bundles, with ground tissue in center.
Also note difference in arrangement of bundles between dicot and monocot.
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Figure 35.10 Locations of major meristems
Plant Growth
1.  Meristems and overview of plant growth
2.  Apical meristems and primary growth
3.  Lateral meristems and secondary
growth
Figure 35.18 Secondary growth of a stem (Layer 1)
Remember:
Secondary growth
happens at the 2
lateral meristems
The interior lateral
meristem, called the
vascular cambium,
produces secondary
xylem (to the interior)
and phloem (to the
exterior).
The exterior lateral
meristem, called the
cork cambium,
produces cork cells to
the exterior.
Figure 35.18 Secondary growth of a stem (Layer 2)
Vascular cambium:
Fusiform initials make cells
elongated vertically, form
secondary xylem (to inside) and
secondary phloem (to the outside)
Ray initials make cells elongated
horizontally-transfer water and
nutrients, store starch
Cork cambium: meristem for tough
thick covering - replaces epidermis.
Forms from cortex to fill in gaps as
epidermis is stretched and broken
by lateral expansion of stem
Rays maintain connectivity
between secondary xylem and
secondary phloem, allow exchange
of nutrients and water, store starch
and organic nutrients
Figure 35.18 Secondary growth of a stem (Layer 3)
Anatomy of a three-year-old stem. How can you tell the stem is 3 years old?
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Secondary growth of a stem. How many years old is it?
Figure 35.20 Anatomy of a tree trunk
Notes:
“Wood” = secondary xylem, or
everything on the interior side of the
vascular cambium
Oldest xyelm
nonfuctional
“Bark” = everything exterior of the
vascular cambium, including the
secondary phloem and the periderm
(cork cambium + cork)
Also remember: Secondary growth
happens in roots too.
Oldest phloem
sloughed off
A summary of primary and secondary growth in a woody stem
A summary
of primary
and
secondary
growth in a
woody stem
Remember: A major
adaptation of land
plants is the meristem
—a region of
perpetual cell division
that allows the plant
to grow rapidly
Figure 35.10 Locations of major meristems
Oldest xyelm
nonfuctional
There are two types of
meristems: Apical and
lateral.
Apical meristems
lengthen the plant
(“primary growth”).
Lateral meristems
thicken the plant with
bark and wood
(“secondary growth”).
There are two of these
Oldest phloem
sloughed off
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Record of events from xylem rings
•  Old growth trees can provide disease and
fire records
Oldest xyelm
nonfuctional
Oldest phloem
sloughed off
Aztecs and plagues…
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