Transcript Plants

Plants
Tissues, Transport & Growth Factors
Angiosperms – flowering plants

Angiosperms are divided
into two categories
– Monocotyledon
 Water lilies, onions,
orchids, grasses,
wheat, corn
– Dicotyledon
 Maples, oaks, cacti,
peas, beans, potatoes

A cotyledon is a seed leaf
that stores carbohydrates
for the seedling
Plant Structure and Function
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Meristems
– Regions of the plant where
some cells have the ability
to divide repeatedly by
mitosis.
– Root and shoot tips this
area is called apical
meristems.

This is referred to as primary
growth.
•Lateral meristems are cylindrical regions in roots and stems
where growth can occur.
•This is referred to as secondary growth.
•Cell division within the vascular cambium will become xylem
and phloem…more on those later.
Plant Tissues
3 types
Dermal Tissue System
1.
–
–
Ground Tissue System
2.
–
3.
Epidermis - outermost layer, waxy non cellular
layer called the cuticle
Periderm  created in secondary growth areas of
the roots and stems. Usually dead cells that
facilitate protection of inner cells (ex. bark). When
the plant matures
Make up all internal non-vascular regions
Vascular Tissue System – xylem and
phloem…coming soon.
Ground Tissues
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Parenchyma
– Living ground tissue.
– Location of photosynthesis and
storage of nutrients and comprises
bulk of plant body (pith).
– Cacti – large amounts of
parenchyma to store water

Collenchyma
– Living ground tissue.
– Thickened cell walls provide
flexibility to the plants and these
areas provide support for the plant’s
primary growth regions.
– Celery stalks
Ground Tissues

Sclerenchyma
– Dead ground tissue.
– Supports mature plants
and assists in
development of hard
shells (nuts and spines).
– Secondary cell wall
composed of cellulose
and lignin for strength
and rigidity.
– Pear
All three types of
tissues in cross and
longitudinal
sections
Transport in Plants

Malpighi in the seventeenth century
– Stripped bark and outer layer of tissue off of a tree with a
swelling above the stripped area with sweet water
– Observations
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Water not transported in this outer layer
Sweet water was nutrients going down to be stored
– Roots continued to live due to prior stored nutrients
Translocation – movement of materials in a plant from
one area to another, at this point, had been discovered.
 Welcome to the world of the xylem and phloem.
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Transport in Plants
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Xylem Tissue
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Formed when certain plant cells
thicken, providing structural support
to the plant.
This tissue actually works when it is
dead as the strong cylinders left
behind are stacked one atop another
to form hollow tubes up the plant.
– Tracheids (pits) and vessels (longer,
fewer openings)
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Xylem cells carry water and minerals
from roots up to the stem and leaves.
Phloem Tissue
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Formed of cells that contain living
tissue.
Cell walls are porous allowing
exchange of materials to neighboring
cells.
Phloem cells transport organic
materials including nutrient and
hormones throughout the plant.
Leaves

Why are leaves important?
– What do they do?

Blades are located at nodes
along the stem
– Stem to blade is called a petiole
– Petiole branches into net venation
(dicots), parallel venation (monocots).
– Leaves can be single, undivided blades
called simple leaves
– Leaves can be divided into two or
more leaflets called compound leaves.
(p.502, fig. 2 & 3)
Leaves
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Stomata
–
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Where the action happens for a leaf and is controlled by guard cells
Mesophyll
–
Palisade mesophyll
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–
Cells are tightly packed, right under the upper epidermis
Primary photosynthetic site
Spongy mesophyll
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Between palisade mesophyll and lower epidermis with lots of spacing to allow gasses to quickly diffuse
Leaves
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Adaptations
– Abiotic
 Broad leaves trap low light emissions but die in open fields
 Early spring leaf spread
 Conifers keep leaves year round so energy is not wasted
also reduce water loss due to thick cuticle
Roots
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Primary root  Secondary
roots (lateral)
Two main types of roots 
Tap and Fibrous
Adventitious roots  are outof-sequence from the more
usual root formation of
branches of a primary root,
and instead originate from the
stem, branches, leaves, or old
woody roots.
Root Cap is protective
Root hairs increase surface
area
Roots

Surrounding the vascular cylinder is the
pericycle (meristematic tissue leading to
secondary roots) and then the endodermis (acts
as a boundary layer).
Roots
Stems
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Two main types
– Herbaceous
 Thin, soft, green, short lived and contain
little or no wood
– Woody
 More traditional dicot trees
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In the first year of growth both will
look similar with meristematic
growth at lateral ends but vascular
tissue within will be different.
Cambium is where new xylem and
phloem are being created…as such
the oldest xylem is more towards the
middle of the stem with the newest
growth beside the cambium.
Similarly, the oldest phloem is out
near the bark and the newest phloem
is beside the cambium.
Reproduction
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Flowers
– Angiosperms are flowering
plants
– Main goal is pollination with
indirect connection to protect
and distribute seeds.
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Seed Growth and
Development
– Seed has an embryo, nutrients
for embryo and protective
covering
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If the plant is a monocot, one seed
leaf (cotyledon) develops, if it is a
dicot, two seed leaves develop
Plant Propagation
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Layering is a means of plant propagation
in which a portion of an aerial stem
grows roots while still attached to the
parent plant and then detaches as an
independent plant
– Raspberries, gooseberries, rubber plant
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Grafting is a technique whereby tissues
from one plant are inserted into those of
another so that the two sets of vascular
tissues may join together.
– In most cases, one plant is selected for
its roots and this is called the stock.
The other plant is selected for its
stems, leaves, flowers, or fruits and is
Plant Propagation

Plant cutting, also known as
striking or cloning, is a technique
for vegetatively (asexually)
propagating plants in which a piece
of the source plant containing at
least one stem cell is placed in a
suitable medium such as moist soil
or potting mix. The cutting
produces new roots, stems, or both,
and thus becomes a new plant
independent of the parent.
– Geraniums, begonia, violets, horse radish
Transport in Plants
Root Pressure
–
Plant roots build up pressure that
forces water upward
1.
2.
Water is actively pumped into
xylem tissues
Minerals and ions actively
pumped into roots and water
follows
–
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Either way water in the xylem
builds pressure and forces
water up
This process is effective in short
plants but if our tree is 100m tall
this can equate to 1000 kPa!
Transport in Plants
Capillary Action
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Relies on adhesive properties
of water
If you touch a capillary tube to
the surface of water the water
will rise up the tube because
the polarity of the capillary
walls attracts water molecules,
which cling to the side of the
tube.
The more narrow the tube, the
higher the water will climb
Very narrow vessels will
facilitate a height of 60 to 90
m
Transport in Plants
Cohesion-tension or
transpiration pull
– Each molecule of water vapour
evaporates from a stomata in the leaf
to the air, and another molecule is
right behind the first
– Transpiration is the key (which means
water loss) however it has been found
that water will move even if
transpiration is not occurring
– Widely accepted however how does
water move up a tree in the spring?
– Mineral Transport – considered
different but not separate from
transport of water
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Believed to be taken in through active
transport and then incorporated with
water.
Transport in Plants
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Transport in phloem is still not fully understood:
– Phloem cells must be living for transport to occur
– Material can move through the phloem in more then one
direction at the same time
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Radioactive carbon and phosphorous in geraniums
– Phloem may transport large amounts of material rapidly
within a plant
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Pumpkin can gain 5.5kg (12 pounds) in less than a month
– Oxygen deficiencies and low temperatures inhibit but do not
stop phloem transport
– Characteristics of movement of a particular substance may
vary from one plant to another
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Carbohydrates enter cotton bolls during the day, but tend to enter date
fruits at night.
Transport in Plants
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Mass-flow theory – phloem
– Relies on combination of osmosis
and pressure dynamics to explain
movement of materials
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Sucrose is manufactured in leaves and
it travels to other parts of the plant for
storage (starch) or used by the plant
(plant tissues)
Transportation in Plants
– This theory is widely accepted however pressures involved in
mass flow should lead to higher internal pressure within the
phloem then what is actually observed.
– Another problem is that it is not clear that mass flow can
account for the speed or distance over which transport in
phloem occurs.
– Also simultaneous bi-directional transport and low oxygen and
low temperature meaning slow transport are not explained.
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However, these are addressed by saying that the living tissue of the
phloem itself plays a role in movement of organic materials possibly by
utilizing cytoplasmic streaming
External Plant Growth Factors
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Light Requirements
– Photoperiodism – amount of light that a plant requires to grow.
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Soil Nutrients
– Macronutrients
Obtained primarily from carbon dioxide and water (95%)
 C, H, O, N, K, P, Ca, Mg, S
– Micronutrients
 Fe, Cl, B, Mn, Zn, Cu, Mb, Ni
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Nitrogen
– Plants that make a lot of proteins need a lot of N
– Organic matter  ammonium  nitrate ions (NO3-) which is
then used by the plant
– Atmospheric nitrogen  ammonium  nitrate ions which is
then used by the plant
 Symbiotic Relationships and root nodules
Internal Plant Growth Factors
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Auxins
– Can stimulate plant growth, usually cell elongation.
– Influence plants dropping fruits and leaves.
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Gibberellins
– Act like auxins
– Bolting  cause the stem to elongate just prior to the plant flowering
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Cytokinins
– Stimulate cell division
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Ethylene
– Fruit ripening
– Released prior to rise in cellular respiration that corresponds to the mass
conversion of starch to sugars.
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Abscisic Acid
– Inhibitor which acts by promoting closure of the stomata.