Transcript chpt 35 plants

Chapter 35
Plant Structure, Growth,
and Development
Shannon Nugent
Austin Wetterau
Erin Strong
Anatomy of a Plant
•
3 Basic Organs:
•
•
Absorb water from below and CO2 from above
•
•
Roots, Stems, Leaves
Root system and Shoot System
Both depend on each other
•
Roots starve without photosynthesis
• Shoot system depends on water and minerals
absorbed
Roots
•
Multicellular organ acting as an anchor, absorbs
nutrients, and stores carbs
•
Most gymnosperms or eudicots have a Taproot main root
•
Lateral roots - roots linked to main taproot
• Monocots - many small roots (fibrous root system)
Stems
•
Stem - an organ consisting of system of nodes
where leaves attach with internodes
•
Axillary bud - in angle of stem and leaf (branch)
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Apical bud - developing leaves
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Buds describe dormancy
• Possible Food storage and asexual reproduction
Leaves
•
Main photosynthetic organ
•
Monocots - parallel major veins
• Eudicots - branched network of veins
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Help taxonomists diversify many different plants
35.2
• Intermediate growth - most plants grow
continuously
•
Plant life cycle: Annual, Biennial, Perennial
• Meristems make intermediate growth possible
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Initials - sources of new
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Derivatives - new cells from meristem
• Growth of Roots
35.3
– Primary growth produces the Primary plant
body: parts of roots and shoot systems
produced by apical meristems
– Tip of root is covered by the root cap:
protects apical meristem during primary
growth
– zone of cell division includes apical
meristem & 3 primary meristems
(protoderm, procambrium, & ground)
35.3 cont.
• Growth occurs in 3 stages:
– zone of cell division (where new root cells are
produced)– zone of elongation: root cells elongate
– -zone of differentiation: zone of maturation,
become distinct cell types
• Primary growth produces epidermis, ground
tissue, and vascular tissue
35.3 cont.
• Growth of Shoots
– vascular tissue runs through stem in strands called
vascular bundles
– dicots = vascular bundles in ring, pith inside ring,
cortex outside
– monocots = vascular bundles scattered through
ground tissue
– Leaves develop from Leaf primordia: projections
along side of apical meristem
35.3 cont.
• Tissue Organization
– Epidermis has stomata: tiny pores controlled
by guard cells that allow gas exchange
– Ground tissue is located in the mesophyll
– Vascular tissue contains xylem and phloem
35.4
• Secondary growth occurs in stems and roots
of woody plants
• Secondary Plant Body: tissues produced by
vascular cambium and cork cambium– vascular cambium: cylinder of meristematic cells
that forms secondary vascular tissue, increases
vascular flow and support for shoots
– cork cambium: produces a tough, thick covering
that protect the stem from water loss and invasion
• Primary and secondary growth occur
simultaneously
35.4 cont.
• Vascular Cambium and Secondary Vascular
Tissue
– As meristematic cells divide, they increase
circumference of vascular cambium and add
layers of secondary xylem (wood) to its interior
and secondary phloem to exterior
– Some parts of vascular cambium are elongated &
other parts are shortened and produce vascular
rays: radial files of cells that connect the
secondary xylem with secondary phloem
35.4 cont.
• A year’s growth appears as
a distinct ring in tree trunks
and roots
• Heartwood= old layers of
secondary xylem that no
longer transport water and
minerals
• Sapwood= newest, outer
layers of secondary xylem,
transports xylem sap
• Cork Cambium & Production of Periderm
35.4 cont.
– During secondary growth, epidermis is falls off and is
replaced by two tissues produced by the first cork
cambium
– Cork tissue functions as a barrier that protects stem/root
from water loss, physical damage, and pathogens
– Periderm: consists of cork cambium plus the layers of
cells it produces
– Lenticels: dot the periderm and enable living cells
within a woody stem or root to exchange gases with
outside air
– Bark: all tissues external to vascular cambium
– Components of bark = secondary phloem, most recent
periderm, and old layers of periderm
35.5- Growth, Morphogenesis,
and Differentiation Produce the
Plant Body
• Scientists believe that if they identify
each gene’s function in a plant, they can
discover a blue print of how plants
develop
35.5 cont.
• GROWTH
– When cell numbers increase, cell
divisions in meristems increase the
potential for growth
– Most increase in growth comes
from cell expansion or elongation
35.5 cont.
• Preprophase band
– Concentrated ring of microtubules.
Disappears before metaphase, but
predicts the future plan for cell division
• Water uptake accounts for 90% of
plant cell expansion
• Vacuoles fill quickly from the water
uptake & take up a lot of space in
cells, letting the plant grow rapidly
35.5 cont.
• Enzymes weaken the cross-links
in cell wall, letting it expand as
water diffuses into the vacuole by
osmosis
• Morphogenesis must occur for
plant to develop properly
– Cells must be organized into
multicellular arrangements of
tissues and organs
35.5 cont.
• Pattern formation- Development
of specific structures in specific
locations
• Positional information is
communicated by signals that
continuously indicate to every
cell its location in the developing
structure
– Ex. Hormones, proteins, mRNAs
provide positional info.
35.5 cont.
• Critical step in morphogenesis is
proper establishment of axial
polarity
• Morphogenesis is under the
control of homeotic genes
(master regulatory genes that
over see major events in
development)
35.5 cont.
• Cellular differentiation depends on the
control of gene expression
• Positional information is important to
all stages of development (growth,
morphogenesis, and differentiation)
• Phase changes- When internal or
environmental changes cause a plant
to switch from developing one part to
another