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Chapter 35
Plant Structure and Growth
I. Two Systems
A. Root System
B. Shoot System
A. Root System
• Used for absorption of minerals and water
• Root hairs are used for most of the
absorption
• Adventitious roots are found above ground
for support
B. Shoot System
1. Stems
- nodes are where the leaves attach
- internodes are segments between nodes
- axilliary buds are found in an angle between
leaf and stem / can produce a branch
- terminal buds are where growth is occurring
- modified shoots: stolons, rhizomes, tubers,
bulbs
2. Leaves
- blade and petiole which attaches the leaf to
node
II. 3 Tissue Types
Plant organs (leaves, stems,
roots) are made of:
• Dermal
• Vascular
• Ground
A. Dermal Tissue
• Responsible for protection
• Epidermis
• Single layer of cells that make up the skin
of the plant
B. Vascular Tissue
• Responsible for Transport of Materials
• Made of xylem and phloem
1. Xylem – carries water and minerals up
- tracheids are pitted, tapered, elongated
cells dead at maturity, with lignified cell
walls
- vessel elements are pitted, squatty,
wide, dead, and lignified and make up
long tubes, form xylem vessels
B. Vascular Tissue
2. Phloem – carries glucose and hormones
down from leaves
- sieve-tube members are alive at
maturity and move sugars with the help
of companion cells that load the sugar,
separated by sieve plates
C. Ground Tissue
• This is a filler with diverse function from
photosynthesis to storage to support
• Divided into the pith which is inside the
vascular tissue, and the cortex with lies
outside the vascular tissue
III. 3 Cell Types
The tissues we just went over are
made up of:
• Paranchyma
• Collenchyma
• Sclerenchyma
A. Paranchyma Cells
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•
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“Typical” Plant Cell
Thin, flexible primary cell wall
No secondary cell wall
Large central vacuole
Least specialized
Most metabolic functions / photosynthesis and
starch storage in plants
• All cells start here / embryonic “stem” cells
• Retain ability to differentiate
• Alive at maturity
B. Collenchyma Cells
• Thicker primary cell wall / unevenly thick
• Grouped in cylinders to provide support to
young shoots
• Lack of secondary cell wall
• Living and flexible / don’t restrict growth
C. Sclerenchyma Cells
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•
•
•
•
•
Thick secondary walls filled with lignin
Rigid
Can not elongate
Dead at maturity
Make up vessel elements and tracheids
Fibers are long, slender, and tapered /
hemp
• Sclereids are shorter with irregular shape /
nutshells
IV. Types of Meristems (Embryonic
Tissue)
A. Apical Meristems allow for growth in
length and are found at the tips of roots
and buds
- They allow for primary growth (length)
B. Lateral Meristems allow for growth in
girth called secondary growth
V. Primary Growth
A. Roots
B. Shoots
A. Roots
1. Root Cap covers the meristem and lubricates
the soil
2. Zone of Cell Division which is where you’ll find
the apical meristem, quiescent center and the
three primary meristem: protoderm (dermal),
procambium (VT, stele, runs down center), and
ground meristem (ground)
3. Zone of Elongation is where the cells lengthen
and push the root tip forward
4. Zone of Maturation is where cells complete
differentiation and become functionally mature
A. Roots
4. Other Terms
Stele – arises from the procambium /
vascular tissue develops here
Pericycle – outermost layer of stele
Endodermis – innermost layer of
endodermis
Monocot Root
Dicot Root
B. Shoots
•
1.
2.
Dome shaped apical meristem still gives rise to
primary meristems: protoderm, procambium, and
ground meristem
Stems
- VT runs through stem in strands of vascular bundles
instead of down the middle
- Dicots have phloem facing out and xylem facing the
pith and monocots have the bundles scattered
throughout
Leaves
- Stomata are holes in epidermis flanked by guard
cells
- Mesophyll is an area of ground tissue mostly made
of paranchyma cells with columnar palisade
parenchyma cells on top and spongy parenchyma cells
on the bottom
Monocot Stem
Dicot Stem
Dicot Leaf
VI. Secondary Growth
• 2 types of lateral meristems function in
secondary growth:
- The vascular cambium which creates
secondary xylem (wood) and the
secondary phloem
- The cork cambium which makes thick
coverings replacing the epidermis
A. Stems
1. Vascular Cambium
- produces secondary xylem in and
secondary phloem out
- forms between primary xylem and
phloem
- as time goes on layers of secondary
xylem accumulate / the spring tracheids
and vessel cells are large with thin walls
and later they become thinner with thick
walls
- form rings of trees
A. Stems
2. Cork Cambium
- early in secondary growth the epidermis falls
off and CC makes new tissue
- produces cork to the outside for protection
and cork and CC are called the periderm
- Bark is the periderm plus primary and
secondary phloem
- old phloem and cork are sloughed off
through growth
- heartwood, dark with no water / sapwood,
carries water and is the secondary xylem
B. Roots
• Very similar to stems but only newest roots
can take in water because the periderm is
waterproof
VII. Mechanisms of Plant Growth
• Asymmetrical Cell Division creates guard
cells and determines the top and bottom of
the plant
• Plane is determined by preprophase
bands
• Gradients effect positional information
• Homeotic Genes play a role (master
genes)