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Chapter 29
Plant Structure and
Function
Section 1
Plant cells and Tissue
• Parenchyma
– Loosely packed
– Cube-shaped or elongated
– Large central vacuole
– Flexible cell walls
– Involved in metabolic functions
2
• Collenchyma
– Thicker than parenchyma
– Support for cells that are still lengthening
• Schlerenchyma
• Thick, even, rigid cell walls
• Support and strengthen where growth
has ended.
Tissue Systems
• 1. Dermal system
– Forms the outside covering of the plant
– Outer layer is made up of parenchyma
cells
– Outer epidermal wall is the Cuticle –waxy
layer.
• 2. Ground tissue system
– Contains all three types of plant cells
– Covered by the dermal tissue
– Storage, metabolism, support
– Parenchyma most common cell found in
the ground tissue.
• 3. Vascular tissue system
– Transports, and supports
– Contains xylem and phloem
– In angiosperms ( flowering plants) xylem
has tracheid's made up of schlerenchyma
cells. Called vessel elements
– water moves through tracheid pits which
are located in the cell wall
– Vessel elements have large holes in the
top or bottom walls or no end walls at all
– Stacked to form long tubes called vessels
– Most seedless and gymnosperms contain
only tracheid's.
– In angiosperms the parenchyma
conducting cells are called sieve tube
member
– Stacked to form long sieve tubes,
compounds move through end walls
called sieve plates
– Sieve tubes have a companion cell next to
them, they help to transport materials.
Plant growth
• Meristems- cells continuously
divide. Two types:
–Apical meristem
• Where plants grow in length
• Located at the tips of stems and
roots
• 2. Lateral meristem
– Gymnosperms (woody) and most Dicots
stems and roots grow in diameter.
– Two types of lateral meristem
• 1. Vascular cambium
– Between the xylem and phloem
– Produces more vascular tissue
2. Cork Cambium
- outside of the phloem
- produces cork
- cork replaces epidermis in woody stems
and roots
Section 2
Roots
• A primary root, first root if it becomes
large it is called a taproot ex. Carrot
• Fibrous root system
– Numerous small branching roots
– Many monocots ex. Grasses
• Adventitious roots
• Grow from uncommon places like stems
and leaves ex. Prop root, aerial root
Root structure
• Root cap- covers the apical meristem
– Produces a lubricating oil to move the root
through the soil.
• Root hairs
• Extensions of epidermal cells
• Increases surface area
• Increases the plants ability to absorb water
• Root grows in length by cell division
– Elongation and maturation occurs in the
apical meristem in the root tip
– Dermal tissue matures to form the
epidermis
– Ground tissue matures into the Cortex,
and endodermis
– Vascular tissue matures innermost core of
the root.
• Outermost layer is called the pericycle
• Pericycle forms the lateral roots
Secondary growth roots
• Dicot and Gymnosperm has secondary
growth
– Cells from pericycle and vascular
cambium form between the primary xylem
and phloem.
– Produces secondary xylem inside and
phloem to the outside.
• Root functions
– Absorbing water and minerals
• Macronutrients- N, K, P, Ca, S
• Micronutrients- Mg in smaller amounts
– Storage of water, and carbohydrates
• Converted to starch and stored in parenchyma
cells
• Stores water for dry periods
Section 3
Stems
• Woody
• Non-woody
• Modified stems
– Stolon
ex. Strawberry
– Tuber
ex. Potato
– Succulent ex. cactus
• Growth in length at the apical meristems
• Growth in circumference is at the lateral
meristems
• Leaf attaches to the stem at a node
• The space between nodes is the
internode.
• Each node has a bud which can form a
new shoot
• Bud is enclosed by specialized leaves
called bud scales
• Stems apical meristem is protected by
bud scales when they aren’t growing
Primary Growth
• Apical meristem gives rise to dermal,
ground, and vascular tissue
• The dermal is the epidermis
• Gymnosperms and dicots the ground
tissue forms the cortex and pith
• Pith is in the center for storage
• Monocots ground tissue doesn’t
separate into pith and cortex it is
mixed up.
Secondary growth
• Secondary xylem (wood)
• Older xylem stops transporting of water and
turns dark.
• Heartwood- in the center and is darker in
color.
• Sapwood- lighter in color, nearer to the
outside
• Bark- phloem produced outside of the stem
• Springwood- formed in wide rings if water is
plentiful
• Summer wood- water is limited, smaller cells
are produced
• Annual rings- the change between
summerwood and springwood.
Stem Function
• Transport of nutrients, water, storage,
and support
• Phloem transports, carbohydrates, and
plant hormones
• Translocation- the movement of
carbohydrates. They are moved from
storage which is called the source to
the use site called sink
• pressure-flow hypothesis- active
transport of the sieve tubes
• Xylem – transports water
• Transpiration when water evaporates
through the stoma
• Cohesion-tension theory
– Water is pulled up the stem by cohesion of
water molecules to each other
– Adhesion of water molecules to the xylem
walls
Section 4
Leaves
• Example of leaf type
– Tendril- found in vines, wrap around
objects
– Tubular- traps food in carnivorous plants
– Spines- protection, reduce water
transpiration
– Blade- broad flat portion
– Petiole- stalk like that attaches the leaf to
the stem
• Simple – only one blade
• Compound- blades divided into leaflets
• Double compound- when the leaflet
divides
Leaves Tissue
• Dermal tissue
– Epidermis
– Cuticle
– Stomata
– Epidermal hairs
• Ground Tissue
– Photosynthesis occurs in the mesophyll
– Mesophyll have two layers
• Palisade- below the upper epidermis, it is the
site for most photosynthesis
• Spongy- irregularly shaped cells, large air
spaces.
• Vascular tissue
– Large bundles- in the veins
– Veins are embedded in the mesophyll
– Venation- arrangement of veins in a leaf.
Monocots- have parallel venation
Dicots- net venation
Leaf Function
• Primary site for photosynthesis
• Modifications for capturing light
– Dry environments, they conserve water by
the closing of stomata
Guard Cells- located on both sides of the
stomata, regulate gas and water exchange
K ions pumped into the guard cells cause
them to bow and open forming a pore.
Darkness, K ions are pumped out closing
the stomata