Transcript Plant Structure and Growth

Plant Structure and Growth
Ch. 35
Plant Tissues
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Plants have three types of tissue:
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Dermal Tissue
Vascular Tissue
Ground Tissue
 Each
tissue has a different function
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Dermal Tissue
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Covers the plant, acts as protection
Made of endodermis, epidermis, guard cells, root
hairs, and cuticle.
Vascular Tissue
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Transports water and nutrients throughout the plant
Made of xylem and phloem
 Xylem:
Carries water and minerals and is made of
two type of cells:
 Tracheids:
long, skinny cells that overlap and
are tapered at the ends.
 Water goes from one cell to the next
through areas with no secondary wall called
pits
 The secondary walls of the tracheids are
hardened with lignin, making tracheids
useful for support as well as transport
 Vessel
Elements: Usually wider, shorter,
thinner walls and less tapered than tracheids
 Linked together end to end, while water
flows from cell to cell through perforated
end walls
 Water can also move laterally to neighbor
cells through pits
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Phloem: Carries sugars from the leaves to the rest of
the plant using active transport.
Consists of:
 Sieve
tube members: end walls contain sieve
plates that allow the flow of fluid from one cell
to the next.
 Unlike xylem, phloem cells are alive at maturity
even though they don’t have nuclei, ribosomes,
or vacuoles.
 Every sieve tube member has at least one
companion cell which has a full set of cell
organelles, so it can nurture the sieve tube
member
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Ground Tissue
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Most common type of tissue in a plant.
Main function is support
Ground tissue consists of three types of cells:
 Parenchyma
 Look like traditional plant cells
 Primary cell wall is thin and flexible
 No secondary wall
 One large vacuole
 Carries out most metabolic functions
 When turgid with water give support and shape
to plant
 Ability to divide and differentiate into other cell
types when a plant has been injured
 Collenchyma
 Unevenly
thickened primary cell walls
 No secondary cell walls
 Mature collenchymal cells are alive
 Function is to support the growing stem
 Sclerenchyma
 Very
thick primary & secondary cell walls that
are fortified with lignin
 Function is to support the plant
 Two forms:
 Fibers: long, thing, fibrous, occur in bundles
 Sclerids: short, irregular shape
Plant Organs
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Plants have three basic organs:
 Roots
 Stems
 Leaves
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Roots
 Absorbs nutrients from soil
 Anchors the plant
 Stores Food
 Root
surfaces are covered by epidermis which
is modified for absorption
 Root hairs: Skinny extensions from the
epidermal cells that extend out and increase
surface area
 Cortex:
parenchymal cells that contain plastids
for storage of starch and other materials
 Stele:
Vascular cylinder of the root made of
xylem and phloem covered by a layer of
pericycle which gives rise to lateral roots
 Endoderm:
Tightly packed layer of cells
surrounding the stele. Selects what minerals
enter the stele and the body of the plant
 Types
of roots:
 Taproot:
single, large root that gives rise to
lateral roots called branch roots
 Taproot is the primary root in many dicots
and some go deep in soil for water
 Fibrous
Root System: Common in monocots
and hold plant firmly in place
 Adventitious
Roots: Rise above ground and
help support the plant
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Stems
 Vascular tissue called vascular bundles run through
stems
 Vascular bundles have xylem facing outward and
phloem facing inward, with meristem tissue
between the two.
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Monocots have vascular bundles scattered
throughout the stem
Dicots have vascular bundles formed in a ring on the
edge of the stem
Ground tissue of the stem is made of parenchymal
tissues modified for storage called cortex and pith
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Leaves
 Designed to maximize sugar production and limit
water loss
 Epidermis is covered with waxy material called
cutin to minimize water loss
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Guard cells: control opening of stomates
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Inner section of leaves are made of palisade and
spongy mesophyll cells used for photosynthesis
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Vascular bundles (also called veins) located in the
mesophyll carry water and nutrients from the soil to
the leaves
 Vascular bundles can also carry sugar from leaves
to other parts of the plant
Plant Growth
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Meristems: embryonic tissue that continually divides,
creating new cells
 Plant growth is based on meristems
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Primary Growth: Elongation of the plant down into soil
and up into the air
 Apical Meristems are responsible for primary growth
and are located at tips of roots and in buds of shoots
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Secondary Growth: Increase in girth
 Lateral Meristems are responsible for secondary
growth
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Growth in length is concentrated at the root’s tip
 There are three zones:
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Zone of Cell Division
 Meristem cells that are actively dividing
 Produce new cells that extend down into soil
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Zone of Elongation
 Cells elongate
 Push root cap down into soil
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Zone of Maturation
 Cells undergo specialization
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Root Cap: Protects root tip by secreting substance
that helps digest earth so the root tip can grow into
soil