Download Secondary growth increases the girth of woody plants

PLANT STRUCTURE
AND FUNCTION
Life - Plants
Copyright © 2009 Pearson Education, Inc.
Evolution and types of plants
Since the earth was once Plants can be placed
covered in water, plants
under two groups
had to make three
 Vascular- having true
adaptations to survive on
roots, leaves, and stems
land
 The ability to prevent
water loss
 The ability to reproduce
in the absence of water
 The ability to absorb
and transport nutrients
 Ex. ferns, conifers,
flowering plants
 Nonvascular- not having
true roots, leaves, and
stems
 Ex. mosses, liverworts,
hornworts
Vascular Plants can be divided into two groups
Seedless Plants
Made up of ferns and
plants closely associated
with ferns
Seed Plants
Two types of seed plants
 Gymnosperms- which
includes pine trees,
produce seeds that are not
encased in fruit
 Angiosperms- aka
flowering plants, produce
seeds within a protective
fruit
The two main groups of angiosperms are the
monocots and the dicots
 Monocots (Ex. Lilies, onions, corn, grasses, wheat)
– One cotyledon
– Parallel leaf venation
– Scattered vascular bundles
– Flower parts in 3s or multiples of 3
– Fibrous roots
The two main groups of angiosperms are the
monocots and the eudicots
 Dicots—most plants are eudicots (Ex. Trees)
– Two cotyledons
– Branched leaf venation
– Ring of vascular bundles
– Flower parts in 4s or 5s (or multiples)
– Taproot system
A typical plant body contains three basic organs:
roots, stems, and leaves
 Plants absorb water and minerals from soil through
roots
 Plants absorb the sun’s energy and carbon dioxide
from the air through shoots (stems and leaves)
 Plant roots depend on shoots for carbohydrates
produced via photosynthesis
 Plant shoots depend on roots for water and minerals
Copyright © 2009 Pearson Education, Inc.
A typical plant body contains three basic organs:
roots, stems, and leaves
 Plant roots
– Anchor plant
– Absorb water and minerals
– Store food
 Plant shoots
– Stems, leaves, and reproductive
structures
– Stems provide support
– Leaves carry out photosynthesis
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Terminal bud
Leaf
Shoot
system
Blade
Flower
Petiole
Axillary bud
Stem
Node
Internode
Root
hairs
Root
hair
Taproot
Root
system
Epidermal cell
Many plants have modified roots, stems, and
leaves
 Modifications of plant parts are adaptations for
various functions
– Food or water storage
– Asexual reproduction
– Protection
– Climbing
– Photosynthesis
Copyright © 2009 Pearson Education, Inc.
Many plants have modified roots, stems, and
leaves
 Root modifications
– Food storage
– Large taproots store starches
– Examples include carrots, turnips, sugar beets,
sweet potatoes
Many plants have modified roots, stems, and
leaves
 Stem modifications
– Stolon—asexual
reproduction
– Rhizomes—storage,
asexual reproduction
– Tubers—storage, asexual
reproduction
– Cactus stem—water
storage and
photosynthesis
Many plants have modified roots, stems, and
leaves
 Leaf modifications
– Protection
– Cactus spine, Thorns
– Climbing
– Pea plant tendril
Three tissue systems make up the plant body
 Dermal tissue
– tightly packed
epidermis cells
– First line of defense
– Waxy layer called
cuticle
– reduces water loss
Three tissue systems make up the plant body
 Vascular tissue
– Composed of xylem and phloem
– Xylem transports water from roots to
leaves
– Phloem transports glucose made in
leaves to nonphotosynthetic parts of
the plant
– Arranged in bundles
 Ground tissue
– Leaf ground tissue is called mesophyll
– Bulk of plant body
– Food production and storage
(because it contains chloroplasts)
Review of 3 types of tissues
Plant cells and tissues are diverse in structure and
function
 Plants cells have three
structures that
distinguish them from
animals cells
– Chloroplasts used in
photosynthesis
– A large, fluid-filled
vacuole
– A cell wall composed
of cellulose
Transpiration
 Transpiration – water is absorbed through roots
(specifically root hairs); as water evaporates from
the stomata openings it pulls water up through the
plant from a combination of cohesion (water
attracted to itself) and adhesion (water attracted to
the tree)
 Transpiration demo
PLANT GROWTH
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Primary growth lengthens roots and shoots
 Plant growth is indeterminate
– Growth occurs throughout a plant’s life
– Plants are categorized based on how long they live
– Annuals complete their life cycle in one year
– Biennials complete their life cycle in two years
– Perennials live for many years
 Animal growth is determinate
– Growth stops after a certain size is reached
Copyright © 2009 Pearson Education, Inc.
Primary Growth and Secondary Growth
 Primary growth is the vertical growth of a plant
(shoot growing up and root growing down).
 Secondary growth is an increase in diameter of
roots and shoots (getting thicker).
 This growth does not occur at all parts of the body
like in animals. This is because not all cells in a plant
divide.
 Meristem – small, unspecialized cells that divide
continually
Meristem
 There are two types of meristem cells.
1. Apical meristem – located at the tips of roots and shoots

Responsible for primary growth
2. Lateral meristem – cells responsible for creating more
xylem / phloem and bark

Responsible for secondary growth
Primary growth
allows roots
to push downward
through the
soil and shoots to
grow upward
Terminal bud
Axillary buds
Arrows =
direction
of growth
Root
tips
Secondary growth increases the girth of woody plants
Year 1
Early Spring
Year 1
Late Summer
Year 2
Late Summer
Key
Dermal tissue system
Ground tissue system
Vascular tissue system
Shed
epidermis
Primary
xylem
Vascular
cambium
Primary
phloem
Epidermis
Cortex
Secondary
xylem (wood)
Cork
Cork
cambium
Secondary
phloem
Bark
Secondary xylem
(2 years’ growth)
Secondary growth increases the girth of woody plants
Vascular cambium produces
cells in two directions
– xylem produces wood
toward the interior of the
stem
– The xylem is responsible for
water transport in plant
– Moves water through
transpiration
– phloem produces the inner
bark toward the exterior of
the stem
– Living tissue of the tree that
is responsible for moving
sugar throughout the plant
Secondary growth increases the girth of woody
plants
 Cork cambium produces
the outer bark, which is
composed of cork cells
Copyright © 2009 Pearson Education, Inc.
Secondary growth increases the girth of woody
plants
 Wood annual rings show layers of xylem
– In temperate regions, periods of dormancy stop growth
of secondary xylem
– Rings occur in areas when new growth starts each year
 The bark (phloem and cork) is sloughed off over
time
Secondary growth increases the girth of woody
plants
 Part of the Xylem
 Sapwood transports water
 Heartwood stores resins and wastes