Download 23–1 Specialized Tissues in Plants

Biology
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Chapter 23: Plants
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23–1 Specialized Tissues in Plants
Seed Plant Structure
Plant Structure
What are the three principal organs of
plants?
roots, stems, and leaves.
These organs perform functions such as the
transport of nutrients, protection, and
coordination of plant activities.
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23–1 Specialized Tissues in Plants
Seed Plant Structure
Roots:
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•
absorb water and dissolved nutrients.
•
protect the plant from harmful soil bacteria and
fungi.
anchor plants in the ground.
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23–1 Specialized Tissues in Plants
Seed Plant Structure
Stems provide:
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a support system for the plant body.
•
a transport system that carries nutrients.
•
a defense system that protects the plant
against predators and disease.
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Seed Plant Structure
Leaves:
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are a plant’s main photosynthetic systems.
•
increase the amount of sunlight plants absorb.
Adjustable pores conserve water and let oxygen and
carbon dioxide enter and exit the leaf.
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23–1 Specialized Tissues in Plants
Vascular Tissue
What specialized cells make up vascular
tissue?
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23–1 Specialized Tissues in Plants
Vascular Tissue
Vascular Tissue
Vascular tissue forms a transport system that moves
water and nutrients throughout the plant.
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23–1 Specialized Tissues in Plants
Vascular tissue is made up of xylem, a waterconducting tissue, and phloem, a food-conducting
tissue.
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23–1 Specialized Tissues in Plants
Types of Roots
Types of Roots
What are the two main types of roots?
The two main types of roots are:
•
taproots, which are found mainly in dicots,
and
•
fibrous roots, which are found mainly in
monocots.
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Types of Roots
In some plants, the primary root grows long and thick.
This primary root is called a taproot.
A carrot is an example of a taproot.
Fibrous Roots
Taproot
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23–1 Specialized Tissues in Plants
Types of Roots
Fibrous roots
branch to such an
extent that no
single root grows
larger than the
rest.
Fibrous roots are
found in grasses.
Fibrous Roots
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23–1 Specialized Tissues in Plants
The root’s surface is
covered with cellular
projections called root
hairs. Root hairs provide
a large surface area
through which water can
enter the plant.
Root Structure and Growth
Root
hairs
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23–1 Specialized Tissues in Plants
Root Functions
Root Functions
What are the different functions of roots?
Roots anchor a plant in the ground and absorb water
and dissolved nutrients from the soil.
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23–1 Specialized Tissues in Plants
Stem Structure and Function
Stem Structure and Function
What are the three main functions of stems?
Stems have three important functions:
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they produce leaves, branches and flowers
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they hold leaves up to the sunlight
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they transport substances between roots and
leaves
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Stem Structure and Function
Stems make up an essential part of the water and
mineral transport systems of the plant.
Xylem and phloem form continuous tubes from the
roots through the stems to the leaves.
This allows water and nutrients to be carried
throughout the plant.
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Monocot and Dicot Stems
Monocot and Dicot Stems
The arrangemnet of tissues in a stem differs among
seed plants.
How do monocot and dicot stems differ?
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Monocot and Dicot Stems
Monocot Stems
•
vascular bundles are scattered throughout
the stem
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23–1 Specialized Tissues in Plants
Dicot Stems
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vascular bundles
are arranged in a
ringlike pattern
Monocot and Dicot Stems
Vascular
bundles
Epidermis
Cortex
Pith
Dicot
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Leaf Structure
Leaf Structure
How does the structure of a leaf enable it to carry
out photosynthesis?
The structure of a leaf is optimized for absorbing
light and carrying out photosynthesis.
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Leaf Structure
To collect sunlight, most leaves have thin, flattened
sections called blades.
Blade
Simple leaf
Leaflet
Petiole
Bud
Stem
Compound leaf
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23–1 Specialized Tissues in Plants
Leaf Structure
Leaves are covered on the top and bottom by
epidermis.
Epidermis
Epidermis
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23–1 Specialized Tissues in Plants
Leaf Structure
The epidermis of many leaves is covered by the
cuticle.
Cuticle
Epidermis
Epidermis
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Leaf Structure
The cuticle and epidermal cells form a waterproof
barrier that protects tissues inside the leaf and limits
the loss of water through evaporation.
The vascular tissues of leaves are connected directly
to the vascular tissues of stems.
In leaves, xylem and phloem tissues are gathered
together into bundles that run from the stem into the
petiole.
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Leaf Structure
All these tissues form the veins of a leaf.
Xylem
Phloem
Vein
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23–1 Specialized Tissues in Plants
Leaf Functions
Leaf Functions
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Most leaves consist of a specialized ground
tissue known as mesophyll.
Palisade
mesophyll
Spongy
mesophyll
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Leaf Functions
The layer of mesophyll cells found directly under the
epidermis is called the palisade mesophyll. These
closely-packed cells absorb light that enters the leaf.
Palisade
mesophyll
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Leaf Functions
Beneath the palisade mesophyll is the spongy
mesophyll, a loose tissue with many air spaces
between its cells.
Spongy
mesophyll
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Leaf Functions
The air spaces connect with the exterior through
stomata.
Stomata are porelike openings in the underside of the
leaf that allow carbon dioxide and oxygen to diffuse
into and out of the leaf.
Stoma
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Leaf Functions
Each stoma consists of
two guard cells.
Guard cells are
specialized cells that
control the opening and
closing of stomata by
responding to changes
in water pressure.
Guard cells
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Leaf Functions
Transpiration
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The surfaces of spongy mesophyll cells are kept
moist so gases can enter and leave the cells
easily.
•
Water evaporates from these surfaces and is
lost to the atmosphere.
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Leaf Functions
Transpiration is the loss of water through its leaves.
This lost water is replaced by water drawn into the
leaf through xylem vessels in the vascular tissue.
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Leaf Functions
Gas Exchange
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How does gas exchange take place in a leaf?
Plant leaves allow gas exchange between air spaces
in the spongy mesophyll and the exterior by opening
their stomata.
Plants keep their stomata open just enough to allow
photosynthesis to take place but not so much that
they lose an excessive amount of water.
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Leaf Functions
Guard cells are specialized cells that control the
stomata.
Stomata open and close in response to changes in
water pressure within guard cells.
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Leaf Functions
When water pressure within guard cells is high, the
stoma open.
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Leaf Functions
When water pressure within guard cells decreases,
the stoma closes.
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Leaf Functions
Plants regulate the opening and closing of their
stomata to balance water loss with rates of
photosynthesis.
Stomata are open in daytime, when photosynthesis is
active, and closed at night, to prevent water loss.
In hot, dry conditions stomata may close even in
bright sunlight, to conserve water.
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