Transcript Roots, Stems and Leaves

Roots, Stems and
Leaves
Chapter 23 p. 578
Structure of Seed Plants
• The cells of seed plants are
organized into different
tissues and organs.
• The three principal organs
of seed plants are:
–Roots
–Stems
–Leaves
Roots
• Absorb water and
dissolved nutrients from
moist soil.
• Anchor Plants in the
ground
• Hold plants upright and
prevents them from being
knocked over by wind
and rain.
• They grow and develop
complex branching
networks that penetrate
the soil and grow
between soil particles.
Stems
• Supports the plant body.
• Transports nutrients
among different parts of
the plant.
• Hold leaves up to the
sun.
• To support the weight of
tall plants, stems have
modified vascular tissue.
• Provides the
passageway for xylem
and phloem to transport
water and nutrients
throughout the plant.
Leaves
• Principle organs for
photosynthesis.
• Broad, flat surfaces help
increase the amount of
sunlight absorbed by
plants.
• Stomata are adjustable
pores that help conserve
water while allowing
oxygen and carbon
dioxide to enter and leave
the leaf.
Types of Plant Tissues
• Plants have specialized tissue systems.
• Plants consist of four tissue systems:
– Meristematic Tissue
– Dermal Tissue
– Vascular Tissue
– Ground Tissue
Meristematic Tissue
• Found ONLY in the tips
of shoots and roots.
• The ONLY plant tissue
that produces new cells
by mitosis.
• Site of rapid cell division.
• The Apical Meristem is a
group of undifferentiated
cells that divide to
produce increased length
of stems and roots.
Lateral Meristems
• Lateral Meristem: cylinders of dividing
cells along the length of roots and stems
and are responsible for secondary
growth (increase in width/girth).
Dermal Tissue
• The outer covering of a plants.
• Typically consists of a single
layer of Epidermal Cells.
• Cuticle – thick, waxy layer that
protects against water loss and
injury.
• Some have Trichomes –
protect the leaf from water
loss or secrete toxic
substances and make it look
fuzzy.
• Also includes root hairs,
guard cells, and stomata.
Vascular Tissue
• Transport water
and nutrients
throughout the
plant.
• Consists of two
major types:
– Xylem
– Phloem
Xylem
• Made of Tracheids – long, narrow cells
with walls that are impermeable to water.
• Angiosperms have a xylem called a
Vessel Element.
– Much wider than tracheids and allow for
greater movement.
Phloem
• The main phloem cells are Sieve Tube
Elements.
– Are arranged end to end to form sieve tubes.
• Materials can move through holes in the tubes
from one adjacent cell to another.
• Companion Cells are phloem cells that
surround sieve tube elements.
• Support the phloem cells and aid
in the movement of substances
in and out of the phloem stream.
Ground Tissue contains
3 Main Plant cell types:
• The cells that lie between dermal and
vascular tissue.
• Parenchyma – thin cell wall and large central
vacuoles, site of most photosynthesis.
• Collenchyma – Strong, flexible cell walls,
used for support (thick ridges in celery).
• Sclerenchyma – Extremely thick, rigid cell
walls, make ground tissue tough and strong.
Dermal Tissue
Tissue Systems
Review Questions…
• 1. List the three tissue systems of plants.
• 2. Describe how each tissue is distributed in
stems, tissues and leaves.
• 3. What is the function of meristematic tissue?
• 4. What two cell types make up the xylem?
• 5. What two cell types make up the phloem?
• 6. In a stem that needs to support heave leaves,
what type of ground tissue might you expect to
find?
• 7. The vascular system of a plant has been
compared to the circulatory system of a human.
How are they similar? Different?
Types of Roots
• The two main types of roots are Taproots and
Fibrous Roots.
• Taproots are found mainly in dicots.
– Have a central primary root and generally
grow deep into the soil.
• Fibrous Roots are found mainly in monocots.
– Branch to such an extent that no single root
grows larger than the rest.
– Typically help topsoil from being washed
away.
Types of Roots
Root Structure and Growth
• A mature root has an outside layer, the
epidermis, and a central cylinder of vascular
tissue.
• Between these two lies a large area of ground
tissue.
• Root Hairs – produce a large surface area
through which water can enter the plant.
• Cortex – spongy layer of ground tissue.
• Endodermis – completely encloses vascular
tissue in a central region called the Vascular
Cylinder.
• Root Cap – protects cells in the apical meristem
while they grow.
Root Structure
Root Functions
• Roots anchor a plant in
the ground and absorb
water and dissolved
nutrients from the soil.
• Plants uptake necessary
nutrients.
• Active transport of
minerals.
• Movement into vascular
tissue.
• Root pressure.
Review Questions
• 1. Compare a taproot and a fibrous root.
• 2. How are tissues distributed in plant
roots?
• 3. Describe the two main functions of
roots.
• 4. How is osmosis involved in the
absorption of water and nutrients?
• 5. Why is it important that the root
endodermis permit only a one-way
passage of materials?
23-3: STEMS
• In general, stems have three important
functions:
– They produce leaves, branches and flowers.
– They hold leaves up in the sunlight.
– They transport substances between roots and
leaves.
• Most plants also contain nodes where leaves
branch from.
• Buds contain undeveloped tissue that can
produce new stems and leaves.
Herbaceous Stems:
• Soft, fleshy stems that produce little or no
secondary growth.
• Partially supported by the water that fills
their cells. The water in each cell causes
the cell to be pressed against the cell wall.
This creates a force called turgor
pressure, which makes the cell rigid.
Woody Stems:
• Many perennial dicots and conifers produce
thick, woody stems that support tall upright
growth.
• The outer portion of woody stems develops bark,
which is composed of phloem and cork
cambium cells, and helps prevent damage to
the stem.
• Lenticels: tiny openings in the bark which
permit air to pass through the epidermis to
green-colored cells.
Stems
Monocot and Dicot Stems
• In monocots, vascular bundles are scattered
throughout the stem.
• In dicots and most gymnosperms, vascular
bundles are arranged in a cylinder.
Monocot Stems
• The cross section of
young monocot stem
shows all three tissue
systems clearly.
• Has a distinct epidermis
that encloses vascular
bundles, containing
xylem and phloem.
• These bundles are
scattered throughout the
ground tissue.
Dicot Stems
• Young dicot stems have
vascular bundles, but
they are generally
arranged in an organized,
ring-like pattern.
• The parenchyma cells are
know as pith.
• These tissue patterns
become more complex as
the plant grows larger
and the stem increases in
diameter.
Growth of Stems
• Growth at the end of the plant is primary growth.
• Primary growth of stems is produced by cell divisions in the apical
meristem (in all seed plants).
• When stems increase in width it is secondary growth.
• In conifers and dicots, secondary growth takes place in lateral
meristematic tissues called the vascular cambium and cork
cambium.
– This tissue forms between the xylem and phloem of the
individual vascular bundles.
– Once the tissue forms it divides to produce xylem cells toward
the center of the stem and phloem cells toward the outside.
– These form the bark and wood of a mature stem.
Growth of Stems
Formation of Wood
• Wood is actually layers of
xylem.
• These can build up year
after year, layer on layer.
• The older xylem becomes
Heartwood.
• Heartwood is surrounded
by Sapwood.
• The alternation of dark
wood and light wood
forms tree rings.
• These rings correspond
to the age of the tree.
Formation of Bark
• Bark includes all of the tissues
outside the vascular cambium.
• These tissues include phloem,
the cork cambium, and cork.
• Phloem grows to
accommodate the larger size
of the tree.
• Tissue is forced outward.
• Cork cambium prevents the
stem from splitting and
breaking.
• The outermost cork cells are
usually dead which is why
bark cracks and breaks.
Adapted Stems
• Tuber – stems grows underground for food
storage.
– Ex: potatoes
• Bulb – made up of a central stem surrounded by
short thick leaves.
– Ex: Amaryllis
• Rhizome – A horizontal, underground stem.
• Ex: Ginger
• Corm – A thickened stem that stores food.
– Ex: Gladiolus
Adapted Stems
Review Questions…
• 1. How do the functions of a stem relate to the
roots and leaves of a plant?
• 2. Describe how the arrangement of vascular
bundles differs between monocot and dicot
stems.
• 3. Define primary and secondary growth.
• 4. Which type of growth involves division of the
apical meristem?
• 5. How do heartwood and sapwood differ?
23-4: Leaves
Leaf Structure
• The structure of a leaf is optimized for
absorbing light and carrying out
photosynthesis.
• Leaves can differ in shape but have the same
structural features.
• Blades are thin flattened sections.
• Petiole – thin stalk that attaches the blade to the
stem.
• The vascular tissue of leaves are connected
directly to the vascular tissue of the stems.
• Xylem and Phloem tissues are gathered
together into bundles that run from the stem into
the petiole.
Leaf Structure
Leaf Function
• Photosynthesis – occurs in specialized ground tissue
known as MESOPHYLL.
• Palisade Mesophyll – closely packed cells that absorb
most of the sunlight.
• Spongy Mesophyll – Loose tissue that connects to the
exterior through Stomata.
• Stomata – pore-like openings for gas exchange.
• Guard cells – control the opening and closing of
stomata.
• The top surface of the leaf is known as the upper
epidermis and the bottom is the lower epidermis.
Secretes a layer of cutin (forms the waxy cuticle) which
slows evaporation from the leaf blade.
Transpiration
• Transpiration is the
loss of water from a
plant through its
leaves.
• This water is replaced
by water drawn into
the leaf through
xylem vessels in the
vascular tissue.
Gas Exchange
• 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.
Review Questions…
• 1. Describe how the structure of a leaf is
optimized for light absorption.
• 2. What factors regulate the opening and
closing of guard cells?
• 3. Are stomata more likely to be open or
closed on a hot day? Explain your
answer.
• 4. Describe the cell types found within a
typical leaf.
Transport in Plants
• The combination of root pressure, capillary
action, and transpiration provides enough
force to move water through the xylem tissue of
even the largest plant.
• Capillary Action – the tendency of water to rise
in a thin tube.
• Adhesion – tendency of water to form hydrogen
bonds.
• Transpiration – pulls water upwards.
– Too much transpiration can cause excess water loss
and wilting.
Transport of Water
Nutrient Transport…
• The phloem is responsible for transporting
nutrients throughout the plant.
• When nutrients are pumped into or
removed from the phloem system, the
change in concentration causes a
movement of fluid in that same direction.
• As a result, phloem is able to move
nutrients in either direction to meet the
nutritional needs of the plant.
Review Questions…
• 1. What three processes work together to
cause water to flow upward through a
plant?
• 2. Why is capillary action insufficient to
move water through a plant?