Download Plant tissues and structures

Plant Structures
Roots, Stems, and Leaves
Chapter 23
Types Roots
Taproots
• Found in dicots
• Long, thick root
• Hickory and oak trees
Fibrous roots
• Found in monocots
• No single root larger than
any other
• Many thin roots
Root Structure
– Outside layer
– Epidermis
Root hairs
Cortex
– Central cylinder –
vascular system
– Root Cap – cellular
production
Key role in
water/mineral
transport
Root Functions
–Anchor plant
–Absorb water
–Absorb nutrients
Essential Plant Nutrients
• Plant Nutrient Uptake
 Soil type determines
plant type
• Plant requirements
 Oxygen, CO2
 Nitrogen
 Phosphorus
 Postassium
 Magnesium
 Calcium
 Trace elements
Uptake of Plant Nutrients
Active Transport in Plants
– Root hairs use ATP
Pump minerals from soil
Causes water molecules to
follow by osmosis
Vascular Cylinder
– Casparian Strip – water
retention
Root Pressure
– Forces water up into the
plant
STEMS
• Stem Structure
– Produce leaves, branches,
and flowers
– Hold leaves up
– Transport substance
between roots and leaves
• Essential part of transport
system
• Function in storage and
photosynthesis
Anatomy of a Stem
• Xylem and phloem – major
tubule systems
 Transport water and
nutrients
• Composed of three tissue
layers
 Contain nodes – attachment
for leaves
 Internodes – regions
between the nodes
 Buds – undeveloped tissue
Stem Types
Monocot – vascular
bundles are scattered
throughout
Distinct epidermis
Dicot – vascular tissue
arranged in a cylinder
– Pith – parenchyma cells
inside the ring
Stem Growth
• Primary growth – new cells
produced at the root tips and
shoots
 Increases the length
• Secondary growth – increase
in stem width
 Vascular cambium – produces
tissue and increases thickness
 Cork cambium – produces outer
covering of stems
Formation of Vascular Cambium
– Xylem and phloem
bundles present
initially
– Secondary growth
initiates production
of a thin layer
– The vascular
cambium divides
Produces new xylem
and phloem
Leaves
• Main site of
photosynthesis
• Consist of:
Blade – thin flattened
section
Petiole – stalk that
attaches stem to blade
• Covered by epidermis
and cuticle
Create water proof
barrier
Leaf Functions
• Photosynthesis – occurs
in the mesophyll
Palisade mesophyll –
absorb light
Spongy mesophyll –
beneath palisade level
Stomata – pores in the
underside of the leaf
Guard Cells – Surround
the stomata
Transpiration
• Loss of water through its
leaves
• How does the water that is
lost through transpiration
get replaced?
Gas Exchange
• Take in CO2 & release O2
• Can also do the opposite –
How?
• Gas exchange takes place at
the stomata
 Not open all the time
• Stomata is controlled by
water pressure in guard cells
Plant Tissue Systems
• DERMAL TISSUE
• VASCULAR TISSUE
• GROUND TISSUE
Dermal Tissue
• protective outer covering of a plant.
• young plants consists of a single layer of cells, called the
epidermis
• cuticle
 thick waxy layer protects against water loss
• older plants
dermal tissue may be many cell layers deep
may be covered with bark
Vascular Tissue
• supports the plant body
• transports water and nutrients
throughout the plant
• Xylem
 water-conducting tissue
• Phloem
 a tissue that carries dissolved food.
Both xylem and phloem consist of long,
slender cells that connect almost like
sections of pipe, as shown in the figure.
Xylem: Tracheids
• all seed plants have xylem
cells called tracheids
• as they mature, tracheids
die, leaving only their cell
walls
 cell walls contain lignin,
a complex molecule
that gives wood much
of its strength.
Xylem: Tracheids
• openings in the walls connect
neighboring cells
• allow water to flow from cell to
cell
Xylem: Vessel Elements
• wider than tracheids and are
arranged end to end on top of
one another like a stack of tin
cans
• after they mature and die, cell
walls at both ends are left with
slit-like openings through which
water can move freely
Xylem: Sieve Tube
Elements
• xylem cells, phloem cells
are alive at maturity
• arranged end to end,
forming sieve tubes.
 end walls have many
small holes through
which nutrients move
from cell to cell
Xylem: Sieve Tube
Elements
As sieve tube elements mature, they
lose their nuclei and most other
organelles. The remaining organelles
hug the inside of the cell wall and are
kept alive by companion cells.
Phloem: Companion Cells
• cells that surround
sieve tube elements
• keep their nuclei and
other organelles
through their lifetime
Ground Tissue
• produces and stores sugars
• contributes to physical support of the plant
• Three types of ground tissue
parenchyma (thin cell walls)
collenchyma (thicker cell walls)
sclerenchyma (thickest cell walls)
Plant Growth and Meristems
Meristems
• regions of unspecialized cells in which mitosis produces
new cells that are ready for differentiation
• found in places where plants grow rapidly, such as the tips
of stems and roots
Apical Meristems
• Because the tip of a stem or root is
known as its apex
• unspecialized cells produced in apical
meristems divide rapidly as stems
and roots increase in length.
Apical Meristems
• At first, the new cells that are pushed out of meristems look
very much alike
• They are unspecialized and have thin cell walls
• Gradually, they develop into mature cells with specialized
structures and functions.
 As the cells differentiate, they produce each of the tissue
systems of the plant, including dermal, vascular, and
ground tissue.