Chapter 23 - Roots, Stems, & Leaves

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Specialized Organs & tissues in plants – plants do
not have organ systems – Fig. 23-2
A. Roots – anchors plant, takes up water and
minerals, provides protection from bacteria &
fungi, some specialized for food storage
B. Stems - provide support, transport substances,
provide protection
C. Leaves – site of photosynthesis, prevent water
loss (guard cells & cuticle), area of gas exchange
D. Dermal tissue – “skin” of plant, outermost layer
1. Single layer of epidermal cells
2. Cuticle – waxy layer that slows down water loss
3. Trichomes – speialized cells that provide
protection
4. Root hairs – specialized for water absorbtion
5. Guard cells – found on the underside of a leaf,
open & close – fig. 23-19
E. Vascular tissue – “bloodstream” of plant,
specialized for transport
1.
Xylem – transports water one way – from root to
leaves
a.
b.
c.
2.
Composed of tracheids and vessel elements
Xylem cells are dead and hollow
Provide support (most of the cells of a tree trunk are
dead xylem cells)
Phloem – transports water and minerals in two
directions
a.
b.
Composed of sieve tube elements and companion
cells
cells are living
F. Ground tissue – most abundant tissue; found
between dermal and vascular tissue – Fig. 23-4
1.
2.
3.
4.
5.
Parenchyma – thin walled; function mainly in
photosynthesis and storage
Collenchyma – thick walled, provide support,
flexible
Sclerenchyma – thick walled, provide support,
very rigid cell walls
Where would you expect to find more
scherenchyma – in the leaves or the stem of a
plant?
Where would you expect to find more
parenchyma – in the leaves or the stem of a plant?
Meristematic tissue – “growth” tissue; made up of
cells that undergo mitosis and cell division
frequently – Fig. 23-5
1.
Meristems – where cell division takes place; found
only at specific locations
a. Apical meristem – present in growing tips of stems
and roots; accounts for an increase in length
b. Cambium – increases thickness of stems & roots;
gives rise to some protective (cork) & vascular
tissue
2.
Not all plant cells or tissue are capable of
producing new plant parts, growth is always
associated with the presence of meristematic
tissue
**** Except for meristematic tissue,
all other tissues are found
continuously throughout plant
organs.****
A. Types
1. primary root – 1st structure to emerge from a seed
2. Secondary root – roots formed from tissues of
B. Systems
1. taproot –
primary root that
grows longer and
thicker than
other roots
2. fibrous –
numerous roots
that branch to
such an extent
that no single root
grows larger than
the rest
B. Systems
3. adventitous –
roots that grow
from stems or
leaves (ex. Ivy &
Spanish moss)
http://www.youtube.
com/watch?v=fPT
J3qD1ikk (root
growth)
C. Root Structure and Growth – Fig. 23-7
1. Made up of all tissue types
1.
2.
3.
2.
Epidermis & endodermis are dermal tissues
Cortex is ground tissue
Vascular cylinder is vascular tissue
Roots are divided into various “zones”
a.
b.
c.
d.
Root cap – protects meristematic tissue
Meristematic zone – actively dividing cells
Elongation zone – cells enlarge
Maturation zone – differentiation 9cellular
specialization)
C. Root Functions – anchor, absorb water and minerals
1.
Nutrients in the soil are needed by the plant in order
for it to be healthy
2. Movement of minerals and water – both active
transport & osmosis are involved in movement from
soil to vascular cylinder
a.
b.
c.
d.
Minerals are actively transported from a low concentration
to a high concentration, requires energy
This causes a difference in water between the root and soil
Therefore, water moves from a high concentration in the
soil to a low water concentration in the cells
Casparian strip – waterproof substance that keeps
substances from “squeezing” between cells of endodermis;
allows endodermis to keep some substances out of vascular
cylinder; ensures one way movement into cylinder
2. Movement of minerals and water - (con’t)
http://www.youtube.com/watch?v=Yli0FcsQmuI&feat
ure=related
e. Root pressure – Fig. 23-10
1. created by one way movement of water & minerals
2. root cells don’t expand, so as water keeps moving
in it has nowhere to go but up (remember cohesion
& adhesion)
3. Root pressure only accounts for water to rise
approx. 1m
Basic function is to support and transport water and
minerals from the soil to the leaves
A. Monocot and Dicot Stems – Fig. 22-25, 23-12
1.
2.
Monocot – vascular bundles are scattered; ground
tissue is fairly uniform
Dicot – vascular bundles are arranged in a ring;
ground tissue makes up pith & cortex
B. Primary growth – increase in length caused by cell
division in apical meristem; Fig. 23-13
C. Secondary growth – increase in width caused by
cell division from meristematic tissue found in
vascular cambium & cork cambium – Fig. 23-14
1.
2.
1.
Vascular cambium produces new xylem & phloem
Wood is formed as xylem cells die each year and form
layers or “rings”
a. Heartwood – older xylem that no longer conducts
water but does provide support
b. Sapwood – active xylem that conducts water
Bark – made up of phloem, cork cambium, & cork;
cork cambium produces cork which helps protect the
stem – Fig. 23-15
C. Secondary growth (con’t)
C. Secondary growth (con’t)
Leaves (most) are specialized for photosynthesis
A. Structure – Fig. 23-17
1.
2.
Flat, broad to increase surface area exposed to the
sun
Arrangement – also maximizes exposure to the sun
B. Internal function & structure – Fig. 23-18, & 23-19
a.
b.
c.
Cuticle – waxy outermost layer, protects & slows down water
loss
Epidermis – clear, with little to no pigment
a.
Stomates – exchange of oxygen and carbon dioxide; guard
cells regulate opening & closing of stomates to balance
water loss with rates of photosynthesis
Guard cells
B. Internal function & structure – Fig. 23-18, &
23-19
c. Mesophyll - two types
1. palisade mesophyll – tightly packed; cells contain
many chloroplasts
2. spongy mesophyll – large air spaces between cells;
fewer chloroplasts
Mesophyll
B. Internal function & structure – Fig. 23-18, &
23-19
d. Veins – made up of xylem and phloem tissue
Veins
A. Transpiration – the evaporation of water from
plant surfaces; most takes place on leaves
through opened stomates – Fig. 23-22
http://www.youtube.com/watch?v=At1BJJDcXhk
B. Water transport
1. Capillary action – involves cohesion & adhesion –
Fig. 23-21
2. root pressure – osmotic pressure in roots caused
by a buildup of solutes
3. transpirational pull – the main process bys
which water moves through the xylem of a plant
B. Water transport (con’t)
3. Transpirational pull – the main process bys which
water moves through the xylem of a plant
a. Water moves molecules exit air spaces in
spongy mesophyll to atmosphere – creates
negative pressure
b. Lost water in air spaces replaced by water
from xylem tissue
c. Cohesion/adhesion keep water moving up
from the roots
d. Is water pulled or pushed in transpiration?
4. Regulation of transpirational is controlled by the
opening & closing of stomates, which depends on
light; temp; and water availability
C. Nutrient transport – involves the movement of
sugars from one area of a plant to another
1. Sugars move from a source to a sink
C. Nutrient transport – (con’t)
2. Pressure flow hypothesis
http://www.youtube.com/watch?v=-b6dvKgWBVY
a. Sugars are actively transported from a
“source” cell into sieve tubes: this causes water
to follow by osmosis (from xylem to phloem)
b. Seive cells in “sink” area lose sugar; this
causes water to move from phloem tissue to
xylem
c. This water pressure gradient causes liquid in
phloem to flow

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