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Roots, Stems & Leaves
Roots, Stems & LeavesSpecialized Organs & tissues in plants – plants do not have organ systems – Fig. 23-2A. 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
Roots, Stems & Leaves
Roots, Stems & Leaves
Roots, Stems & LeavesD. Dermal tissue – “skin” of plant, outermost
layer1. Single layer of epidermal cells2. Cuticle – waxy layer that slows down
water loss3. Trichomes – speialized cells that provide
protection4. Root hairs – specialized for water
absorbtion5. Guard cells – found on the underside of
a leaf, open & close – fig. 23-19
Dermal Tissue
Roots, Stems & LeavesE. Vascular tissue – “bloodstream” of plant,
specialized for transport1. Xylem – transports water one way – from
root to leavesa. Composed of tracheids and vessel elementsb. Xylem cells are dead and hollowc. Provide support (most of the cells of a tree
trunk are dead xylem cells)
2. Phloem – transports water and minerals in two directionsa. Composed of sieve tube elements and
companion cellsb. cells are living
Vascular Tissue
Vascular Tissue
Roots, Stems & LeavesF. Ground tissue – most abundant tissue;
found between dermal and vascular tissue – Fig. 23-41. Parenchyma – thin walled; function mainly
in photosynthesis and storage2. Collenchyma – thick walled, provide
support, flexible3. Sclerenchyma – thick walled, provide
support, very rigid cell walls4. Where would you expect to find more
scherenchyma – in the leaves or the stem of a plant?
5. Where would you expect to find more parenchyma – in the leaves or the stem of a plant?
Ground Tissue
Roots, Stems & LeavesMeristematic tissue – “growth” tissue; made up
of cells that undergo mitosis and cell division frequently – Fig. 23-51. Meristems – where cell division takes place;
found only at specific locationsa. Apical meristem – present in growing tips of stems
and roots; accounts for an increase in lengthb. 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
Meristamic Tissue
Meristamic Tissue
**** Except for meristematic tissue, all other tissues are found continuously throughout plant organs.****
Roots – Fig. 23-6A. Types
1. primary root – 1st structure to emerge from a seed
2. Secondary root – roots formed from tissues of
Roots – Fig. 23-6B. Systems1. taproot – primary root that grows longer and
thicker than other roots2. fibrous – numerous roots that branch to such an extent that no single root grows larger than
the rest
Roots – Fig. 23-6B. Systems3. adventitous – roots that grow from stems or leaves (ex. Ivy & Spanish moss)
http://www.youtube.com/watch?v=fPTJ3qD1ikk
(root growth)
Roots – Fig. 23-6C. Root Structure and Growth – Fig. 23-7
1. Made up of all tissue types1. Epidermis & endodermis are dermal tissues2. Cortex is ground tissue3. Vascular cylinder is vascular tissue
2. Roots are divided into various “zones”a. Root cap – protects meristematic tissueb. Meristematic zone – actively dividing cellsc. Elongation zone – cells enlarged. Maturation zone – differentiation 9cellular
specialization)
Roots – Fig. 23-6
Roots – Fig. 23-6C. Root Functions – anchor, absorb water and
minerals1. Nutrients in the soil are needed by the plant in
order for it to be healthy2. Movement of minerals and water – both active
transport & osmosis are involved in movement from soil to vascular cylindera. Minerals are actively transported from a low
concentration to a high concentration, requires energy
b. This causes a difference in water between the root and soil
c. Therefore, water moves from a high concentration in the soil to a low water concentration in the cells
d. 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
Roots – Fig. 23-6
Roots – Fig. 23-62. Movement of minerals and water -
(con’t)http://www.youtube.com/watch?v=Yli0FcsQmuI&feature=related
e. Root pressure – Fig. 23-101. created by one way movement of water & minerals2. 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
Stems – Fig. 23-11Basic function is to support and transport
water andminerals from the soil to the leaves
Stems – Fig. 23-11A. Monocot and Dicot Stems – Fig. 22-25,
23-121. Monocot – vascular bundles are scattered;
ground tissue is fairly uniform2. Dicot – vascular bundles are arranged in a
ring; ground tissue makes up pith & cortex
Stems – Fig. 23-11B. Primary growth – increase in length
caused by cell division in apical meristem; Fig. 23-13
Stems – Fig. 23-11C. Secondary growth – increase in width
caused by cell division from meristematic tissue found in vascular cambium & cork cambium – Fig. 23-141. Vascular cambium produces new xylem &
phloem2. 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 supportb. Sapwood – active xylem that conducts water
3. Bark – made up of phloem, cork cambium, & cork; cork cambium produces cork which helps protect the stem – Fig. 23-15
Stems – Fig. 23-11C. Secondary growth (con’t)
Stems – Fig. 23-11C. Secondary growth (con’t)
Leaves Leaves (most) are specialized for
photosynthesis A. Structure – Fig. 23-17
1. Flat, broad to increase surface area exposed to the sun
2. Arrangement – also maximizes exposure to the sun
Leaves B. Internal function & structure – Fig. 23-18, & 23-19
a. Cuticle – waxy outermost layer, protects & slows down water loss
b. Epidermis – clear, with little to no pigmenta. Stomates – exchange of oxygen and carbon
dioxide; guard cells regulate opening & closing of stomates to balance water loss with rates of photosynthesis
c.
Leaves Guard cells
B. Internal function & structure – Fig. 23-18, & 23-19
c. Mesophyll - two types1. palisade mesophyll – tightly packed; cells contain many chloroplasts2. spongy mesophyll – large air spaces between cells; fewer chloroplasts
Mesophyll
Leaves B. Internal function & structure – Fig. 23-18, & 23-19
d. Veins – made up of xylem and phloem tissue
Leaves Veins
TransportA. 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=At1BJJDcXhkB. 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
Transport
TransportB. 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
TransportC. Nutrient transport – involves the
movement of sugars from one area of a plant to another 1. Sugars move from a source to a sink
TransportC. 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