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 energyb. This causes a difference in water between the root and

soilc. Therefore, water moves from a high concentration in

the soil to a low water concentration in the cellsd. 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