Roots, Stems & Leaves

Roots, Stems & Leaves Specialized Organs & tissues in plants – plants do not have organ systems – Fig. 23-2 Roots – anchors plant, takes up water and minerals, provides protection from bacteria & fungi, some specialized for food storage Stems - provide support, transport substances, provide protection Leaves – site of photosynthesis, prevent water loss (guard cells & cuticle), area of gas exchange

Roots, Stems & Leaves

Roots, Stems & Leaves

Roots, Stems & Leaves D. Dermal tissue – “skin” of plant, outermost layer Single layer of epidermal cells Cuticle – waxy layer that slows down water loss Trichomes – speialized cells that provide protection Root hairs – specialized for water absorbtion Guard cells – found on the underside of a leaf, open & close – fig. 23-19

Dermal Tissue

Roots, Stems & Leaves E. Vascular tissue – “bloodstream” of plant, specialized for transport Xylem – transports water one way – from root to leaves 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 Composed of sieve tube elements and companion cells cells are living

Vascular Tissue

Vascular Tissue

Roots, Stems & Leaves F. Ground tissue – most abundant tissue; found between dermal and vascular tissue – Fig. 23-4 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?

Ground Tissue

Roots, Stems & Leaves Meristematic tissue – “growth” tissue; made up of cells that undergo mitosis and cell division frequently – Fig. 23-5 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 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. 23-6 Types 1. primary root – 1st structure to emerge from a seed 2. Secondary root – roots formed from tissues of

Roots – Fig. 23-6 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

Roots – Fig. 23-6 B. Systems 3. adventitous – roots that grow from stems or leaves (ex. Ivy & Spanish moss) http://www.youtube.com/watch?v=fPTJ3qD1ikk (root growth)

Roots – Fig. 23-6 Root Structure and Growth – Fig. 23-7 Made up of all tissue types Epidermis & endodermis are dermal tissues Cortex is ground tissue Vascular cylinder is vascular tissue Roots are divided into various “zones” Root cap – protects meristematic tissue Meristematic zone – actively dividing cells Elongation zone – cells enlarge Maturation zone – differentiation 9cellular specialization)

Roots – Fig. 23-6

Roots – Fig. 23-6 Root Functions – anchor, absorb water and minerals Nutrients in the soil are needed by the plant in order for it to be healthy Movement of minerals and water – both active transport & osmosis are involved in movement from soil to vascular cylinder 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

Roots – Fig. 23-6

Roots – Fig. 23-6 2. Movement of minerals and water - (con’t) http://www.youtube.com/watch?v=Yli0FcsQmuI&feature=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

Stems – Fig. 23-11 Basic function is to support and transport water and minerals from the soil to the leaves

Stems – Fig. 23-11 A. Monocot and Dicot Stems – Fig. 22-25, 23-12 Monocot – vascular bundles are scattered; ground tissue is fairly uniform Dicot – vascular bundles are arranged in a ring; ground tissue makes up pith & cortex

Stems – Fig. 23-11 B. Primary growth – increase in length caused by cell division in apical meristem; Fig. 23-13

Stems – Fig. 23-11 C. Secondary growth – increase in width caused by cell division from meristematic tissue found in vascular cambium & cork cambium – Fig. 23-14 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) Stems – Fig. 23-11 C. Secondary growth (con’t)

C. Secondary growth (con’t) Stems – Fig. 23-11 C. Secondary growth (con’t)

Leaves Leaves (most) are specialized for photosynthesis A. Structure – Fig. 23-17 Flat, broad to increase surface area exposed to the sun Arrangement – also maximizes exposure to the sun

Leaves B. Internal function & structure – Fig. 23-18, & 23-19 Cuticle – waxy outermost layer, protects & slows down water loss Epidermis – clear, with little to no pigment Stomates – exchange of oxygen and carbon dioxide; guard cells regulate opening & closing of stomates to balance water loss with rates of photosynthesis

Leaves 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

Leaves B. Internal function & structure – Fig. 23-18, & 23-19 d. Veins – made up of xylem and phloem tissue

Leaves Veins

Transport 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

Transport

Transport 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

Transport Nutrient transport – involves the movement of sugars from one area of a plant to another 1. Sugars move from a source to a sink

Transport 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