Plant Structures Roots Stems and Leaves Chapter 23

Plant Structures Roots, Stems, and Leaves Chapter 23

3 Types of Specialized Tissues in Plants n n Plants are as successful if not more successful than animals Seed plants have three main structures: n n Roots Stems Leaves Linked together by various means

3 Types of Specialized Tissues in Plants n Roots Absorbs water and nutrients n Anchor plant to the ground n Hold soil in place and prevent erosion n Protect from soil bacteria n Transport water and nutrients n Provide upright support n

3 Types of Specialized Tissues in Plants n Stems Support for the plant body n Carries nutrients throughout plant n Defense system to protect against predators and infection n Few millimeters to 100 meters n

3 Types of Specialized Tissues in Plants n Leaves Main photosynthetic systems n Susceptible to extreme drying n Site of oxygen/carbon dioxide intake and release n

Plant Tissue Systems n Exist within the root, stems, and leaves Dermal tissue n Vascular tissue n Ground tissue n

Plant Tissue Systems: Dermal Tissue n n n Outer covering Single layer of cells Cuticle – waxy coating n n Roots have dermal tissue n n Trichomes – Spiny projections on the leaf Root hairs Guard Cells

Plant Tissue Systems: Vascular Tissue n Vascular Tissue Transport System n Subsystems n Xylem n Phloem n n Subsystems are used to carry fluids throughout plant

Plant Tissue Systems: Vascular Tissue n Xylem n Two types Seed plants n Angiosperms n Tracheid – long narrow cells n Walls are connected to neighboring cells n Will eventually die n Vessel Element – wider that trachieds n

Plant Tissue Systems: Vascular Tissue n Phloem n Sieve Tube Elements Cells arranged end to end n Pump sugars and other foods n n Companion Cells Surround sieve tube elements n Support phloem cells n

Specialized Tissues in Plants: Ground Tissue n n Cells between dermal and vascular tissue Parenchyma n n Collenchyma n n Thin cell walls, large vacuoles Strong, flexible cell walls Sclerenchyma n Extremely thick, rigid cell walls

Plant Growth n Meristems – tissues responsible for growth n n Apical Meristem n n Produce growth increased length Differentiation n n Undifferentiated cells Cells will assume roles in the plant Flower Development n Starts in the meristem

Roots

Types of Roots n Taproots Found in dicots n Long, thick root n Hickory and oak trees n n Fibrous roots Found in monocots n No single root larger than any other n Many thin roots n

Root Structure n n Outside layer Epidermis Root hairs n Cortex n n Central cylinder – vascular system Root Cap – cellular production Key role in water/mineral transport

Root Functions Anchor plant n Absorb water n Absorb nutrients n

Nutrient Uptake n Plant Nutrient Uptake n n Soil type determines plant type Plant requirements n n n n Oxygen, CO 2 Nitrogen Phosphorus Postassium Magnesium Calcium Trace elements

Active Transport in Plants n Root hairs use ATP n n n Vascular Cylinder n n Pump minerals from soil Causes water molecules to follow by osmosis Casparian Strip – water retention Root Pressure n Forces water up into the plant

Stems

Stem Structure n n n Produce leaves, branches, and flowers Hold leaves up Transport substance between roots and leaves Essential part of transport system Function in storage and photosynthesis

Stem System n Xylem and phloem – major tubule systems n n n Transport water and nutrients Composed of three tissue layers Contain nodes – attachment for leaves Internodes – regions between the nodes Buds – undeveloped tissue

Stem Types n Monocot – vascular bundles are scattered throughout n n Distinct epidermis Dicot – vascular tissue arranged in a cylinder n Pith – parenchyma cells inside the ring

Stem Growth n Primary growth – new cells produced at the root tips and shoots n n Increases the length Secondary growth – increase in stem width n n Vascular cambium – produces tissue and increases thickness Cork cambium – produces outer covering of stems

Vascular Cambium n Formation of Vascular Cambium n n n Xylem and phloem bundles present intially Secondary growth initiates production of a thin layer The vascular cambium divides n Produces new xylem and phloem

Formation of Wood n Formation of wood n n n Wood – layers of exlem Produced year after year Results from the older xylem not conducting water – heartwood Becomes darker with age Sapwood – surrounds heartwood

Formation of Wood n Formation of Bark n n n All the tissues outside the vascular cambium Consists of outermost layers of dead cork Water proof

Leaves

Leaves n n Main site of photosynthesis Consist of: n n n Blade – thin flattened section Petiole – stalk that attaches stem to blade Covered by epidermis and cuticle n Create water proof barrier

Function of Leaves n Leaf Functions n Photosynthesis – occurs in the mesophyll n n Palisade mesophyll – absorb light Spongy mesophyll – beneath palisede level Stomata – pores in the underside of the leaf Guard Cells – Surround the stomata

Transpiration n n Loss of water through its leaves Replaced by water drawn into the leaf

Function of Leaves n Gas Exchange n n n Take in CO 2 and release O 2 Can also do the opposite – How? Gas exchange takes place at the stomata n n Not open all the time Stomata is controlled by water pressure in guard cells

Plant Transportation

Transport in Plants n Water Transport n Active transport and root pressure n n Cause water to move from soil to roots Capillary action n Combined with active transport and root pressure, moves materials throughout the plant

Transport in Plants n Capillary Transport n n Capillary transport results from both cohesive and adhesive forces Water molecules attracted to one another Water is also attracted to the xylem tubes in the plant Causes water to move from roots to the stem and upward

Transpiration n n n n Evaporation is the major moving force As water is lost, osmotic pressure moves water out of vascular tissue This pulls water up from the stem to the leaves Affected by heat, humidity, and wind

Transpiration n Controlling Transpiration n n Open the stomata – increase water loss Close the stomata – decrease water loss

Transpiration n Transpiration and Wilting n n n Osmotic pressure – keeps plants semi-rigid Wilting is a result of high transpiration rates Loss of water causes a drop in osmotic pressure Loss of rigidity Conserves water

Nutrient Transportation n Nutrient Transport n n n Most nutrients are pushed through plant Nutrient movement takes place in phloem Source to Sink n n n Source – any cell that produces sugars Sink – any cell where sugars are used Pressure-flow Hypothesis