307 Exam 1 Vocabulary

Apical Meristem

Region of actively dividing cells responsible for primary growth

Lateral meristem

Cylindrical meristem responsible for secondary growth

Shoot apical meristem (SAM)

Produces stems, leaves axillary buds, floral structures

Root apical mersitem (RAM)

Produces the primary tissues of the root

Primary growth

Increase in root or shoot length

Secondary growth

Increase in stem or root diameter

Dermal tissue system

Epidermis and related tissues protecting the plant surface

Ground tissue system

Parenchyma, collenchyma, and sclerenchyma tissues

Vascular tissue system

Xylem and phloem responsible for long distance transport

Epidermis

Outermost protective cell layer of primary plant organs

Cuticle

Waxy surface layer that restricts water loss

Stoma

Epidermal pore regulating gas exchange and transpiration

Guard cells

Specialized cells controlling stomatal opening

Trichome

Epidermal outgrowth serving protective, secretory, or absorptive functions

Parenchyma

Living, relatively unspecialized cells involved in metabolism and storage

Collenchyma

Living support tissue with unevenly thickened primary walls

Sclerenchyma

Support tissue with thick, usually lignified secondary walls

Xylem

Vascular tissue transporting water and mineral nutrients

Tracheid

Elongated water conducting xylem cell with pits

Vessel element

Xylem cell joined end to end to form vessels

Phloem

Vascular tissue transporting sugars and other organic solutes

Sieve-tube element

Principal conducting cell of angiosperm phloem

Companion cell

Metabolically supports an associated sieve tube element

Plasmodesmata

Cytoplasmic channels connecting neighboring plant cells

Symplast

Interconnected cytoplasm linked by plasmodesmata

Apoplast

Cell walls and extracellular spaces outside the plasma membrane

Totipotency

Capacity of a cell to regenerate an entire plant

Protoplastid

Undifferentiated plastid that can develop into specialized plastid types

Chloroplast

Plastid responsible for photosynthesis

Amyloplast

Plastid specialized for starch synthesis and storage

Vacuole

Compartment involved in storage, degradation, tugor, and ion balance

Tonoplast

Membrane surrounding the vacuole

Primary cell wall

Flexible wall depositied while a cell is growing

Secondary cell wall

Additional wall deposited after cell expansion largely ends

Middle lamella

Pectin rich layer that binds neighboring cells

Cellulose

Beta 1,4 linked glucose polymer forming load-bearing microfibrils

Cellulose microfibril

Crystalline bundle of cellulose chains

Celluolse synthase complex

Plasma membrane complex that synthesizes cellulose

Cellulose synthase (CESA)

Catalytic protein responsible for cellulose chain formation

Hemicellulose

Wall polysaccharide that interacts with cellulose microfibrils

Xyloglucan

Major hemicellulose in many primary cell walls

Pectin

Hydrated wall polysaccharide important in adhesion and wall porosity

Homogalacturonan

Major pectic polymer composed principally of galacturonic acid

Lignin

Phenolic polymer that strengthens and waterproofs secondary walls

Suberin

Hydrophobic polymer deposited in cork and root barrier tissues

Callose

Beta 1,3 glucan deposited at plasmodesmata, sieve plates, and wound sites

Cell-wall matrix

Hemicelluloses, pectins, and proteins surrounding microfibrils

Wall loosening

Modification that permits irreversible cell wall extension

Expansin

Proein that promotes wall extension by weakening noncovalent wall interactions

Acid-growth hypothesis

Model in which proton extrusion activates wall loosening and expansion

Turgor pressure

Hydrostatic pressure that supplies the force for cell expansion

Cell-wall stress

Force per unit wall area produced by internal pressure

Cell-wall strain

Relative deformation of the wall under stress

Wall extensibility

Capacity of the wall to undergo irreversible expansion

Cortical microtubules

Cytoskeletal elements guiding cellulose deposition and growth direction

Anisotropic growth

Unequal expansion along different cellular axes

Oligosaccharins

Wall derived oligosaccharides that can act as signaling molecules

Water potential (Psi w)

Chemical potential expression predicting the direction of water movement

Solute potential (Psi s)

Reduction in water potential caused by dissolved solutes; also called osmotic potential

Pressure potential (Psi p)

Hydrostatic pressure contribution to water potential

Matric potential (Psi m)

Water potential effect of water binding to surfaces and matricies

Gravitational potential (Psi g)

Water potential component resulting from elevation

Chemical potential

Free energy per mole of a substance relative to a reference state

Osmosis

Movement of water accross a selectively permeable membrane

Osmotic pressure

Pressure required to prevent osmotic water movement

Van’t Hoff equation

Relationship used to estimate the osmotic potential of dilute solutions

Turgor presure

Positive pressure exerted by cell contents against the wall

Plasmolysis

Separation of the protoplast from the wall after water loss

Incipient plasmolysis

Point at which turgor pressure approaches zero

Water-potential gradient

Difference in water potential that drives water movement

Bulk flow

Coordinated movement of water and solutes caused by a pressure gradient

Diffusion

Net molecular movement for higher to lower chemical potential

Hydraulic conductivity

Ease with which water moves through a membrane or tissue

Aquaporin

Membrane channel protein facilitating water movement

Reflection coefficient

Measure of a membrane’s selectivity for a particular solute

Osmotic adjustment

Accumulation of solutes that helps maintain turgor under water stress

Pressure probe

Instrument used to measure cell turgor direclty

Psychrometer

Instrument that estimates water potential from vapor pressure measurements

Pressure chamber

Instrument commonly used to estimate leaf or xylem water potential

Relative water content

Tissue water content relative to its fully hydrated condition

Soil-plant-atmosphere continuum

Transpiration

Transpiration stream

Cohesion-tension theory

Cohesion

Adhesion

Surface tension

Capillarity

Negative pressure

Cavitation

Embolism

Root pressure

Guttation

Hydathode

Casparian strip

Endodermis

Exodermis

Apoplastic pathway

Symplastic pathway

Transmembrane pathway