30 OpenStax Biology 2e Chapter 30 Plant Form and Physiology

abscisic acid (ABA)

plant hormone that induces dormancy in seeds and other organs

abscission

physiological process that leads to the fall of a plant organ (such as leaf or petal drop)

adventitious root

aboveground root that arises from a plant part other than the radicle of the plant embryo

apical bud

bud formed at the tip of the shoot

apical meristem

meristematic tissue located at the tips of stems and roots; enables a plant to extend in length

auxin

plant hormone that influences cell elongation (in phototropism), gravitropism, apical dominance, and root growth

axillary bud

bud located in the axil: the stem area where the petiole connects to the stem

bark

tough, waterproof, outer epidermal layer of cork cells

bulb

modified underground stem that consists of a large bud surrounded by numerous leaf scales

Casparian strip

waxy coating that forces water to cross endodermal plasma membranes before entering the vascular cylinder, instead of moving between endodermal cells

chromophore

molecule that absorbs light

collenchyma cell

elongated plant cell with unevenly thickened walls; provides structural support to the stem and leaves

companion cell

phloem cell that is connected to sieve-tube cells; has large amounts of ribosomes and mitochondria

compound leaf

leaf in which the leaf blade is subdivided to form leaflets, all attached to the midrib

corm

rounded, fleshy underground stem that contains stored food

cortex

ground tissue found between the vascular tissue and the epidermis in a stem or root

cryptochrome

protein that absorbs light in the blue and ultraviolet regions of the light spectrum

cuticle

waxy protective layer on the leaf surface

cuticle

waxy covering on the outside of the leaf and stem that prevents the loss of water

cytokinin

plant hormone that promotes cell division

dermal tissue

protective plant tissue covering the outermost part of the plant; controls gas exchange

endodermis

layer of cells in the root that forms a selective barrier between the ground tissue and the vascular tissue, allowing water and minerals to enter the root while excluding toxins and pathogens

epidermis

single layer of cells found in plant dermal tissue; covers and protects underlying tissue

ethylene

volatile plant hormone that is associated with fruit ripening, flower wilting, and leaf fall

fibrous root system

type of root system in which the roots arise from the base of the stem in a cluster, forming a dense network of roots; found in monocots

gibberellin (GA)

plant hormone that stimulates shoot elongation, seed germination, and the maturation and dropping of fruit and flowers

ground tissue

plant tissue involved in photosynthesis; provides support, and stores water and sugars

guard cells

paired cells on either side of a stoma that control stomatal opening and thereby regulate the movement of gases and water vapor

intercalary meristem

meristematic tissue located at nodes and the bases of leaf blades; found only in monocots

internode

region between nodes on the stem

jasmonates

small family of compounds derived from the fatty acid linoleic acid

lamina

leaf blade

lateral meristem

meristematic tissue that enables a plant to increase in thickness or girth

lenticel

opening on the surface of mature woody stems that facilitates gas exchange

megapascal (MPa)

pressure units that measure water potential

meristem

plant region of continuous growth

meristematic tissue

tissue containing cells that constantly divide; contributes to plant growth

negative gravitropism

growth away from Earth's gravity

node

point along the stem at which leaves, flowers, or aerial roots originate

oligosaccharin

hormone important in plant defenses against bacterial and fungal infections

palmately compound leaf

leaf type with leaflets that emerge from a point, resembling the palm of a hand

parenchyma cell

most common type of plant cell; found in the stem, root, leaf, and in fruit pulp; site of photosynthesis and starch storage

pericycle

outer boundary of the stele from which lateral roots can arise

periderm

outermost covering of woody stems; consists of the cork cambium, cork cells, and the phelloderm

permanent tissue

plant tissue composed of cells that are no longer actively dividing

petiole

stalk of the leaf

photomorphogenesis

growth and development of plants in response to light

photoperiodism

occurrence of plant processes, such as germination and flowering, according to the time of year

phototropin

blue-light receptor that promotes phototropism, stomatal opening and closing, and other responses that promote photosynthesis

phototropism

directional bending of a plant toward a light source

phyllotaxy

arrangement of leaves on a stem

phytochrome

plant pigment protein that exists in two reversible forms (Pr and Pfr) and mediates morphologic changes in response to red light

pinnately compound leaf

leaf type with a divided leaf blade consisting of leaflets arranged on both sides of the midrib

pith

ground tissue found towards the interior of the vascular tissue in a stem or root

positive gravitropism

growth toward Earth's gravitational center

primary growth

growth resulting in an increase in length of the stem and the root; caused by cell division in the shoot or root apical meristem

rhizome

modified underground stem that grows horizontally to the soil surface and has nodes and internodes

root cap

protective cells covering the tip of the growing root

root hair

hair-like structure that is an extension of epidermal cells; increases the root surface area and aids in absorption of water and minerals

root system

belowground portion of the plant that supports the plant and absorbs water and minerals

runner

stolon that runs above the ground and produces new clone plants at nodes

sclerenchyma cell

plant cell that has thick secondary walls and provides structural support; usually dead at maturity

secondary growth

growth resulting in an increase in thickness or girth; caused by the lateral meristem and cork cambium

sessile

leaf without a petiole that is attached directly to the plant stem

shoot system

aboveground portion of the plant; consists of nonreproductive plant parts, such as leaves and stems, and reproductive parts, such as flowers and fruits

sieve-tube cell

phloem cell arranged end to end to form a sieve tube that transports organic substances such as sugars and amino acids

simple leaf

leaf type in which the lamina is completely undivided or merely lobed

sink

growing parts of a plant, such as roots and young leaves, which require photosynthate

source

organ that produces photosynthate for a plant

statolith (also amyloplast)

plant organelle that contains heavy starch granules

stele

inner portion of the root containing the vascular tissue; surrounded by the endodermis

stipule

small green structure found on either side of the leaf stalk or petiole

stolon

modified stem that runs parallel to the ground and can give rise to new plants at the nodes

strigolactone

hormone that promotes seed germination in some species and inhibits lateral apical development in the absence of auxins

tap root system

type of root system with a main root that grows vertically with few lateral roots; found in dicots

tendril

modified stem consisting of slender, twining strands used for support or climbing

thigmomorphogenesis

developmental response to touch

thigmonastic

directional growth of a plant independent of the direction in which contact is applied

thigmotropism

directional growth of a plant in response to constant contact

thorn

modified stem branch appearing as a sharp outgrowth that protects the plant

tracheid

xylem cell with thick secondary walls that helps transport water

translocation

mass transport of photosynthates from source to sink in vascular plants

transpiration

loss of water vapor to the atmosphere through stomata

trichome

hair-like structure on the epidermal surface

tuber

modified underground stem adapted for starch storage; has many adventitious buds

vascular bundle

strands of stem tissue made up of xylem and phloem

vascular stele

strands of root tissue made up of xylem and phloem

vascular tissue

tissue made up of xylem and phloem that transports food and water throughout the plant

venation

pattern of veins in a leaf; may be parallel (as in monocots), reticulate (as in dicots), or dichotomous (as in Gingko biloba)

vessel element

xylem cell that is shorter than a tracheid and has thinner walls

water potential (Ψw)

the potential energy of a water solution per unit volume in relation to pure water at atmospheric pressure and ambient temperature

whorled

pattern of leaf arrangement in which three or more leaves are connected at a node