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7.1: Key Terms

  • Page ID
    115068
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    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 covering on the outside of the leaf and stem that prevents the loss of water
    cuticle
    waxy protective layer on the leaf surface
    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 ginkgo 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

    7.1: Key Terms is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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