Chapter Twenty One
Vocabulary
21.1
Parenchyma cell: cell with thin walls that forms tissues within leaves, roots,
stems, and fruit of plants.
Collenchyma cell: elongated cells with unevenly thick walls that form a
supportive tissue of plants.
Sclerenchyma cell: thick-walled, lignin-rich cells that form a supportive plant
tissue.
Dermal tissue: tissue system that covers the outside of plants and animals.
Ground tissue: tissue system that makes up the majority of a plant.
Vascular tissue: supportive and conductive tissue in plants, consisting of xylem
and phloem.
Xylem: tissue that transports water and dissolved minerals in vascular plants.
Phloem: tissue that transports sugars in vascular plants.
21.2
Cohesion-tension theory: theory that explains how the physical properties of
water allow it to move the xylem of plants.
Transpiration: release of vapor through the pores of the skin or the stomata of
plant tissue.
Pressure-flow model: model for predicting how sugars are transported from
photosynthetic tissue to the rest of a plant.
21.3
Vascular cylinder: center of a root or stem that contains xylem and phloem.
Root hair: thin hair-like outgrowth of an epidermal cell of a plant root that absorbs
water and minerals from the soil.
Root cap: mass of cells that covers and protects the tips of plant roots.
Meristem: undifferentiated plant tissue from which new cells are formed.
Fibrous root: root system made up of many threadlike members of more or less
equal length.
Taproot: main root of some plants, usually larger than other roots and growing
straight down from a stem.
Primary growth: growth in vascular plants resulting in elongation of the plant
body.
Secondary growth: growth in woody plants resulting in wider roots, branches, and
stems.
21.4
Blade: broad part of a leaf where most of the photosynthesis of a plant takes place.
Petiole: stalk that attaches a leaf blade to a stem.
Mesophyll: photosynthetic tissue of a leaf, located between the upper and lower
epidermis.
Guard cell: one of a pair of cells that controls the opening and closing of a stoma
in plant tissue.