Chapter Summary
33.1 The Plant Body Is Organized in a Distinctive Way
The vegetative organs of flowering plants are roots, which form a root system, and stems, leaves, and flowers, which form a shoot system. Review Figure 33.1
Plant development differs from animal development in that plants have apical meristems, cell walls, vacuoles, and totipotent cells.
Plants have apical–
basal and radial axes of symmetry. Review Figure 33.4
33.2 Plant Organs Are Made Up of Three Tissue Systems
Three tissue systems, arranged concentrically, extend throughout the plant body: the vascular tissue, dermal tissue, and ground tissue systems. Review Focus: Key Figure 33.6
The dermal tissue system protects the plant body surface. Dermal cells form the epidermis and, in woody plants, the periderm.
The ground tissue system contains cells of three types. Some parenchyma cells carry out photosynthesis; others store starch. Collenchyma cells provide flexible support. Sclerenchyma cells include fibers and sclereids, which provide strength and mechanical support. Review Figure 33.7
The vascular tissue system includes xylem, which conducts water and minerals absorbed by the roots, and phloem, which conducts the products of photosynthesis throughout the plant body.
Tracheary elements include tracheids and vessel elements, which are the conducting cells of the xylem. Sieve tube elements are the conducting cells of the phloem. Review Figure 33.8
33.3 Meristems Build a Continuously Growing Plant
All seed plants possess a primary plant body consisting of nonwoody tissues. Woody plants also possess a secondary plant body consisting of wood and bark. Apical meristems generate the primary plant body, and lateral meristems generate the secondary plant body. Review Figure 33.9
Apical meristems are responsible for primary growth (lengthening of roots and shoots). Apical meristems at the tips of shoots and roots give rise to three primary meristems (protoderm, ground meristem, and procambium), which in turn produce the three tissue systems of the primary plant body.
The root apical meristem gives rise to the root cap and to three primary meristems. Root tips have overlapping zones of cell division, cell elongation, and cell maturation. Review Figure 33.10
The vascular tissue of roots is contained within the stele. It is arranged differently in eudicot and monocot roots. Review Figures 33.11, 33.12, Activities 33.1, 33.2
In nonwoody stems, the vascular tissue is divided into vascular bundles, each containing both xylem and phloem. Review Figure 33.14, Activities 33.3, 33.4
Eudicot leaves have two zones of photosynthetic mesophyll that are supplied by veins with water and minerals. Veins also carry the products of photosynthesis to other parts of the plant body. A waxy cuticle limits water loss from the leaf. Guard cells control openings called stomata in the leaf that allow CO2 to enter, but also allow some water to escape. Review Figure 33.16, Activity 33.5
Two lateral meristems, the vascular cambium and cork cambium, are responsible for secondary growth. The vascular cambium produces secondary xylem (wood) and secondary phloem. The cork cambium produces a protective tissue called cork. Review Figure 33.17, Animation 33.1
33.4 Domestication Has Altered Plant Form
The plant body plan is simple, yet it can be changed dramatically by minor differences in genes, as evidenced by the natural diversity of wild plants.
Crop domestication involves artificial selection of certain desirable traits found in wild populations. Review Figure 33.20
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