Answers to Review Questions
Chapter 38 (p. 776)
1. The three major tissue systems in plants are ground tissue, dermal tissue, and vascular tissue. Ground tissue is composed of parenchyma that may be used for storage, photosynthesis, or secretion. Dermal tissue forms epidermis and its protective coatings. In longer-lived plants, the dermal tissue forms the bark. Vascular tissue conducts water and dissolved nutrients about the plant.
2. Xylem conduct water. Primary xylem are derived from procambium, apical meristem. Secondary xylem are derived from vascular cambium, lateral meristem. The conducting cells are tracheids and vessel elements. These cells are both elongated and fiber-like and not alive at maturity. Tracheids have pits in the secondary walls, and vessels have pits on the side walls and perforations in the end walls.
3. Phloem conducts food and contains sieve cells and sieve-tube members. They are slender and elongated and lack nuclei. They are alive at maturity. Companion cells are specialized parenchyma cells associated with sieve-tube members; they carry out metabolic functions for the sieve-tube members.
4. A cross-section through a monocot root has bundles of xylem and phloem scattered throughout the section. The primary xylem and phloem in a dicot root is centralized within the stele, surrounded by the pericycle and then the endodermis. Monocot roots have discrete vascular bundles arranged in a ring around the central pith. The xylem of dicots is central. Seen in cross section the xylem forms a star shape with the phloem nestled between the rays of the star. Both monocots and dicots enclose the vascular region with an endodermis and pericycle followed by cortex and epidermis.
5. Roots form lateral branches that are initiated deep within the root tissues through cell divisions in the pericycle.
6. As the stem grows in diameter, phloem, xylem, and more cambium is produced.
7. Secondary growth requires a ring of vascular cambium to increase girth. Monocots have scattered vascular bundles rather than a ring, as seen in dicots.
8. Simple leaves are undivided, and compound leaves consist of clearly divided leaflets. The three types of growth patterns of leaves are as follows: (1) alternate – leaves spirally arranged along the length of the stem; (2) opposite - leaves occur in pairs along the stem; and (3) whorled - more than two leaves are attached at any one level on a stem.