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CHAPTER 25 S TRUCTURE AND O RGANIZATION OF P LANTS Chapter Outline 25.1 Plant Organs A. Diverse Flowering Plant Structure 1. Structures of flowering plants are well-adapted to varied environments including water. 2. Flowering plants usually have three vegetative organs: root, stem and leaf. 3. The flower itself contains a number of organs. B. Roots 1. We speak of “a root” but it is more appropriate to call it a root system. 2. The root system is the main root plus its lateral (side) branches. 3. It is generally equal in size to the shoot system , the part above ground. 4. Root systems have the following functions. a. Roots anchor a plant in soil and give support. b. Roots absorb water and minerals from soil; root hairs are central to this process. 1) Root hair cells are in a zone near root tip. 2) Root hairs are numerous to increase absorptive surface of a root. 3) Transplanting plants damages a plant when the root hairs are torn off. 4) Water and nutrients absorbed are distributed to the rest of the plant. 5) Roots produce hormones that must be distributed to the plant c. Perennials “die back” to regrow the next season; roots of herbaceous perennials store food (e.g., carrots, sweet potatoes). C. Stems 1. The shoot system of a plant consists of the stem, the branches, and the leaves. 2. The stem forms the main axis of the plant, along with lateral branches. 3. Upright stems produce leaves and array them to be exposed to as much sun as possible. 4. A node occurs where a leaf attaches to the stem and an internode is the region between nodes; nodes and internodes identify a stem even if it is underground. 5. The stem has vascular tissue to transport water and minerals from roots and sugar from leaves. 6. Nonliving cells form a continuous pipeline through vascular tissue. 7. A cylindrical stem expands in girth and length; trees use woody tissue to strengthen stems. 8. Stems function in storage: cactus stems store water and tubers are horizontal stems that store nutrients. D. Leaves 1. A leaf is the major organ of photosynthesis in most plants. 2. Leaves receive water from roots by way of the stem. 3. Broad, thin leaves have a maximum surface area to absorb CO 2 and collect solar energy. 4. A blade is the wide portion of a leaf with most photosynthetic tissue. 5. Petiole is a stalk that attaches a leaf blade to stem. 6. The leaf axil is the upper acute angle between petiole and stem where an axillary (lateral) bud originates. 7. Some leaves protect buds, attach to objects (tendrils), store food (bulbs), or capture insects. 25.2 Monocot Versus Eudicot Plants A. Criteria for Monocots and Eudicots 1. Cotyledons are embryonic seed leaves providing nutrition from the endosperm before the mature leaves begin photosynthesis.
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2. Flowering plants are divided into monocots and eudicots based on these traits. Monocots
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This note was uploaded on 10/24/2009 for the course BIO 172 taught by Professor Clark during the Fall '08 term at University of Michigan.

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