Ch35WordLectureOutline

Ch35WordLectureOutline - CHAPTER 35 PLANT STRUCTURE AND...

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CHAPTER 35 PLANT STRUCTURE AND GROWTH Introduction With about 250,000 known species, the angiosperms are by far the most diverse and widespread group of land plants. As primary producers, flowering plants are at the base of the food web of nearly every terrestrial ecosystem. Most land animals, including humans, depend on plants directly or indirectly for sustenance. A. The Plant Body 1. Both genes and environment affect plant structure A plant’s structure reflects interactions with the environment on two time scales. Over the long term, entire plant species have, by natural selection, accumulated morphological adaptations that enhance survival and reproductive success. For example, some desert plants have so reduced their leaves that the stem is actually the primary photosynthetic organ. This is a morphological adaptation that reduces water loss. Over the short term, individual plants, even more than individual animals, exhibit structural responses to their specific environments. For example, the submerged aquatic leaves of Cabomba are feathery, enhancing the surface area available for the uptake of bicarbonate ion (HCO 3 - ), the form of CO 2 in water. Leaves that extend above the surface form oval pads that aid in flotation.
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The architecture of a plant is a dynamic process, continuously shaped by the plant’s genetically directed growth pattern along with fine-tuning to the environment. Even faster than a plant’s structural responses to environmental changes are its physiological (functional) adjustments. Most plants are rarely exposed to severe drought and rely mainly on physiological adaptations to cope with drought stress. In the most common response, the plant produces a hormone that cause the stomata, the pores in the leaves through which most of the water is lost, to close. 2. Plants have three basic organs: roots, stems, and leaves The plant body is a hierarchy of structural levels, with emergent properties arising from the ordered arrangement and interactions of component parts. The plant body consists of organs that are composed of different tissues, and these tissues are teams of different cell types. Although all angiosperms have a number of features in common, two plants groups, the monocots and dicots, differ in many anatomical details. The basic morphology of plants reflects their evolutionary history as terrestrial organisms that must simultaneously inhabit and draw resources from two very different environments. Soil provides water and minerals, but air is the main source of CO 2 and light does not penetrate far into soil. Plants have evolved two systems: a subterranean root system and an aerial shoot system of stems and leaves. Each system depends on the other.
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Ch35WordLectureOutline - CHAPTER 35 PLANT STRUCTURE AND...

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