04%20and%2005%20Leaves%20Stems%20and%20Roots

04%20and%2005%20Leaves%20Stems%20and%20Roots - Plant...

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Plant Structure and Function - Leaves, Stems and Roots Objectives of the next two lectures: Learn the typical structure of plant leaves, stems and roots Develop an understanding of how these structures support the functions of these organs Identify meristems as structures that are important for growth of these organs Learn about modifications of these organs
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ADP & NADP ATP & NADPH CO 2 & H 2 O (CH 2 O) O 2 H 2 O Light Chlorophyll Light Reaction Calvin Cycle Photosynthesis Photosynthesis can be described in this series of coupled reactions: How does leaf structure contribute to and facilitate these reactions of photosynthesis?
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Required features for a typical leaf Exposed to sunlight Large surface area Capable of exchanging gases CO 2 in, O 2 out Import mineral nutrients and water these are not obtained from the atmosphere Export fixed carbon (photosynthate) to “sinks” - seeds, roots Control water loss Resist biotic and abiotic stresses
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A “typical” leaf leaf blade petiole node internode stem axil with axillary bud leaf
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A “typical” leaf
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The leaf blade Broad expanded part of the leaf frequently has the following characteristics: Large surface area Thin with a small distance between upper and lower surfaces
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The leaf blade These anatomical features: Maximize the surface area while minimizing volume Reduce the distance that gases have to diffuse through the leaf Remember that plant species are adapted to a wide variety of environments. Leaf structure varies to
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Leaf tissues - epidermis Epidermis epi - upon of cells number of different cell types
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Leaf tissues - epidermis Cell types of the epidermis Epidermal cells most abundant cell type in the epidermis, variable arrangement lack chloroplasts stomata epidermal cells
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Leaf epidermis Epidermis is covered by a waxy cuticle Secreted from epidermal cells Impermeable to water - water does not pass through the cuticle, from the inside of the leaf to the exterior Helps to retain water in the leaf Cuticle
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Leaf epidermis Other specialized cells in the epidermis Guard cells, which form stomata Trichomes, leaf hairs guard cells trichomes
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Stomata and Guard Cells Stomata (from the Greek “stoma”, meaning mouth) are pores in the epidermis that lead to intercellular spaces within the leaf Found on both upper (adaxial) and lower (abaxial) surfaces of the leaf Formed by specialized guard cells
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Stomata and Guard Cells Stomata are important for photosynthesis as they allow gasses to move in and out of the interior part of the leaf - gas exchange CO 2 into the leaf, O 2 out Water (H 2 O) is also lost through stomata
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Why are stomata important for photosynthesis?
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04%20and%2005%20Leaves%20Stems%20and%20Roots - Plant...

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