1.25.10 - Plant nutrition, gas exchange, and transport T a...

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1 Plant nutrition, gas exchange, and transport • Essential nutrients • Nitrogen assimilation Nitrogen fixation, bacterial symbiosis • Mycorrhizae fungal symbiosis • Uptake of CO 2 Diffusion between leaves and air Water loss and transpiration • Fluid transport Xylem and phloem Physiology: How organisms work A fundamental principle of physiology: all organisms must exchange materials and energy with their environments. In the next two lectures we cover the most important of these exchanges for plants. Table 37-1 Fig. 37-2 A horizon B horizon C horizon Inorganic Components • Cations (for example K + , Ca 2+ , Mg 2+ ) adhere to negatively charged soil particles; this prevents them from leaching out of the soil through percolating groundwater
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2 • During cation exchange , cations are displaced from soil particles by other cations • Displaced cations enter the soil solution and can be taken up by plant roots • Negatively charged ions do not bind with soil particles and can be lost from the soil by leaching --salts Fig. 37-3 Soil particle K + K + K + Ca 2+ Ca 2+ Mg 2+ H + H + H 2 O + CO 2 H 2 CO 3 HCO 3 + Root hair Cell wall Organic Components • Humus builds a crumbly soil that retains water but is still porous • It also increases the soil’s capacity to exchange cations and serves as a reservoir of mineral nutrients • Topsoil contains bacteria, fungi, algae, other protists, insects, earthworms, nematodes, and plant roots • These organisms help to decompose organic material and mix the soil Adjusting Soil pH • Soil pH affects cation exchange and the chemical form of minerals • Cations are more available in slightly acidic soil, as H + ions displace mineral cations from clay particles
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3 Epiphytes, Parasitic Plants, and Carnivorous Plants • Some plants have nutritional adaptations that use other organisms in nonmutualistic ways • An epiphyte grows on another plant and obtains water and minerals from rain Fig. 37-14a Staghorn fern, an epiphyte • Parasitic plants absorb sugars and minerals from their living host plant Fig. 37-14b Mistletoe, a photosynthetic parasite
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4 Fig. 37-14c-1 Dodder, a nonphotosynthetic parasite Dodder Host’s phloem Haustoria • Carnivorous plants are photosynthetic but obtain nitrogen by killing and digesting mostly insects Fig. 37-14e-1 Venus flytrap Fig. 37-14f-1 Pitcher plants
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5 Fig. 37-14g Sundews Fig. 37-UN1 N 2 (from atmosphere) Nitrogen-fixing bacteria H + (from soil) (to atmosphere) Denitrifying bacteria N 2 NO 3 (nitrate) Nitrifying bacteria NH 4 + (ammonium) NH 3 (ammonia) Ammonifying bacteria Organic material (humus) Root NH 4 + Plant transport systems To grow and reproduce, plants need resources: • O 2 , for respiration • water • if photosynthetic, CO 2 and access to light • in addition to the C, H, and O in water and CO 2 , 14 essential elements • if not photosynthetic (i.e., if heterotrophic), a
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1.25.10 - Plant nutrition, gas exchange, and transport T a...

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