Plant Nutrition & Transport PDF

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Plant Nutrition and Transport ➢ Plants need CHNOPS ○ Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulfur ■ NPS- taken in thru roots ➢ Shoots is above ground, roots is above ground ➢ Sugars make up bulk of the plant & used for energy within the plant ➢ Water flows through roots, moves up xylem, and eventually evaporates through their leaves ➢ Plants also take in oxygen ○ Take in oxygen through their roots ○ After converting CO2 thru photosynthesis, they use those sugars, and to use them, they do cellular respiration ■ Also need oxygen because any part of a plant that’s growing or requires energy is also going to require oxygen ➢ Dicots ○ Sunflower; dandelion ○ Veins on leaves ➢ Monocots ○ Corn; grass ○ Parallel veins on leaves ➢ 3 types of tissue ○ Epidermis ○ Ground tissue ○ Vascular tissue ■ Phloem and xylem ○ In the roots of the vascular tissue, is where the movement of water and the movement of nutrients is going to be centered in the middle of the root ○ Function of root hairs is to increase surface area; absorb even more nutrients ○ In stems ■ Still have epidermis on the outside ■ Have cuticle on the outside of that ■ In dicots, vascular tissue moving from the center of the root towards the edge of the stem because it eventually has to flow out into the leaves so the xylem is closer to the edge ➢ Palisade mesophyll ○ Like a waterfall, area where we have photosynthesis going on; light hitting chloroplasts ➢ Water is flowing in plants through osmosis ○ Cell membrane is what allows things in or out ○ Water moving between cell wall: Apoplastic ○ Water moving through cytoplasm: symplastic ➢ Function of casparian strip is to force water eventually to go across the membrane so we have control ➢ Transpiration ○ Think of it as a “pull” ○ Water is slightly charged, so oxygen is going to have a slightly negative charge and Hydrogen with a slight positive charge ■ Water with a hydrogen bond ○ So once a little bit of water starts flowing up the tree, the ones are going to follow

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■ Call this Cohesion Adhesion ■ Adhesion inside the xylem of water Xylem ■ Dead at maturity ■ Empty cells ■ Just a container or a vessel for the water to flow through Every time one water molecule evaporates in the leaf, it’s going to pull the whole chain up ■ Xylem and the water is moved through a pulling process What generates all that energy to pull it up? ■ Sun Phloem ■ Cells ■ Empty but alive ■ Have companion cells that have nuclei and they are connected to the phloem and provide the metabolic support for the phloem ■ Sap and sugar is actually pushed around in a tree ■ Phloem pushed from the source to the sink ■ Sugar pushed into direction of the phloem ■ Sugar pushed from source to sink ■ Source ● Place of high sugar ■ Sink ● Place of no sugar ■ Water also moves from the source to the sink

Article: Water Uptake and Transport in Vascular Plants ➢ Why do plants need so much water? ○ Water is the most limiting abiotic (non-living) factor to plant growth and productivity, and a principal determinant of vegetation distributions worldwide ○ Plants retain less than 5% of the water absorbed by roots for cell expansion and plant growth ■ The remainder passes through plants directly into the atmosphere, a process referred to as transpiration ■ The amount of water lost via transpiration can be incredibly high; a single irrigated corn plant growing in Kansas can use 200 L of water during a typical summer, while some large rainforest trees can use nearly 1200 L of water in a single day ○ When stomata open, water is lost to the atmosphere at a prolific rate relative to the small amount of CO2 absorbed; across plant species an average of 400 water molecules are lost for each CO2 molecule  gained. The balance between transpiration and photosynthesis forms an essential compromise in the existence of plants; stomata must remain open to build sugars but risk dehydration in the process ➢ From the soil into the plant ○ Essentially all of the water used by land plants is absorbed from the soil by roots. ○ Roots grow from their tips and initially produce thin and non-woody fine roots. ○ Fine roots are the most permeable portion of a root system, and are thought to have the greatest ability to absorb water, particularly in herbaceous (i.e., non-woody) plants ○ Fine roots can be covered by root hairs that significantly increase the absorptive surface area and improve contact between roots and the soil ■ Some plants also improve water uptake by establishing symbiotic relationships with mycorrhizal fungi, which functionally increase the total absorptive surface area of the root system. ○ While bark formation decreases the permeability of older roots they can still absorb considerable amounts of water ■ This is important for trees and shrubs since woody roots can constitute ~99% of the root surface in some forests ○ Hydrotropism ■ Roots ability to grow away from dry sites toward wetter patches in the soil ■ Positive hydrotropism occurs when cell elongation is inhibited on the humid side of a root, while elongation on the dry side is unaffected or slightly stimulated resulting in a curvature of the root and growth toward a moist patch ● The root cap is most likely the site of hydro sensing; while the exact mechanism of hydrotropism is not known, recent work with the plant model Arabidopsis has shed some light on the mechanism at the molecular level ➢ Through the plant into the atmosphere ○ Water flows more efficiently through some parts of the plant than others. For example, water absorbed by roots must cross several cell layers before entering the specialized water transport tissue (referred to as xylem) ○ These cell layers act as a filtration system in the root and have a much greater resistance to water flow than the xylem, where transport occurs in open tubes. ○ Upon absorption by the root, water first crosses the epidermis and then makes its way toward the center of the root crossing the cortex and endodermis before arriving at the xylem

■ Once in the xylem tissue, water moves easily over long distances in these open tubes ○ After traveling from the roots to stems through the xylem, water enters leaves via petiole (i.e., the leaf stalk) xylem that branches off from that in the stem....