Lecture_7.Plant_Transport

Lecture_7.Plant_Transport - Resource Acquisition and...

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Unformatted text preview: Resource Acquisition and Transport in Vascular Plants • Vascular tissues made possible the development of extensive root and shoot systems – Xylem transports water and minerals from roots to shoots – Phloem transports sugars from where they are produced or stored to where they are needed for growth and metabolism • Roots and shoots help plants acquire resources Shoot Systems and Light Capture • Stems – Supporting structures for leaves – Conduits for transport of water and nutrients • Leaves – Account for much of the diversity of plant form • Light capture by leaves – Arrangement of leaves on a stem • Phyllotaxy – Leaf orientation – The branching pattern also allows plants to acquire sunlight and CO 2 Root Systems and Acquisition of Water and Minerals • Root branching allows plants to effectively acquire water and nutrients from the soil – It also help to anchor the plant • ~ 80% of plants have roots associated with mycorrhizae – It enhances surface area for absorption Short Distance Transport in Plants • Selective permeability of the plasma membrane – Controls movement of solutes between the cell and the extracellular solution • Passive and active transport mechanisms • Passive Transport – Diffusion – Osmosis • Active Transport – Transport proteins • Specific carriers • Selective channels Transport Proteins in Plant Cells • Proton pumps in plant cells use ATP to pump H + out of the cell – This results in a proton gradient – The movement of positive charges out of the cell by the pump contributes to a voltage known as a membrane potential • Both the concentration gradient and the membrane potential are forms of potential energy that is used to drive the transport of many solutes • Membrane potential and cation uptake – Cations are driven into the cell by membrane potentials • Cotransport of a solute with H + – a transport protein couples the downhill passage of H + to the uphill passage of another • Accumulated anions and neutral solutes in the ECF cotransport as a proton diffuses down its concentration gradient Osmosis • To survive, plants must balance water uptake and loss • The net uptake or loss of water by a cell occurs by osmosis – In plant cells, the direction of water movement depends on • solute concentration • physical pressure of the cell wall pushing against the protoplast • Water potential is a measurement that combines the effects of solute concentration and physical pressure – Represented by the Greek letter “ psi” ( ψ ) • Water potential determines the direction of water movement – Water flows from regions of higher water potential to regions of lower water potential – As water moves it can perform work – water potential equation: ψ = ψ s + ψ p • ψ s = solute potential (osmotic potential) • ψ p = pressure potential – Ψ is measured in megapascals (Mpa) – 1 ψ ~ 10 atmospheres •...
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This note was uploaded on 11/02/2010 for the course CHEM 51LA 56555 taught by Professor Guan during the Spring '10 term at UC Irvine.

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Lecture_7.Plant_Transport - Resource Acquisition and...

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