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Lecture 10

GENERAL BIOLOGY II Complete Lecture 10 Notes

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Lecture 10 Plant Nutrition  Chapter 3 I. Root Anatomy A. Epidermis 1. Root hairs  ▯absorption of water & minerals 2. No cuticle in regions of root hairs B. Cortex 1. Loosely packed parenchyma cells 2. Large intracellular spaces a. Pathway for H2O b. Aeration C. Endodermis 1. Inner layer of cortex 2. Single layer of cells 3. Boundary between cortex & stele (where vascular tissue is located) 4. Regulate movement of H2O & minerals into xylem 5. Casparian strip  ▯band a. Not in cell wall, but surrounds each cell b. Suberin  ▯fatty material; waterproof c. Radial walls & transverse walls covered D. Stele ­ Central cylinder in which we find vascular tissue 1. Pericycle a. Outermost layer b. Single layer of parenchyma cells 2. Xylem 3. Phloem ­ Figure 35.14 E. Mycorrhizae ­ Indirectly increase surface area of roots  ▯benefits plants II. Short distance transport of H2O across plasma membrane A. Osmosis 1. Diffusion of free water across a membrane B. Water potential 1. Psi 2. Free energy of H2O 3. Measured relative to reference point a. Pure water in container open to atmosphere at sea level b. Psi = 0 MP (megaPascals) 4. Higher psi  ▯more potential energy to perform work 5. Psi decreases when solutes dissolved in H2O a. Solutes reduce movement of water molecules  ▯reduces work b. Psi reduced to a negative number 6. Water moves from a region of higher (less negative) Psi to a region of  lower (more negative) Psi a. H2O moves from hypotonic to hypertonic b. Solution #1  ▯less solute, hypotonic, less negative Psi c. Solution #2  ▯more solute, hypertonic, more negative Psi d.  ▯(net movement of H2O) C. Uptake of H2O & minerals by roots 1. Soil Psi a. Varies b. Dry i. Relatively more solute in solution ii. Hypertonic iii. Psi very low c. Moister i. Psi higher (less neg.) 2. Root Psi a. Negative 3. Movement of H2O a. Dry soil i. Soil hypertonic relative to root ii. Psi more negative iii. H2O does not move from soil into root b. Moist soil i. H2O moves from soil into root D. Movement of H2O across membrane 1. Osmosis 2. Aquaporins a. Transmembrane proteins b. Channels 3. Diffusion a. Movement of H2O over small scales b. Cellular III. Water & mineral transport into xylem A. 2 major compartments in plant tissues 1. Apoplast  ▯external to plasma membrane of living cells a. Cell wall b. Extracellular spaces c. Interior of dead cells  ▯vessel elements, tracheids 2. Symplast a. Entire mass of cytosol of all living cells in plant & also the  plasmodesmata B. 3 routes of transport 1. Apoplastic route a. H2O & solutes move along continuum of cell walls & extracellular  spaces b. Interconnected porous cell walls c. Most H2O & minerals move via this route 2. Symplastic route a. H2O & solutes move along a continuum
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