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AP Biology, Chapter 36 Resource Acquisition and Transport in Vascular Plants Underground Plants 36.1 Adaptations for acquiring resources were key steps in the evolution of vascular plants Intro Shoot Architecture and Light Capture Root Architecture and Acquisition of Water and Minerals 36.2 Different mechanisms transport substances over short or long distances Intro 1. Compare the processes of passive and active transport. Distinguish between the two main categories of transport proteins. Passive Does not require the use of cellular energy; higher lower Ex.: osmosis, CO2 into parenchyma Active Requires the use of cellular energy; lower higher Ex.: sugar into phloem, protons out of the cell Transport protein mechanisms Undergo a conformational change; ex.: ?? Form a selective channel; ex.: K+ channels, aquaporins The Apoplast and Symplast: Transport Continuums 2. Describe the three major compartments in vacuolated plant cells, noting their interrelationships. Cell wall: soaked in extramembraneous fluid; continuous with neighbors Cytoplasm: modified by transport through membranes and plamsodesmata Vacuole: contents = cell sap; not continuous from cell-to-cell 3. Describe the three routes available for lateral transport in plants. Apoplast: transport through extramembraneous fluid Symplast: cytoplasms are continuous by plasmodesmata Cell-to-cell across cell membranes Short-Distance Transport of Solutes Across Plasma Membranes 4. Describe the role and importance of proton pumps in transport across plant membranes. ATP is used to pump H+ out Chemical gradient since H+ is higher outside Voltage or potential positive outside Uses Positive ions like K+ are attracted into the cell Diffusion of H+ can power transport of other materials Short-Distance Transport of Water Across Plasma Membranes Intro 5. Define osmosis and water potential. Explain how water potential is measured. Osmosis = diffusion of water through a selectively permeable membrane Water potential Tendency of water to move taking into account concentration and pressure Measured in megapascals (MPa), a unit of pressure How Solutes and Pressure Affect Water Potential 6. Explain how solutes and pressure affect water potential. Water pressure (Ψ) = solute potential (ΨS) + pressure potential (ΨP) Adding solutes makes ΨS negative, lowering water potential Increasing the pressure increases water potential Water Movement Across Plant cell membranes 7. Explain how the physical properties of plant cells are changed when the plant is placed into solutions that have higher, lower, or the same solute concentrations. Define flaccid, plasmolyze, turgor pressure, and turgid. Solution effects: hypo, bigger; hyper, smaller; iso, the same Definitions Flaccid: not exerting outward pressure Plasmolyze: lose water, membrane shrinks away from cell wall Turgor pressure: pressure of the cell against the cell wall Turgid: solute potential balances pressure potential, stiff with water Aquaporins: Facilitating Diffusion of Water Long-Distance Transport: The Role of Bulk Flow 8. Relate the structure of sieve-tube cells, vessel cells, and tracheids to their functions in bulk flow. Sieve-tube members are cells Must maintain sugar concentration Simplified for lower resistance Vessel elements and tracheids are dead and empty for lower resistance 36.3 Transpiration drives the transport of water and minerals from roots to shoots via the xylem Intro Absorption of Water and Minerals by Root Cells Transport of Water and Minerals into the Xylem 9. Explain how the endodermis functions as a selective barrier between the root cortex and vascular tissue. Apoplast is blocked by suberin in the Casparian strip around each endodermal cell Water and minerals must pass through the symplast to enter stele Minerals are pumped out of the endodermal cells into the stele apoplast Endodermis especially prevents leakage back out of the stele Bulk Flow Transport via the Xylem Intro Pushing Xylem Sap: Root Pressure 10. Describe the potential and limits of root pressure to move xylem sap. Define root pressure, transpiration, and guttation. Root pressure At night, transpiration stops Roots are still absorbing water Xylem in the stele has higher solutes Pressure builds up in root xylem, pushing the water up Transpiration is the evaporation of water out of the leaves If the root pressure is high enough drops of water come out the leaves = guttation. Pulling Xylem Sap: The Cohesion-Transpiration Hypothesis Intro Transpirational Pull 11. Explain how transpirational pull moves xylem sap up from the root tips to the leaves. Water evaporates from spaces in spongy parenchyma Water film forms strong menisci in the corners of the spaces Surface tension of the menisci pulls water through apoplast Cohesion of water molecules pulls on the entire water column Adhesion and Cohesion in the Ascent of Xylem Sap Xylem Sap Ascent by Bulk Flow: A Review 36.4 The rate of transpiration is regulated by stomata Intro Stomata: Major Pathways for Water Loss 12. Describe the role of guard cells in photosynthesis-transpiration. Plant must balance needs to exchange gases and save water Guard cells can open and close stomata 13. Explain the advantages and disadvantages of the extensive inner surface area of a leaf. Advantages Increases surface area for absorption of CO2 Most photosynthetic cells are close to air Disadvantages Increases surface area for water loss 90% of water loss is through stomata 14. Explain how the transpiration-to-photosynthesis ratio is calculated and what it indicates about a plant. Calculation: water lost per gram of fixed CO2 Indicates efficiency of water usage: C 4 plants use half the water Mechanisms of Stomatal Opening and Closing 15. Explain how and when stomata open and close. During the day: guard cells are turgid, more curved, stomata open Proton pumps export H+ K+ flows in, water follows by osmosis At night: guard cells are flaccid, less curved, stomata closed At dawn Light receptors turn on proton pumps Photosynthesis begins, CO2 in mesophyll goes down Circadian rhythm Close in the daytime in response to stress Stimuli for Stomatal Opening and Closing Effects of Transpiration on Wilting and Leaf Temperature 16. Explain how transpiration changes the temperatures of leaves and why this is adaptive. Explain how plants with low transpiration rates compensate for higher temperatures. Transpiration is evaporative cooling Keeps photosynthetic enzymes from denaturing Desert plant enzymes are adapted to be stable at higher temperatures Adaptations That Reduce Evaporative Water Loss 17. Explain how xerophytes reduce transpiration. Small thick leaves with a thick cuticle Stomata in depressions with trichomes CAM plants store CO2 at night; close stomata in the day 36.5 Sugars are transported from sources to sinks via the phloem Intro Movement of Sugar Sources to Sugar Sinks Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms 18. Define and describe the process of translocation. Trace the path of phloem sap from the primary sugar source to common sugar sinks. Translocation is the transport of food Phloem sap Flows through sieve tube members As much as 30% sucrose; also minerals, amino acids, hormones Translocation mechanism = pressure flow Sugar is actively transported into sieve tube members Water follows by osmosis Increased pressure pushes sap through sieve plates Pathway Sources: leaves, storage tissues Through sieve tube members Sinks: growing tissues, storage tissues, any living tissue 19. Describe the process of sugar loading and unloading. Various combinations of symplast and apoplast Into sieve tube members by cotransport with protons 36.6 The symplast is highly dynamic Intro Changes in Plasmodesmata Phloem: An Information Superhighway