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Chap. 36 Resource Ac
Campbell Biology Chapter 36: Resource Acquisition & Transport in Vascular Plants
| Question | Answer |
|---|---|
| Active transport | The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy. |
| Passive transport | The diffusion of a substance across a biological membrane with no expenditure of energy. |
| Cotransport | The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient. • a transport protein couples the diffusion of one solute to the active transport of another |
| Membrane potential | The difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances. |
| Water potential and water movement | The physical property predicting the direction in which water will flow, governed by solute concentration and applied pressure. • Water potential is a measurement that combines the effects of solute concentration and pressure • Water potential determine |
| Positive and negative pressure | Negative pressure decreases water potential. Positive pressure increases water potential. • can be negative à transpiration in the xylem tissue of a plant (water tension) • can be positive à water in living plant cells is under positive pressure (turgi |
| Tonoplast | The cytoplasmic membrane that surrounds a vacuole of a plant cell. Also called vacuolar membrane. |
| Routes of water movement through a plant | 1. Transmembrane route: out of one cell, across a cell wall, and into another cell 2. Symplastic route: via the continuum of cytosol 3. Apoplastic route: via the cell walls and extracellular spaces |
| Casparian strip | A water-impermeable ring of wax in the endodermal cells of plants that blocks the passive flow of water and solutes into the stele by way of cell walls. |
| Guttation | The exudation of water droplets from leaves, caused by root pressure in certain plants. |
| Transpiration | The evaporative loss of water from a plant. |
| Transpirational pull (1) | • Water is pulled upward by negative pressure in the xylem • Water vapor in the airspaces of a leaf diffuses down its water potential gradient and exits the leaf via stomata |
| Transpirational pull (2) | • Transpiration produces negative pressure (tension) in the leaf, which exerts a pulling force on water in the xylem, pulling water into the leaf • Transpirational pull is based on these properties of water: adhesion, cohesion, and surface tension. |
| Adhesion and Cohesion | Facilitate the transport of water by bulk flow. |
| Adhesion | • The attractive force between water molecules and other polar substances. • The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds. |
| Cohesion | • The attractive force between molecules of the same substance. • The linking together of like molecules, often by hydrogen bonds. |
| Stomata | A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant. |
| Guard cells | The two cells that flank the stomatal pore and regulate the opening and closing of the pore. |
| K+ Potassium | The absorption of K+ (potassium ions) causes the water potential to become more negative within the guard cells, and the cells become more turgid as water enters by osmosis. |
| Stomatal opening cues | Three cues contribute to stomatal opening at dawn: 1. Light 2. CO2 depletion 3. Internal “clock” in guard cells |
| Xerophytes | Plants adapted to arid (dry) environments (climates). |
| (Sugar) Source | A plant organ that is a net producer of sugar, by photosynthesis or by breakdown of starch. (mature leaves) |
| (Sugar) Sink | An organ that is a net consumer or depository of sugar. (growing roots, buds, stems, and fruits) |
| Phloem loading and transport (1) | • The products of photosynthesis are transported through phloem by the process of translocation • In many plants, phloem loading requires active transport • Proton pumping and cotransport of sucrose and H+ enable the cells to accumulate sucrose |
| Phloem loading and transport (2) | • At the sink, sugar molecules diffuse from the phloem to sink tissues and are followed by water. The pressure flow hypothesis explains why phloem sap always flows from source to sink |
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