Chapter 36 Reading Quiz

1. Chapter 36 Reading Quiz • What is the diffusion of water called? • What are “aquaporins”? • What is the symbiotic association between roots and fungi called? • The evaporation of water through leaves is called…? • What are xerophytes?

2. 1. List three levels in which transport in plants occurs. • The uptake and release of water and solutes by individual cells • Short-distance transport of substances from cell to cell at the levels of tissues and organs, such as loading of sugar from photosynthetic cells of a mature leaf into the sieve tubes of phloem • Long-distance transport of sap within xylem & phloem at the level of the whole plant 

4. 2. Describe briefly how transport proteins and selective channels play a role in plant transport. • Transport proteins facilitate diffusion by binding selectively to a solute on one side of the membrane and releasing it on the other • Transport proteins can act as selective channels which are passageways across a membrane 

5. 3. Describe how proton pumps help with active transport in plants. • Proton pumps hydrolyze ATP and use the released energy to pump H+ ions out of the cell - this results in a proton gradient, that is used by the plant to drive the transport of other substances across the membrane 

7. 4. Describe how differences in water potential within a plant cause water transport. • Water always moves from a higher concentration to a lower concentration, resulting in water transport (osmosis) 

8. 5. Define “turgor pressure” and describe what is means for a plant cell to be “turgid”. • Turgor pressure  the pressure inside a cell that begins to push against the plant cell wall • “turgid” cells are those that have a greater solute concentration than the surroundings - refers to the turgor pressure that keeps them firm - opposite is a “flaccid” cell 

11. 6. Identify the role that aquaporins have in water transport. • Aquaporins  channels that are water-specific transport proteins • These do not actively transport water, but facilitate water diffusion (osmosis) • Existence raises the possibility that a cell can regulate the rate of water uptake or loss when it has a different water potential than its surroundings 

12. 7. Describe the three major compartments that vacuolated plant cells have and their functions. • Symplast  the continuous pathway for transport of certain molecules between cells • Apoplast  the continuum of cell walls of the adjacent plant cells • Vacuole  can occupy up to 90% of the cell, for storage (water) 

15. 8. What is bulk flow? • It is the movement of a fluid driven by pressure • This is how water and solutes travel in plants • Diffusion is much too slow to function in this long-distance transport 

17. 9. Distinguish among the three adaptations plant roots have to increase water and mineral absorption. • Root hairs  extensions of the root’s epidermal cells; account for much of the root surface area • Mycorrhizae  symbiotic fungi which absorb water & minerals and transfer most to the plant’s roots • Large surface area  obviously helps to absorb more water and minerals the more surface that the roots can cover 

20. 10. What is the function of the endodermis? The Casparian strip? • Endodermis  the innermost layer of cells in the root cortex, surrounds the stele and functions as a last checkpoint for the selective passage of minerals from the cortex into the vascular tissue • Casparian strip  found in the wall of each endodermal cell; is a belt made of a waxy material impervious to water and dissolved mineral (can’t cross) 

21. 11. What do transpiration, root pressure, and guttation have to do with the ascent of xylem sap? • Transpiration  the loss of water vapor from leaves and other aerial plant parts • Root pressure  the upward push of xylem sap caused by the positive pressure of water flowing into the root cortex • Guttation  caused by root pressure; it is the exudation of water droplets that can be seen in the morning on tips of grass & leaf margins 

24. 12. Briefly overview how the transpiration-cohesion-tension mechanism works. Essentially how is this mechanism powered? • Transpiration provides the pull of xylem sap upwards • Cohesion & adhesion of the water molecules up the xylem path is a result of the polar quality of water • The transpirational pull creates a tension within the xylem 

26. 13. Describe the Photosynthesis-Transpiration Compromise. Why is this a compromise? • A plant must spread its leaves for photosynthesis and open its stomata to take in CO2 • By doing this, evaporation increases, water loss occurs • It is a compromise in that water loss must occur for transpiration, but that water is needed for photosynthesis 

28. 14. How are the stomata opened and closed? What determines their status? • Each stoma is flanked by guard cells • Changes in the leaf’s turgor pressure is what opens and closes the stomata • In general, stomata are open during the day and closed at night as this prevents the plant from needlessly losing water during the night • Light stimulates guard cells to become turgid and open 

30. 15. Describe what Circadian rhythms are and why they are important. • Cycles that have intervals of approximately 25 hours • All eukaryotic organisms have these internal clocks that somehow keep track of time and regulate cyclical processes 

31. 16. What are xerophytes? • Xerophytes are plants that are adapted to arid climates and have various leaf modifications that reduce the rate of transpiration • Examples: small, thick leaves, thick cuticle, stomata underneath leaf 

32. 17. List the components of phloem sap. Where does this substance go in the plant? • Phloem sap is an aqueous solution with a sucrose concentration as high as 30% • It may also contain minerals, amino acids, and hormones going from one part of the plant to another • The direction that phloem sap travels in is variable; sometimes it travels to growing areas of the plant or a sugar sink, an organ that stores sugars 

33. 18. Describe briefly the pathways that phloem may take in loading and unloading. • For sugars made in the mesophyll, symplastic, apoplastic, or a combination of both pathways can be used for sugars to get to the sieve-tube members (depends on the species) • At the end of the stream, the phloem is unloaded using active transport (in conjunction with proton pumps) 

35. 19. What is the main mechanism for the movement of phloem in angiosperms? • Pressure flow is the mechanism of translocation in angiosperms • Bulk flow is what is responsible for the huge amount of phloem movement in angiosperms 