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
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
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 