Transcript 1. List three levels in which transport in plants occurs.

Chapter 36 Reading Quiz
1. What is the diffusion of water
called?
2. What are “aquaporins”?
3. What is the symbiotic association
between roots and fungi called?
4. The evaporation of water through
leaves is called…?
5. What are xerophytes?
1. List three levels in which transport in
plants occurs.
1.
The uptake and release of water and
solutes by individual cells
2. 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
3. Long-distance transport of sap within
xylem & phloem at the level of the whole
plant 
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 
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 
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) 
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 
6. Identify the role that aquaporins have in
water transport.
• Aquaporins  channels that are waterspecific 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 
7. Describe the three major compartments
that vacuolated plant cells have and their
functions.
1.
Symplast  the continuous pathway for
transport of certain molecules between
cells
2. Apoplast  the continuum of cell walls of
the adjacent plant cells
3. Vacuole  can occupy up to 90% of the
cell, for storage (water) 
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 
9. Distinguish among the three adaptations
plant roots have to increase water and
mineral absorption.
1.
Root hairs  extensions of the root’s
epidermal cells; account for much of the
root surface area
2. Mycorrhizae  symbiotic fungi which
absorb water & minerals and transfer
most to the plant’s roots
3. Large surface area  obviously helps to
absorb more water and minerals the more
surface that the roots can cover 
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) 
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 
12. Briefly overview how the transpirationcohesion-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 
13. Describe the PhotosynthesisTranspiration 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 
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 
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 
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 
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 
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) 
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 