Chapter 36
暂无描述。系统推荐的高质量记忆内容，适合每天坚持背诵学习。
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xylem
a transport tissue in vascular plants which transports water from roots to leaves
phloem
the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation.
apoplastic
space outside the plasma membrane within which material can diffuse freely. The apoplastic route facilitates the transport of water and solutes across a tissue or organ. This process is known as apoplastic transport.
symplastic
he inner side of the plasma membrane in which water and low-molecular-weight solutes can freely diffuse. Symplast could also refer to the cytoplasmic connection made between cells by the plasmodesmata.
plasmodesmata
allows the direct flow of small molecules such as sugars, amino acids, and ions between cells. Larger molecules, including transcription factors and plant viruses, can also be transported through with the help of actin structures.
casparian strip
a band-like thickening in the center of the root endodermis (radial and cell walls) of vascular plants (Pteridophytes and Spermatophytes). The composition of the region is mainly lignin, and its width varies between species.
Psi Ψ
the gravity potential - Water potential is a measure of the potential energy in water as well as the difference between the potential in a given water sample and pure water. Water always moves from the system with a higher water potential to the system with a lower water potential.
bulk flow
process by which proteins travel throughout different areas of the plant
do stomata increase plant productivity?
yes - because they are responsible for gas exchange
is stomata density related to CO2 concentration in the air?
yes -
are stomata open or closed at night?
closed at night because they cannot perform photosynthesis
why is stomata density higher on the underside of leaves?
so that they dont lose too much water
which reflects the correct relationship of water potentials for a typical tree on a sunny day? • Leaf Ψ < trunk Ψ < soil Ψ • outside air Ψ> leaf mesophyll Ψ< root Ψ • leaf Ψ> trunk Ψ> soil Ψ • soil Ψ< root Ψ > leaf Ψ • none of the above
• Leaf Ψ < trunk Ψ < soil Ψ
the basis of the pull generated by transpiration in the xylem is ____.
negative pressure at the air-water interface in the leaf
water can follow two pathways in plants, apoplastic and symplastc. How do these pathways differ?
the apoplastic route is entirely external to cell membranes; the symplastic route is inside of cells
transport of xylem sap involves ___
transpiration - evaporation of water from plant’s surface ; negative pressure
water flows from root to cortex which generates ____
root pressure, a push of xylem sap ; positive pressure - at night root cells lower water potential by actively pumping mineral ions into the xylem
cohesion-tension hypothesis for xylem sap
transpiration provides the pull for the ascent of xylem sap and water cohesion transmits this pull along the entire length of the xylem from shoots to roots; xylem sap is normally under negative pressure or tension
Which of the following statements does NOT describe a function resulting from the action of guard cells? • lowering the loss of water upon detecting certain signals from water-stressed roots • keeping leaves at a more positive water potential relative to roots • allowing an optimal rate of photosynthesis to occur by letting CO2 enter the leaf • permitting cooling of the leaf by evaporative loss of water • allowing water to exit the leaf and so generating tension in the xylem tissue
keeping leaves at a more positive water potential relative to roots
water potential gradient
water potential decreases as you go further from the routes
mechanisms of stomatal opening and closing
the stomatal opening and closing depending on the generation of a potassium ion gradient. ATP produced in the guard cells during photosynthesis is utilized to pump the potassium ions of the adjacent cells into the guard cells. An increase in K+ion concentration in the guard cells makes them hypertonic, so more water is drawn inside the cells. Thus, the guard cells become turgid, widening the stomatal opening
if a potato tuber sends sugar to the rest of the plant during spring but receives sugar from the rest of the plant during summer, it moves from being _____
a source to a sink
translocation
the process by which products of photosynthesis are transported through the phloem
with sunny, warm, dry, and windy conditions the transpiration rates will ____
increase