Water and Sugar Flashcards
what enters through the roots
Oxygen, minerals, and H2O
What enters through the leaves
CO2
What was the advantage of the evolution of xylem and phloem in land plants
made possible the long-distance transport of water, minerals, and products of photosynthesis
- plants gain the ability to maximize access to light, increase dispersal distance, occupy new habitats
Disadvantages of Xylem and Phloem
loss of H2O
Selective permeability
the control of movement of substances into and out of cells
Diffusion
Passive movement of particles across membrane
No energy is required for facilitating movement
Active transport
Pumping of solutes across membrane
what does active transport require
transport proteins embedded in the cell membrane
What does transport begin with
the absorption of resources by plant cells
Proton pump
Most important protein for active transport
Create hydrogen ion gradient that is a form of potential energy that can be harnessed to do work
Contribute to a voltage known as a membrane potential
Plant cells use energy stored in the ___
Proton gradient and membrane potential to drive the transport of many different solutes
Symport or cotransport
A transport protein couples the diffusion of one solute to the active transport of another
The “coattail” effect of cotransport
also responsible for the uptake of the sugar sucrose by plant cells
Aquaporins
water-selective pores in plasma membrane that increase the rate of osmosis because they allow bulk flow
restrict the flow of solutes
The rate of water movement is likely regulated by phosphorylation of the aquaporin proteins
Why do plants need to uptake water
to offset the loss of water
Osmosis
Movement of water across a semi-permeable membrane down a water potential gradient
determines the net uptake or water loss by a cell and is affected by solute concentration and pressure
Water potential
a measurement that combines the effects of solute concentration and pressure
Water potential determines
the direction of movement of water
water flows from region of ____ potential to regions of ____ lower water potential
higher
lower
water potential is measured in units of pressure called
megapascals (MPa)
pressure of water at sea level and room temp
0 MPa
solute potential of a solution
proportional to the number of dissolved molecules
osmotic potential
another name for solute potential
Pressure potential
the physical pressure on a solution
Turgor pressure
the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast
Water potential =
Pressure potential + Solute potential
Plasmolysis
cell membrane pulls away from cell wall
Turgid
cell membrane pushed against the cell wall
Transport is also regulated by
the compartmental structure of plant cells
The plasma membrane
directly controls the traffic of molecules into and out of the protoplast
is a barrier between two major compartments, the cell wall and the cytosol
Third major compartment in most mature plant cells is the
vacuole
vacuole
a large organelle that occupies as much as 90% or more of the protoplast’s volume
vacuolar membrane
regulates transport between the cytosol and the vacuole
In most plant tissues, the cell wall and cytosol are
continuous from cell to cell
symplast
the cytoplasmic continuum
plasmodesmata
the cytoplasm of neighboring cells is connected by channels called the plasmodesmata
apoplast
the continuum of cell walls and extracellular spaces
Water and minerals can travel through a plant by these three routes
symplastic, apoplectic, transmembrane
symplastic route
via the continuum of cytosol
Apoplastic route
via the cell walls and extracellular spaces
Transmembrane route
out of one cell, across a cell wall, and into another cell
bulk flow
the movement of a fluid driven by pressure
Efficient long distance transport of fluid requires bulk flow
Water and solutes move together through
tracheids and vessel elements of xylem, and sieve-tube elements of phloem
Efficient movement is possible because
mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm
what accounts for much of the surface area of roots
root hairs
most water and mineral absorption occurs near
root tips, where the epidermis is permeable to water and root hairs are located
After soil solution enters the roots, the extensive surface area of Cortical Cell membranes
enhances uptake of water and selected minerals
Water can cross the cortex via the
symplast or apoplast
Endodermis
The innermost layer of cells in the root cortex
Surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue
Waxy Casparian strip of the endodermal wall
blocks apoplectic transfer of minerals from the cortex to the vascular cylinder
Transpiration
the evaporation of water from a plant’s surface
Xylem sap
Bulk flow of water and minerals replacing water lost
From the steles of roots to the stems and leaves
Root pressure sometimes results in
guttation
guttation
the exudation of water droplets on tips or edges of leaves
Positive root pressure is _____ and is a ______ of xylem bulk flow
relatively weak, minor mechanism
Transpiration produces a ____pressure in the leaf, which exerts a
negative,
pulling force on water in the xylem, pulling water into the leaf
Transpirational pull is facilitated by ______ of water molecules to each other and _____ of water molecules to cell walls
Cohesion
Adhesion
What accounts for 95% water loss
Stomata
Three cues signal stomatal opening
Light stimulates the uptake of K+ in guard cells
- Blue wavelengths
Depletion of CO2 within the leaf
Internal clock
Internal clock
Circcadian rhythm
plants kept in the dark continue to open stomata on a 24 cycle
What is the major cue for closing during the day
water stress
Guard Cell Movement
Active pumping of sucrose out of guard cells in the evening leads to loss of turgor and closes the guard cell
Xerophytes
plants adapted to low water conditions that have morphological adaptations
Xerophyte adaptations
reduced leaves
dormancy
loss of leaves - deciduous plants
covering leaves with cuticle and wooly trichomes
reducing the number of stomata
having stomata in pits on the leaf surface
Crassulacean Acid Metabolism (CAM)
stomata open at night
CO2 stored as malate
released during the day to the Calvin cycle allowing the stomata to be closed during the day
Ferns, gymnosperms, monocots all have species that use CAM
Most of CAM species are angiosperms
Phloem sap
an aqueous solution that is high in sucrose
Sugar sources move from
a sugar source to a sugar sink
sugar source
an organ that is a net producer of sugar, such as mature leaves
sugar sink
an organ that is a net consumer or storer of sugar, such as a tuber or bulb
storage organ can be both
a sugar sing in summer and a sugar source in winter
sugar must be loaded into ______ before being exposed to sinks
sieve-tube elements
Sugar may be moved by ________ or both _______ and ______ pathways
symplastic or both symplastic and apoplastic
Transfer cells
modified companion cells that enhance solute movement between the app-last and symplast
What do some plants use the phloem for
a form of electrical signaling
What does the phloem do in some plants
moves macromolecules and some types of RNA via plasmodesmata
Movement of proteins and RNA unique to plants
