Chapter 36 Flashcards
Early nonvascular land plants
lived in shallow water and had aerial roots
What is the tradeoff in plants?
Enhancing photosynthesis
Minimizing water loss
Phyllotaxy
the arrangement of leaves on a stem
important for light capture
As water availability increases,
Leaf size normally increases
Self-pruning
shedding of lower shaded leaves
they loose more than they gain through photosynthesis, so they are removed
Horizontal leaves
Better in low-light conditions since they capture more sunlight
Vertical leaves
Better in sunny conditions because they are less damaged by sun and allow light to reach lower leaves
Mycorrhizae
Roots and hyphae of soil fungi form mutualistic associations
Increases surface area
Helps plants colonize land
Apoplast
refers to transport outside of the plasma membrane (not cell wall)
Symplast
refers to transport within the cytosol and plasmodesmata
The Apoplastic Route
through cell walls and extracellular spaces
The Symplastic Route
through the cytosol and plasmodesmata
The Transmembrane Route
Across cell walls
How is membrane potential established?
Pumping hydrogen ions by proton pumps
this establishes a concentration gradient
Water potential
a measurement that combines the effects of solute concentration and pressure
Which way does water potential flow?
From regions of higher water potential to regions of lower water potential
Solute potential
always negative. lowers the water potential
Pressure potential
physical pressure on a solution, like from a cell wall
Turgor pressure
the pressure exerted by the plasma membrane against the cell wall and protoplast
Protoplast
living part of the cell, which also includes the membrane
What will happen to a flaccid cell?
Plasmolysis
If placed in a salty surrounding environment
Plasmolysis
occurs when the protoplast shrinks and pulls away from the cell wall
Turgid
cell gains water
flaccid cell placed in lower solute concentration outside the cell
Aquaporins
transport proteins in the cell membrane that facilitate the passage of water
affect the rate of water movement across the membrane
Endodermis
intermost layer of cells in root cortex
last checkpoint for selective passage into vascular tissue
Casparian strip
blocks apoplectic transfer of minerals from the cortex to vascular tissue
water and minerals forced to cross a plasma membrane
Xylem sap
water and dissolved minerals now in the vascular system
Transpiration
the evaporation of water from a plant’s surgace
How does transpiration pull water?
When it evaporates, it needs more water to replace it
Creates negative pressure
Root pressure
the water potential is low in the xylem, so it flows there
push of xylem sap
minor mechanism
Guttation
effect of root pressure
exudation of water droplets on tips of leaves
Adhesion
water molecules are attracted to cellulose in xylem cells
offsets the force of gravity
Cohesion
water molecules are attractched to eachother
Does bulk flow require energy?
No. Largely driven by transpiration which relies on sunlight to open and close stomata
Bulk flow versus diffusion
Driven by differences in pressure potential, not solute potential
occurs in dead and alive cells
moves the entire solution
faster
What opens and closes stomata
Changes in turgid pressure
When turgid, guard cells bow outward and the pore opens
When flaccid, guard cells are less bowed and the pore closes
Results from K+ solute potential
Stomatal opening at dawn is triggered by
Light
CO2 depletion
Circadian rhythms
Abscisic acid
hormone produced in response to water deficiency and causes closure of stomata
How does sugar move?
From source to sink through the phloem, specifically sieve tube
often requires active transport
What else does the phloem transfer
Viruses, information, electrical signals
The symplast does NOT transport
DNA
Active transport at the cellular level does not require
Xylem membranes
Which of the following would not normally function as a sink?
Mature leaf
What process is not affected by proton gradients?
Xylem transport
Which of the following experimental procedures would most likely reduce transpiration while allowing the normal growth of a plant?
Increasing the level of carbon dioxide around the plant
If the guard cells and surrounding epidermal cells in a plant are deficient in potassium ions, all of the following would occur except
Leaf temperatures would decrease
What drives water through the xylem?
Evaporation in leaves
What does bulk flow not depend on?
Force of gravity
Which is false of phloem cells?
Companion cells control the rate and direction of movement of phloem sap.
One would expect to find the highest density of aquaporins in which of the following
the plasma membrane of guard cells
CAM plants
Keep stomatas open at night for CO2
Keep stomatas closed during day to prevent transpiration
What causes cohesion
Hydrogen bonds between oxygen atom of one water molecule and hydrogen atom of another water molecule
Sugar movement in phloem
Can go upwards and downwards
primarily goes downwards
Tomato problem
Stomata apertures
All of the following involve active transport across membranes except
the movement of sugar from one sieve-tube element to the next
