Lectures 5-6-7 Flashcards
Passive Transport
Refers to the spontaneous movement of molecules down a chemical potential gradient, from high to low
At equilibrium, no further movement occurs unless _________
energy is applied (energy input)
Involves the movement of substances against a chemical potential gradient. This process is not spontaneous and requires energy.
Active Transport
A common way to do active transport
ATP hydrolysis for energy
Movement along a concentration gradient is complicated by
membrane permeability and ion passage.
think ions
Diffusion of salts across membranes creates
electrical membrane potentials
A small concentration difference, such as one extra anion in 100,000, can result in a significant membrane potential of around
-100 mv
K+ ions cross membranes ____________ than Cl- ions, causing a charge separation (diffusion potential).
faster
Some ions are passively transported, while others require active transport, true or false
true
Ions and Proton Transport
the diffusion potential is caused by
ions moving across the membrane causing a voltage
Ion and Proton Transport
Membrane potential in plant cells ranges from
-200 mV to -100 mV.
Ion and Proton Transport
[ blank ] is crucial for generating membrane potential through [blank]
H+-ATPase, ATP hydrolysis.
ATP hydrolysis is for energy
Proton Transport
Mitochondrial poisons like [blank], [blank] ATP, affecting membrane potential and passive ion transport.
what do these poisons do
cyanide, deplete
Membrane Transport
Biological membranes contain transport proteins such as …… (3)
channels, carriers, pumps
Membrane Transport Proteins
Channels have….
Selective pores extending across the membrane, enhancing diffusion
Channel proteins follow what kind of diffusion
passive transport (high to low), down the gradient
A transported molecule follows what kind of diffusion
simple diffusion (high to low, down the gradient)
Carriers Proteins…
Do not have pores but bind and transport specific molecules across the membrane (down, high to low)
Membrane Transport
Pumps….
Use energy (ATP hydrolysis) for primary active transport.
Membrane Transport
Secondary Active Transport…
Uses proton motive force (energy by H+ gradients) for transport
Types of Transporters:
Symports: Transport two molecules in the [blank] direction.
Antiports: Transport two molecules in [blank] directions.
same, opposite
pumps move protons against or across the gradient
against (low to high)
membrane transport
symports and antiports are type of channels, carriers or pumps?
pumps
how do symporters work
transports two molecules in the same direction across the membrane. One molecule moves down its electrochemical gradient (providing the energy), while the other molecule is transported against its concentration gradient.
how do antiports work
An antiporter moves two molecules in opposite directions. One molecule moves down its electrochemical gradient, which provides the energy to move another molecule in the opposite direction, against its gradient.
membrane transport
most transport processes are energized by a [blank] [blank] transport system coupled to [blank]
primary active, atp for hydrolysis
Phloem
Phloem in Secondary Growth is found where
Found in inner bark
phloem is generally found where
outer side of xylem in vascular bundles
in the primary xylem, cells might be red because
may contain lignin
Sieve Elements
Conduct sugars and organic compounds
in angiosperms, how specialized are sieve tubes
highly specialized
In gymnosperms, how specialized are sieve cells
less specialized
xylem transport
[blank] elements lack nuclei, vacuoles, Golgi bodies, ribosomes, and cytoskeletal elements, making them efficient conduits for transport.
sieve elements
phloem transport
Associated with sieve elements and perform crucial functions like protein synthesis and ATP supply.
companion and parenchyma cells
phloem transport
sieve elements have [blank] primary cell walls with no [blank]
thinner, lignin
phloem cells are [blank] at maturity
alive
Sieve elements are associated 1:1 with a helper cell or companion cell, the companion cell is complete with everything, so any of the proteins found in metabolic functions, not able to be made by sieve elements are taken over by [blank]
companion cell (nurse cell)
sieve areas are found in [blank] while sieve plates are found in [blank]
gymnosperm, angiosperms
Sieve plates (in angiosperms) contain
pores that interconnect cells.
In gymnosperms (sieve areas), pores are obstructed by the
ER
Damaged sieve tubes are initially sealed by [blank] (not found in gymnosperms)
p-proteins
p-protein are associated with
angiosperms so sieve plates
[blank] (a β-1,3-glucan) is deposited long-term to repair damaged sieve plates.
callose
sieve plates found in angiosperms
companion cells
Sieve elements are connected/associated with to [blank] cells and connect via [blank]
plasmodesmata
Companion cells are responsible for: (they take over these functions from sieve elements)
protein synthesis and atp supply
companion cells
Have chloroplasts and a smooth inner cell wall.
Ordinary companion cells
companion cells
Have finger-like wall ingrowths to facilitate solute transfer.
transfer cells
companion cells
Highly connected to surrounding cells, aiding in efficient transport.
intermediary cells
xylem flows in how many directions
one, roots to leaves
phloem moves in which direction
bi-directional, but not at the same time
can the direction of the phloem reverse
yes
A [blank] is any tissue that has more sucrose than it needs, so it can export that solute. A [blank] does not produce enough product to support themselves.
source, sink
why does water only flow from roots to leaves and not the other way
transpiration pull causing negative pressure, cohesion-tension theory, water potential gradient (moves from high in roots to low in leaves bc water is lost in leaves via transpiration), root pressure causing positive pressure
Sources involve
organs like mature leaves and storage roots.
Sinks involve Organs that need more photosynthetic products than they produce, such as
roots, developing fruits, immature leaves
source and sink status of the same organ can change, true or false
true
is the pressure flow model passive or active
passive
The [blank] is driven by an osmotically generated pressure gradient between the source (leaf) and the sink (root, fruit, etc.).
bulk flow of phloem sap
phlome sap movement (pressure flow model)
Bulk flow refers to the
mass movement of the sap due to pressure differences.
how does the osmotic (solute) gradient work in the bulk flow of phloem sap
- sugars loaded in phloem (high solute)
- high solute = low water.
- water moves into phloem from xylem, creatives positive turgor in sieve elements
- sugars unloaded into sink
- less solute = high water, water moves out and reduces this pressure
Why is energy is needed at both the source and sink:
At the source, active phloem loading occurs (requiring ATP). At the sink, phloem unloading also requires energy.
3 mechanisms generate high sugar [ ] in sieve elements
- photosynthesis
- photoassimilate into sugars
- active membrane transport
which sieve element maintains water potential
sieve plate cross walls, water dissipates via open tubes
sieve plate pores must be totally [blank] (open or closed)
unobstructed
how does limitation of atp affected bulk flow movement of phloem sap
does not immediately stop phloem transport
pressure gradient must be greater than [blank] for bulk flow occur
resistance in sieve plates
apoplast loading of phloem sugar
- Active Transport
- Sucrose moves from mesophyll into the apoplast (the cell wall space)
- actively transported into sieve and companion cells.
-Requires (ATP) to actively transport sucrose into the phloem using sucrose-H+ symporter. - (H+ ions) drive this symport, created by H+-ATPase (proton pump), which uses ATP to pump protons into the cell.
symplastic loading of phloem sap
- sucrose moves from mesophyll to phloem cells via plasmodesmata (cytoplasmic connections between cells).
- No energy required
- Larger sugars like raffinose and stachyose are synthesized in intermediary cells
- prevents them from diffusing back into mesophyll cells, ensuring they move into sieve elements (this is known as the polymer-trapping model).
polymer trapping model
Larger sugars like raffinose and stachyose may be synthesized in intermediary cells, preventing them from diffusing back into mesophyll cells, ensuring they move into sieve elements (this is known as the polymer-trapping model).
symplastic unloading is [blank] while apoplastic unloading is [blank]
passive, active
How do you drive diffusion in symplastic unloading
Once in the sink cells, sugars are metabolized or stored, maintaining a low sugar concentration, which drives the diffusion from the sieve elements.
apoplastic unloading
especially in tissues like seeds, sugars are unloaded into the apoplast (the space outside cells) and then transported into sink cells by active transporters.
symplastic pathways have a high or low sucrose [ ]
low, which drives concentration gradient of sugars form sieves to sink
how do sinks become sources
- young leaves start as sinks
- becomes sources when 25% expanded
- starts at the tip to the base
- plasmodesmata close and become few
- reduced symplastic connectivtiy
allocation vs partitioning
Allocation: how much of the carbon fixed in photosynthesis is used for various functions (e.g., growth, storage, respiration).
Partitioning: Refers to how the fixed carbon (sugars) is distributed between different plant organs (e.g., roots, shoots, fruits).
