transport in vascular plants Flashcards
chapter 36
what nutrients do shoots acquire above ground
carbon dioxide and sunlight
what nutrients do roots acquire below ground
water and minerals
describe the earliest plants
nonvascular and produced photosynthetic shoots above the shallow fresh water in which they lived
the shoots were leafless and had waxy cuticles and few stomata which allowed them to avoid excessive water loss while still permitting some exchange of CO2 and O2 for photosynthesis
as plants evolved and increased in number competition for resources increased. what adaptations did plants have to make to survive
some became taller with broad, flat appendages to absorb more light but this lead to a greater need for water and stronger root anchorage
these needs favoured production of multicellular branching roots
natural selection favoured plants capable of efficient long distance transport of water, minerals and products of photosynthesis
evolution of vascular tissue consisting of xylem and phloem made this possible
what are xylem
they transport water and minerals upwards from roots to shoots
what are phloem
they transport products form where they are made or stored to where they are needed
what is transpiration
the loss of water through leaves - mainly through the stomata
this creates a force within the leaves that pulls xylem sap upwards
if a plant is a photoautotroph what is its success largely dependent on
their ability to photosynthesise
why is there so much variation in branching patterns among different plants
plants only have a finite amount of energy to devote to shoot growth
if most of that goes into branching, there is less available for growing tall and the risk of being shaded by taller plants increases
on the other hand, if plants use all their energy in growing tall then the plants aren’t optimally harvesting sunlight
in what kind of environment do plants usually have smaller leaves
dry or cold environments where liquid water is scarce and evaporative loss is more problematic
what is phyllotaxy
the arrangement of leaves on a stem
what is phyllotaxy determined by
the shoot apical meristem
what is self pruning
when non productive leaves or branches undergo programmed cell death and are eventually shed
what is the leaf area index
the ratio of the total upper leaf surface area of a single plant or an entire crop divided by the surface area on the land n which the plant or crop grows
what factors affect light capture in plants
leaf area index
leaf orientation
when is it advantageous to have vertical leaves
when there is a lot of sunlight exposure
open stomatal pores allow diffusion of CO2 into photosynthetic tissues but what is a disadvantage of having open stomatal pores
they promote evaporation of water from the plant - this is why stomatal pore opening needs to be regulated and there needs to be a compromise between minimising water loss and enhancing photosynthesis
what are the 2 major compartments of plants
the apoplast and the symplast
what is the apoplast
consists of everything external to the plasma membrane of living cells and includes cells walls, extracellular spaces and the interior of dead cells
what is the symplast
consists of the entire mass of the cytosol of all the living cells in a plant as well as the plasmodesmata - the cytoplasmic channels that interconnect them
what are the 3 routes for transport in plants
apoplastic, symplastic and transmembrane routes
what is the apoplastic route of transport
water and solutes move along the continuum of cell walls and extracellular spaces
what is the symplastic route
water and solutes move along the continuum of cytosol. this requires substances to cross a plasma membrane once - when they first enter the plant
what is the transmembrane route
water and solutes move out of the cell across the cell wall and into the neighbouring cell
how is the voltage across the membrane (membrane potential) of a plant cell established
mainly through the pumping of hydrogen ions by proton pumps rather than by Na ions in animal cells
describe cotransport in plants using hydrogen ions
plants use the energy in the H gradient and membrane potential to drive active transport of many different solutes
e.g. a H/sucrose cotransporter couples movement of sucrose against its concentration gradient with movement of H down it electrochemical gradient
what is water potential
a physical property (considering solute concentration and physical pressure) that predicts the direction in which water will flow
measured in megapascals
water moves from a higher/lower water potential to a higher/lower water potential
higher to lower
what are the 4 main types of transport seen in plants
- H and the membrane potential (proton pump)
- H and the cotransport of neutral solutes (e.g. sucrose)
- H and the cotransport of ions (e.g. nitrate)
- ion channels (e.g. K channel)
what is solute potential proportional to
molarity
as solute concentration increases solute potential inc/dec
decrease
why is water in living plant cells usually under positive pressure
due to the osmotic uptake of water (its being pushed into the cell)
what decreases the permeability of aquaporin to water
an increase in cytosolic Ca or a decrease in cytosolic pH
long distance transport in plants occurs by which process
bulk flow - the movement liquid in response to a pressure gradient (from higher to lower pressure) and is independent of solute concentration
where does bulk flow occur
mainly in the vascular tissue i.e. the xylem and the phloem
what about the xylem and phloem facilitate bulk flow
the lack of cytoplasm - this makes the diameter larger and the substance being transported is able to flow faster
what is the equation for water potential
water potential = pressure potential + solute potential
if the water pressure is negative what can happen to the plant cell
the cell can plasmolyze - there is a net loss of water so the cell shrivels and the plasma membrane pulls away from the cell wall
what is the water potential of a turgid cell - explain
0 mpa - there is a net uptake of water - the cell wall creates a backwards pressure to offset the entry of water - water potential becomes for the cell and its surroundings
