Water Transport Flashcards
What are the advantages of living on land (2)
more light
oxygen and carbon dioxide more plentiful
what are the challenges of living on land (4)
overcoming gravity (early plants lacked lignin)
water less plentiful (maintain moisture)
water/nutrients at different locations than gases
dispersal of gametes
what are the five adaptations to living on land
- maintaining moisture
- reproduction an dispersal
- obtaining resources from two locations
- support body against gravity
- protection against stresses (abiotic and biotic)
how did plants adapt to maintain moisture on land
water transport systems (soil —> leaves)
cuticle/stomata to avoid/regulate water loss
pollen/seeds resistant to desiccation
how did plants adapt to reproduce on land
animal pollination, fruits, more targeted dispersal
how did plants adapt to obtain resources from two locations
larger leaves increase photosynthesis, larger plants, shoot and root system, transport systems (xylem and phloem)
how did plants adapt to gravity
thicker cell walls and lignin
how did plants adapt to protect against stresses
secondary metabolites
what came first? increased photosynthetic surfaces or increased water transport infrastructure
water transport
why did the first plant grow upwards
because of new lignified xylem tissue
why do mosses not grow tall like trees
they lack vascular tissues and lignin
what is the function of primary growth, how does this occur
to grow tall, growth at the tip
what is the function of secondary growth, how is this done?
to grow thicker, growth from the center
what is the secondary xylem
wood
how is secondary growth arranged going from centre to outside
primary xylem, secondary xylem, cambium/lateral meristem, secondary phloem, primary phloem
what are the two lateral meristems
vascular and cork cambium
what is the vascular cambium, which direction is growth
separates xylem and phloem, growth is inward and outward
what is the cork cambium and direction of secondary growth
secondary dermal tissue on the outside, outwards
what is bark
secondary phloem and cork
what is the vascular cambium
stem cells
how does leaves and wood help transport water
leaves evaporate water and help pull up xylem sap
wood stabilizes stem and forms new xylem each year
what are the three pathways water and nutrients move
apoplastic, symplastic, transmembrane
what is the apoplastic route
easy, through the cell wall
what is the symplastic pathway
transport through the cytosol via plasmodesmata
what is the transmembrane route
crossing plasma membrane, not as easy
what is an example of active transport of solute
pH gradient via proton pump (pumps H+ out of cell)
what is an example of co-transport of neutral solutes with protons
sucrose with the pH gradient (H+), occurs in the phloem
what is an example of co-transport of ions/nitrates with protons
H+ gradient with nitrate, mineral uptake into roots
what are aquaporins
bidirectional channel proteins that allow only water molecules to pass
why do are aquaporins needed
because the plasma membrane in made of fats making it water repellent, however not water impermeable
what is water potential
potential energy of water under given conditions compared to pure water under reference conditions
what is driven by water potential
direction of water flow (high potential to low potential)
what are two factors that affect water potential
pressure and solute concentration
what is an example of pressure potential
turgor pressure = pressure of plasma membrane against cell wall, and wall against protoplast
what occurs when the surroundings have lower water potential
plasmolysis
what occurs when the cell has lower water potential than pure water
turgid
where does water enter roots
via root hairs
what transport occurs at the casparian strip
symplastic
what transport occurs at the tracheary element loading
transmembrane
what transport occurs within the xylem
apoplastic
where does water evaporate
at leafs surface
what is water and mineral transport in the xylem driven by
transpiration in leaves
what does transpiration in leaves involve and create
water vapour diffuses from moist air spaces in the lead to drier air outside via stomata creating a steep water vapour gradient
what are the three general steps in water transport
water uptake from soil in roots, cohesion and adhesion in the xylem, transpiration in leaves
what is cohesion and adhesion
cohesion = water molecules stick to each other
adhesion = water molecules stick to the walls of cells
what type of bond is involved in cohesion/adhesion
hydrogen
what happens if the hydrogen bonds break?
cavitation
what is bulk flow driven by
evaporation: difference in pressure potential
do cells need to be alive to perform bulk water flow?
no
how much ATP/energy is used for the bulk flow of water?
none —> flow is not driven by biochemical processes but by the physical force of evaporation
what is transpiration
water loss by aerial organs
what is the function of the cuticle
prevents water loss at surface
where does water loss occur
through the stomata
how is water loss regulated
by stomatal density and pore opening/closing
how do stoma open
K+ ions pumped into cell, water follows K+ making guard cells turgid
how do stoma close
K+ ions pumped out, water follows, guard cell lose water and become flaccid
when are stomata usually open or closed and why
day = open, night = closed
to balance CO2 uptake and water loss —> driven by light/CO2 status/circadian rhythm
what environmental stresses can stomata respond to and how
heat/drought/wind = closure of stomata = hormone driven via abscidic acid
