3.3 Transport in Plants Flashcards
why is transport systems needed in plants?
small SA:V ratio
high metabolic demand
long distance from external surface
diffusion is too slow
what are the vascular tissues made up of
xylem and phloem
describe how to dissect a plant to view the distribution of vascular bundles
cut a plant transversely
dip into dye
view under microscope
explain mass flow hypothesis
the movement of water and solutes from an area of high concentration to an area of low concentration due to turgor pressure
describe translocation (6 marks)
- loading of sucrose into the top of the phloem from the SOURCE
- creates a high hydrostatic pressure at the top and a low water potential
- water moves in from the xylem by osmosis because of the low water potential
- the bottom of the phloem has a low hydrostatic pressure, so creates a hydrostatic pressure gradient
- the assimilates move down through the sieve plates
- water leaves the bottom of the phloem by osmosis, and is pulled back up to the top of the xylem because of transpiration
- assimilates loaded to the SINK
describe the active loading of sucrose from companion cell to sieve tube elements (6marks)
- H+ is pumped out of companion cell in proton pumps, by active transport
- Concentration of H+ outside is higher than inside so H+ moves back in, WITH sucrose, via a co-transporter protein
- the concentration of sucrose inside companion cells is higher than the concentration of sucrose in sieve tube elements so diffuse into sieve tube element down a conc. gradient, through PLASMODESMATA
- water moves in as well by osmosis generating a turgid pressure for MASS FLOW
describe the apoplast pathway
Goes through the cell walls and spaces between them
passive diffusion
describe the symplast pathway
Goes through the cytoplasm and plasmodesmata
Water moves through via osmosis
What does the Casparian strip do?
Blocks the apoplast pathway, forcing water into the symplast pathway
Symplast pathway is partially permeable, controls what substance can enter and get to the xylem
what is transpiration
the process by which plants release water vapour into the atmosphere through their leaves,
How is water transported in the xylem ?
(6 marks)
- transpiration - water evaporates from leaves - creates low pressure - pulls water up from root
- cohesion and adhesion
- transpiration stream
what is cohesion
water molecules stick together - forms a continuous column
what are the main factors affecting transpiration?
- Light intensity
- Temperature
- Humidity
- Wind movement
how does temperature effect transpiration rate ?
Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises.
how does light intensity effect transpiration rate ?
causes more stomata to open, which allows water vapor to escape
rate of transpiration increases
how does wind effect transpiration rate ?
faster wind = increased rate of transpiration
how does humidity effect transpiration rate ?
Concentration gradient decreased because:
More H2O molecules in air than leaves
Rate of transpiration decreases
What are xerophytes?
plants that are adapted to live in very dry conditions
What are some adaptions of xerophytes?
Smaller leaves – reduces surface area
Thick, waxy cuticles
Hairy - traps moist air
Deep roots
what are hydrophytes?
plants which can live in water
what are some adaptations of hydrophtes?
Thin waxy cuticle – no need to conserve water
Flat and wide leaves – large SA for light absorption
Air sacs - for buoyancy
what is adhesion
water molecules stick to xylem walls - counteract gravity
define the transpiration stream
the continuous flow of water from roots to leaves
how does water and minerals move up roots
- water enters by osmosis
- minerals enter by active transport
pathways taken by water
- apoplast - water moves through cell walls
- symplast - through cytoplasm of cells
action of Caspirian strip
- at endodermis
- blocks apoplast
- forces water to take symplast pathway
why does water have to take symplast pathway if blocked by casparian strip?
- controlled by the plasma membrane which allows what can enter or cant
similarity between xylem and phloem
made of cells joined end to end
