mass movement plants (JPB) Flashcards
what is the vascular bundle
it is composed of xylem and phloem cells
what is the purpose of the xylem
it transports water and mineral ions
what is the purpose of the phloem
it transports sugars and plant hormones
what are the stomata
they are pores on the leaf, usually on the underside.
it is where water is evaporated from and is controlled by the guard cells
what are features of the xylem vessels
they are hollow tubes with no end walls which provides a continuous water column
they have no organelles preventing chemical reactions that would slow down the process
they are covered in lignin providing structural support and making them waterproof
they have pits in the walls which allows lateral movement of water if there is a blockage
what is the role of the stomata
they control water loss and regulate gas exchange
how does the stomata do its job
the stomata are surrounded by guard cells
when it is light k+ ions move into the guard cells making it more concentrated so water moves in by osmosis and cells become more turgid causing them to open
the spongey mesophyll in leaf only have a few mesophyll cells and may air spaces making it easier for water and gas to move through the leaf
what is appoplastic
through the cell wall
what is symplastic
through the cytoplasm
how does water move through the leaf
the evaporation of water from the stomata lowers the water potential in the mesophyll of the leaf, a transpiration pull is created. water molecules are pulled up through the xylem, they have hydrogen bonds and cohesion. this allows a continuous water column to . the water molecules also stick to the wall of the xylem due to adhesion and pull the walls of the xylem in
what are the factors affecting the rate of transpiration
humidity / greater concentration gradient between inside and outside
temperature / water has more kinetic energy so faster evaporation
wind / water carried away maintaining concentration gradient
light / more stomata open so more evaporation
evidence for CTT (cohesion tension theory)
1) if xylem vessel is damaged air gets in and there is no longer a continuous water column , cohesion is lost and so is the transpiration pull
2)the diameter of tree trunks change during the day. daytime photosynthesis= transpiration= tension = adhesion
what is a potometer
they measure the rate of transpiration
what three things do you do when you use a potometer
air tight rubber bung = no air in xylem
cut under mater so air doesn’t get in
cut at 45 angle so no cell damaged
what is translocation
the movement of sugars up and down the phloem
what is the source of a plant
give an example
it is the place where photosynthesis occurs and where sugars are made
e.g. leaf
what is the sink of a plant
give example
if sugars are not used in respiration they are stored as starch in the roots
what is the structure of the phloem
there are end walls called the sieve plates
sieve tube elements (STE)/sieve cells
companion cells
they keep the STE alive by providing nutrience and are packed with mitochondria
what are features of the phloem
there are very few organelles so more space for sugars
there are no end walls
long hollow tubes
how are sugars transported from the source to the sink
in source high conc of sucrose, this is actively transported from CC to STE using ATP
this decreases the water potential in the STE so water moves in by osmosis creating high hydrostatic pressure
this forces solutes down the phloem to sink
the sink uses or breaks down the solute so lower conc at sink, this increases the water potential inside the STE as there is less solute and more water causing water to move back into the xylem by osmosis
this decreases the pressure in the phloem resulting in mass movement
what is evidence for MFH ( mass flow hypothesis )
pressure in STE released when cut
concentration of sucrose higher in leaves than roots
downward flow in phloem during day opposite during night
increase sucrose level in leaf flowed by similar increase in the phloem
pyric acid , metabolic poisons and lack of oxygen inhibits translocation of sucrose
companion cells contain many mitochondria and readily produce ATP
what is the ringing experiment
the sugars of phloem build up above ring causing swelling
eventually regions below ring begin to die
what is the tracer experiment
radioactive label carbon dioxide is absorbed by the plant
the isotope incorporated into sugars is produced during photosynthesis
it can be traced as it moves within the plant
