mass transport in plants Flashcards
what is water made up from
- 2 atoms of hydrogen
- 2 atom of oxygen
- attraction between positively charged hydrogen and one water molecule and negatively charged oxygen of another water molecules causes water molecules to group together, called hydrogen bonds
- individually they are weak but form important forces which hold water molecules together
why is water important
- metabolite/ reactant in many metabolic reactions e.g. hyrdolysis
- polar molecule - acts as a universal solvent which metabolic reactions occur faster
- relatively high heat capacity, buffering changes in temp
- large latent heat of vapourisation, provides cooling effect with little loss of water through evaporation
- strong cohesion between water molecules, supports water in the tube like transport of cells of plants and produces surface tension were water meets air supporting small organisms
inorganic iosn and their functions
- iron ions = component of hb
- sodium ions = involved in co transort of glucose and amino acids in the small intenstine
- phosphate ions = component of ATP, phospholipid, DNA, RNA
- hyrdrogen ions = involved in co transport of sucrose in the phloem
- lower the pH of blood
- cause the bohr shift
what is a root hair cell do
nitrate ions move into the cell via active transport - this lowers water potential of cytoplams - water enters via osmosis
what is the cohesion- tension theory of water transport ( transpiration )
1) water is lost from the leaf due to transpiration, this is the evaporation of water molecules which then diffuse out of the spongey mesophyll, through the stomata, out of the leaf
2) this lowers water potential of mesophyll cells, drawing out of the xylem by osmosis
3) water is then pulled up the xylem, creating tension, as the water molecules stick together due to cohesion by hyrdogen bodning
4) forms a continuous collumn of water
5 ) adhesion of water molecules to walls of xylem prevents movement back down the xylem
where does transpiration occur
in the xylem
what happens to transpiration on a hot day
- rapid transpiration ( more heat energy, more rapid evaporation of water vapour )
- diameter of a tree trunk will reduce slightly owing to the movement of water making the xylme vessels slightly narrower
what is a potometer
- measures the volume of water uptake, not rate of transpiration
this is because : - water is used for structural suport of the plant
- water is used as a reactant in the ld stage of photosynthesis
- water used in hydrolysis reactions, to break a bond via the insertion of water
- water is prodcued during respiration
how to use a potometer
1) leafy shoot is cut under water
2) dry leaves
3) potometer filled with water making sure there are no air bubbles
4) using a rubber tube, the leafy shoot is fitted to the potometer under water
5) an air bubble is introduces into the capillary to track the movement of water taken up by the shoot. As transpiration occurs, water moves through the capillary tube and the bubble of air moves with it
6) measure the distance the bubble moves ( start and final position ), this gives you your length
7) repeat by opening the tap on the resevoir which returns bubble to start
8) measure diameter of capillary tube
9) divide by 2 to get radius
10) use formula pi x radius squared x mean lenght to get volume of water taken up
how do you calculate rate of uptake
volume / divided by time
how to calculate surafce area of a leaf
draw around the leaf on graph paper and count the number of squares covered
how does temp affect rate of transpiration
as temp increases there is a higher rate of transpiration
more water vapour is lost through the stomata, creating higher tension in the xylem
how does humidity affect rate of transpiration
an increase in humidity will decrease the water potential between the air outside the stomata and the spongey mesophyll, decreasing the rate of transpiration
how does air movement affect transpiration
an increase in air movement around the stomata will increase the water potential gradient between the air previously saturated with water vapour and the spongey mesophyll, increasing the rate of transpiration
how does light intesnity affect transpiration
as light intensity increases, the stomagta will open up for longer allowing co2 to diffuse for photosynthesis.
this causes higher rates of transpiration through the open stomata
what is dry mass
samples are dried in an oven at 100 degrees, wiegh and repeat until you get a constant mass
this will evaporate all the water but not burn the organic compounds leaving only biomass
what is the mass flow hypothesis for the mechanism of translocation
- at a source, phloem is actively transported into the sieve tube element of the phloem by companian cells
- this lowers the water potential in the sieve tube element of the phloem
- water enters by osmosis, increasing the volume causing high hydrostatic pressure
- this increase in pressure causes mass movement, transporting sucrose towards the roots and the other storage tissues ( known as a sink ) down a pressure graident
- at the sink/roots, sucrose is removed from the phloem where it is unloaded and can be used in respiration to produce ATP or stored
what is the sieve tube
part of the phloem
thin walled, have pores at each end
what is a metabolic inhibitor
stops ATP, stops translocation
what is a ringing experiment
- in the stem, phloem vessels are exterior to the xlyem vessels, meaning the phloem can be selectively removed byb cutting a ring in the stem deep enough to cut the phloem but not the xylem
- after a week there is swelling above the ring, but reduced growth below the ring.
this is evidnece for mass flow hypothesis that sugars were transported downwards
what is autoradioradiography using radioactive tracers
- used to determine which tissue carries radiocatively labelled sucrose
- one leaf is exposed to carbin dioxide containing the radioactive isotope 14c
- this 14co2 will be taken up by photosynthesis and the 14c incorporated into glucose and then sucrose
- the plant is then frozen in liquid nitrogen to kill it ad fix it quickly
- take thin horizontal sections of plant tissue / stem and place them againts photographic film for several hours
what are puncture experiments
- if the phloem is punctured with a hollow tube the sap will ooze out, showing that there is high pressure inside the phloem
- if the xylem is punctured then air is sucked in, showing that there is a low pressure inside the xylem
- an aphid may leave mothparts in
- evidence that shows the xylem and phloem transport substances differently
- water is pulled up the xylem, sap is pushed down in the phloem
