TRANSLOCATION Flashcards
1
Q
translocation
A
- transport of soluble materials i.e sucrose/amino acids
2
Q
structure of phloem (inc. sieve tube elements, plasmodesmata, companion cell, pores)
A
- labeled diagram
3
Q
experiments showing phloem transports organic substances (4)
A
- ringing experiments
- radioactive tracers & audiography
- aphid experiments
- aphids and radioactive tracers
4
Q
ringing experiments (5)
A
- remove cylinders of outer bark, removing phloem
- after leaving plant to photosynthesis phloem content below and above ring analysed
- above ring was lots of sucrose (translocated via the phloem
- below the ring was no sucrose, as it had been used and not replaced bc. could not move down
- bark above the ring swelled slightly bc. solutes were accumulating but couldn’t go down
5
Q
radioactive tracers and autoradiography (4)
A
- plant photosynthesises in presence of carbon-14 (radioactive)
- stem section is placed on photographic film, exposed if there is a radiation source and produces autoradiograph
- position of exposure shows radioactivity and coincides with phloem location
- shows phloem translocates sucrose from CO2 (14)
6
Q
aphid experiment (5)
A
- has hollow needle mouth called stylet
- inserted into sieve-tube and phloem contents
- sap exudes under pressure into stylet
- sometimes the aphid is anaethetised & removed while stylet remained
- sap collected analysed to contain sucrose
7
Q
aphids and radioactive tracers (3)
A
- aphids inserted into plants with carbon-14
- showed radioactivity and the speed of phloem
- faster than normal diffusion so there must be a mechanism
8
Q
mass flow
A
passive mass flow of sugars from the phloem of the leaf (source) (high conc.) to the growing tissues (sink) (low conc.)
9
Q
diagram
A
labels flow of solution concentrated sucrose partially permeable water movement from high to low water water or dilute sucrose water movement by hydrostatic pressure
10
Q
steps of mass flow (6)
A
- leaves, source of sucrose, have a very neg. water potential so water passes in via osmosis
- some water passes into sink but very little
- as water enters leaves hydrostatic pressure builds up forcing water into phloem
- pressure pushes water down phloem in mass flow
- water moves from leaf, down phloem, to sink
- increased pressure forces water out of sink into xylem to flow back to source
11
Q
why doesn’t mass flow explain everything? (5)
A
- rate is phloem transport is much faster than diffusion
- doesn’t take sieve plates into account
- sucrose & amino acids move at different rates
- phloem has high o2 consumption and slows at low temps and when respiration is compromised
- companion cells are very biochemically active but mass flow does not give them a role
12
Q
other theories (3)
A
- active process as cyanide and resp. inhibitors stop it, suggesting ATP is used
- protein filaments pas through sieve pores so perhaps different solutes take different routes through the same sieve tube element
- cytoplasmic streaming could cause movement in different direction if there was a mechanism for transport through sieve tube elemets
