translocation

Question 1

define translocation

Answer 1

movement of assimilates throughout the plant in the phloem

Question 2

what are assimilates

Answer 2

substances made by plant, using substances absorbed from environment
incl sugar(transported as sucrose , soluble + metabolically inactive, doesnt get used up) ,amino acid

Question 3

define source

Answer 3

part of plant that loads assimilates into phloem sieve tubes

Question 4

example of source

Answer 4

green leaves/stem
storage organs such as tubers and parts of roots that are unloading their stores at the beginning of the growth season
food stores in seeds when they germinate

Question 5

define sink

Answer 5

part of plant that remove assimilate from phloem sieve tube

Question 6

examples of sink

Answer 6

growing roots
roots that are actively absorbing mineral ions
meristems, actively dividing
any part of plant that is laying down stores, such as developing seeds, fruit/storage organs

Question 7

routes for transporting assimilates to phloem

Answer 7

symplast route (passive)

apoplast route (active)

Question 8

symplast route

Answer 8

assimilates stored in vacuoles of cell
assimilates diffuse through cytoplast of mesophyll cells into sieve tube across connecting plasmodesmata
assimilates move by changes of water potential of cells

Question 9

apoplast route

Answer 9

assimilates diffuse through cell wall + intermembrane spaces
concentration gradient maintained bc sucrose moved into phloem
assimilate transport into cytoplasm of sieve tube elements aided by co-transporter proteins, alongside H+ ions, active process

H+ ions actively pumped out of companion cells using energy from ATP
high concen of H+ ions outside cell, diffusion og H Ions back into companion cell via cotransporter proteins (passive), sucrose carried with H+ ions through cotransporter proteins
increasing concen of sucrose in companion cell cause diffusion through plasmodesmata into sieve tube element

Question 10

movement of sucrose through phloem

Answer 10

mass flow
surcose loaded at source, assimilate concentration increase, water potential decrease, high hydrostatic
pressure
sink, low hydrostatic pressure, high water potential
pressure gradient cause sap to flow

Question 11

define mass flow

Answer 11

movement of fluids down a presure gradient

Question 11

unloading at sink

Answer 11

passive transport
sucrose unloaded from phloem at any point into cell that needs it, diffusion via plasmodesmata/ active transport
in cell, sucrose moves rapidly into other cell/ converted into another substance so sucrose can continue diffusing into cell
maintain concentration gradient between phloem and surrounding cells

Question 12

evidence for theory of translocation

Answer 12

microscopy ,can see adaptations in companion cells for active transport, lots of mitochondria

use of cyanide to poison mitochondria, translocation stop, active transport

aphid studies

Question 13

how are aphid studies evidence for translocation

Answer 13

if an aphid is anaesthetised + removed from stylet, sap continues to flow out of stylet due to pressure differences
sap flows faster near source than the sink bc of pressure
concentration of sucrose in phloem sap higher near source than near sink