Vasculature 2: phloem and phloem loading

Question 1

what is phloem

Answer 1

specialized in the movement of large organic compounds throughout the plant

Question 2

what are photosynthates

Answer 2

sugar products of photosynthesis

Question 3

what is phloem sap

Answer 3

solution of sugars, water and other organic compounds found in the phloem

Question 4

what are the types of phloem cells

Answer 4

sieve-tube elements
fibers
parenchyma cells

Question 5

what are sieve-tube element cells

Answer 5

highly specialized unique cells

lack nucleus, ribosomes, vacuole

Question 6

what are 2 types of sieve tube elements

Answer 6

sieve tube members

sieve cells

Question 7

how are sieve tube elements divided

Answer 7

along taxonomic lines

Question 8

what are sieve tube members

Answer 8

specialized phloem cell found mainly in angiosperms
contains a sieve plate
growth supported by a companion cell

Question 9

what is a sieve plate

Answer 9

dividing structure between adjacent sieve tube member cells

Question 10

what does a sieve plate consist of

Answer 10

many plasodesmata enlarged to allow for the efficient transport of nutrients betweencells

Question 11

how does xylem support growth

Answer 11

doesnt because cells are dead at amturity

Question 12

how does phloem support growth

Answer 12

partners with companion cell

Question 13

what is a companion cells role

Answer 13

provides most of the proteins and other metabolites that the sieve tube member needs to remain alive

Question 14

characterizations of the companion cells

Answer 14

are specialized parenchyma cells

connect to a sieve tube member through plasmodesmata

Question 15

what are sieve cells

Answer 15

phloem cell found mainly in gymnosperms and seedless vasc plants

Question 16

what characterizes sieve cells

Answer 16

a lack of sieve plate
being generally longer and thinner than sieve tube members
associate with an albuminous cell

Question 17

what is an albuminous cell

Answer 17

a modified parenchyma cell that supports the metabolic activity of the sieve cell

Question 18

difference between albuminous cell and companion cell

Answer 18

albuminous does not arise from the same mother cell as the sieve cell

Question 19

what is translocation

Answer 19

process of sugars moving through the plant

moves substances from source to sink in the plant

Question 20

what is the main form of sugar transported through the phloem

Answer 20

sucrose

Question 21

what are source tissues

Answer 21

any plant part which generates more sugars than it consumes

Question 22

what do source tissue include

Answer 22

storage organs

young and fully expanded leaves

Question 23

what are sink tissues

Answer 23

any plant part which is unable to meet its nutritional sugar needs

Question 24

what do sink tissues include

Answer 24

roots
storage organs
older leaves
leaves which are expanding
flowers/fruits

Question 25

what is the vegetative stage of development

Answer 25

- younest matur leaves send sugars toward apical stem - oldest leaves send sugars to roots - middle leaves send sugars in either direction

Question 26

what is the reproductive stage of development

Answer 26

fruits require vast majority of sugars in the plant vegetative growth slows down through lack of sugars for growth middle leaves will send all their sugars to the developing repro structures

Question 27

what drives movement of phloem

Answer 27

source and sink tissues | phloem sap can move up or down the plant

Question 28

what drives the movement of xylem

Answer 28

transpiration | water can only move up the plant

Question 29

what is phloem loading/unloading

Answer 29

movement of sugars in and out of the phloem

Question 30

what is pressure-flow hypthesis

Answer 30

movement of sugars through the phloem

Question 31

what is passive phloem loading

Answer 31

- movement of sugars from the mesophyll cels of the leaf to the phloem cells along a concentration gradient - driven by a concentration gradient of sucrose - sucrose moves through plasmodesmata of adjacent cells through a symplastic pathway driven by simply diffusion

Question 32

what is active phloem loading

Answer 32

- movement of sugars from the mesophyll cells of the leaf to the phloem cell against a concentration gradient through the spending of ATP - sugars travel by the symplastic pathway until the cell layer before the companion cell

Question 33

what happens in active phloem loading

Answer 33

ATP powered protons pumps create a proton gradient | sucrose is cotransported with protons as they move down their concentration gradient

Question 34

what is polymer trapping

Answer 34

how some plants can move sucrose agaisnt a concentration gradient without the need for membrane transporters

Question 35

what happens in polymer trapping

Answer 35

concentrating sucrose by converting it to different, larger, sugar polymers

Question 36

what is an intermediary cell

Answer 36

special type of parenchyma cell where sugars are concentrated

Question 37

what are the steps of sugar transport in polymer trapping

Answer 37

- sugars move into the intermediary cell through symplastic active transport - sucrose is actively combined with other sugars to form larger sugar polymers - polymers too large move back into the mesophyll cell

Question 38

what is symplastic

Answer 38

when something moves with the concentration gradient

Question 39

what is apoplastic

Answer 39

when something moves agaisnt the concentration gradient

Question 40

what is phloem unloading

Answer 40

the process of unloading sugars to the sink parnchyma cells from the phloem cells

Question 41

when is phloem unloading passive

Answer 41

in young leaves, actively growing tissues, roots

Question 42

when is phloem unloading active

Answer 42

in storage

Question 43

once in the phloem cells, how does sugar move in the vasculature

Answer 43

with pressure flow

Question 44

what is pressure flow hypothesis

Answer 44

a combination of osmosis, concentration gradients, water pressure and water movement in the xylem

Question 45

steps of pressure flow

Answer 45

- phloem loading (high concentration of sucrose in the phloem) - water pulled from xylem into phloem - increased water pressure in cell - water moves to area of lower pressure through bulk flow (source to sink) - phloem unloading (reduces sucrose concentration in phloem - water moves back to xylem through transpiration

Question 46

what directions can water flow in the xylem and phloem in pressure flow hypothesis

Answer 46

same direction opposite direction only 1 direction in phloem even i it can do both

Question 47

why dont we expect water to flow toward the source

Answer 47

water along with solutes moves down the pressure gradient and not the potential gradient

Question 48

how is sucrose transported to seeds/flowers

Answer 48

water pressure in the source region of the phloem drives the movement of sucrose into the developing seeds or flowers