transport in plants

Question 1

what do xylem and phloem make up ?

Answer 1

vascular system in a plant

Question 2

where are xylem / phloem in root ?

Answer 2

center to provide support

xylem in middle

Question 3

where are xylem / phloem in stem ?

Answer 3

near outside to reduce bending

xylem in middle

Question 4

where are xylem / phloem in leaf ?

Answer 4

make up network of veins which supports the leaves

xylem on outer surface

Question 5

describe the tubes of the xylem

Answer 5

long tube structure with no cell walls

Question 6

describe cells of xylem

Answer 6

dead, so no cytoplasm

Question 7

describe xylem walls

Answer 7

thickened with lignin, which helps support xylem and prevents collapsing (amount of lignin increases as gets older)

Question 8

how does water / ions move in / out of xylem ?

Answer 8

small pits in walls where there’s no lignin

Question 9

what are sieve tube elements ?

Answer 9

• living cells that form phloem
• joined end to end to form tubes
• holes in end walls to allow solute to pass

Question 10

what are companion cells ?

Answer 10

• carry out living function for both themselves and sieve element (like provide energy for active transport)

Question 11

how does water move up a plant against gravity ?

Answer 11

adhesion, cohesion and tension

Question 12

name the two examples of xerophytes

Answer 12

cacti / marram grass

Question 13

what is a xerophyte ?

Answer 13

plant adapted to live in dry climates

Question 14

name the adaptations of marram grass

Answer 14

• stomata in sunken pits to shelter from wind (micro climate)
• hairs on epidermis which traps moist air around stomata
• rolls leaves (micro climate)

Question 15

name adaptation both cacti / marram grass have

Answer 15

thick waxy cuticle on epidermis to reduce water loss by evaporation as layer is waterproof

Question 16

name the adaptations of cacti

Answer 16

• spines instead of leaves (less SA)

- close stomata at hottest times of day

Question 17

name a hydrophyte

Answer 17

water lily

Question 18

name adaptions of a hydrophyte

Answer 18

• air spaces help plant float (more light) and store oxygen
• stomata on upper surface of leaves
• flexible as don’t have to support their own weight (flexibility prevents damage from currents)

Question 19

what are assimilates ?

Answer 19

dissolved substances (transported in translocation)

Question 20

where does translocation move substances from / to ?

Answer 20

sources to sinks

Question 21

what is a source ?

Answer 21

where assimilates are made

Question 22

what is a sink ?

Answer 22

where assimilates are used / converted for storage

Question 23

what are sugars transported as in translocation ?

why ?

Answer 23

sucrose, as it is both soluble and metabolically inactive

Question 24

what is the symplast pathway ?

Answer 24

water passes through cytoplasm and plasmodesmata (osmosis)

Question 25

what is the apoplast pathway ?

Answer 25

water passes through cell walls (diffusion), until reaches endodermis, where Casparian strip blocks water so must go symplast pathway

Question 26

why is symplast pathway useful ?

Answer 26

passes through cell membrane so can control which substances pass

Question 27

why is apoplast pathway the main pathway ?

Answer 27

has the least resistance

Question 28

outline the the route water takes from roots

Answer 28

roots – xylem – leaves – transpiration

Question 29

outline the process of mas flow in phloem

Answer 29

• solutes actively loaded into sieve tubes
• water moves in
• increase in hydrostatic pressure
• at sink end, solutes actively unloaded
• pressure decreases
• pressure gradient formed

Question 30

outline the process of active loading in phloem

Answer 30

• ATP used to actively transport H+ ions out of companion cell
• conc gradient set up
• H+ binds to co-transporter protein, which binds to sucrose
• H+ moves back into companion cell
• same process used to move sucrose to sieve element