transport in plants

Question 1

State two adaptations of sieve tubes that enable mass flow to occur.(2)

Answer 1

elongated elements ;
2 elements , joined end to end / form column ;
3 sieve plates / pores in end walls /

perforated end plates / sieve pores ;
4 little cytoplasm / cytoplasm pushed to cell edges /
thin (layer of) cytoplasm ;

5 no nucleus / few organelles ;

Question 2

Describe how assimilates are loaded into the phloem.

Answer 2

active transport of, hydrogen ions / protons / H+ ,
out of companion cells ;

2 creates , hydrogen ion / concentration / diffusion ,
gradient ;

3 (facilitated) diffusion (of H+

) back into companion
cells ;
4 sucrose / assimilates , move in with hydrogen ions ;
5 by cotransport / through cotransport protein ;
6 sucrose / assimilates , (diffuse) through

plasmodesmata (from companion cell
to sieve element) ;

7 into sieve, tube / element ;

Question 3

Describe the features of the xylem that enable the steam to pass from the heated end of the stem to the cut end.

Answer 3

no cross walls / cells joined end to end / continuous ;
hollow / no contents / no organelles / no cytoplasm ;
(walls / vessels) lignified ;

(bordered) pits in walls ;

Question 4

Describe and explain how transpiration contributes to the mechanism of water transport up the stem.

Answer 4

idea of :
1 water loss (from leaf) is replaced ;
2 via, apoplast / symplast / vacuolar, pathways ;
3 down water potential gradient / AW ;
4 (lost water replaced) by water from the xylem ;
In the xylem:
5 (loss of water) causes, low / negative, (hydrostatic)
pressure (at top / in leaf)
OR
creates pressure gradient ;
idea of :
6 water moves, from higher pressure to lower pressure /
down pressure gradient ;
7 under tension / pulled up / drawn up ;

8 by mass flow ;
9 cohesion / attraction, between water molecules ;
idea of :
10 column / stream / chain, of water (molecules) ;

Question 5

Explain why the potometer only gives an estimate of the rate of transpiration.

Answer 5

(potometer) measures (water) uptake ;

not all water (taken up) is lost ;
ACCEPT ref to figs e.g. 99% water taken up is lost

some water used (in photosynthesis / making cells turgid) ;

Question 6

State and explain two adaptations of leaves that reduce evaporation. (5)

Answer 6

hairy leaves ;
trap water vapour / moisture ;

stomata, in pits / sunken ;
pits trap, water vapour / moisture ;

rolled leaves / presence of hinge cells ;
reduce surface area OR (rolled leaves) trap water vapour /
moisture ;

thick(er) cuticle ;
(which is) waterproof / (relatively) impermeable ;

small leaves / needles ;
smaller surface area ;

fewer stomata ;
reduces diffusion (of water vapour)