transport in plants

Question 1

Neonicotinoid insecticide molecules are absorbed by the roots and leaves of maize plants.
Describe how, once these molecules have been absorbed, they may be transported to the fruits of the maize plant.

Answer 1

in xylem (by),cohesion-tension / transpiration (stream);
in phloem (by), translocation / mass flow ;

Question 2

Name the pores through which most water vapour is lost from a leaf.

Answer 2

stomata

Question 3

Describe how the guard cells surrounding the leaf pores are adapted to their role.

Answer 3

idea of: unevenly thickened (cell) wall ;
able to, change shape / bend ;
transport proteins / ion pumps, in plasma
membrane ;
(presence of) chloroplasts (to provide, ATP /
energy) ;

Question 4

Name one other part of the leaf from which water may be lost.

Answer 4

epidermis / cuticle ;

Question 5

The cohesion-tension theory is often used to explain the mechanism by which water moves up the xylem from the roots to the leaves.
Use this theory to explain how water moves from the roots to the leaves.

Answer 5

evaporation at top of, plant / xylem ;
(creates) tension in xylem ;
water molecules, stick together / are cohesive /
 form a chain or column ;
(column / chain) pulled up (by tension);

Question 6

Name two types of cell that can be found in phloem tissue.

Answer 6

sieve (tube) element ;
companion (cell) ;
parenchyma ;

Question 7

The pathway that transports water along cell walls and between cells in plants.

Answer 7

apoplast

Question 8

Explain the significance of the relationship between rate of diffusion and the surface area to volume ratio for large plants.

Answer 8

(large plants) have a, small / low, SA : VOL ratio ;
idea of diffusion too slow (to supply requirements) ;
idea of need transport system (for water / minerals /
assimilates) ;
idea of need (special) surface area for, gaseous exchange
/ uptake of minerals ;

Question 9

Name the type of nuclear division that occurs in plant growth.

Answer 9

mitosis

Question 10

Name one other location where growth occurs in a plant.

Answer 10

tip / apex, of, shoot / root ;
meristem ;
bud ;

Question 11

Look at the areas labelled L on Fig. 3.2. These are areas of loosely packed cells in the bark called lenticels. Lenticels allow gases to diffuse into the living tissues of the trunk.Suggest why lenticels are essential to the survival of large multicellular plants and explain why similar structures are not found in large multicellular animals.

Answer 11

allow oxygen to reach, cells / tissues (under bark) ;
for (aerobic) respiration ;
animals transport oxygen in, blood / circulation /
transport system ;
plants do not transport (much) oxygen in transport
system ;
idea that (oxygen not supplied from leaves as) stomata
only open in day / no leaves in winter ;

Question 12

Distinguish between the term transpiration and the transpiration stream.

Answer 12

transpiration
loss of water vapour / evaporation of water ;
from, aerial parts of plant / leaves / stomata ;
transpiration stream
movement of water (up xylem vessels) ;
from roots to, leaves / air surrounding leaves ;

Question 13

Explain why lignin is essential in the wall of a xylem vessel.

Answer 13

provides, strength / support ;
to keep, it / the vessel / the tube, open
OR
prevent collapse of, vessel / tube ;
(because) transpiration produces, tension / negative
pressure ;
to waterproof the, cell / vessel / tube / wall ;
(so) cell, dies / content decays ;
to create a hollow, tube / vessel
OR
to create a continuous column / allow unimpeded flow ;
to limit lateral flow of water ;
ref to adhesion (between water molecules and wall) ;

Question 14

Name the sugar most commonly transported through the stem of a plant and the tissue that transports this sugar.

Answer 14

sucrose

phloem

Question 15

Sugar molecules are actively loaded into the transport tissue.
Describe how active loading takes place.

Answer 15

1 hydrogen ions / H+ / protons, pumped out of companion
cells ;
2 increases, hydrogen ion / H+ / proton, concentration
(gradient) (outside companion cell) ;
3 hydrogen ions, re-enter / flow back into,
companion cells ;
4 sucrose / sugar, moves with hydrogen ions / AW ;
5 down concentration gradient ;
6 ref. cotransporter proteins / cotransport(ation) ;
7 by facilitated diffusion ;
8 sucrose / sugar, diffuses into sieve tube (element) ;
9 through plasmodesmata ;

Question 16

In more advanced organisms, cells are organised into tissues consisting of one or more types of specialised cells.Describe how cells are organised into tissues, using xylem and phloem as examples.

Answer 16

xylem
consists of vessels ;
one cell specialisation described ;
transpiration stream OR
movement of, water / minerals ;
phloem
sieve tube element(s) and companion cell(s) ;
one cell specialisation described ;
translocation OR
transports, sucrose / assimilates / products of
 photosynthesis / amino acids ;

Question 17

Explain why transpiration is unavoidable during the day.

Answer 17

1
2
3
4
5
6
7
stomata are open ;
allow, gaseous exchange / entry of carbon dioxide / exit
 of oxygen ;
for photosynthesis ;
water vapour leaves (the leaf) ;
down a water (vapour) potential gradient ;
high(er) temperatures (during the day) ;
causes greater evaporation / some water vapour loss
 through leaf surface all the time ;

Question 18

transverse section of a leaf taken from a xerophyte.

Describe the xerophytic features of this leaf and explain how each feature reduces loss of water vapour.

Answer 18

thick , cuticle / waxy or layer ;
leaf is, folded / rolled / curled / curved / AW ;
reduces (exposed) surface area (for evaporation) ;
hairs ;
reduces, evaporation / diffusion through leaf, surface /
epidermis) ;
for points 6, 7 & 8 credit only in context of folded leaf or
hairs:
trap water vapour ;
creates high water (vapour) potential
outside (stomata) ;
reduces water (vapour) potential gradient ;
QWC
cuticle (derivatives of) evaporation
water vapour potential gradient
epidermis surface area diffusion

Question 19

Name two parts of a plant where meristematic tissue can be found.

Answer 19

just behind) tip / apex , of root ;
(just behind) tip / apex , of shoot ;
cambium / pericycle / vascular bundle ;
bud ;

Question 20

Name the sugar molecule most commonly translocated.

Answer 20

sucrose

Question 21

The sap in the phloem sieve tubes is moved by mass flow.State two adaptations of sieve tubes that enable mass flow to occur.

Answer 21

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 22

Describe how assimilates are loaded into the phloem.

Answer 22

1 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 ;
QWC
companion, diffuse / diffusion,
gradient, concentration,
facilitated, cotransport,
plasmodesmata, sieve tube,
sieve element, hydrogen ions / protons

Question 23

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

Answer 23

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

Question 24

Define the term transpiration.

Answer 24

evaporation / loss of water vapour ;
from, aerial parts of plant / leaf / leaves ;
via stomata ;

Question 25

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

Answer 25

In the leaf: 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) ; QWC xylem , apoplast/symplast/vacuolar , hydrostatic , gradient , cohesion / cohesive , tension , mass flow , water potential

Question 26

Suggest why a bunch of flowers may survive longer if the ends of the stems are removed immediately before the flowers are placed in water.

Answer 26

Ref to : bubbles / air (present / being removed) ; (blockage) in xylem ; restore (continuous) column of water (in xylem) ;

Question 27

Name the process by which water leaves a cell.

Answer 27

osmosis

Question 28

Describe the routes that water molecules take through the cell surface membrane

Answer 28

``` fit between (phospho)lipids / through (phospho)lipid (bi)layer ; via, protein channels / protein pores / aquaporins ; ```

Question 29

Describe and explain how water is moved up the xylem from the roots to the leaves.

Answer 29

1 water moves into xylem down water potential gradient ; 2 root pressure / high (hydrostatic) pressure at bottom of xylem ; 3 water vapour loss / transpiration / evaporation, at leaves / top of plant ; 4 (creating) low (hydrostatic) pressure at top of xylem ; 5 water, under tension / pulled up (in a continuous column) ; 6 cohesion between water molecules / described ; 7 adhesion of water molecules to xylem / described ; 8 capillary action / described ; 9 water moves up (xylem / stem) by mass flow ; 10 from high(er) (hydrostatic) pressure to low(er) (hydrostatic) pressure / down (hydrostatic) pressure gradient ; QWC water potential, hydrostatic pressure, transpiration / evaporation, cohesion / cohesive, adhesion / adhesive, tension, root pressure, capillary action / capillarity, mass flow

Question 30

Name the process by which water enters cells in root cortext from the soil.

Answer 30

osmosis

Question 31

State one function of xylem tissue.

Answer 31

transports water (up plant) transports, minerals / ions, (up plant) support (plant / stem / shoot) ;

Question 32

State the function of this spiral band of lignin and explain why it is important that the xylem vessel becomes lignified in this way.

Answer 32

Functions: F1 (lignin), strengthens / thickens, the (xylem) wall ; F2 waterproofing (wall) / AW ; F3 (improving) adhesion of water (molecules) ; F4 (spiral) pattern allows flexibility / stretching / movement; Explanation: E1 prevents collapse of xylem ; E2 (water) under tension / at low pressure / negative pressure; E3 reduces (lateral) loss of water, through wall ; E4 increases capillarity / AW ; E5 prevents stem breaking / AW ;

Question 33

Explain the function of the pits in xylem

Answer 33

(pits) allow water to move, in / out / between, vessel(s) ; to bypass blockage ; supply water to other, tissues / (other types) cells / parts of plant ;

Question 34

State one essential component of the potometer, that must be added before any results can be recorded.

Answer 34

timer/scale/ruler

Question 35

Describe three steps a student should take when setting up the potometer to ensure that the apparatus works correctly.

Answer 35

shoot is healthy ; assemble apparatus / cut shoot, under water ; cut last 2-3 cm off cut end / cut at an angle ; check there are no air bubbles in apparatus ; apparatus, water tight / air tight / has no leaks ; leaves dry ;

Question 36

Suggest two possible reasons, other than light and temperature, why the rate of transpiration was lower in the afternoon than in the morning.

Answer 36

``` in afternoon: plant dying / less healthy / wilting ; ref to stomatal closure ; more humid / higher water (vapour) potential in air ; less air movement / wind / draughts ; ```

Question 37

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

Answer 37

some water used (in photosynthesis / making cells turgid) ; (potometer) measures (water) uptake ; not all water (taken up) is lost ;

Question 38

Name one tissue in plants that contains stem cells.

Answer 38

cambium / meristem / early embryonic cells ;

Question 39

State what is meant by the terms source and sink.

Answer 39

source site where, sucrose / sugars / assimilates, loaded (into phloem) / AW ; sink site where, sucrose / sugars / assimilates, unloaded / removed (from phloem) / AW ;

Question 40

When the bark is removed from a tree, the phloem is also removed. If a complete ring of bark is removed, the tree trunk can be seen to swell above the cut. Suggest two reasons why the trunk swells above the cut.

Answer 40

``` (sugars) cannot pass the cut / AW ; decrease water potential ; water moves into cells ; (damage triggers) increased cell division ; to produce cells to store sugars ; cut causes, gall / infection ; ```

Question 41

Explain why the plugging of xylem vessels will result in the leaves of the upper branches turning yellow.

Answer 41

1 less / no , movement of water or less / no , water reaches leaves ; 2 less / no , minerals / nitrate / phosphate / magnesium / iron ; 3 less / no , chlorophyll formation ; 4 chlorophyll breakdown / leaf senescence ;

Question 42

Explain why the loss of leaves from the tree may result in the death of the tree’s roots.

Answer 42

``` 1 less / no , photosynthesis ; 2 less / no , sugar(s) / amino acid(s) / assimilates / organic molecules ; 3 roots cannot , respire / do active transport / metabolise ; 4 the falling leaves carry the fungus ; ```