Plant Transport

Question 1

Describe how the guard cells surrounding the leaf pores are adapted to their roles: (2mks) f211 jun15 1aii

Answer 1

1 unevenly thickened (cell) wall ; [CREDIT wall beside pore thicker / wall is thicker on one side// refs to: thick inner and thin outer walls / inner wall thicker / outer wall thinner// thickened for thicker]
2 able to, change shape / bend ; [
3 transport proteins / ion pumps, in plasma
membrane ;
4 (presence of) chloroplasts (to provide, ATP /
energy) ; [mitochondria]

Question 2

Name one other part of the leaf from which water may be lost: f211 jun15 1aiii

Answer 2

epidermis / cuticle ; [guard cell]

Question 3

The cohesion-tension theory is often used to explain the mechanism by which water moves up the xylem from roots to the leaves. use this theory to explain how water from the roots to the leaves: (3mks) f211 jun15 1c

Answer 3

1 evaporation at top of, plant / xylem ; [leaf or named part of leaf]
2 (creates) tension in xylem ;
3 water molecules, stick together / are cohesive /
form a chain or column ; [water molecules, attracted together / (hydrogen) bonded together / form a continuous stream]
4 (column / chain) pulled up (by tension); [column drawn up// description if linked to tension at top
e.g. tension at top forces water up]

Question 4

State the features shown in Fig 2.1 which would NOT present in mature xylem. (2mks) f211 jun15 2bii

Answer 4

nucleus / nucleolus / chromatin ;
cytoplasm ;
cross / end, (cell) walls ; [end plates// no end walls / no nucleus / no cytoplasm// walls between cells]

Question 5

Describe how the structure of cell walls in mature xylem vessels would differ from the from the cells walls shown in fig 2.1 (2mks) f211 jun15 2biii

Answer 5

thicker ;
lignified ; [have lignin /contain lignin / reinforced with lignin / impregnated with lignin]
contain (bordered) pits ;

Question 6

Name two types of cell that can be found in phloem tissue. (2mks) f211 jun15 2c

Answer 6

sieve (tube) element ; [fibres / sclereids / sclerenchyma]
companion (cell) ;
parenchyma ;

Question 7

The majority of cells in phloem tissue are either companion cells or sieve tube elements. A scientist isolated companion cells and conducted some experiments to investigate the mechanism involved in loading sucrose into the sieve tubes.
Observation 1 isolated companion cells became slightly negatively charged compared
with their surroundings
Observation 2 companion cells could decrease the pH of the surrounding solution from
7.0 to 5.6
Observation 3 the pH inside the companion cells rose from 7.0 to 8.2
Observation 4 treatment with cyanide (which stops aerobic respiration) prevents the
change in pH occurring
From observation 1, the scientist concluded that the mechanism involved a transfer of charged particles (ions) between the companion cells and their surroundings.
What conclusions can be drawn from observations 2 and 3 about the mechanism? (2mks) [f211 june14 q4bi]

Answer 7

(the charged particles are) hydrogen ions; (ions are) moved out of the cells/ move into surrounding (solution);

Question 8

The majority of cells in phloem tissue are either companion cells or sieve tube elements. A scientist isolated companion cells and conducted some experiments to investigate the mechanism involved in loading sucrose into the sieve tubes.
Observation 1 isolated companion cells became slightly negatively charged compared
with their surroundings
Observation 2 companion cells could decrease the pH of the surrounding solution from
7.0 to 5.6
Observation 3 the pH inside the companion cells rose from 7.0 to 8.2
Observation 4 treatment with cyanide (which stops aerobic respiration) prevents the
change in pH occurring
From observation 1, the scientist concluded that the mechanism involved a transfer of charged particles (ions) between the companion cells and their surroundings.
What conclusions can be drawn from observation 4 about the mechanism? (1mk) [f211 june14 q4bii]

Answer 8

active transport involved/ cyanide prevents active
transport/ (mechanism) is active/ (mechanism) needs
energy/ATP;

Question 9

The scientist used an electron microscope to look for further evidence to support the mechanism involved in loading sucrose into the sieve tubes. Suggest what evidence the scientist might expect to see in companion cells, using an electron microscope: (3mks) [f211 june14 q4cii]

Answer 9

many/ large, mitochondria; plasmodesmata (between companion cell and sieve tube)/ described; many ribosomes/ extensive RER; many proteins in the, plasma/ cell surface, membrane;

Question 10

Explain the significance of the relationship between rate of diffusion and the surface area to volume ratio for large plants: (3mks) [f211 june14 q3b]

Answer 10

(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 11

Name one other location where growth occurs in a plant. [f211 june13 q3c]

Answer 11

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

Question 12

Lenticels (areas of loosely packed cells in the bark) 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 12

allow oxygen/ gases, 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 13

Distinguish between the term transpiration and the transpiration stream.

Answer 13

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

Question 14

The cells in the epidermis of a plant root are specialised to absorb minerals from the
surrounding soil.
State the process by which root epidermal cells absorb minerals from the soil and describe
how these cells are specialised to achieve absorption.

Answer 14

1 active, transport / uptake; [facilitated diffusion]
plus any two from:
2 cells have, extensions / hairs; [cells have root hairs]
3 thin cell wall;
4 large / increased, surface area; [high, surface area to volume ratio / SA:vol; credit in context on root hair cell or root having large surface area]
5 many / more, mitochondria;
6 (many) carrier proteins in cell (surface) membrane; [transport proteins / protein pumps; channel protein in context of facilitated diffusion]

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

A classic experiment investigated the effect of temperature on the rate of sugar transport in a
potted plant. Aphid mouthparts were used to take samples of sugar solution from the transport tissue in
the stem. The sugary solution dripped from the mouthparts. The number of drips per minute
was counted. The procedure was repeated at different temperatures.
temperature (°C) number of drips per minute
5, 10, 20, 30, 40, 50
number of drips per minute
3, 6, 14, 26, 19, 0
Suggest brief explanations for these results.

Answer 16

1 active transport requires ATP ;
–At low temperatures:
2 (molecules have) little kinetic energy ;
3 (therefore) less, respiration / ATP made ;
4 less active transport or less, movement / loading, of
sugars into sieve tube (element) ;
5 less, osmosis / movement of water, into sieve tube
(element) ;
6 low (hydrostatic) pressure created ;
–As temperature increases:
7 (molecules have) more kinetic energy ;
8 (therefore) more, respiration / ATP made ;
9 more active transport or more, movement / loading, of sugars into sieve tube (element) ;
10 more , osmosis / movement of water, into sieve tube
(element) ;
11 higher / more (hydrostatic) pressure created ;
12 at high temperature (plant), enzymes / proteins,
denatured ;

Question 17

Name two parts of a plant where meristematic tissue can be found. (2mks)

Answer 17

(just behind) tip / apex , of root; [behind root cap]
(just behind) tip/ apex, of shoot;
cambium/ pericycle/ vascular bundle; [between xylem and phloem]
bud;

Question 18

In an investigation, a student observed the cells in a stained section of meristematic tissue. The student counted how many cells could be seen in each stage of the cell cycle.
stage of cell cycle - percentage cells in stage (%)
interphase - 82.00
prophase - 4.34
metaphase - 3.23
anaphase - 3.23
telophase - 7.20
Explain why the meristematic tissue needed to be stained for this investigation. (2mks)

Answer 18

1 [DNA] chromosomes/ chromatin/ nucleus, can be seen/ are visible ;
2 determine/ distinguish between, different stages (of mitosis/ division/ cell cycle);
3 (staining) provide contrast (between cell structures);
4 (because) different, structures/ chemicals, take up different amounts of stain;

Question 19

Name the type of nuclear division that occurs in a plant meristem.

Answer 19

mitosis/ mitotic

Question 20

State one way in which the products of meiosis are different from the products of nuclear
division in meristematic tissue.

Answer 20

in meiosis: (cells produced are) not genetically identical [not clones]; one set of chromosomes/ haploid [half number of chromosomes/ half genetic material]; (they are) gametes; 4 cells produced;

Question 21

a source, a sink or neither: a developing bud

Answer 21

sink

Question 22

a source, a sink or neither: xylem

Answer 22

neither

Question 23

a source, a sink or neither: an actively growing root tip

Answer 23

sink

Question 24

The sap in the phloem sieve tubes is moved by mass flow. State two adaptations of sieve tubes that enable mass flow to occur. (2mks)

Answer 24

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 25

Describe how assimilates are loaded into the phloem.

Answer 25

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;

Question 26

Describe and explain how water is moved up the xylem from the roots to the leaves. (4mks)

Answer 26

1 water moves into xylem down water potential gradient; [ψ for water potential; water moves from high ψ to low ψ]
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; [xylem being very narrow so water]
9 water moves up (xylem/ stem) by mass flow;
10 from high(er) (hydrostatic) pressure to low(er) (hydrostatic) pressure/ down (hydrostatic) pressure gradient;

Question 27

xylem vessel // phloem sieve tube element

bordered pits present or absent

Answer 27

present // absent

Question 28

xylem vessel // phloem sieve tube element

lignin present or absent

Answer 28

present // absent

Question 29

xylem vessel /// phloem sieve tube element

substances transported

Answer 29

(water and), minerals / ions / salts ///

products of photosynthesis/ sucrose/ assimilates/ amino acids/ minerals/ ions/ salts/ plant ‘hormones’

Question 30

xylem vessel /// phloem sieve tube element

direction of transport

Answer 30

(only) up stem / towards leaves ///

both directions/ up and down/ from source to sink

Question 31

Explain why water loss from the leaves of a plant is unavoidable.

Answer 31

stomata (open to) allow, gaseous exchange / carbon dioxide in /oxygen out; (gaseous exchange) for photosynthesis ; (photosynthesis) essential for plant to, gain energy / make sugars ; some water lost through cuticle [‘gases in and out’]

Question 32

State and explain two adaptations of leaves that reduce evaporation.

Answer 32

[A 1] hairy leaves ;
trap water vapour / moisture ;
[A 2] stomata, in pits / sunken ;
pits trap, water vapour / moisture ;
[A 3] rolled leaves / presence of hinge cells ;
reduce surface area OR (rolled leaves) trap water vapour / moisture ;
[A 4] high solute concentration in cells ;
reduces water potential inside leaf cells ;
[A 5] thick(er) cuticle ;
(which is) waterproof / (relatively) impermeable ;
[A 6] small leaves / needles ; [‘spines’]
smaller surface area ;
[A 7] fewer stomata ;
reduces diffusion (of water vapour) ;
[A 8] stomata close, during the day ;
reduces diffusion (of water vapour) ;
[A 9] most stomata on lower surface ;
less exposure to sun OR cooler OR reduces diffusion (of water vapour) ;
[A 10] more densely packed spongy mesophyll; smaller surface area for evaporation (from mesophyll cell surface)

Question 33

A student used a potometer to investigate the effect of leaf area on the rate of transpiration.
table: Number of leaves present on shoot
attached to potometer /// Mean rate of bubble movement
0 /// 7
2 /// 28
4 /// 49
6 /// 73
8 /// 92
(i) State what information the student has not included in their table of results.
[F211-Jan12 q4a]

Answer 33

units; mm s-1; raw data; leaf area;

[e.g. individual trial results / the repeat readings / data used to calculate the mean]

Question 34

A student used a potometer to investigate the effect of leaf area on the rate of transpiration.
table: Number of leaves present on shoot
attached to potometer /// Mean rate of bubble movement
0 /// 7
2 /// 28
4 /// 49
6 /// 73
8 /// 92
(ii) Describe and explain the data shown by the student’s results. [F211-Jan12 q4a]

Answer 34

description:
as number of leaves increases the (rate of) bubble movement increases; [must be pair of figures illustrating change eg 7 bubble movement with 0 leaves and 92 bubble movement with 8 leaves]
(pair of) figs to illustrate the change; [ calculated difference e.g. increase of 21 between 2 & 4]
explanation:
larger (surface) area; [‘surface area increases’]
more stomata;
more / fast(er), evaporation / transpiration / loss of water vapour; [ e.g. more, stomata / surface area for transpiration = 2 marks (as more transpiration implied) ]
more / fast(er), uptake of water (by shoot);
idea that: (some) bubble movement with no leaves as not all uptake due to transpiration from leaves; [e.g some loss from other parts of stem / uptake into cells]

Question 35

A student used a potometer to investigate the effect of leaf area on the rate of transpiration.
table: Number of leaves present on shoot
attached to potometer /// Mean rate of bubble movement
0 /// 7
2 /// 28
4 /// 49
6 /// 73
8 /// 92
For each statement, explain why this may affect the results and suggest how the student could improve the investigation.
As part of the evaluation of the investigation, the student wrote the following statements:
1 One limitation is that the leaves were not all the same size.
[F211-Jan12 q4a]

Answer 35

surface area / SA, of leaves is different OR different number of stomata;
(choose shoot(s) with), similar sized leaves / similar
surface area OR repeats to calculate mean;
[measure surface area of each leaf and calculate rate
of movement per unit area; measure leaves to check they are same size]

Question 36

A student used a potometer to investigate the effect of leaf area on the rate of transpiration.
table: Number of leaves present on shoot
attached to potometer /// Mean rate of bubble movement
0 /// 7
2 /// 28
4 /// 49
6 /// 73
8 /// 92
For each statement, explain why this may affect the results and suggest how the student could improve the investigation.
As part of the evaluation of the investigation, the student wrote the following statements:
2 I assembled the potometer under water and the leaves got wet.
[F211-Jan12 q4a]

Answer 36

reduces water (vapour) potential gradient (between inside and outside of leaf); [water potential outside leaf is too high/ WP outside higher than inside];
assemble without wetting leaves/ dry the leaves/ wait until leaves dry;

Question 37

A student used a potometer to investigate the effect of leaf area on the rate of transpiration.
table: Number of leaves present on shoot
attached to potometer /// Mean rate of bubble movement
0 /// 7
2 /// 28
4 /// 49
6 /// 73
8 /// 92
For each statement, explain why this may affect the results and suggest how the student could improve the investigation.
As part of the evaluation of the investigation, the student wrote the following statements:
3 During my investigation the sun came out and the lab warmed up very quickly.
[F211-Jan12 q4a]

Answer 37

(increased temperature) will increase, evaporation / transpiration / loss of water vapour;
control the temperature / carry out in room with controlled temperature;

Question 38

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

Answer 38

1 provides, strength / support;
2 to keep, it / the vessel / the tube, open OR prevent collapse of, vessel / tube;
3 (because) transpiration produces, tension / negative
pressure;
4 to waterproof the, cell / vessel / tube / wall;
5 (so) cell, dies / content decays;
6 to create a hollow, tube / vessel OR to create a continuous column / allow unimpeded flow;
7 to limit lateral flow of water; [reduce / prevent lateral movement ]
8 ref to adhesion (between water molecules and wall); [lignin helps water move by adhesion]

Question 39

In plants, ….. tissue also contains cells that are not specialised. [f211 jan 12]

Answer 39

meristem(atic) / cambium; [callus]

Question 40

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. (jan12)

Answer 40

xylem:
X1 consists of vessels; [ cells joined end to end; continuous column / tube]
X2 one cell specialisation described; [eg wall water proof/ wall lignified/ no end walls/ (bordered) pits/ hollow/ no organelles/ no cell contents]
X3 transpiration stream OR movement of, water / minerals;
phloem:
P1 sieve tube element(s) and companion cell(s); [sieve element / sieve tube, and companion cell]
P2 one cell specialisation described; [eg. sieve plates (between phloem elements); no nucleus / few organelles, in sieve tube (elements); little cytoplasm in sieve tube (elements); many plasmodesmata; many mitochondria / dense cytoplasm, in companion cells ]
P3 translocation OR transports, sucrose / assimilates / products of photosynthesis / amino acids; [sugar]

Question 41

New growth in a stem or trunk comes from the cambium, which is situated between the xylem and phloem tissues. Explain why the new branches in Fig. 3.2 are seen growing from a position just under the bark of the cut surface. [f211 june13 q3b]

Answer 41

This is where the cambium/ meristem/ xylem/ phloem/ vascular bundle, is found;
mitosis/ cell division, occurs in the cambium; new cells differentiate/ specialise (into xylem+phloem); [cambium differentiates]
xylem supplies water for, (cell) elongation/ growth; phloem supplies sugars/ assimilates for energy/ growth/ respiration;

Question 42

Suggest why the rate of transpiration did not change between light intensities 10 a.u. and 20 a.u. (jan12)

Answer 42

stomata are (nearly) closed ; [no extra stomata are opened / stomata are not opened wider]
idea that: light intensity not high enough;

Question 43

Explain why transpiration is unavoidable during the day. (3mks) [jan12]

Answer 43

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

Question 45

Name the type of nuclear division that occurs in plant growth. [f211 june13 q3(a)(i)]

Answer 45

mitosis/ mitotic;

Question 46

Name one other location where growth occurs in a plant. [f211 june13 q3c]

Answer 46

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

Question 46

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. [f211 june13 q3c]

Answer 46

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;