Q1.
(a) Describe how water is moved through a plant according to the cohesion-tension
hypothesis.
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(4)
(b)
The mass of water lost from a plant was investigated. The same plant was used in every
treatment and the plant was subjected to identical environmental conditions. In some
treatments, the leaves were coated with a type of grease. This grease provides a
waterproof barrier. The results of the investigation are given in the table.
Treatment
(i)
Mass lost in 5 days / g
No grease applied
10.0
Grease applied only to the
upper surface of every leaf
8.7
Grease applied to both
surfaces of every leaf
0.1
What is the advantage of using the same plant in every treatment?
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(1)
(ii)
Why was it important to keep the environmental conditions constant?
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(1)
(iii)
What is the evidence that the grease provides a waterproof barrier?
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(1)
Page 1 of 29
(c)
(i)
Calculate the mass of water lost in 5 days through the upper surface of the leaves.
Answer ................................................................
(1)
(ii)
Use your knowledge of leaf structure to explain why less water is lost through the
upper surface of leaves than is lost through the lower surface.
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(2)
(Total 10 marks)
Q2.
(a) The apoplast pathway is one of the routes followed by water from a root hair, through
the cortex, to the endodermis of the root.
(i)
What is meant by the apoplast pathway?
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(1)
(ii)
Explain how the structure of the endodermis affects the passage of water by this
pathway.
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(3)
Page 2 of 29
(b)
The diameter of a branch of a tree and the rate of flow of water through the branch were
measured over a 24-hour period. The results are shown in the graph.
Using your knowledge of cohesion-tension theory
(i)
describe and explain the changes in rate of flow of water in the branch over the
24 hour period;
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(3)
(ii)
explain why the diameter of the branch decreased during the first 12 hours.
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(1)
Page 3 of 29
(c)
A stem was cut from a transpiring plant. The cut end of the stem was put into a solution of
picric acid, which kills plant cells. The transpiration stream continued. Suggest an
explanation for this observation.
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(2)
(Total 10 marks)
Q3.
(a) Explain how water enters xylem from the endodermis in the root and is then transported
to the leaves.
(6)
Large insects contract muscles associated with the abdomen to force air in and out of the
spiracles. This is known as ‘abdominal pumping’. The table shows the mean rate of
abdominal pumping of an insect before and during flight.
Stage of flight
(b)
Mean rate of
abdominal pumping
/ dm 3 of air kg −1 hour −1
Before
42
During
186
Calculate the percentage increase in the rate of abdominal pumping before and during
flight. Show your working.
Answer ..................................... %
(2)
Page 4 of 29
(c)
Abdominal pumping increases the efficiency of gas exchange between the tracheoles and
muscle tissue of the insect. Explain why.
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(2)
(d)
Abdominal pumping is an adaptation not found in many small insects. These small insects
obtain sufficient oxygen by diffusion.
Explain how their small size enables gas exchange to be efficient without the need for
abdominal pumping.
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(1)
Page 5 of 29
The graph shows the concentration of oxygen inside the tracheoles of an insect when at
rest. It also shows when the spiracles are fully open.
(e)
Use the graph to calculate the frequency of spiracle opening. Show your working.
Frequency ..................................... times per minute
(2)
(f)
The insect opens its spiracles at a lower frequency in very dry conditions. Suggest one
advantage of this.
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(1)
Page 6 of 29
(g)
The ends of tracheoles connect directly with the insect’s muscle tissue and are filled with
water. When flying, water is absorbed into the muscle tissue. Removal of water from the
tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle
tissue. Suggest one reason why.
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(1)
(Total 15 marks)
Q4.
(a)
(i)
Explain how each of the following is related to the function of xylem tissue.
Xylem tissue contains hollow tubes.
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(ii)
Lignin is present in xylem cell walls.
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(2)
(b)
In an investigation the total area of the stomatal openings and the rate of flow of water
through xylem were measured in a plant over a period of 24 hours. The results are shown
in the graph.
(i)
Describe the relationship between the rate of flow of water and the total area of the
stomatal openings for the period of time between midday and midnight.
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(1)
Page 7 of 29
(ii)
Between 8 am and midday the rate of flow of water continues to rise although the
total area of the stomatal openings remains constant. Explain why the rate of flow of
water rises.
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(1)
(iii)
How would the curve showing the total area of the stomatal openings differ if the
investigation was repeated on a dull day?
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(1)
(c)
Some xerophytic plants have sunken stomata. Explain the advantage of this adaptation.
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(2)
(Total 7 marks)
Page 8 of 29
Q5.
The diagram shows part of a leaf. The arrows show one pathway taken by water through the
leaf and into the atmosphere.
(a)
(i)
Name the pathway shown.
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(1)
(ii)
Describe and explain how water in the mesophyll cells passes out of the leaf.
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(3)
Page 9 of 29
(b)
Explain how two adaptations of their leaves reduce water loss from xerophytes.
Adaptation....................................................................................................
Explanation...................................................................................................
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Adaptation.....................................................................................................
Explanation ..................................................................................................
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(2)
(Total 6 marks)
Page 10 of 29
Q6.
(a) Scientists measured the rate of water flow and the pressure in the xylem in a small
branch. Their results are shown in the graph.
(i)
Use your knowledge of transpiration to explain the changes in the rate of flow in the
xylem shown in the graph.
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(Extra space) ........................................................................................
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(3)
(ii)
Explain why the values for the pressure in the xylem are negative.
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(1)
Page 11 of 29
(b)
Doctors measured the thickness of the walls of three blood vessels in a large group of
people. Their results are given in the table.
Name of vessel
(i)
Mean wall thickness /mm
(± standard deviation)
Aorta
5.7 ± 1.2
Pulmonary artery
1.0 ± 0.2
Pulmonary vein
0.5 ± 0.2
Explain the difference in thickness between the pulmonary artery and the pulmonary
vein.
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(1)
(ii)
The thickness of the aorta wall changes all the time during each cardiac cycle.
Explain why
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(Extra space) ........................................................................................
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(3)
(iii)
Which of the three blood vessels shows the greatest variation in wall thickness?
Explain your answer.
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(1)
Page 12 of 29
(c)
Describe how tissue fluid is formed and how it is returned to the circulatory system.
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(Extra space) .................................................................................................
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(6)
(Total 15 marks)
Page 13 of 29
Q7.
(a)
Root pressure moves water through the xylem. Describe what causes root pressure.
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(Extra space) .................................................................................................
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(3)
(b)
A biologist investigated the rate of water movement during the day in different parts of a
tree. The results are shown in the graph.
(i)
Describe how the rate of water movement in the upper branches changed over the
period shown in the graph.
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(2)
Page 14 of 29
(ii)
The rate of water movement in the upper branches was different from the rate of
water movement in the trunk. Describe how.
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(2)
(iii)
The results of this investigation support the cohesion tension theory. Explain how
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(2)
(Total 9 marks)
Q8.
Two theories have been put forward to explain the upward movement of water in the xylem
in a tree.
•
the cohesion-tension theory
•
the root pressure theory
(a)
Describe one piece of evidence that supports the root pressure theory and explain how it
supports this theory.
Evidence ......................................................................................................
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Explanation ...................................................................................................
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(2)
(b)
The diameter of a tree is less during the day, when the tree is transpiring, than it is at night.
Explain how this
(i)
supports the cohesion-tension theory;
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Page 15 of 29
(ii)
does not support the root pressure theory.
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(3)
(Total 5 marks)
Q9.
(a) Explain how water enters a plant root from the soil and travels through to the
endodermis.
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(5)
(b)
From the root, water is transported upwards through the stem. Explain how evaporation
from the leaves can cause the water to move upwards.
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(4)
Page 16 of 29
S
(c)
In daylight, most of the water evaporates from the leaves but some is used by the plant.
Describe the ways in which this water could be used by the plant.
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(6)
(Total 15 marks)
Q10.
(a)
Figure 1 shows a section through the root of a young plant.
Figure 1
(i)
Name the part of the plant labelled R.
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(1)
Page 17 of 29
(ii)
Give the letter which labels a tissue that transports solutes from the leaves.
Answer ......................................
(1)
(iii)
Give the letter which labels a tissue that prevents the movement of water through the
apoplast pathway.
Answer ......................................
(1)
(b)
Figure 2 shows a single stoma and surrounding cells from the leaf of a xerophytic plant.
Figure 2
(i)
Explain how the cuticle reduces water loss.
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(1)
Page 18 of 29
(ii)
Explain how one of the other labelled parts reduces water loss.
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(2)
(Total 6 marks)
Q11.
The volumes of water absorbed by the roots of a plant and lost by transpiration were
measured over periods of 4 hours during one day. The bar chart shows the results.
(a)
(i)
Describe the changes in the volumes of water absorbed and transpired between
midnight and 1600.
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(2)
Page 19 of 29
(ii)
Explain these changes in the volumes.
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(2)
(b)
Use your knowledge of the cohesion-tension theory to explain how water in the xylem in
the roots moves up the stem.
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(4)
(Total 8 marks)
Page 20 of 29
M1.
(a) 1. water evaporates/transpires from leaves;
2. reduces water potential in cell /water potential/osmotic gradient across
cells (ignore reference to air space);
3. water is drawn out of xylem;
4. creates tension (accept negative pressure, not reduced pressure);
5. cohesive forces between water molecules;
6. water pulled up as a column;
4 max
(b)
(i)
same surface area of leaf / number of leaves / age/thickness of
cuticle;
1
(ii)
(environmental conditions) affect rate of transpiration/evaporation;
1
(iii)
presence of grease reduces water loss;
1
(c)
(i)
1.2 / 1.3g;
1
(ii)
more stomata on the lower surface;
(thicker) waxy cuticle on the upper surface;
2
[10]
M2.
(a)
(i)
movement (of water) through cell walls / intercellular spaces;
1
(ii)
Casparian bands;
accept ref to suberin
which are impermeable/waterproof;
lower water potential in the cytoplasm of endodermis cell;
enters symplastic pathway / cytoplasm of cell;
by osmosis;
3 max
(b)
(i)
rate of flow increases to max at 1200 and then decreases;
increasing transpiration/evaporation from leaves;
transpiration creates tension / increases transpirational pull;
water molecules are cohesive/stick together;
produces a water column;
3 max
(ii)
(increase transpiration) produce a higher tension / reduces the
pressure in the xylem reducing the diameter;
adhesive forces between xylem and water;
1 max
Page 21 of 29
(c)
water moves in dead cells / xylem is non-living tissue;
the process is passive / no energy is needed;
2
[10]
M3.
(a)
(In the root)
1.
Casparian strip blocks apoplast pathway / only allows symplast pathway;
Assume all points are in the correct location unless context
suggests otherwise
2.
Active transport by endodermis;
3.
(Of) ions / salts into xylem;
4.
Lower water potential in xylem / water enters xylem by osmosis / down a water
potential gradient
4. Q Neutral: ‘along’ a water potential gradient
(Xylem to leaf)
5.
Evaporation / transpiration (from leaves);
‘Transpiration pull’ = 2 marks(5. & 6.)
6.
(Creates) cohesion / tension / H-bonding between water molecules / negative
pressure;
6. Accept ‘pulling’
6. Q Neutral: ‘suction’
7.
Adhesion / water molecules bind to xylem;
8.
(Creates continuous) water column;
6 max
(b)
Correct answer of 342.8 − 343 = 2 marks;;
Credit incorrect answers that show the numerator as 144 (or 186-42) or
denominator as 42 for 1 mark;
2
(c)
1.
More air / oxygen enters / air / oxygen enters quickly / quicker;
1. Accept: converse for carbon dioxide
1. Can be in any correct context eg insect, tracheoles, muscle
1. Neutral: air/oxygen enters
(So) maintains / greater diffusion or concentration gradient;
2
(d)
Large(r) SA:VOL / short(er) diffusion distance (to tissues);
Accept: thin diffusion pathway
1
Page 22 of 29
(e)
6 / 6.6 / 6.7 / 7 / 7.5 / 8 = 2 marks;;
Different answers given for different interpretations of the graph
Award 1 mark for incorrect answers that have divided 60 by any number;
2
(f)
Less / no water lost / (more) water retained;
Accept: less dehydration / less evaporation
Q Reject: less ‘transpiration’
Q Reject: less water lost by osmosis
1
(g)
1.
Greater surface area exposed to air;
Neutral: shorter diffusion distance
2.
Gases move / diffuse faster in air than through water;
2. Q Neutral: ‘harder to diffuse’
2. Accept gases diffuse directly, rather than through water
3.
Increases volume / amount of air;
1 max
[15]
M4.
(a)
(i)
unrestricted/free/quick/easy water flow/continuous column /
maintains transpiration stream;
1
(ii)
resists tension in water (column) / provides support/strength /
maintains column of water/adhesion / prevents water loss
(allow waterproofing in correct context i.e. not absorbing);
1
(b)
(i)
as total area of stomata decreases the rate of water flow decreases /
decrease is proportional;
(reject proportional, ‘as one goes up the other goes up’ and ‘same
shape’)
1
(ii)
increasing/higher temperature causes increasing/higher rate of
evaporation/transpiration;
(not water loss)
1
(iii)
lower plateau (start and finish at same point);
(allow if curve sketched on original graph, reject ‘curve is lower’)
1
(c)
conserves water / reduces water loss / reduces transpiration / reduces evaporation;
high humidity (in pit) / reduced water potential gradient / less water blown away / increased
diffusion pathway;
2
[7]
Page 23 of 29
M5.
(a)
(i)
apoplast;
1
(ii)
(pathway from cells) along cell walls /
through spaces and out through stoma(ta);
by diffusion (disqualify if osmosis mentioned);
down a WP/diffusion/concentration gradient;
3
(b)
two suitable adaptations plus explanation, e.g.
sunken stomata, reduce air movement/diffusion gradient;
rolled leaves, reduce surface area (for evaporation) /
enclose still air around stomata;
waxy cuticle, reduce (cuticular) evaporation / impermeable to water;
(reject waterproof)
few stomata, to reduce SA for diffusion;
small leaves, reduce SA for diffusion;
2
[6]
M6.
(a)
(i)
1.
Stomata open;
Allow converse
2.
Transpiration highest around mid-day;
3.
Middle of day warmer / lighter;
3. Allow ‘Sun is at its hottest’
4.
(Increased) tension / water potential gradient;
Ignore ‘pull, suck’
5.
Cohesion (between water molecules);
Reject increased cohesion in the context of cohesion tension
3 max
(ii)
(Inside xylem) lower than atmospheric pressure / (water is under)
tension;
Accept cohesion tension. Ignore vacuum
1
(b)
(i)
High pressure / smoothes out blood flow / artery wall contains more
collagen / muscle / elastic (fibres) / connective tissue;
Accept converse for pulmonary vein
Incorrect function of artery disqualifies mark
1
Page 24 of 29
(ii)
1.
(Aorta wall) stretches;
1. Allow expand
2.
Because ventricle / heart contracts / systole / pressure increases;
2. Reject if MP1 wrong
3.
(Aorta wall) recoils;
3. Allow spring back
4.
Because ventricle relaxes / heart relaxes / diastole / pressure falls;
Reject any reference to contract / relax in MP1 and 3
5.
Maintain smooth flow / pressure;
4. Reject if MP3 wrong
3 max
(iii)
Aorta 1.2 / largest SD;
Allow pulmonary vein provided candidate relates standard deviation
to mean
1
(c)
Formation
1.
High blood / hydrostatic pressure / pressure filtration;
2.
Forces water / fluid out;
2. Reject plasma, ignore tissue
3.
Large proteins remain in capillary;
Return
4.
Low water potential in capillary / blood;
5.
Due to (plasma) proteins;
6.
Water enters capillary / blood;
7.
(By) osmosis;
7. Osmosis must be in correct context
8.
Correct reference to lymph;
6 max
[15]
M7.
(a)
1.
Active transport by endodermis;
2.
ions / salts into xylem;
3.
Lowers water potential (in xylem);
4.
(Water enters) by osmosis;
4. Allow mark point 4 in any context of water movement
in the root e.g. into root hair.
3 max
Page 25 of 29
(b)
(i)
1.
Increases then decreases;
Allow peak / maximum at any time between 13.00 - 14.00 or
7.8 - 8.0;
2.
Peak / maximum at 13.00 / 14.00 (hours) / 7.8 - 8.0;
2
(ii)
1.
Maximum / overall rate is higher (in branches);
Allow converse for all marking points.
2.
Reaches maximum / peak earlier (in the day) (in branches);
3.
Starts higher / ends lower (in branches)
2
(iii)
1.
Movement starts / peaks earlier in branches / higher up;
2.
Creates tension / ‘negative pressure’ / ‘pull’
2
[9]
M8.
(a) Suitable accepted evidence, 1 mark for evidence and 1 mark for explanation –
EITHER e.g.guttation
(only) upward pressure could force liquid water out of leaves;
OR
Sap exuding from a cut, rooted stem;
(only) upward force could make this happen;
2
(b)
(Note: max. two for any component)
(i)
Evaporation from leaves during daytime only/mainly;
tension/negative pressure (on water) in xylem creates inward pull
(on walls of xylem vessel);
xylem vessels become narrower;
due to adhesion of water molecules (to walls of xylem vessels);
(ii)
root pressure gives outward force/push on walls of xylem vessels;
tree would become wider/stay same diameter;
xylem vessels become wider/stay same diameter;
max 3
[5]
M9.
(a) water enters root hair cells;
by osmosis;
because active uptake of mineral ions has created a WP gradient;
water moves through the cortex;
(by osmosis) down a WP gradient;
through cell vacuoles and cytoplasms / symplastic pathway;
through cell walls / apoplastic pathway;
max 5
Page 26 of 29
(b)
WP in leaf cells decreases / becomes more negative;
therefore water moves out of xylem (into surrounding tissues)
by osmosis; this creates a pull/tension on the water in xylem;
which is in a continuous column / water molecules cohere;
cohesion due to H bonding;
column doesn’t break because of adhesion with xylem walls;
max 4
(c)
(water is used in) the light-dependent reactions of photosynthesis;
electrons from water enable ATP production / H+ are used to reduce
NADP / produces O2 ;
(water can be used in) hydrolysis reactions within the plant;
to create turgor;
as a solvent for transport;
as a medium for chemical reactions;
component of cells / cytoplasm;
6
[15]
M10.
(a)
(i)
Endodermis(reject pericycle / suberin);
(accept endodermis and / containing Casparian strip)
1
(ii)
S;
1
(iii)
R;
1
(b)
(i)
(waxy so) impermeable to water/waterproof/stops water
passing through;
1
(ii)
reference to hairs / position of stomata (sunken stomata /
stomata in pits )
LINKED to reduced air movement / trap layer of air /
trap water vapour (reject water) / maintains humidity;
reduces diffusion gradient / concentration gradient of water /
water potential gradient;
OR
stoma can close;
reduces area for evaporation or transpiration;
2
[6]
Page 27 of 29
M11.
(a)
(i)
absorption rate stays level (initially) then rises;
transpiration rate rises regularly / transpiration increases at a
faster rate than absorption;
(principle that both increase 1 max awarded)
2
(ii)
increased stomatal aperture/light/temperature(increases
transpiration rate);
decreases water potential in root / increased uptake by osmosis;
2
(b)
water evaporates/transpires;
reduces water potential / creates water potential gradient / increases
osmotic gradient /
moves via apoplast pathway;
water drawn out of xylem;
creates tension/pulling effect / creates negative pressure (in context);
cohesive forces or H bonding between water molecules / water moves
as a column;
(accept continuous stream)
4 max
[8]
Page 28 of 29
Page 29 of 29