Feversham College
Q1.
(a)
Explain how water enters a plant root from the soil and travels through to the
endodermis.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(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.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(4)
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.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
Page 1
Feversham College
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(6)
(Total 15 marks)
Page 2
Feversham College
Q2.
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.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(ii)
(2)
Explain these changes in the volumes.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(b)
Use your knowledge of the cohesion-tension theory to explain how water in the xylem
in the roots moves up the stem.
......................................................................................................................
......................................................................................................................
......................................................................................................................
Page 3
(2)
Feversham College
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(4)
(Total 8 marks)
Page 4
Feversham College
(a)
Describe how water is moved through a plant according to the cohesion-tension
hypothesis.
Q3.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(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
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
(i)
What is the advantage of using the same plant in every treatment?
.............................................................................................................
.............................................................................................................
(1)
(ii)
Why was it important to keep the environmental conditions constant?
.............................................................................................................
.............................................................................................................
(iii)
(1)
What is the evidence that the grease provides a waterproof barrier?
.............................................................................................................
.............................................................................................................
(1)
Page 5
Feversham College
(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.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(2)
(Total 10 marks)
Page 6
Feversham College
Q4.
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.
.............................................................................................................
(1)
(ii)
Describe and explain how water in the mesophyll cells passes out of the leaf.
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
.............................................................................................................
(3)
(b)
Explain how two adaptations of their leaves reduce water loss from xerophytes.
Adaptation....................................................................................................
Explanation...................................................................................................
......................................................................................................................
Adaptation.....................................................................................................
Explanation ..................................................................................................
......................................................................................................................
(2)
(Total 6 marks)
Page 7
Feversham College
Q5.Students investigated the effect of removing leaves from a plant shoot on the rate of water
uptake. Each student set up a potometer with a shoot that had eight leaves. All the shoots
came from the same plant. The potometer they used is shown in the diagram.
(a)
Describe how the students would have returned the air bubble to the start of the
capillary tube in this investigation.
........................................................................................................................
........................................................................................................................
........................................................................................................................
(b)
(1)
Give two precautions the students should have taken when setting up the potometer to
obtain reliable measurements of water uptake by the plant shoot.
1......................................................................................................................
2......................................................................................................................
(c)
(2)
A potometer measures the rate of water uptake rather than the rate of transpiration.
Give two reasons why the potometer does not truly measure the rate of transpiration.
1......................................................................................................................
2......................................................................................................................
(2)
Page 8
Feversham College
(d)
The students’ results are shown in the table.
Number of leaves removed
from the plant shoot
Mean rate of water uptake
/
3
cm per minute
0
0.10
2
0.08
4
0.04
6
0.02
8
0.01
Explain the relationship between the number of leaves removed from the plant shoot and
the mean rate of water uptake.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(Extra space)..................................................................................................
........................................................................................................................
........................................................................................................................
(3)
(Total 8 marks)
Page 9
Feversham College
M1.
(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;
(b)
5
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;
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
M2.
(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)
(ii)
2
increased stomatal aperture / light / temperature(increases
transpiration rate);
decreases water potential in root / increased uptake by osmosis;
2
(b)
water evaporates / transpires, this reduces water potential / creates water
potential gradient / increases osmotic gradient;
water drawn out of xylem;
creates tension / pulling effect / creates negative pressure (in context);
cohesive forces or H bonding between
water molecules / water moves
Page 10
[15]
Feversham College
as a column;
(accept continuous stream)
4
[8]
M3.
(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
(c)
(ii)
(environmental conditions) affect rate of transpiration / evaporation;
(iii)
presence of grease reduces water loss;
(i)
1
1
1.2 / 1.3g;
1
(ii)
more stomata on the lower surface;
(thicker) waxy cuticle on the upper surface;
2
M4.
(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
Page 11
[10]
Feversham College
(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
Page 12
[6]
Feversham College
M5.(a)
Open / use tap / add water from reservoir;
1
(b)
1.
Seal joints / ensure airtight / ensure watertight;
Answer must refer to precautions when setting up the apparatus
Ignore: references to keeping other factors constant
(c)
2.
Cut shoot under water;
3.
Cut shoot at a slant;
4.
Dry off leaves;
5.
Insert into apparatus under water;
6.
Ensure no air bubbles are present;
7.
Shut tap;
8.
Note where bubble is at start / move bubble to the start position;
1.
2 max
Water used for support / turgidity;
Accept: water used in (the cell’s) hydrolysis or condensation
(reactions) for one mark. Allow a named example of these
reactions
2.
Water used in photosynthesis;
3.
Water produced in respiration;
4.
Apparatus not sealed / ‘leaks’;
2 max
(d)
As number of leaves are reduced (no mark),
Accept: converse arguments
1.
Less surface area / fewer stomata;
3.
Less evaporation / transpiration;
4.
Less cohesion / tension / pulling (force);
3
[8]
Page 13
Feversham College
E1.
(a)
The question was specific in its requirement, yet the majority of candidates gave
description of the movement from the endodermis to the xylem (and then up the xylem
to the leaves in many cases). This irrelevant information was often to the detriment of
the relevant answer. About 25% of candidates failed to realise that water can pass
through the symplast before reaching the endodermis.
(b)
Many candidates took this question as an opportunity to describe all they knew about
the movement of water in xylem and produced lengthy responses with detailed treatment
of root pressure and capillarity. Some candidates confused cohesion with adhesion, while
others made very superficial references to cohesion-tension.
(c)
This question produced a range of responses. Some candidates produced excellent
accounts drawing on several areas of the specification. Others produced very detailed
accounts of photosynthesis but failed to give any other uses of water. Worryingly, several
answers read like the mark scheme for question 9(c) from June 2003 - quite a different
question. On the other hand there were some very simplistic responses effectively saying
no more than that water “kept the plant moist”.
E2.
(a)
Most candidates were able to score one mark by describing the changes in
absorption or transpiration. Candidates failed to gain marks due to lack of accuracy. For
example, many candidates stated that the volume of water absorbed increases, rather
than stating that the volume stays level initially and then increases. Most candidates were
able to explain changes in the rate of transpiration in terms of increasing temperature,
light intensity or stomatal aperture. However, some candidates failed to gain credit
because of careless and imprecise expression. It was common to see phrases such
‘transpiration is low when there is no sun’. Very few candidates were able to relate the
loss of water by transpiration to the water potential of root cells, leading to an increased
rate of absorption.
(b)
Answers to this part were surprisingly disappointing. Good candidates were able to
explain the sequence of events clearly using appropriate terminology, with a significant
proportion obtaining full marks.
Page 14However, many candidates were unable
Feversham College
to explain how water loss by transpiration causes the movement of water from xylem
tissue and how this creates tension. Often the terms cohesion and tension were
mentioned but not explained. Many candidates explained the process of water transport
as ‘moving by the cohesion tension theory’. Answers often contained incomplete
explanations such as ‘water is pulled upwards’ with no mention of what causes the pulling
effect, or ‘water is cohesive’ with no reference to water molecules.
E3.
(a)
There were some very good answers achieving maximum marks. However, many
answers used very vague language, such as ‘water is pulled up by cohesion-tension’, with
no description of what cohesion involves, or what creates the tension. Water was said by
many to be ‘sticky’. This was the lowest level of answer accepted for a mark about
cohesion. Root pressure was often included in the description of cohesion-tension, which
cost candidates time but gained no credit.
(b)
(i)
(ii)
(iii)
(c)
(i)
(ii)
E4.
(a)
Many candidates appear to confuse the concept of fair testing with reliability;
both terms being used interchangeably.
More able candidates answered in terms of how an environmental variable could
affect the rate of transpiration, or the rate of evaporation, rather than just stating
‘to keep water loss the same’.
Most candidates gave the correct answer.
Most candidates calculated the mass of water lost accurately.
Many candidates missed marks by failing to give a comparison between the upper
and lower surfaces of leaves. There were many references to ‘pores’ rather than
‘stomata’, or a ‘waxy layer’ rather than a ‘cuticle’, indicating a poor knowledge of
leaf structure.
In part (i), most candidates
recognised the apoplast pathway. A
Page 15
Feversham College
common error in part (ii) was to ignore water movement into air spaces and out through
the stoma, and to explain water movement through cell walls and through air spaces in
terms of osmosis. Many candidates, however, were able to correctly explain the
movement of water in terms of water potential gradients.
(b)
Candidates often failed to gain marks on this question by a failure to relate the
adaptation to how water is lost or retained, such as reducing evaporation or enclosing still
air. Vague statements such as trapping water, trapping air or just reducing water loss
were common.
E5.It appeared that some students had not used a potometer. The investigative and practical skills
section of the specification for this unit clearly states that students require specific knowledge
of the use of a potometer to measure the rate of water uptake. It also makes clear that
students can be tested on this in the examination.
(a)
Many students were aware that opening the tap would return the air bubble to the start.
Students who appeared unfamiliar with a potometer usually made incorrect guesses from
the diagram, e.g. ‘add water to the reservoir’, ‘remove the plant’ or ‘remove the bung’.
(b)
60% of students gained at least one mark. Better responses usually went beyond
ensuring that the apparatus was airtight. The question asked for specific precautions that
should have been taken when setting up the potometer. Despite this, weaker responses
typically named factors that should be kept constant.
(c)
Given that this question has been asked in a previous series, it is disappointing that over
60% of students scored zero. Better responses showed appreciation that water is used
for support and photosynthesis and produced during respiration. However, weaker
responses seemed to focus on the word ‘transpiration’ in the question stem.
Consequently, references to the opening and closing of stomata, effects of environmental
factors and not all water being used in transpiration were widespread. Similarly, some
students thought that water is used in respiration, or produced during photosynthesis.
(d)
This proved to be an excellent discriminator. Just under half of students scored at least
two marks. This was usually for appreciating that removing more leaves meant fewer
stomata, less transpiration and less tension. Unfortunately, weaker responses often did
no more than describe the relationship
between the number of leaves removed
Page 16
Feversham College
and the rate of transpiration. Some students had difficulty in applying their knowledge to
an unfamiliar context. They wrote all they knew about cohesion-tension, without linking
this directly to the data in the table.
Page 17