Web viewIn some treatments, the leaves were coated with a type of grease. ... However, weaker...

Feversham College

Q1. (a) Explain how water enters a plant root from the soil and travels through to the endodermis.

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(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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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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Feversham College

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(Total 15 marks)

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.

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(ii) Explain these changes in the volumes.

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(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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(Total 8 marks)

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Q3. (a) Describe how water is moved through a plant according to the cohesion-tension hypothesis.

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(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?

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(ii) Why was it important to keep the environmental conditions constant?

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(iii) What is the evidence that the grease provides a waterproof barrier?

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(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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(Total 10 marks)

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.

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(ii) Describe and explain how water in the mesophyll cells passes out of the leaf.

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(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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(Total 6 marks)

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.

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(b) Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot.

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(c) 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.

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(d) The students’ results are shown in the table.

Number of leaves removed from the plant

shoot

Mean rate of water uptake /

cm3 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.

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(Total 8 marks)

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;

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(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 cohesiondue to H bonding column doesn’t break because of adhesion with xylem walls;

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(c) (water is used in) the light-dependent reactions of photosynthesis;electrons from water enable ATP production / H+ are used to reduceNADP / 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;

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M2. (a) (i) absorption rate stays level (initially) then rises;transpiration rate rises regularly / transpiration increases at afaster rate than absorption;

(principle that both increase 1 max awarded)2

(ii) increased stomatal aperture / light / temperature(increasestranspiration rate);decreases water potential in root / increased uptake by osmosis;

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(b) water evaporates / transpires, this reduces water potential / creates waterpotential gradient / increases osmotic gradient;water drawn out of xylem;creates tension / pulling effect / creates negative pressure (in context);

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cohesive forces or H bonding between water molecules / water movesas 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 ofcuticle;

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(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;

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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;

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(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]

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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 apparatusIgnore: references to keeping other factors constant

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;2 max

(c) 1. 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]

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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.

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(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. However, many candidates were unable 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) Many candidates appear to confuse the concept of fair testing with reliability; both terms being used interchangeably.

(ii) 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’.

(iii) Most candidates gave the correct answer.

(c) (i) Most candidates calculated the mass of water lost accurately.

(ii) 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.

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E4. (a) In part (i), most candidates recognised the apoplast pathway. A 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.

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(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 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.

Web viewIn some treatments, the leaves were coated with a type of grease. ... However, weaker...

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