Syllabus Edition

First teaching 2014

Last exams 2024

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Transport in the Xylem of Plants (DP IB Biology: HL)

Exam Questions

3 hours35 questions
1a1 mark

The image shows the cross section of a leaf.

7-2-fig-2-1Identify the substance which is represented by the arrows in the diagram.

1b3 marks

Draw three lines to correctly identify the method of particle movement shown in the diagram from part a).

4~MdS3aW_transport-mechanism-sq
1c2 marks
(i)

Identify the letters from the diagram in part a) that represents the xylem.

[1]

(ii)

Describe one adaptation of the xylem which makes it suitable for its function.

[1]

1d1 mark

The diagram below represents a plant organ.

iiQrQbZs_xylem-in-the-root-sq

State the name of this organ.

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2a1 mark

The transpiration stream relies on cohesion to maintain a continuous column of water in the xylem.

Define the meaning of the term 'cohesion'.

2b1 mark

Capillarity is a term used to describe the movement of water through narrow diameter tubing, called capillary tubing, against the force of gravity. This phenomenon is represented by the image in the diagram.

capilarity-and-adhesion-sq

In combination with the cohesion described at part a), identify one other property of water which allows transport through the capillary tube.

2c1 mark

Capillary tubing, such as that shown in part b), can be used to model the process of transpiration.

State a reason for the use of models in science.

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3a3 marks

The image shows the movement of water through the cells in the root.

KB2PuSdK_replacing-losses-from-transpiration

Label the diagram by adding the following to the correct parts:

  • Apoplast pathway
  • Symplast pathway
  • Casparian strip
3b2 marks

Explain the effect that the casparian strip have on the movement of water through the root.

3c2 marks

Movement of water into the root occurs by osmosis.

Describe the process used by plant roots to ensure the osmolarity of the root cells is higher than the surrounding soil.

3d1 mark

Some plants develop mutualistic relationships with soil fungi.

Identify the key benefit to the fungus of this relationship with the plant.

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4a3 marks

A bubble potometer can be used to investigate the rate of transpiration.

The diagram shows the apparatus required in a bubble potometer. 

HcAG7PNx_bubble-potometer-sq

The table shows some of the functions of this apparatus.

Function Letter
Used to measure the distance moved by the bubble in cm  
Prevents evaporation of water from the equipment  
Adds water to the equipment to reset the bubble  
Indicates the volume of water used in transpiration  

Complete the table with the letters which correctly represent the feature described.

4b
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2 marks

Some students set up a potometer similar to the one in part a), in a classroom at 20 °C with no air movement. Over the course of 25 minutes, they calculated that 7.5 mm3 of water was lost through transpiration.

Calculate the rate of transpiration shown by the shoot, in mm3 hr-1.

4c4 marks

To see the effect of different environmental factors on the rate of transpiration, the students adjusted the temperature, air movement, humidity and light intensity in the room.

Identify what the students would expect to happen to the rate of transpiration in the following scenarios, by completing the table below:

Scenario Effect on transpiration (increase/decrease/no effect)
Increased the room temperature  
Turned on a fan  
Turned on a humidifier  
Surrounded the plant by lamps  

4d2 marks

During the set up of the potometer shown in part a), the plant stem was cut underneath water before being positioned in the equipment as shown.

Explain why is it necessary to cut the stem underneath the water for this investigation.

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5a4 marks

One mark is available for clarity of communication throughout this question.

Draw a labelled diagram of the vascular system seen in the cross section of a plant stem.

5b6 marks

Outline the features of xerophytes which make them adapted for living in areas where water is scarce.

5c5 marks

Describe the route of water as it moves through a plant in the transpiration stream.

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1a1 mark

Define the term transpiration.

1b2 marks

Holly is a common type of evergreen plant that can be found in British gardens. The leaves of holly bushes possess particularly thick waxy cuticles. A student investigated the rate of transpiration in holly leaves. They cut 10 leaves for set X and 10 leaves for set Y. The student then covered the leaves in set Y in petroleum jelly. After weighing each set of leaves, they attached the leaves in each set to a separate wire.The student then weighed each set of leaves at 30-minute intervals for a duration of 3 hours.

Their results are seen in the graph below.q1b_9-1_transport_in_the_xylem_of_plants_medium_ib_hl_biology_sq

Environmental conditions can affect the rate of transpiration in plants. State two environmental variables that should be controlled in this investigation.

1c3 marks

As seen in the graph in part b), between 90 minutes and 120 minutes the rate of transpiration begins to slow in both sets of leaves.

Explain why this happens.

1d2 marks

The results for the leaves in set X are different from the leaves in set Y.

Suggest an explanation for this.

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2a1 mark

A potometer can be used to investigate the water uptake of plants under different conditions. The diagram below shows how a student set up a potometer to investigate the rate of water uptake in a plant shoot.

q2a_9-1_transport_in_the_xylem_of_plants_medium_ib_hl_biology_sq

When setting up the potometer one of the precautions the student took to ensure reliable measurements of water uptake was to dry off the leaves before taking any measurements.

Suggest a reason for this.

2b2 marks

Identify two other precautions the student should take when setting up the potometer apparatus to ensure they obtain reliable results.

2c3 marks

A potometer measures the water uptake of a plant in a given time.

Suggest three reasons why the measurements taken from a potometer do not represent the true rate of transpiration in a plant.

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3a2 marks

The diagram below shows a transverse section (TS) of a plant stem.

q3a_9-1_transport_in_the_xylem_of_plants_medium_ib_hl_biology_sq

Identify the structure found at J and state its function.

3b3 marks

In xylem vessels, hydrogen bonds form between polar water molecules.

Describe the role that hydrogen bonding plays in the cohesion-tension theory of water transport in the xylem of plants.

3c3 marks

Marram grass is commonly found on sand dunes, an example of a dry environment where plants have evolved to survive.

Explain how marram grass leaves are adapted to minimise water loss.

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4a4 marks

Explain how a plant replaces the water it loses via transpiration.

4b1 mark

Explain what is meant by the term halophyte.

4c2 marks

Give two adaptations that a typical halophyte might have to help it survive in these conditions.

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5a3 marks

One mark is available for clarity of communication throughout this question.

Describe how a porous pot can be used to model the evaporation of water that occurs from the leaves of a plant.

5b4 marks

Angiosperms (commonly known as flowering plants) are a group of plants that have vascular tissue, whereas bryophytes (mosses, liverworts and hornworts) are a group of plants that lack vascular tissue.

Suggest some advantages of possessing vascular tissue.

5c8 marks

Explain how minerals are absorbed into plant roots from the soil.

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1a6 marks

The graph shows the effect of three different environmental factors on the rate of transpiration in a terrestrial plant.

X9utcuvA_environmental-factors-transpiration-rate-sq

(i)
Identify which environmental conditions may be represented by the lines X, Y and Z.
X  
Y  
Z  

[3]

(ii)
Explain the reasons for your choice.

[3]

1b3 marks

Explain why the trend shown by line Y in the graph at part a), could result in decreased growth of a terrestrial plant.

1c3 marks

Hydrophytes are aquatic plants which are adapted to living in very wet environments.

Water lilies are an example of a hydrophyte which has evolved to show higher rates of transpiration in order to support their growth in garden ponds.

water-lily-sqSome adaptations of water lilies include the following:

  • A thinner or absent waxy cuticle
  • Stomata on the upper side of the leaf 
  • Large flat leaves

Use the image above and your knowledge of plant leaf structure and transpiration to explain how these adaptations may help to maximise the rate of transpiration in hydrophytes.

1d3 marks

Terrestrial plants will often not survive if they are surrounded by water in the same way as the hydrophytes described in part c). Flooding of crop fields has become a severe problem in the US with detrimental effects on the growth of crop plants such as potatoes and beans. Crops growing in flooded soil are unable to absorb sufficient amounts of water through their roots, leading to wilting of their leaves.

Explain why, in the event of a flood, the uptake of water into the root cells may be reduced.

1e2 marks

Suggest what effect flooding may have on the rate of transpiration in crop plants.

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2a4 marks

The effect of humidity on the transpiration stream within the xylem of an oak tree was investigated, the results are displayed in the graphs below.

7vWwP4N8_humidity-and-cohesion-tension-sq

Describe how the trends shown in graph A compare with the trends shown in graph B.

2b4 marks

Outline how the changes in humidity lead to the changes in water tension measured in the xylem at the top of the tree.

2c4 marks

During the investigation, the scientist also measured the diameter of the tree trunk, the results can be seen in the table below:

Time Circumference of the trunk (cm)
7:00 97.5
9:00 97.4
11:00 96.5
13:00 95.7
15:00 95.7
17:00 96.3
19:00 97.3
21:00 97.4
23:00 97.5

Explain how this data and the data in the graphs from part a) support the cohesion-tension theory.

2d5 marks

The scientist who carried out the investigation in part a) concluded from his data that water moves through the xylem through the cohesion tension mechanism.

Evaluate his conclusion based on the validity of the evidence provided by the results of this investigation.

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3a
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1 mark

The graph shows the relationship between vapour pressure deficit and the rate of transpiration in wheat plants.

af5UinOX_transpiration-and-concentration-gradient-sq

Vapour pressure deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when its saturated.

Using this information, state whether a high vapour pressure deficit would indicate that air humidity was high or low.

3b3 marks

With reference to the data shown in the graph from part a), explain the effect that VPD has on transpiration of wheat between 6:00 and 12:00.

3c2 marks

Explain the pattern seen in the results from part a) between 13:00 and 18:00.

3d3 marks

Suggest how information about vapour pressure deficit may be useful for growers of wheat plants.

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4a2 marks

Some students were investigating the effect of capillary tube diameter on the uptake of water by capillary action.

They set up three capillary tubes with diameters of 0.6 mm, 0.8 mm and 1.0 mm and measured the distance moved by water in 30 seconds. Their results can be seen below:

tS0gWo9H_cappilary-tube-decreasing-diameter-sq

Explain the observations made by the students.

4b2 marks

The graph shows the differences in water movement in the xylem of a tree. The measurements were taken in the branches at the top of the tree and in the trunk of the tree.

UT-Rd-KC_watermovement-branches-and-trunk-sq

Using ideas illustrated by the capillary model in part a), explain the results shown in the graph.

4c2 marks

Identify a limitation of using capillary tubing as a model to represent the movement of water through the xylem.

4d
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3 marks

The students set up a potometer with a 0.8 mm diameter capillary tube to measure the rate of transpiration in a branch removed from a tree. Over a period of 30 minutes, the students noted that the bubble moved 13.7 cm.

Calculate the rate of transpiration shown by the leaf in mm3hr-1. Use the equation πr2 to calculate the area of a circle.

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5a4 marks

One mark is available for clarity of communication throughout this question.

Describe the pressure changes which occur in the xylem as a result of water moving through the transpiration stream.

5b7 marks

Compare and contrast the different adaptations of xerophytes and halophytes.

5c4 marks

Outline the routes that water can take from the soil, through the root cortex to the xylem.

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