Syllabus Edition

First teaching 2023

First exams 2025

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Transport Mechanisms (CIE AS Biology)

Exam Questions

3 hours42 questions
1a
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3 marks

Fig. 1 shows the movement of water through the cells in the root.

KB2PuSdK_replacing-losses-from-transpiration

Fig. 1

Identify X, Y and Z in Fig. 1 above.

1b
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2 marks

Explain the effect that Z in Fig. 1 has on the movement of water through the root.

1c
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1 mark

Movement of water into the root occurs by osmosis.

State how plant roots ensure that there is a water potential gradient between the surrounding soil and the cells of the root.

1d
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2 marks

The movement of water across a plant root, as shown in Fig. 1, generates root pressure. Root pressure plays a role in establishing and maintaining the transpiration stream of a plant.

Other than root pressure, explain how the transpiration stream of a plant is maintained.

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2a
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1 mark

Fig. 1 shows a cross section through a leaf.

7-2-fig-2-1

Fig. 1

Identify the substance which is represented by the arrows in Fig. 1.

2b
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3 marks

Draw three lines to correctly identify the methods of movement shown in Fig. 1.

4~MdS3aW_transport-mechanism-sq

2c
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3 marks
(i)

Identify the letter from Fig. 1 that represents the xylem.

[1]

(ii)

State two structural features of the xylem which makes it suitable for its function.

[2]

2d
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3 marks

Fig. 2 below shows a cactus plant, an example of a xerophyte.

untitled-5

Nabin K. Sapkota, CC BY-SA 4.0, via Wikimedia Commons

Fig. 2

(i)

Define the term xerophyte.

[1]

(ii)

Explain one feature, visible in Fig. 2, that enables the cactus to be a xerophyte.

[2]

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3a
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4 marks

The following sentences relate to the mechanism of sugar transport in plants.

Identify the words that should be used to complete the sentences.

............... is actively transported into the phloem by a group of specialised cells.

The increased solute concentration causes the water potential of the phloem to ..............., causing water to enter by ............... .

The movement of water into the phloem increases the ............... pressure at the source, resulting in a ............... gradient in the phloem between the source and the sink.

Sugars move by mass flow towards the sink, where they are ............... .

3b
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1 mark

Fig. 1 shows a cross section of phloem tissue in a plant.

q1a_9-2_transport_in_the_phloem_of_plants_medium_ib_hl_biology_sq

Fig. 1

Identify the structure labelled B in Fig. 1.

3c
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4 marks

Structure B in Fig. 1 is involved with the loading of sugars into the phloem sieve tubes.

Describe the role of the following membrane proteins in the loading of sugars into the sieve tubes.

(i)

Proton pumps

[2]

(ii)

Cotransporter proteins

[2]

3d
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2 marks
The locations of sources and sinks for sugar transport do not remain constant throughout the year in a growing plant.

Suggest a possible location for the following during early spring while a plant is producing new leaf buds.

(i)

Source

[1]

(ii)

Sink

[1]

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4a
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3 marks

The statements below each describe a xerophytic adaptation found in some plants.

Explain each of the adaptations given.

(i)

Marram grass leaves roll up when water supply becomes limited

[1]

(ii)

Sedum plants have stomata that are closed during the day and open at night

[1]

(iii)

Holly leaves have thick waxy cuticles

[1]

4b
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4 marks

Fig. 1 contains microscope images of transverse sections though a xerophyte leaf (A) and a non-xerophyte leaf (B).

5FCR9FcW_xerophyte-micrograph

Public domain, via Flickr

Fig. 1

(i)

State how the stomata in leaf A differ from the stomata in leaf B.

[1]

(ii)

Explain how the difference observed in part (i) functions as a xerophytic adaptation in leaf A.

[1]

(iii)

Identify two other structural differences between leaf A and leaf B.

[2]

4c
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1 mark

Xylem vessels are clearly visible in leaf A in Fig. 1.

Identify a feature visible in Fig. 1 that allows the xylem to be identified.

4d
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3 marks

Fig. 2 shows an enlarged section from part of Fig. 1.

xerophyte-micrograph-section
Public domain, via Flickr

Fig. 2

State the leaf features that would be visible on a tissue plan drawing of Fig. 2.

[3]

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1a2 marks

Fig. 1 shows the movement of water through part of a leaf.

7-2-fig-2-1

Fig. 1

Identify the processes labelled X and Y in Fig. 1.

1b4 marks

The process labelled Z in Fig. 1 is transpiration.

Explain how the process of transpiration enables water to be drawn up the stem from the roots.

1c3 marks
(i)

Identify which of cell types, G or H, in Fig. 1 is involved in the process of transpiration.

[1]

(ii)

State and explain one structural feature of the cell type given in part (i) that aids transpiration.

[2]

1d2 marks

The process of transpiration causes water loss in plants, yet it is an unavoidable plant process.

Explain why this is the case.

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2a
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4 marks

Fig. 1 shows a micrograph image of the lower epidermis of a leaf.

7-2-fig-3-1

Fig. 1

(i)

Use the scale bar in Fig. 1 to calculate the magnification of the micrograph image.

[2]

(ii)

Use the answer to part (i) to calculate the actual length of a guard cell, represented by the line marked X. The length of the line marked X in the image is 4.2 cm.

[2]

2b2 marks

The guard cell marked X in Fig. 1 surrounds a single stoma, plural stomata.

Describe the process of water loss that occurs at the stomata.

2c4 marks

One way of measuring the rate at which the process described in part (b) is taking place in a tree is to observe the diameter of the tree trunk.

Fig. 2 below shows the results of an experiment in which tree trunk diameter was measured, along with light intensity and temperature, during the course of a 24 hour period.

7-2-fig-3-2

Fig. 2

Explain the changes in trunk diameter shown in Fig. 2 throughout the 24 hour period.

2d2 marks

The concentration of water vapour in the air, known as humidity, can also influence the rate at which the process described in part (b) can occur.

State and explain the impact that increased humidity would have on the process described in part (b).

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3a
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2 marks

An investigation was carried out into mass change in two sets of leaves over a 3-hour period. The two sets of leaves, set X and set Y, were removed from two different species of plant and were suspended from a wire throughout the investigation. The mass of the leaves was measured every 30 minutes.

The results of the investigation are shown in Fig. 1 below.

7-2-fig-4-1

Fig. 1

The starting mean mass of the leaves in set X in Fig. 1 was 0.1 g. After 90 minutes the mean mass was 0.096 g.

Calculate the percentage change in mass.

3b3 marks

Explain the change in mass of the leaves in set X.

3c3 marks

Fig. 2 shows images of light micrographs of a leaf from set X and a leaf from set Y.

7-2-fig-4-2

Fig. 2

(i)

Identify the leaf that comes from set Y.

[1]

(ii)

Explain your choice from part (i).

[2]

3d4 marks

Xerophytic plants have adaptations to reduce water loss.

Other than those relevant to part (c), state and explain two structural leaf adaptations that reduce water loss.

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4a
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4 marks

Fig. 1 is a diagram of a section through part of a young root.

fig4-1-qp-specimen-2022-9700-02

Fig. 1

Describe the pathways by which water passes from the soil to the cells of the cortex shown in Fig. 1.

4b
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2 marks

Fig. 1 shows the location where mineral ions in the soil enter the plant.

There is a greater density of mitochondria in cell X than in a cell of the root cortex.

With reference to the uptake and transport of mineral ions, suggest why there is a greater density of mitochondria in cell X than in a cell of the root cortex.

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5a
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5 marks

Transpiration in plants can be investigated using a potometer, which measures water uptake by plants. Fig. 1 shows a potometer that was used by a student.

fig1-1-qp-octnov-2018-9700-51

Fig. 1

As water is lost by the leaves through transpiration, the air bubble moves along the graduated tube.

The student used this apparatus to investigate the effect of light intensity on the rate of transpiration in plants.

(i)

State the independent variable and the dependent variable in this investigation.

[2]

(ii)

List three variables that should be controlled in this investigation and describe how the student could standardise two of these variables.

[3]

5b
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6 marks

Describe how the student could set up and use the potometer shown in Fig. 1 to investigate the rate of transpiration at different light intensities.

Your method should be set out in a logical way and be detailed enough to let another person follow it.

5c
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4 marks

The student carried out further experiments, using the same apparatus, to investigate the effect of two different environmental carbon dioxide concentrations on the rate of transpiration.

These experiments were carried out at a high light intensity and at a low light intensity.

The leafy shoots used in the experiments were taken from the same plant and each shoot had five leaves.

The student calculated the percentage reduction in the transpiration rate from 50 ppm to 730 ppm of carbon dioxide at low light intensities.

The results are shown in Table 1.

ppm = parts per million

Table 1

concentration of
carbon dioxide
/ppm
light intensity transpiration rate / g dm-3 hr-1 percentage reduction in
transpiration rate from 50 ppm
to 730 ppm of carbon dioxide
50 low 1.28 36.7
730 low 0.81
50 high 3.03  
730 high 2.12

(i)

Complete Table 1 by calculating the percentage reduction in transpiration rate from 50 ppm to 730 ppm of carbon dioxide at the high light intensity.

Show your working.

[2]

(ii)

The student concluded that, as carbon dioxide concentration increased, the transpiration rate in plants decreased at all light intensities.

Explain why this conclusion may not be valid.

[2]

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1a3 marks

Fig. 1 shows a cross-section across the root of a dicotyledonous plant.

7-2-fig-1-1

Fig. 1

Identify the tissues marked W, X, and Y in Fig. 1.

1b2 marks

Structure Z in Fig. 1 is known as the root cortex. Water travels across the cortex from the outside of the root to the central structure by several different routes, one of which involves the passage of water through plasmodesmata.

One factor that influences the permeability of plasmodesmata is the quantity of a carbohydrate called callose that accumulates in the cell walls surrounding plasmodesmata.

The location of callose in plasmodesmata can be seen in Fig. 2.

7-2-fig-1-2

Fig. 2

Suggest how increasing the deposition of callose might influence the permeability of plasmodesmata.

1c3 marks

Research suggests that the presence of heavy metals such as lead in the soil influences the activity of an enzyme called callose synthase, the role of which is to produce callose. For some plants, the presence of heavy metals in the soil reduces their ability to take up water from the soil.

Suggest how the presence of lead in soil might reduce the ability of a plant to take up water from the soil by the route described in part (b).

1d3 marks

Parts (b) and (c) above refer to the movement of water across the cortex via the plasmodesmata.

Describe another pathway by which water can move across the root cortex from the outside of the root towards the centre.

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2a2 marks

A study investigated the sucrose levels in a courgette leaf during leaf development. The results of the study can be seen in Fig. 1.

7-2-fig-5-1

Fig. 1

(i)

State the days during which the courgette leaf functions as a sink.

[1]

(ii)

State the days during which the courgette leaf could function as a source.

[1]

2b2 marks

Use the information in Fig. 1 to explain why the leaf is able to transition from being a sink to a source.

2c5 marks

Sucrose is transported from sources to sinks in specialised vascular tissue. Fig. 2 shows the vascular tissue used for the transport of sucrose in plants. 

7-2-fig-5-2

Fig. 2

Tissue B in Fig. 2 contains many mitochondria.

Explain how this assists in the loading of sucrose into the sieve tube.

2d3 marks

Explain how the process in part (c) enables mass flow of sucrose in the sieve tube.

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3a
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8 marks

Fig. 1 shows apparatus that can be used to measure the loss of water vapour from leaves.

fig1-1-qp-octnov-2018-9700-52

Fig. 1

The water vapour given out by the area of leaf under the cup increases the pressure inside the tubing, causing the water level in the graduated tube to go down.

Some students used the apparatus in Fig. 1 to test the hypothesis:

The loss of water vapour from the lower surface of the leaves of a plant is greater per unit time than the loss of water vapour from the upper surface of the leaves of the same plant.

(i)

State the independent variable and the dependent variable in this investigation.

[2]

(ii)

Describe a method by which the students could use the apparatus shown in Fig. 1 to measure loss of water vapour in order to test the hypothesis.

Your method should be set out in a logical order and be detailed enough to let another person follow it.

[6]

3b
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8 marks

The hypothesis that the students tested was:

The loss of water vapour from the lower surface of the leaves of a plant is greater per unit time than the loss of water vapour from the upper surface of the leaves of the same plant.

The students decided that, to make a valid comparison, they needed to work out the water loss per unit time per unit area of leaf.

(i)

Describe how the students obtained the measurement needed to work out the results as per unit area of leaf.

[2]

(ii)

Describe how the students could use this measurement and their results for the loss of water vapour to find out if their results support the hypothesis.

[3]

(iii)

Sketch a bar chart on Fig. 2 to show the results if the hypothesis was supported. You should include the axis labels and the units.

[3]

fig1-2-qp-octnov-2018-9700-52
Fig. 2

3c
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3 marks

The apparatus shown in Fig. 1 was used in another series of experiments to measure water vapour loss from the same leaf in different experimental conditions for the same period of time.

Table 1 shows the results.

Table 1

experimental condition distance moved by water column
/ cm per unit time
trial 1 trial 2 trial 3 trial 4 trial 5
high light intensity 7.3 7.5 7.8 6.2 7.0
no light 0.0 0.0 1.5 0.2 0.0
high temperature 4.4 2.8 3.2 4.8 3.1
strong air current 1.5 2.4 1.1 0.9 1.0

(i)

On Table 1, draw circles around two of the values that may be anomalous.

[2]

(ii)

The aperture of stomata affects the loss of water vapour.

State one conclusion that can be made about the effect of experimental conditions on the aperture of stomata in this plant.

[1]

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4a
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4 marks

Fig. 1 shows a cross-section through a needle taken from a pine tree.

xerophyte-pine-needle-micrograph

Public domain, via Flickr

Fig. 1

Explain two features that indicate that pine trees are xerophytic plants.

4b
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4 marks

Fig. 2 shows an enlarged section taken from Fig. 1.

xerophyte-pine-needle-micrograph-section

Public domain, via Flickr

Fig. 2

Make an annotated biological drawing of the area indicated by the black box

4c
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6 marks

'Translocation in the phloem can be regarded as the plant equivalent of mammalian circulation'

Evaluate this statement. 

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