ASBiologyOCRTopic Questions3. Exchange & Transport3.3 Transport in Plants

Transport in Plants (OCR AS Biology)

Topic Questions

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1a1 mark

A potometer can be used to investigate the water uptake of plants under different conditions. Figure 1.1 shows how a student investigated the effect of covering the leaves from plant shoots with grease on the water uptake of the shoots. All of the shoots were from the same plant and had 7 leaves.

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Figure 1.1

When setting up the potometer in Figure 1.1, one of the precautions the students took to ensure reliable measurements of water uptake was to cut the shoots underwater.

Suggest a reason for this. 

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1b3 marks

List three features of xylem vessels that make them specialised for the transport of water.

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1c3 marks

A potometer measures the water uptake of a plant in a given time. Water uptake does not represent the true rate of transpiration in a plant due to the other functions of water in plants.

Name three functions of water in plants (not including transpiration).

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1d2 marks

The results of the experiment are shown in the table below.

Number of leaves covered with grease on plant shoot

Mean rate of water uptake / cm3 min-1
0 0.11
1 0.10
2 0.08
3 0.07
4 0.06
5 0.05
6 0.02
7 0.01

Describe the result produced when all 7 leaves have been covered in grease and suggest an explanation for this.

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2a3 marks

Figure 2.1 shows a cross section of a stem.

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Figure 2.1

The structures labelled I and J in Figure 2.1 make up the vascular bundle.

Describe the functions of the vascular bundles of plants. 

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2b1 mark

Figure 2.2 shows how the changes in environmental temperature and light intensity throughout the day can cause the diameter of a spruce tree to fluctuate.

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Figure 2.2

State at what time of the day the trunk of the spruce tree is most narrow.

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2c3 marks

Suggest the combination of environmental factors that would result in the highest rate of transpiration in the spruce trees.

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2d3 marks

Spruce trees belong to a group of plants known as conifers, which have various xerophytic adaptations.

List three ways in which the leaves of xerophytic plants are adapted to live in dry environments. 

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3a
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Figure 3.1 shows the movement of water through the cells in the root.

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Figure 3.1

Identify which of the following labels corresponds to X, Y and Z in Figure 3.1 above:

  • Apoplast pathway
  • Symplast pathway
  • Casparian strip

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3b
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Explain the effect that the Casparian strip has on the movement of water through the root.

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3c
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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.

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3d
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The movement of water across a plant root, as shown in Figure 3.1, 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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4a
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Figure 4.1 shows the cross section of a leaf.

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Figure 4.1

Identify the substance which is represented by the arrows in Figure 4.1

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4b
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Draw three lines to correctly identify the methods of movement shown in Figure 4.1

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4c
Sme Calculator3 marks
(i)

Identify the letter from Figure 4.1 that represents the xylem.

[1]

(ii)

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

[2]

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4d
Sme Calculator3 marks

Figure 4.2 below shows a cactus plant, an example of a xerophyte.

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Nabin K. Sapkota, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Figure 4.2

(i)
Define the term xerophyte.

[1]

(ii)

Explain one feature, visible in Figure 4.2, that enables the cactus to be a xerophyte.

[2]

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5a
Sme Calculator4 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 ............... .

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5b
Sme Calculator1 mark

Figure 5.1 shows a cross section of phloem tissue in a plant.

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Figure 5.1

Identify the structure labelled B in Figure 5.1

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5c
Sme Calculator4 marks

Structure B in Figure 5.1 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]

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5d
Sme Calculator2 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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1
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Sago pondweed has evolved many adaptations to its aquatic environment. Three such adaptations are described below.

Explain the advantage of each adaptation.

Adaptation 1: No waxy cuticle

Adaptation 2: Stem tissue that contains air spaces

Adaptation 3: A thin, flexible stem

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2
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Plants lose water by transpiration.

The rate of transpiration varies between different species of plant.

The rate of transpiration can be measured using a potometer.

Plan an investigation into the rate of transpiration in two species of plant that would allow valid data to be collected.

Details of how to set up a potometer are not required.

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3
Sme Calculator4 marks

This question is about the impact of potentially harmful chemicals and microorganisms.

(i)

Salts that a plant needs, such as nitrates and phosphates, are taken into root hair cells by active transport.

For which macromolecule does a plant need both nitrogen and phosphorus?

[1]

(ii)

Flooding of fields by seawater can damage crops. Seawater contains dissolved salts, including sodium chloride.

How would flooding affect soil water potential?

[1]

(iii)

Sodium chloride in solution dissociates into Na+ and Cl-. 

Explain how the Casparian strip prevents these ions from reaching the xylem of the plant by the apoplast pathway.

[2]

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4a
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Following their formation, assimilates are transported throughout the plant by translocation in phloem.

Phloem sap mainly consists of carbohydrate in the form of sucrose, but also contains other solutes.

(i)

Suggest why it is beneficial to the plant for the carbohydrate to be transferred throughout the plant in the form of sucrose rather than as an alternative carbohydrate.

[2]

(ii)

How is transport in the phloem similar to and different from transport in the xylem?

[2]

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4b
Sme Calculator8 marks

Assimilates are loaded into the phloem at the ‘source’ and then transported to the ‘sink’.

(i)

Explain, with a suitable example, how some parts of the plant can act as both a ‘source’ and a ‘sink’.

[2]

(ii)

Fig. 19.1 is a diagram that represents the loading of sucrose into the phloem at the ‘source’.

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Fig. 19.1

With reference to Fig. 19.1, explain the process of the loading of sucrose into the phloem and its movement in the phloem.

[6]

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4c
Sme Calculator10 marks

Fig. 19.2 is a diagram of a potato plant. Potatoes are tubers which are underground storage organs.

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Fig. 19.2

Actively growing tissues have a high demand for carbohydrates. This means that a lot of phloem sap is directed to these tissues and requires sucrose to be unloaded in large amounts. 

In an investigation, potato plants were modified by having a gene for invertase inserted into their DNA so that the gene for invertase would be expressed in the tubers. Invertase is responsible for catalysing the hydrolysis of the disaccharide sucrose. 

A trial experiment was carried out to compare the properties of the modified plants with those that had not been modified. After harvesting, the tubers of three of each type of plant were compared. The results shown in Table 19.1

  Modified Not modified
Mean number of tubers per plant 2.2 5.3
Mean mass per tube (g) 49.7 16.8
Mean sucrose concentration
(mg g-1 tuber mass)		 1.4 13.7
Mean glucose concentration
(mg g-1 tuber mass)		 36.3 ± 3.5 1.9 ± 0.3
Invertase activity (arbitrary units) 62.1 1

Table 19.1

(i)

Name the bond that is hydrolysed by invertase.

[1]

(ii)

The potato tubers contain monosaccharides.

Compare the concentration of monosaccharides in the modified tubers with those that were not modified.

[2]

(iii)

In the modified plants, the unloading of sucrose is increased in the tubers compared with those that were not modified.

The transport of sucrose to the tubers was also increased in the modified plants.

Using the data and the information given, deduce a possible mechanism to account for the increased unloading and transport of sucrose in the modified plants.

[4]

(iv)

The trial experiment compared the properties of modified potato plants with those that were not modified.

Analyse the data and draw conclusions about the yield of the tubers of modified plants compared with those tubers from plants which had not been modified.

[3]

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5a
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Fig. 1 below shows a microscope cross section through the centre of a plant root.


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Fig. 1

Identify the tissue types labelled M and N in Fig. 1.

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5b
Sme Calculator2 marks

Table 1 below shows some results from an investigation into the effect of temperature on root pressure in celery plants.

Temperature / °C Root pressure / MPa
8 0.00
10 0.01
16 0.04
20 0.09
24 0.14

Table 1

State which statistical test could be used to analyse the results in Table 1. Give a reason for your answer.

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5c
Sme Calculator4 marks

The investigation in part (b) also measured the effect of temperature on the activity of celery ATPase enzymes. The results are shown in Table 2 below.

Temperature / °C ATPase activity / μmol Pi mg protein-1 h-1
24 32
8 16

Table 2

Use the data in Table 2 and your own knowledge to explain the effect of temperature on root pressure shown in Table1 in part (b).

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5d
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Once water enters the vascular tissue in the root, it is drawn up the plant stem in the transpiration stream.

Explain the upward movement of water via the transpiration stream.

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