ASBiologyCIETopic Questions7. Transport in Plants7.2 Transport Mechanisms

Syllabus Edition

First teaching 2023

First exams 2025

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Transport Mechanisms (CIE AS Biology)

Topic Questions

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11 mark

Which of the following describes the location from which most water evaporates during transpiration?

  • The outer surface of epidermal cells

  • The surface of palisade mesophyll cells

  • The surface of spongy mesophyll cells

  • The surface of guard cells

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21 mark

Which of the following plant transport processes requires ATP?

  • Evapotranspiration from the leaves

  • Uptake of minerals from the soil

  • Capillary action in the xylem

  • Movement of water into the xylem by osmosis

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31 mark

During high tides and stormy weather, some areas of coastal land may become flooded by sea water.

Why might land flooded in this way not be suitable for growing plants even after the floods have receded?

  • A lack of oxygen in the soil

  • Too much nitrogen in the soil

  • Too much CO2 in the soil

  • The soil water potential is too low

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41 mark

The diagram represents part of the phloem.q4-easy-7-2-transport-mechanism-cie-ial-biology

Which of the cells labelled A-D is a companion cell?

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5
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Which of the following does not correctly explain the movement of water in the xylem of plants?

  • Water molecules are attracted to each other by forces of cohesion

  • Water molecules are attracted to the walls of xylem vessels due to forces of adhesion

  • Hydrogen bonds between water molecules results in cohesion-tension

  • The activity of cotransporter proteins generates a hydrostatic pressure gradient

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61 mark

Which xerophytic adaptation does not directly reduce water loss?

  • Lower stomatal abundance

  • Sunken stomata

  • Fleshy leaves

  • Epidermal hairs

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71 mark

The diagram shows several pathways that could be taken by water.

q7-easy-7-2-transport-mechanism
Which of pathways A-D shows the apoplast pathway?

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81 mark

Which row correctly identifies the changes in water potential and hydrostatic pressure that occur in the phloem after sucrose loading?

  water potential hydrostatic pressure
A increases decreases
B increases increases
C decreases increases
D decreases decreases

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91 mark

Which statements about the Casparian strip are correct? 

1 it is a band of waxy material that is located in the root cortex
2 it blocks the apoplast pathway
3 it allows control over the substances entering the xylem

  • 1 and 2

  • 2 only

  • 2 and 3

  • 1, 2 and 3

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10
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Which of the following statements about phloem transport are correct?

1 phloem transport involves carbohydrates in the form of sucrose
2 locations of sources and sinks change at different times of year
3 phloem loading is a passive process
4 phloem assimilates include amino acids from photosynthesis and nitrates from the soil

  • 1 and 2

  • 1, 2 and 3

  • 2 and 3

  • 1, 2 and 4

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11 mark

This diagram represents part of the phloem in a plant.

q1-hard-7-2-transport-mechanism-cie-ial-biology

Assuming that the leaf cells are carrying out photosynthesis, which process is occurring at each stage?

  between X and Y water potential at Z hydrostatic pressure at T
A active transport of sucrose decreases decreases
B active transport of sucrose increases increases
C passive transport of sucrose decreases increases
D passive transport of sucrose increases decreases

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21 mark

Which processes occur in the phloem and xylem of plants?

  xylem phloem
  diffusion mass flow osmosis diffusion mass flow osmosis
A ✓ ✓ X X ✓ ✓
B X ✓ ✓ ✓ ✓ X
C ✓ ✓ ✓ ✓ ✓ ✓
D X X ✓ ✓ ✓ ✓

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31 mark

Cadmium (Cd) is a heavy metal that can have negative effects on the growth of plants. A group of scientists researched Cd uptake in plants by treating plants with different concentrations of Cd (0 mg, 20 mg and 40 mg). The graph shows the presence of Cd in different pathways in the plant roots after treatment. Note that the error bars show standard deviation.cie-ial-7-2h-mcq-3

Which of the following statements about the results of the study are correct?

1 The size of the Cd dose does not significantly influence its concentration in plant root pathways
2 Cd in the symplast pathway is less likely to enter the xylem
3 After a 40 mg dose of Cd, the heavy metal is approximately 2.5x more likely to be present in the symplast pathway than the apoplast pathway
4 The soil in which the plants were grow contained Cd in a very low dose

  • 1, 2 and 3

  • 1 and 3

  • 1, 3 and 4

  • 2, 3 and 4

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41 mark

Which of these statements provides the best evidence that translocation occurs due to pressure-driven mass flow?

  • The circumference of a plant stem is slightly smaller during the day than it is at night

  • Translocation stops in the presence of a metabolic poison that inhibits mitochondrial enzymes

  • When aphids pierce plant stems with their mouth parts, sap flows into their bodies without any suction; this occurs faster nearer the source

  • Sieve plates allow for uninterrupted flow of solutes from source to sink

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51 mark

Which feature of xylem vessel elements allows them to stay open as transpiration rate increases?

  • The narrow lumen of the xylem vessels

  • The absence of cross walls within xylem vessels

  • The lignification of the walls of the xylem vessel elements

  • Cohesion between water molecules in the xylem vessel elements

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61 mark

Which of the following statements indicates that the mass flow of sap in the phloem is an active process?

  • Sap in the phloem can move against the pull of gravity

  • Sucrose enters the phloem against its concentration gradient

  • Movement of sucrose in the phloem occurs against its concentration gradient

  • Water enters the phloem via osmosis

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71 mark

All of the scenarios in the table involve the movement of water by either the symplast pathway or the apoplast pathway.

Which pathway is being used in each instance?

  water moves between cells via plasmodesmata water crosses the endodermis in the root water passes through cell membrane into cytoplasm water enters cell wall but not the cytoplasm
A apoplast symplast apoplast symplast
B apoplast apoplast symplast symplast
C symplast symplast symplast apoplast
D symplast apoplast apoplast apoplast

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81 mark

Which of the following affect the rate at which water moves up the xylem?

  • The volume of water absorbed by the roots

  • The rate at which water diffuses out through the stomata

  • The rate at which water evaporates from the surface of spongy mesophyll cells

  • The steepness of the water vapour potential gradient between leaf air spaces and the surrounding environment

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91 mark

Which statement best explains why the glucose produced by photosynthesis is converted into sucrose before it is transported in the phloem?

  • Sucrose is a larger molecule and is more easily converted to starch

  • Sucrose is a non-reducing sugar so is less reactive than glucose

  • Sucrose can pass through plant cell surface membranes more easily

  • Sucrose is insoluble and therefore doesn’t affect water potential

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101 mark

Which of the following correctly explain how root pressure in a plant be affected by waterlogged soil?

  • Root pressure will not change as waterlogged soil has no impact on root transport

  • Root pressure will increase due to a high water potential in the soil

  • Root pressure will increase due to an increased transpiration pull

  • Root pressure will decrease due to a lack of oxygen in the soil

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11 mark

This diagram shows a transverse section of Ammophila arenaria, also known as marram grass.

marram-grass-micrograph

Public domain, via Flickr

Which of the following statements correctly describes xerophytic adaptations of marram grass that are visible in the image?

1 Hairs reduce the water vapour concentration gradient
2 Stomata in pits allow water vapour to be trapped
3 Dense spongy mesophyll reduces evaporation into the air spaces
4 Water loss by evaporation is reduced by the rolled leaf shape

  •  1, 3 and 4

  • 2, 3 and 4

  • 1, 2 and 4

  •  1, 2, 3 and 4

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21 mark

This diagram represents part of the phloem in a plant.

q2-medium-7-2-transport-mechanism-cie-ial-biology

Which statement about phloem transport is correct? 

  • X can be either a source or a sink

  • Sucrose is transported from X to W

  • Y is not actively involved in phloem transport

  • Sucrose is actively transported between Z and T

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31 mark

Which of the following correctly explains why the circumference of a tree trunk is larger at night than in the middle of the day?

  • At night the stomata are closed so there is a build-up of water in the xylem

  • At night the root pressure has decreased due to reduced mineral uptake by the root hair cells

  • At night there is less tension in the xylem vessels because the rate of transpiration is reduced

  • At night the sieve tube elements are full of dissolved solutes due to a reduced translocation rate

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41 mark

Which of the following statements about water uptake in plant roots are correct?

1 Water moves down its water potential gradient into root hair cells
2 Inhibiting respiration in root hair cells can impair the uptake of water
3 Water uptake is the main driving force for the transpiration stream

  • 1 only

  • 1 and 2

  • 1, 2 and 3

  • 2 and 3

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51 mark

Which of the statements about water transport in plants is correct?

  • Water exits mature xylem vessels via the cell walls

  • Transpiration pull is generated by the transpiration stream

  • Transpiration occurs due to evaporation of water from the surface of palisade mesophyll cells

  • The transpiration stream plays a role in structural support in plants

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61 mark

Sucrose and other products of photosynthesis can move both up and down the plant stem at the same time.

Which statement is the most likely description of how this occurs?

  • Mass flow occurs in both directions within a single phloem sieve tube

  • Mass flow occurs in different directions in different phloem sieve tubes

  • Mass flow overpowers the effects of active transport

  • Active transport moves substances up and mass flow moves substances down

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71 mark

Which of the following properties of water does not directly explain the movement of water in the xylem vessels?

  • Forces of cohesion

  • Forces of adhesion

  • Water can act as a solvent

  • Water is a polar molecule

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81 mark

The rate at which water flows through xylem vessels is influenced by numerous external factors.

An increase in which factor would reduce the flow of water in the xylem?

  • Air temperature

  • Light intensity

  • Wind speed

  • Atmospheric humidity

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91 mark

Which statements about the uptake and transport of water in plants are correct?

1 Water is transported in xylem via the symplast and apoplast pathways to reach the leaves
2 Water transported by the symplast pathway enters root hair cells down a water potential gradient
3 Water absorbed in the root must always pass through the symplast pathway on its way to the xylem
4 Water transported by the apoplast pathway through plasmodesmata must pass through cell surface membranes of endodermal cells

  • 1, 2 and 4

  • 1, 2 and 3

  • 2 and 3

  • 3 and 4

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101 mark

Water absorbed by a root hair cell can travel via different pathways to reach the xylem.

Which of the following best describes the route taken by water as it crosses the root?

  apoplast pathway symplast pathway
A always sometimes
B always always
C sometimes always
D sometimes sometimes

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