CIE AS Biology

Topic Questions

ASBiologyCIETopic Questions7. Transport in Plants7.2 Transport Mechanisms

Syllabus Edition

First teaching 2020

Last exams 2024

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7.2 Transport Mechanisms

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11 mark

Where does the majority of the water evaporate from during transpiration?

  • outer surface of the epidermal cell layer

  • the surface of the palisade mesophyll

  • the surface of the spongy mesophyll

  • inside guard cells

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21 mark

Which of the following processes involving transport in the xylem requires the use of ATP?

  • evapotranspiration from the leaves

  • uptake of minerals from the soil

  • capillary action in the xylem

  • osmosis of water into the xylem 

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31 mark

Why might land flooded by the sea not be suitable for growing plants even after the flood water has evaporated?

  • not enough oxygen in the soil 

  • too much nitrogen in the soil

  • too much CO2 in the soil

  • low water potential of soil

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41 mark

This diagram represents part of the phloem pathway, from leaf to root in a plant.q4-easy-7-2-transport-mechanism-cie-ial-biology

Which cell is a companion cell?

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51 mark

A student used a potometer to measure the rate of water loss from a plant by transpiration.

The internal diameter of the capillary tube and the distance moved by the bubble in fifteen seconds were recorded.

The results are shown in the table.

internal diameter of capillary tube / mm
1.2

distance moved by bubble in fifteen seconds / mm
7

Which calculation correctly shows how to determine the rate of transpiration in mm3 min–1?

  • π(1.22 x 7) x 4

  • π(0.62 x 7) x 4

  • π(1.22 x 7) / 4

  • π(1.2 x 7) x 4

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61 mark

Which xerophytic adaptation does not directly reduce water loss in a desert dwelling plant?

  • lower stomatal abundance

  • sunken stomata

  • hardened spines

  • epidermal hairs

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71 mark

Which is the apoplast pathway? q7-easy-7-2-transport-mechanism-cie-ial-biology

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81 mark

What happens to the water potential and the hydrostatic pressure in the phloem when carbohydrate is moved into it?

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

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91 mark

Which pathways in the root are blocked by the casparian strip? 

1 apoplast
2 symplast
3 vacuolar

  • 1 and 2

  • 2 and 3

  • 1, 2 and 3

  • 1 only

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101 mark

Which process is not responsible for the upward movement of water through the xylem?

  • root pressure 

  • capillary action

  • transpiration pull

  • translocation

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11 mark

This diagram represents part of the phloem pathway, from leaf to root in a plant.q1-hard-7-2-transport-mechanism-cie-ial-biology

Which process is occurring at each stage?

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

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21 mark

Which processes are involved in transport in the phloem and xylem?

  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

A leafy shoot was attached to a potometer and the time taken for the meniscus to move along the capillary tubing was recorded. The capillary tubing has a 0.5 mm diameter.  

In one session, the student measured the bubble to be moving at a rate of 3 mm min-1

How much water would the plant absorb in 30 minutes at this rate in mm3 to two significant figures?

  • 18

  • 90

  • 45

  • 17.67

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41 mark

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

  • flow of sugars in phloem is 10,000x faster than diffusion alone

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

  • positive pressure from inside the phloem forces sap out through aphid stylets (mouth parts) and this pressure lowers closer to the source

  • sieve tube 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 increases?

  • the narrow lumen of the xylem vessel tubes

  • the absence of cross walls between xylem vessel elements

  • the lignification of the walls of the xylem vessel elements

  • the cohesion of water in the xylem vessel elements

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61 mark

Which of these statements indicates that the mass flow of sap through sieve elements is an active process?

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

  • sucrose is loaded into the phloem against the concentration gradient

  • movement of sucrose in the phloem occurs many times faster than the speed of diffusion

  • water enters the phloem via osmosis down a concentration gradient

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71 mark

All of these scenarios 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 a plants cell wall
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

What determines the speed of water movement in the xylem?

  • the amount of water absorbed by the roots

  • diffusion of water through the stomata

  • evaporation of water from the mesophyll cells

  • the maintaining of a diffusion gradient in the leaves

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91 mark

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

How will the root pressure in a plant be affected by waterlogged soil?

  • no change

  • increase due to a low water potential in the soil

  • increase due to an increased transpiration pull

  • decrease due to a lack of oxygen in the soil

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11 mark

This diagram shows a transverse section of Ammophila arenariaq1-medium-7-2-transport-mechanism-cie-ial-biology

Which xerophytic adaptations are visible in the diagram?

1 hairs on lower epidermal surface
2 sunken stomata
3 extensive root network
4 external cuticle
5 defensive spines

  •  1, 2 and 3

  • 2, 3 and 4

  • 1, 2 and 4

  •  1, 3 and 5

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21 mark

This diagram represents part of the phloem pathway, from leaf to root in a plant.q2-medium-7-2-transport-mechanism-cie-ial-biology

Which process is occurring between Y and Z? 

  • diffusion of sucrose

  • active transport of sucrose

  • diffusion of water

  • active transport of water

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31 mark

Why is the circumference of a tree trunk larger at night than in the middle of the day?

  • at night the stomata are open 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 xerophytic adaptations reduce the water potential gradient?

1 epidermal hairs
2 sunken stomata
3 reduced number of stomata
4 rolled leaves
5 defensive spines

  • all 5

  • 1,2 and 4

  • 1,4 and 5

  • 1, 2, 3 and 5

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51 mark

A student used a potometer to measure the rate of water loss from a plant by transpiration.

The internal diameter of the capillary tube and the distance moved by the bubble in 30 seconds were recorded.

The results are shown in the table.

internal diameter of capillary tube / mm
0.6		 distance moved by bubble in 30 seconds / mm
14

What is the amount of water lost by transpiration in mm3 min-1 to 3 s.f.?

  • 15.8

  • 3.96

  • 31.7

  • 7.92

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61 mark

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

Which statement best explains how this occurs?

  • mass flow occurs in both directions in a phloem sieve tubes at the same time

  • mass flow occurs in different directions in different phloem sieve tubes at the same time

  • 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 feature of water is least likely to affect the climate in a tropical rainforest?

  • capillary action

  • cohesion to other water molecules

  • maximum density at 4oC

  • low viscosity

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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 by 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 being absorbed in the root must always pass through the symplast pathway at some point
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?

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

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