Question 1

The loading of sucrose into companion cells involves a number of processes.

Which of these is an active process?

  A  

the movement of H+ ions from companion cells

  B  

the movement of H+ ions into companion cells

  C  

the movement of sucrose from companion cells

  D  

the movement of sucrose into companion cells

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Question 2

Which processes are involved in transpiration?

1 - the diffusion of water vapour from stomata

2 - the mass flow of water through the xylem

3 - the evaporation of water from the surface of mesophyll cells

4 - the evaporation of water vapour from air spaces

  A  

1, 2, and 3

  B  

2, 3, and 4

  C  

1 and 3 only

  D  

1 and 4

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Question 3

Which feature of xylem vessel elements allows them to have reduced resistance to water movement?

  A  

lignin forms an incomplete secondary wall


  B  

new vessels carry extra water as a plant grows

  C  

there are no cross walls between vessel elements

  D  

vessel elements join to form narrow tubes

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Question 4

Which statement(s) explain why a stem is both cut and connected to a potometer under water?

1 - to prevent plasmolysis of xylem vessel elements

2 - to prevent the collapse of xylem vessel elements

3 - to prevent air entering xylem vessel elements

  A  

1 only

  B  

3 only

  C  

2 and 3 only

  D  

1, 2, and 3

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Question 5

What could increase the rate of transpiration?

  A  

increasing the humidity

  B  

increasing the light intensity

  C  

decreasing the temperature

  D  

decreasing the wind speed

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Question 6

Which description is correct for xylem vessel elements?

  A  

cells joined to form a tube, pits at intervals, sieve plates between cells, surrounded by the endodermis in roots

  B  

contains cells joined end to end, containing cytoplasm, cell walls with lignin, located to the outside of phloem in vascular bundles

  C  

contains elongated cells with end walls broken down, located in vascular bundles in the stem and centrally in the roots

  D  

dead elongated cells, lignified cell walls with pits at intervals, associated with companion cells in the roots only

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Question 7

What is a correct definition of the term transpiration?

  A  

diffusion of water from intercellular air spaces to the atmosphere where it evaporates


  B  

evaporation of water from the leaf surface of a plant via the stomata

  C  

 loss of water vapour from the aerial parts of a plant to the atmosphere

  D  

movement of water from the xylem to the atmosphere through the cell walls only

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Question 8

By which process does sucrose move through phloem sieve tube elements?

  A  

active transport


  B  

diffusion

  C  

facilitated diffusion

  D  

mass flow

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Question 9

What is the role of ATP in a companion cell when sucrose is loaded into a sieve tube element?

  A  

moving sucrose into the sieve tube element

  B  

removing protons out of the cytoplasm of the companion cell

  C  

removing protons from the sieve tube element

  D  

taking up sucrose into the cytoplasm of the companion cell

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Question 10

Which describes possible mechanisms by which sucrose is transferred from a mesophyll cell into a companion cell?

1 - co-transport with the active transport of hydrogen ions

2 - co-transport by passive diffusion of hydrogen ions

3 - facilitated diffusion through plasmodesmata

  A  

1 and 3

  B  

2 and 3

  C  

1 only

  D  

2 only

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Question 11

Which statements correctly describe transport pathways in dicotyledonous plants?

1 - in the apoplast pathway, water does not move through plasmodesmata.

2 - in the symplast pathway, water does not move through intercellular spaces.

3 - the apoplast pathway may be blocked by the Casparian strip

  A  

1, 2, and 3

  B  

1 and 2 only

  C  

1 and 3 only

  D  

2 and 3 only

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Question 12

Which statement explains how mass flow arises in sieve tube elements?

  A  

sucrose actively loaded into sieve tube elements decreases the water potential causing the hydrostatic pressure to increase

  B  

sucrose actively loaded into sieve tube elements increases the water potential causing the hydrostatic pressure to decrease

  C  

sucrose diffused into sieve tube elements decreases the water potential causing the hydrostatic pressure to increase

  D  

sucrose diffused into sieve tube elements increases the water potential causing the hydrostatic pressure to decrease

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Question 13

Which statement concerning transpiration is correct?

  A  

on a humid day, the water potential gradient between the intercellular air space and the external atmosphere increases to stimulate water loss by evaporation

  B  

water arriving at the spongy mesophyll cells via the symplast pathway must move by osmosis through the cell surface membrane before evaporation from the surface of the cells

  C  

water diffuses down the water potential gradient from the saturated air space through the guard cells before evaporating from the surface of the cells into the atmosphere

  D  

water moves up the xylem in the apoplast pathway and can continue on this pathway by osmosis to reach the spongy mesophyll cells before evaporating into the intercellular air space

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