CAIE A-Level Biology AS 7.2 Transport Mechanisms Questions

Practise plant-transport mechanism questions by tracing root water pathways, explaining transpiration pull and modelling phloem loading and mass flow.

Exam points

Identify mineral ions and organic compounds transported within plants in dissolved form.
Explain apoplast and symplast water routes to xylem, including lignin, suberin and the Casparian strip.
Link leaf evaporation and vapour diffusion to xylem pull through hydrogen-bond cohesion and cellulose adhesion.
Annotate xerophyte leaf cross-sections to show how rolled leaves, sunken stomata or cuticles reduce water loss.
Trace sucrose and amino acids through phloem sieve tubes from sources to sinks.
Explain proton pumping and cotransporter proteins in companion-cell loading of sucrose into phloem.
Explain phloem mass flow from source to sink using the hydrostatic pressure gradient.

Covered syllabus points

7.2.1—Solutes transported in water 7.2.2—Water transport from soil to xylem 7.2.3—Transpiration from leaves 7.2.4—Hydrogen bonding in water movement 7.2.5—Xerophytic adaptations 7.2.6—Assimilate transport in phloem 7.2.7—Companion cells transfer assimilates 7.2.8—Mass flow in phloem

[Maximum number: 1]

The diagrams show transverse sections of parts of a plant. Transport tissues are labelled 1 to 6.

Figure for Question 1 — CAIE A-Level Biology AS

Which row shows tissues that mainly transport water and tissues that mainly transport sucrose?

mainly transport

water

mainly transport

sucrose

1 and 3

4 and 6

2 and 3

4 and 5

3 and 5

2 and 6

4 and 6

2 and 3

[Maximum number: 1]

Which statement correctly describes the movement of solutes in the symplast pathway?

Cell surface membranes regulate the selective absorption of solutes into the symplast pathway.

Plasmodesmata control the movement of solutes from the symplast pathway to the apoplast pathway.

The symplast pathway transports dissolved mineral ions from the soil that cannot be transported by the apoplast pathway.

The movement of solutes through plasmodesmata in the symplast pathway is prevented in the endodermis by suberin.

[Maximum number: 1]

Which row correctly shows processes required for the movement of water from a root hair cell to the atmosphere?

cohesion

diffusion

evaporation

key

✓

$\boldsymbol{\chi}$

✓

$\boldsymbol{\chi}$

✓ = required

✓

$\boldsymbol{\chi}$

✓

$\boldsymbol{x}=$ not required

$\boldsymbol{\chi}$

✓

[Maximum number: 1]

Which statement helps to explain why water molecules are forced to move through xylem vessel elements as a consequence of transpiration?

Water molecules form hydrogen bonds with cellulose in the walls of xylem vessel elements in a process known as adhesion.

Water molecules form hydrogen bonds with neighbouring water molecules in a process known as cohesion.

Water molecules form ionic bonds with dissolved mineral ions, which helps to keep the water molecules together in a continuous column.

Water has a high latent heat of vaporisation and this prevents the evaporation of water in the xylem vessel elements.

[Maximum number: 1]

The photomicrograph shows some xerophytic adaptations in leaf tissue.

Figure for Question 5 — CAIE A-Level Biology AS

Which row shows the correct functions for structures 1,2 and 3 ?

reduces the water vapour concentration gradient between the inside and outside of the leaf

reduces evaporation from the epidermis of the leaf

traps a layer of moist air

1, 2 and 3

3 only

2 only

1 and 2 only

1, 2 and 3

1 and 2

1 only

2 and 3 only

1 and 2

2 and 3 only

1 and 2 only

1 only

[Maximum number: 1]

Which row correctly identifies sinks for sucrose transported by mass flow in plants?

root storage organ

growing leaf bud

growing shoot tip

✓

$\boldsymbol{\chi}$

✓

$\boldsymbol{\chi}$

✓

key

✓ = sink

$\boldsymbol{x}=$ not a sink

[Maximum number: 1]

Carrier proteins in the cell surface membranes of companion cells are involved in the transfer of assimilates to phloem sieve tubes. The diagram represents the use of two types of carrier protein in this process.

Figure for Question 7 — CAIE A-Level Biology AS

What are the substances labelled X and Y ?

$\mathrm{H}^{+}$ ions

sucrose

$\mathrm{H}^{+}$ ions

glucose

sucrose

$\mathrm{H}^{+}$ ions

glucose

$\mathrm{H}^{+}$ ions

[Maximum number: 1]

Which conditions are needed to allow the mass flow of sucrose in phloem sieve tubes?

phloem sieve tube in sources

phloem sieve tube in sinks

higher hydrostatic pressure higher water potential

lower hydrostatic pressure lower water potential

higher hydrostatic pressure lower water potential

lower hydrostatic pressure higher water potential

higher hydrostatic pressure lower water potential

lower hydrostatic pressure lower water potential

higher hydrostatic pressure higher water potential

All question bank results loaded

Covered syllabus points

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8