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Date May 2017 Marks available 3 Reference code 17M.2.HL.TZ1.4
Level Higher level Paper Paper 2 Time zone Time zone 1
Command term Explain Question number 4 Adapted from N/A

Question

Most of the surface of the Earth is covered with a wide diversity of ecosystems. Outline two general characteristics of all ecosystems.

[2]
b.

Vascular plants can be found in a wide variety of ecosystems.

Outline active transport in phloem tissue.

[2]
c.i.

Vascular plants can be found in a wide variety of ecosystems.

Explain how a plant replaces the water it loses in transpiration.

[3]
c.ii.

Markscheme

a. organisms/community plus the environment / biotic and abiotic «components» 

b. interactions 

c. ecosystems show sustainability 

d. nutrients are recycled in ecosystems 

e. energy flows through ecosystems 

f. producers «are part of all ecosystems» 

g. decomposers/saprotrophs «are part of all ecosystems»

b.

a. active transport/pumps used to load sugars/sucrose into phloem/companion cells/sieve tubes 

b. loading in sources/unloading in sinks
OR
sucrose/sugars moved from source to sink 

c. active transport moves H+ out of phloem/sieve tubes «to make H+ gradient in the leaf/source» 

d. H+ gradient used for co-transport of sucrose into phloem/sieve tubes/companion cells

Accept protons or hydrogen ions instead of H+ ions.

Accept the equivalent of mpc and mpd for unloading in the sink.

c.i.

a. transpiration/evaporation of water causes suction/tension 

b. water sucked/drawn out of xylem «in leaf» 

c. water moves up in xylem 

d. due to suction/tension/pulling forces 

e. cohesion of water/hydrogen bonds between water molecules 

f. movement from roots to leaves 

g. water enters root by osmosis/due to higher solute concentration inside root

c.ii.

Examiners report

[N/A]
b.
[N/A]
c.i.
[N/A]
c.ii.

Syllabus sections

Additional higher level » Topic 9: Plant biology » 9.1 Transport in the xylem of plants
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Additional higher level » Topic 9: Plant biology
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