Date | May 2017 | Marks available | 2 | Reference code | 17M.2.HL.TZ1.4 |
Level | Higher level | Paper | Paper 2 | Time zone | Time zone 1 |
Command term | Outline | 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.
Vascular plants can be found in a wide variety of ecosystems.
Outline active transport in phloem tissue.
Vascular plants can be found in a wide variety of ecosystems.
Explain how a plant replaces the water it loses in transpiration.
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»
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.
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