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Date	November 2018	Marks available	2	Reference code	18N.2.HL.TZ0.4
Level	Higher level	Paper	Paper 2	Time zone	TZ0 / no time zone
Command term	Explain	Question number	4	Adapted from	N/A

Question

Boreal forests stretch across Canada, Russia and Scandinavia. This northern ecosystem accounts for 29 % of the world’s forest areas. The long, cold winters favour tall evergreen trees with either needles or scale-like leaves. These trees are wind-pollinated and their seeds are not enclosed in a fruit. The photograph shows a typical boreal forest in winter.

Identify the dominant plant phylum in the boreal forest.

[1]

In some areas there are gaps in the boreal forest where trees fail to grow and peat tends to accumulate. Suggest reasons for this.

[2]

An increase in global temperatures poses a critical threat to boreal forests. Explain the consequences of climate change to this northern ecosystem.

[2]

Suggest one advantage for the evergreen trees of the boreal forest being pollinated by wind.

[1]

d.i.

Discuss the advantages of the production of seeds enclosed in fruit.

[2]

d.ii.

The boreal forests are situated close to the north pole and even in summer the intensity of sunlight is lower than at the equator. Sketch a graph showing the effect of light on the rate of photosynthesis, labelling the axes.

[2]

e.i.

In some boreal species, Rubisco is down-regulated during the winter months. Describe the role of Rubisco in photosynthesis.

[2]

e.ii.

Markscheme

coniferophyta/conifer/coniferous/gymnosperms/pinophyta ✔

a. waterlogged soils/poor drainage
OR
acidic soil
OR
anaerobic conditions/soil ✔

b. organic matter not «fully» decomposed «leading to peat formation»
OR
decomposers/saprotrophs less active/fewer in cold «temperatures» ✔

a. higher temperatures so more transpiration/droughts/dehydration/water shortage ✔

b. more forest fires ✔

c. more/new pests/diseases because of the changed conditions ✔

d. competition from trees/plants «that colonize/spread to boreal forests» ✔

e. trees/«named» organisms «of boreal forests» not adapted to warmer conditions
OR
trees/«named» organisms migrate/change their distribution due to warmer conditions ✔

f. trees die so loss of habitat for animals ✔

g. faster decomposition/nutrient cycling «so conditions in the ecosystem change» ✔

h. standing water/floods due to more snow/permafrost melting ✔

animals/insects/mutualistic «relationships» not needed «for pollination»
OR
pollen not eaten by animals/insects ✔

d.i.

a. seeds are protected «inside the fruit» ✔

b. seed dispersal by fruits ✔

c. example of a strategy for seed dispersal by a fruit ✔

d. dispersal reduces competition/spreads seeds away from parent plant/to colonize new areas ✔

For mpc suitable strategies are dispersal by wind, by animals ingesting/carrying away succulent fruits, by animals being attracted to colourful/sweet/tasty fruits, by animals burying nuts, by burrs or other hooked fruits sticking to animals and by self-explosion.

d.ii.

a. x-axis labelled as light intensity/amount of light AND y-axis labelled as rate of photosynthesis/rate of oxygen release/rate of carbon dioxide uptake ✔

b. curve starting at/slightly to the right of the x-axis origin and rising rapidly and then more slowly and plateauing but never dropping ✔

e.i.

a. carbon fixation/fixes carbon dioxide/carboxylation
OR
rubisco is used in the Calvin cycle/light independent stage ✔

b. carbon dioxide linked to RuBP/ribulose bisphosphate «by rubisco» ✔

c. glycerate 3-phosphate/glycerate phosphate produced «by rubisco» ✔

e.ii.