Question 18N.2.HL.TZ0.4
| Date | November 2018 | Marks available | [Maximum mark: 12] | Reference code | 18N.2.HL.TZ0.4 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Describe, Discuss, Explain, Identify, Sketch, Suggest | Question number | 4 | Adapted from | N/A |
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]
coniferophyta/conifer/coniferous/gymnosperms/pinophyta ✔
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]
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» ✔
An increase in global temperatures poses a critical threat to boreal forests. Explain the consequences of climate change to this northern ecosystem.
[2]
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 ✔
Suggest one advantage for the evergreen trees of the boreal forest being pollinated by wind.
[1]
animals/insects/mutualistic «relationships» not needed «for pollination»
OR
pollen not eaten by animals/insects ✔
Discuss the advantages of the production of seeds enclosed in fruit.
[2]
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.
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]
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 ✔
In some boreal species, Rubisco is down-regulated during the winter months. Describe the role of Rubisco in photosynthesis.
[2]
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» ✔