Question 18N.2.HL.TZ0.8
| Date | November 2018 | Marks available | [Maximum mark: 15] | Reference code | 18N.2.HL.TZ0.8 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Describe, Distinguish, Explain | Question number | 8 | Adapted from | N/A |
Extensive areas of the rainforest in Cambodia are being cleared for large-scale rubber plantations. Distinguish between the sustainability of natural ecosystems such as rainforests and the sustainability of areas used for agriculture.
[3]
a. sustainable communities/ecosystems allow continued survival of organisms/OWTTE ✔
b. natural ecosystems can be sustainable over long periods of time/OWTTE ✔
c. natural ecosystems/rainforest more sustainable than agricultural areas/plantations ✔
d. diverse community/high biodiversity/higher biodiversity in natural ecosystems/rainforest
OR
less/low biodiversity in agricultural areas/agricultural soils ✔
e. agricultural areas/monocultures more affected by pests/diseases ✔
f. nutrient recycling «efficient» in natural ecosystems/rainforest ✔
g. nutrients removed with crops/nutrients removed when crops are harvested
OR
less formation of humus/less organic matter in agricultural soils ✔
h. more water recycling/more rainfall/more transpiration in natural ecosystems/rainforest ✔
i. larger biomass/more carbon stored «in biomass» in natural ecosystems/rainforest ✔
j. shallower soils/less soil erosion/degraded soils/infertile soils in agricultural areas ✔
Describe the roles of the shoot apex in the growth of plants.
[5]
a. shoot apex is an «apical» meristem/has undifferentiated cells ✔
b. mitosis «in shoot apex» ✔
c. cell division/cytokinesis/cells produced «in shoot apex» ✔
d. cell elongation «in shoot apex» ✔
e. stem/shoot growth «due to the cell division and elongation in the shoot apex» ✔
f. produces auxin ✔
g. auxin stimulates growth/cell elongation ✔
h. growth towards light ✔
i. differentiation of cells «produced by the shoot apex» ✔
j. leaf initiation/leaf development begins/leaf «primordia» formation «at shoot apex» ✔
k. flowers produced «by shoot apex» ✔
Research suggests that many living plant species are polyploid. Explain how polyploidy occurs and, using a named example, how polyploidy can lead to speciation.
[7]
a. polyploidy is having more than two sets of «homologous» chromosomes ✔
b. triploid has three sets/is 3n ✔
c. tetraploid has four sets/is 4n ✔
d. Allium/vizcacha rats/other named example» ✔
e. details of chromosome numbers in diploid and polyploid species in the example ✔
f. non-disjunction/failure of chromosome pairs to separate during meiosis ✔
g. diploid gamete «can lead to polyploidy» ✔
h. fusion of diploid and haploid gamete produces triploid cells ✔
i. DNA replication but no subsequent mitosis doubles the chromosome number/produces tetraploid «from diploid»
OR
fusion of two diploid gametes produces tetraploid/4n ✔
j. polyploid/tetraploid «crossed» with diploid/non-polyploid produces infertile offspring ✔
k. meiosis fails in triploids because «homologous» chromosomes cannot pair up ✔
l. polyploid individuals are reproductively isolated
OR
polyploidy causes instant/immediate speciation
OR
tetraploids can form a new species because they can cross with each other
OR
polyploids cannot cross/produce fertile offspring with diploids ✔
m. speciation by polyploidy is common in plants/commoner in plants than animals ✔
n. polyploid individuals tend to be larger ✔