Question 19M.2.SL.TZ1.c
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.2.SL.TZ1.c |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Explain how natural selection can lead to speciation.
[7]
a. natural selection is caused by selection pressures in the environment
OR
example of a selection pressure ✔
b. natural selection requires that variation exists within a species ✔
c. variation arises randomly due to mutation
OR
variation is enhanced by meiosis/sexual reproduction ✔
d. over-production of offspring promotes selection
OR
natural selection occurs when there is competition/overpopulation/predators/environmental changes/changes in selection pressures ✔
e. well adapted individuals/individuals with best variations survive to reproduce/survival of fittest ✔
f. «frequency of» genes/alleles conferring an advantage are selected for
OR
genes/alleles conferring a disadvantage are selected against ✔
g. genetic divergence/difference increases
OR
natural selection «genetically» isolates members of a species so eventually they can no longer produce fertile offspring ✔
h. genetic divergence» leads to reproductive isolation ✔
i. geographical/behavioural/ecological factors may lead to «reproductive» isolation ✔
j. prolonged «reproductive» isolation leads to speciation ✔
k. up to one additional mark for AHL information ✔
There were some excellent explanations given in well-structured responses. Many candidates avoided talking about natural selection in genetics terms, losing marks in the process. Darwin’s finches, industrial melanism and the giraffe were common examples. Some students invented their own creative examples.
The idea that natural selection limits biodiversity appeared a few times. The flawed case of the peppered moth was given to exemplify speciation, however Darwin's finches were the most frequent example.
