Outline two possible consequences of global warming for organisms living in arctic ecosystems.

The changes that result from global warming may lead to evolution. Define evolution.

Explain how sexual reproduction promotes variation in a species.

reduced space/habitat (for ice-dwelling species) / valid example;
increased competition (from temperate species);
arctic species forced to migrate (in search of suitable habitats/food);
changes in patterns of (seasonal) migration;
extinction of some species due to inability to adapt quickly/compete successfully;
increased activity of decomposers;
increased success of pest species including pathogens;
changes in the distribution of prey species;

(cumulative) change in heritable/genetic characteristics of a population;
new species arise from pre-existing species;
change/adaptation of a population due to natural selection / descent with modification;

sexual reproduction involves interbreeding/genetic material from two parents;
new combinations of paternal and maternal chromosomes/alleles/genes / (random) fertilization;
which leads to new genetic combinations/greater variation;
meiosis creates a great variety of gametes;
by crossing-over / by random orientation of alleles (during meiosis);

Most candidates performed well here, but a significant number of candidates lacked the appropriate vocabulary (habitat, competition, and extinction). Some poor answers focused on the effect of warming on the environment rather than the organisms in the arctic. Others focused only on the problems posed for polar bears. Answers that did not earn credit were release/increase in greenhouse gases, rising water levels, and references to animals “dying out” which was vague.  

Given the pivotal position of evolution in biology, it is disturbing that so many definitions missed the mark.  Candidates who did well were familiar with the Teacher's notes in the Biology syllabus (p. 66) which accompany A.S. 5.4.1.  The concept of change in the heritable characteristics of a population was often expanded to include adaptation through natural selection. Others candidates expanded their answer with the idea of species arising from pre-existing species. Candidates who performed poorly did not specify change in terms of heritable/genetic characteristics. Many weak answers stressed mutation rather than natural selection as the basis for adaptation.  

Among all candidates as a group, every marking point for the question about the promotion of variation in a species through sexual reproduction was eventually awarded. However, most candidates could only produce one or two creditable ideas in their answers. Most common was the involvement of two parents leading to new genetic combinations which cause variation in offspring.  Many candidates mentioned crossing-over and/or random orientation during meiosis. A few candidates mentioned random fertilization.  Some weak answers talked about interbreeding of different species because the candidates misread the question and overlooked “in a species.” Also, many candidates talked about the genes of an organism or adaptation of an organism when the discussion should have been on a species or population. Finally, some candidates mixed up meiosis with mitosis while other made irrelevant comparisons to asexual reproduction.