| Date | November 2016 | Marks available | 2 | Reference code | 16N.1.SL.TZ0.2 |
| Level | Standard Level | Paper | Paper 1 | Time zone | Time zone 0 |
| Command term | Explain | Question number | 2 | Adapted from | N/A |
Question
Figure 2: A graph showing past mass extinctions.
[Source: The Earth Through Time, Eighth Edition by Harold L. Levin. John Wiley & Sons. ISBN: 9780471697435. 2006. Chapter 14 Life of the Mesozoic. Graph:Diversity of marine animals through geologic time, as indicated by number of known fossil genera. Used with permission from Wiley. Permission conveyed through Copyright Clearance Center, Inc.]
State two possible causes of these past mass extinctions.
Identify two ways in which the current extinction differs from mass extinctions in the past.
Explain one factor that may make a species less prone to extinction.
Outline how the process of natural selection is a mechanism for evolution.
Markscheme
meteorite/asteroid/comet impacts;
significant volcanic events/volcanic eruptions/basalt flows;
climate change/ice age;
catastrophic methane release (e.g. from methane clathrate);
drop in oxygen levels;
sea level changes;
cosmic events/radiation from space that depletes atmospheric ozone.
Do not accept ‘natural disasters/disease/earthquakes/floods/water levels rising’.
[2 max]
rate of change is faster/happening over a shorter time frame;
caused by another species changing the environment/not caused by natural phenomena as in the past/caused by humans;
humans can prevent current extinction.
[2 max]
reach sexual maturity early;
…which means they are able to produce offspring early/have more offspring/have larger populations (and increase their species chances of success);
they can have high reproductive success/produce large number of offspring;
…large populations can increase the chances of their survival;
they are opportunistic /r species able to adapt to a wide variety of conditions;
…this allows them to be present in many habitats / have wide geographical coverage;
they have fast lifecycles (e.g. r species);
…which allows them to adapt quickly to change;
they have a number of habitats they can shelter/live/ are widely distributed;
...so if a population is affected in one habitat (e.g. by disease/predation) the species will still survive in another habitat/location;
they are omnivores/generalist feeders/switching predators;
...this adaptability to eating different foods results in potentially a large available food source/with some food source available even under harsh conditions;
ability to hide/camouflage/successfully fight;
...which can reduce predation rates and increase chances of species survival;
have high genetic diversity;
...they are able to adapt to changing environmental conditions;
valued by humans (e.g. as keystone/flagship species);
..increases human investment/action into conserving the species/its habitat (e.g. Giant Panda);
not considered valuable by humans (e.g. as pets or making ornaments);
...it is not hunted /removed from habitat thereby reducing risk of extinction.
Award 1 mark for identifying the factor and 1 mark for the explanation.
Accept other reasonable responses.
[2 max]
organisms in any population vary;
some traits make them better adapted to survive / selection pressures in the environment may favour some variations over others/‘the survival of the fittest’;
thus organisms become adapted to environmental conditions;
some of these variations give it a competitive advantage leading to breeding success / those organisms that survive are able to breed and pass on their traits to their offspring;
where conditions (e.g. climate) change, the organism may respond by adapting to it;
isolation (geographical/ecological/reproductive) may separate a part of a population from others;
differences in the environments may cause speciation/evolution of new species as the population adapts to the new environment;
the new species may be unable to interbreed with the parent species to produce fertile offspring.
[2 max]
Examiners report
Most students were able to state two correct reasons.
Most candidates were able to identify at least one way in which current extinction is different from past mass extinctions.
This question was answered well by the majority of candidates. Some responses identified a factor but did not give an explanation.
Responses to this question varied widely from well-focused answers to those that gave a vague description of evolution.
