Outline the ways in which natural selection has contributed to biodiversity.

Atmospheric and plate activity have affected the distribution and diversity of systems within the biosphere.

Explain the role that the atmosphere has in the distribution of biomes.

Atmospheric and plate activity have affected the distribution and diversity of systems within the biosphere.

Explain the role that plate activity has in the diversity of ecosystems.

Discuss how global warming may affect the distribution and diversity of ecosystems.

natural selection is survival of the fittest/best adapted;
survivors will pass on favourable, inheritable traits to their offspring;
populations of a species may become isolated from one another;
….this may lead to speciation/greater species diversity;
with natural selection populations will change/adapt over time to their different environments;
…up to a point where they can no longer interbreed (ie new species formed/speciation);
natural selection may also favour new mutations/genes adding to the genetic diversity;
adaptive radiation through natural selection in newly formed/diverse habitats can increase species/genetic diversity in a population;
natural selection may favour species that modify habitats generating habitat diversity;

Accept any other reasonable answer.

Answers that incorporate good/strong examples can help the student gain marks for EoI. And no marks for just giving egs here.

[4 max]

Role of atmosphere:
atmosphere contributes to patterns of climate/heat/temperature/ precipitation;
rising hot, damp air at equator condenses as it meets colder air;
…causing high rainfall and ideal conditions for rainforests in that region;
descending dry air at slightly higher latitudes/30 degrees N/S;
…gives rise to desert systems;
atmospheric circulation transfers heat from equator to higher latitudes;
…allowing for life-supporting temperatures in temperate grasslands/ forests/tundra biomes;

Note to examiners: Credit must be given for answers that address biomes not species.
Full credit can be given for a well drawn annotated tri-cellular model with biomes and atmospheric flows shown.

[3 max]

Please note: although "quality of expression" marking is no longer used in exams, this question from a past syllabus may still be useful for student practice. There is less detail expected regarding plate activity in the current programme, such that the markscheme may be less extensive.

Role of plate activity:
volcanic activity/plate movement forms mountains;
…that show a gradient/zonation of ecosystems changing with altitude;
volcanic activity may also give rise to oceanic islands/land bridges;
…often, due to their isolation, carrying unique ecosystems/communities;
plate activity also gives rise to deep oceanic trenches;
…with unique ecosystems often based on chemosynthetic production;
plate movement may cause separation of previously contiguous ecosystems;
...bringing ecosystems into new climatic regions;
Volcanic eruptions can wipe out entire ecosystems;
.... and may lead to succession/development of new ecosystems;

Note to examiners: Credit must be given for answers that address diversity of ecosystems not species.

[3 max]

The sub-headings below are for guidance only. Credit should be given for the Marking points whether the student identifies them under these titles or not.

Global Warming element:
climate change/biomes shift;
Distribution:
biomes move towards higher latitudes / altitudes;
Credit a detailed example
Diversity:
if the shift is too rapid some species will not be able to survive, decreasing diversity;
if the species are on islands or mountains they may run out of space to migrate to;
keystone species/critical to ecosystem, whole ecosystems may be lost/damaged;
changes to the precipitation/temperature/humidity may make an area more or less conducive to the existing ecosystems;
For example, desert areas may receive more rainfall so allowing a more diverse ecosystem;
For example, Sub-Saharan areas receive less rainfall leading to desertification / (southward) expansion of Sahara desert increased fires in tropical rain forests (due to higher temperatures or increased aridity) would lead to loss of species / reduce niches;
altered rainfall patterns might reduce habitat diversity;

Global Warming element:
melting ice caps/permafrost;
Distribution:
exposed areas after melting in high latitudes and/or altitudes;
Diversity:
the newly exposed areas might support new tundra ecosystems, potentially increasing diversity;
if ecosystems space in the tundra is reduced then diversity decreases;
flooding of coastal area ecosystems will reduce ecosystem diversity;
positive feedback loops might occur with the release of methane/clathrates accelerating further global warming/ climate change, stressing ecosystems even more;

Global Warming element:
Changes to the oceans/aquatic areas (higher water temperatures/change in El Nino frequency and intensity);
Distribution:
areas closer to the surface/shallow depth ecosystems are more exposed to the changes;
Diversity:
higher temperatures are likely to bleach/destroy some coral ecosystems;
…and accelerate ocean acidification, damaging plankton/base of marine ecosystems;
ocean circulation may alter allowing some areas to become more diverse;
a possible change of deep sea currents may benefit some areas that would receive more nutrients, thus increase species diversity;
a possible northward movement of Gulf Stream may benefit Iceland and Greenland (ameliorate temperature);

Global Warming element:
thermal expansion of sea/ sea level rise;
Distribution of biomes:
increased erosion of coast/ alteration of continental shelf landscape may alter the extent of littoral/shallow coastal zone;
flooding of coastal ecosystem may destroy them, e.g., mangroves;
...but at the same time create new littoral/tidal ecosystems;
Diversity:
reduce intertidal habitat diversity as some species won't tolerate the shift of tide lines (low & high);
creation of new tidal fronts may bring more nutrients thus increase aquatic species diversity;

Award [7 max] for marking points above, and [1 max] for a clear conclusion that is justified by points raised.

Note to examiners: An isolated statement/opinion e.g. “global warming will alter distribution / diversity of ecosystems” should not be considered as a valid conclusion. A valid conclusion may, however, be stated within the body of the response rather than at the end, and may involve some balanced decision:

e.g. effect of global warming would be higher in Polar ecosystems as temperature increase is higher there, so low latitude ecosystems may be only partly affected; [1 max]

Award [2 max] for part (c) if response just identifies global warming elements with no reference to effect of global warming on either distribution or diversity.

Award [5 Max] if the answer addresses only negatives or only positives of distribution and diversity changes

[8 max]

Expression of ideas [2 max]

Most candidates gave a reasonable description of natural selection and linked this to biodiversity. This indicates good progress as natural selection questions in the past have been poorly answered. Gaining full marks for this question was generally the stronger candidates.

The use of the term atmosphere did seem to confuse many candidates who answered this question. However the candidates are expected to be able to explain biome distribution and so should have been able to link the atmosphere to the climatic conditions required for biomes. For those candidates who recognized the link they generally gained 2 or 3 marks for the question. A few candidates did mention the tri-cellular model of atmospheric circulation, but this was not required to gain marks.

The term plate activity is in 4.1.4 of the Guide. The candidates generally had no difficulty mentioning plate separation isolating species and leading to speciation. Also popular were mountain building and the creation of volcanic islands.

The candidates obviously know plenty about global warming. Many candidates had no problem discussing the positive and negatives of both the distribution and diversity of ecosystems. Weaker candidates tended to focus on the negatives only. The only area most candidates missed was writing a conclusion.