The importance of respiration, photosynthesis and human activity in giving rise to short-term fluctuation and long-term change in global carbon dioxide concentration. The roles of carbon dioxide and methane in enhancing the greenhouse effect and bringing about global warming. Candidates should be able to analyse, interpret and evaluate data relating to evidence of global warming and its effects on • the yield of crop plants • the life-cycles and numbers of insect pests • the distribution and numbers of wild animals and plants.

Carbon goes round in a cycle, below is a diagram to show this. The three grey lines, from plants, animals and decomposers, show carbon being put back into the atmosphere by respiration.

Atmospheric levels of carbon dioxide can be changed short term or long term.

A short term change could be brought about by the balance of photosynthesis and respiration: there is more photosynthesis in the day-light which takes CO2 out of the atmosphere and more respiration at night which gives CO2 into the atmosphere.

A long term change may be brought about by a decrease in plants, as they carry out photosynthesis, or a release of carbon from a store. These are both things that humans cause to happen in deforestation and the combustion of wood and fossil fuels.

Light is radiated to the earth by the sun, it is then reflected back off the earth as heat. Gasses in the atmosphere such as CO2 and methane trap heat, so when it is reflected back off the earth it is not lost, but kept and warms our globe. A rise in greenhouse gasses (ones that stop the heat escaping) causes a rise in the temperature of the earth which is global warming.

The potential effects of global warming are wide spread:
Yield

• Certain plants cannot function at high temperatures
• Land may be flooded, leaching nitrogen and increasing denitrifying bacteria
• More energy for reactions (more respiration at night uses up energy stores and decreases yield)

Life cycle

• Change in seasons may disrupt breeding or metamorphosis
• Change in heat may mean some plants or animals miss cues that or based on heat

Distribution

• Warmer temperatures higher up mean that cold loving things are forced to migrate northwards
• More weather extremes and the heat change will mean new selection pressures so different species or characteristics are favoured