The Carbon Cycle

Why is carbon an important molecule for organisms?

Carbon is a major component of all organic molecules, including carbohydrates, fats and proteins.

What does the carbon cycle involves?

• Photosynthesis: photoautotrophs remove carbon dioxide from the atmosphere and ‘fix’ it into organic molecules.

• Respiration by all organisms (plants, animals, microbes) returns carbon dioxide to the atmosphere.

• Fossil fuels were formed millions of years ago and are derived from the partially decayed remains of plants. Combustion of plant material and fossil fuels releases carbon dioxide into the atmosphere.

What 2 human activities have been the main cause of increasing carbon dioxide in the atmosphere?

• Burning fossil fuels releases carbon dioxide that was previously locked up in them, into the atmosphere.

• Deforestation has removed large quantities of photosynthesising biomass and so less carbon dioxide is being removed from the atmosphere.

What does increased carbon dioxide lead to?

• Increased carbon dioxide leads to the ‘greenhouse’ effect.

• Heat from the sun gets reflected to the planet by the carbon dioxide (and other greenhouse gases like methane). This leads to temperature increases.

• Up to a certain CO₂ level, the greenhouse effect makes the planet more habitable. However, one of the consequences of an enhanced greenhouse effect is climate change.

Describe some effects of global warming.

Global warming causes polar ice to melt and pushes the organisms adapted to live there to the brink of extinction. The ranges of organisms are increasing as a result of global warming, organisms adapted to warmer climates closer to the Equator are thriving further north and south. This is pushing the ‘usual’ organisms further north and south and there are limits to how far they can go. So global warming is affecting species distribution on the planet and leading to extinction.