Humans release large amounts of carbon dioxide and methane into the atmosphere. Explain how these gases contribute to climate change and describe two effects that climate change can have on living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Carbon dioxide and methane are greenhouse gases.
They absorb infrared radiation emitted by the Earth’s surface and re‑radiate it back, trapping heat in the atmosphere.
This enhanced greenhouse effect raises global temperatures, causing global warming.
One effect on living organisms is that species distributions shift; animals and plants move to new areas as their habitats become unsuitable.
A second effect is altered phenology – for example, breeding or flowering times change, and coral reefs suffer bleaching when ocean temperatures rise.
They absorb infrared radiation emitted by the Earth’s surface and re‑radiate it back, trapping heat in the atmosphere.
This enhanced greenhouse effect raises global temperatures, causing global warming.
One effect on living organisms is that species distributions shift; animals and plants move to new areas as their habitats become unsuitable.
A second effect is altered phenology – for example, breeding or flowering times change, and coral reefs suffer bleaching when ocean temperatures rise.
Examiner tips
- Use the exact terms ‘greenhouse gases’, ‘trap/absorb heat’, ‘enhanced greenhouse effect’, and ‘global warming’.
- Show the causal chain: gas → heat trapping → temperature rise → impact on organisms.
- Name two specific effects (distribution shift, phenological change, or bleaching).
Common mistakes
- Confusing greenhouse gases with all atmospheric gases; only CO₂ and CH₄ are relevant here.
- Failing to link the temperature rise to a specific effect on organisms, or giving a non‑biological effect such as sea‑level rise alone.
Mark scheme (5 marks)
- Carbon dioxide and methane are greenhouse gases
- Greenhouse gases trap/absorb heat (infrared radiation) in the atmosphere
- This causes global temperatures to rise (enhanced greenhouse effect / global warming)
- First named effect on living organisms — e.g. species distributions shift / species migrate to new areas / species face extinction because habitats are lost
- Second named effect on living organisms — e.g. changes in breeding/flowering seasons / rising sea levels flood coastal habitats / coral bleaching due to warmer oceans
Key terms in this question
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Human impact on the environment questions
- Explain how the use of pesticides in farming can have harmful effects on organis…
- Acid rain is formed when sulfur dioxide and nitrogen oxides are released into th…
- Deforestation is carried out on a large scale in many parts of the world. Explai…
- Describe the effects of eutrophication on the organisms living in a lake.