Describe the process of photosynthesis and its importance in increasing atmospheric oxygen levels.

Photosynthesis is the process by which green plants and algae convert carbon dioxide and water into glucose and oxygen using sunlight. This process is crucial for increasing atmospheric oxygen levels as it releases oxygen into the air, supporting life on Earth.

A strong answer should directly address the approved learning objective to explain that algae and plants produced oxygen by photosynthesis. This question belongs to How oxygen increased within The composition and evolution of the Earth's atmosphere, so the response should use that exact curriculum context rather than a generic statement. The answer is correct when it names the key idea, explains the link to oxygen, and keeps the wording specific to AQA GCSE revision.