The Amazon rainforests are often referred to as the "lungs of the planet" due to their significant contribution to the oxygen levels in the Earth's atmosphere. Approximately 20% of the total oxygen produced by photosynthesis on Earth is generated by the Amazon rainforests.

Here's a detailed explanation of why the Amazon rainforests are considered as the lungs of the planet:

1. The Importance of Oxygen:
- Oxygen is vital for sustaining life on Earth. It is required by all living organisms, including humans, animals, and plants, for respiration.
- During respiration, oxygen is used by organisms to produce energy, and carbon dioxide is released as a byproduct.

2. Photosynthesis and Oxygen Production:
- Photosynthesis is the process by which green plants, including trees in the Amazon rainforests, convert sunlight, water, and carbon dioxide into glucose (energy-rich sugar) and oxygen.
- The primary photosynthetic organisms in the Amazon rainforests are the trees, which have a large surface area for photosynthesis due to their extensive canopy cover.

3. Oxygen Production in the Amazon Rainforests:
- The Amazon rainforests cover an area of about 5.5 million square kilometers, making them the largest tropical rainforest in the world.
- The vast number of trees in the Amazon rainforests contribute significantly to the total oxygen production through photosynthesis.
- The high biodiversity of plant species in the Amazon rainforests further enhances their oxygen production capacity.

4. Oxygen-Consuming Processes:
- While the Amazon rainforests produce a substantial amount of oxygen, they also consume a significant portion of it through various processes.
- Trees and other plants in the rainforest utilize oxygen during respiration, similar to other living organisms.
- Additionally, decay and decomposition of organic matter in the forest also consume oxygen.

5. Net Oxygen Production:
- Despite the oxygen-consuming processes, the Amazon rainforests are still considered as the lungs of the planet because the oxygen production outweighs the consumption.
- The net oxygen production is estimated to be around 20% of the total oxygen in the Earth's atmosphere.
- This means that one-fifth of the oxygen we breathe is produced by the Amazon rainforests.

In conclusion, the Amazon rainforests contribute approximately 20% of the total oxygen in the Earth's atmosphere. Their extensive tree cover and high biodiversity make them the largest source of oxygen through photosynthesis. Despite the oxygen consumed by various processes, the net oxygen production by the Amazon rainforests outweighs the consumption, earning them the title of the "lungs of the planet."