Answer:

The balance between carbon dioxide (CO2) and oxygen (O2) in the Earth's atmosphere is maintained primarily through the processes of photosynthesis and respiration.

Photosynthesis:
- Photosynthesis is a process carried out by green plants, algae, and some bacteria in which they convert sunlight, water, and carbon dioxide into glucose (a type of sugar) and oxygen.
- During photosynthesis, plants take in carbon dioxide from the atmosphere through tiny pores on their leaves called stomata.
- Inside the plant cells, carbon dioxide combines with water and sunlight to produce glucose and oxygen.
- The glucose is used as an energy source for the plant's growth and development, while the oxygen is released back into the atmosphere as a byproduct.

Respiration:
- Respiration is the process by which living organisms, including plants, animals, and humans, release energy from glucose and convert it into a usable form.
- During respiration, glucose and oxygen are used to produce carbon dioxide, water, and energy.
- Plants and animals both undergo respiration, but plants also undergo photosynthesis, which balances out the carbon dioxide produced during respiration.
- While plants release oxygen during photosynthesis, they take in oxygen and release carbon dioxide during respiration.

Balance between CO2 and O2:
- The process of photosynthesis helps to remove carbon dioxide from the atmosphere, reducing its concentration.
- At the same time, photosynthesis releases oxygen into the atmosphere, increasing its concentration.
- On the other hand, respiration by plants and animals consumes oxygen and produces carbon dioxide, which slightly increases the concentration of carbon dioxide in the atmosphere.
- However, the overall balance is maintained because the amount of oxygen released during photosynthesis is roughly equal to the amount of oxygen consumed during respiration.
- This balance between photosynthesis and respiration ensures a stable level of carbon dioxide and oxygen in the Earth's atmosphere, which is essential for the survival of all living organisms.
- Any disruption in this balance, such as excessive deforestation or burning of fossil fuels, can lead to an increase in carbon dioxide levels and a decrease in oxygen levels, resulting in negative impacts on the environment and human health.