The source of oxygen is aquatic plants, which release it through photosynthesis. The sources of carbon dioxide are aquatic organisms and organic residues. Organisms produce carbon dioxide when they breathe and organic matter when they decompose.
The limiting factor is the oxygen content, since its content in water is 20-30 times less than in air. And the deeper, the less oxygen.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.