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# Why Oxygen is Necessary In Topic 2.1 on Photosynthesis, we learn that plants trap light energy and produce organic compounds. Most animals, including humans, can't directly use sunlight for energy, as they lack chlorophyll. Instead, they obtain energy from eating plants or animals that have cons...

# Why Oxygen is Necessary In Topic 2.1 on Photosynthesis, we learn that plants trap light energy and produce organic compounds. Most animals, including humans, can't directly use sunlight for energy, as they lack chlorophyll. Instead, they obtain energy from eating plants or animals that have consumed plants. This transfers light energy to all living organisms. Humans, like all other animals, need a way to release energy stored in food. This process, called cellular respiration, requires oxygen. Without oxygen, we can't utilize the energy from food. Cellular respiration is detailed in Topic 2.4. The purpose of this topic is understanding the uptake of oxygen from the atmosphere and removal of carbon dioxide. Oxygen moves from the lungs into the blood, then to the cells, and carbon dioxide moves in the opposite direction. This exchange process is called gas exchange. # Why Gas Exchange is Necessary Gas exchange ensures oxygen from the air can enter the body.