The source of all forms of energy found on the earth except nuclear energy is the sun . So energy used by us to do daily activities also comes from the sun .
The plants trap the solar energy in the form of light to make food material for us like sugar , carbohydrates etc . This energy is stored here in the chemical bonds formed in them.
We take this food in the form of carbohydrate, fat etc. We digest it to mix this food carbohydrate in blood . It is further broken down on being absorbed by the cell in our body . They break them to produce a compound like ATP ( adenocine triphosphate ) which is energy rich compound . It is converted into ADP and difference of energy is released . This energy is used by us in moving body parts.
Ventilation is very important because it helps remove the gas form people’s homes and schools and it redirects the random gas outside so it is less likely to hurt people
