Question

unlike what occurs when fuel is burned to make a fire, all living systems use the energy from heat-generating reactions to create and maintain

Answer 1

The process of conversion of fuel to fire is called as combustion reaction. Combustion can be classified into two types,

Complete combustion

Incomplete combustion

During combustion what realy happens is the bonds present in the fuels(hydrocarbon) break down which results in so much of energy like heat and light. Compared to water, fuels have strong bonds. So that fuels release more energy. For the process of combustion oxygen or any other oxidant is needed. without oxygen combustion wont occur. Air contain 21% oxygen. If the combustion happens in sufficient oxygen environment, that is called as complete combustion which release carbon dioxide to the environment. If the oxygen is insufficient, that reaction is called as imcomplete combustion which releases carbon monoxide(harmful).

In human body also, combustion plays a important role in energy production. In body the fuel is carbohydrate and fatty acids, which we gain by food. For combustion oxygen is important, that we get by inhaling and transported to lungs. Red blood cells (oxygen transporter) tranfers the oxygen from the lungs to heart and other living cells. And then combustion occurs which produces energy and carbo dioxide. carbon dioxide releasd from our body.