"Respiration is very similar to burning." Is this true? Illustrate your answer by describing 3 similarities and 3 differences between the two.

Respiration is a process which releases energy from energy-rich molecules such as glucose. The glucose is converted into energy which is usable for life processes. Burning, or combustion, is a reaction between a substance and a gas to release energy. These two reactions have many similarities but are not the same. This essay will identify some of similarities and differences between the two processes.

The first similarity is that both respiration and burning use oxidation to release energy. In respiration, oxygen combines with glucose to release energy which can be used in the body. Also some heat is produced to keep the body warm. Burning normally occurs in oxygen (in form of O2) to form oxide. However, burning can take place in other gases such as chlorine. Also both of these reactions are exothermic - both reactions release heat after reacting with oxygen.

Another similarity is that both reactions release energy after oxidation. For respiration, the equation for the oxidation of glucose is:

Glucose + Oxygen → Carbon dioxide + Water + Energy

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

A substance called ADP (adenosine diphosphate) reacts with a phosphate group to form an ATP molecule (adenosine triphosphate).

ADP + phosphate + energy → ATP

In burning, the energy released is in form of heat and light.

The final similarity is that both reactions produce waste products. Respiration produces energy, carbon dioxide and water. Carbon dioxide and water are waste products as they are not needed in the body. In burning, the products include water as well as carbon monoxide (CO) or carbon dioxide (CO2), or both. Other by-products from reactions such as burning fuel and coal, may produce smoke and soot.

The first difference is that respiration needs sugar and oxygen (unless it's anaerobic respiration) to produce energy. The sugar is normally glucose in the equation: Glucose + Oxygen → Carbon Dioxide + Water + Energy

Burning doesn't needs anything specific in the reaction. Anything, from wood to coal, can be burned to release heat energy. Also, gases other than oxygen can be used in burning.

Another difference is that respiration oxidises sugar in stages while burning releases energy very quickly and violently. In respiration, the sugar is oxidised very gradually in many small reactions. These reactions are controlled by enzymes. In burning, a large amount of heat and light energy is released very quickly. These reactions are not controlled and if sugar are oxidised like this, the cells would get very hot that they would be killed.

The final difference is that energy released from respiration can be stored as ATP (adenosine triphosphate) but the energy from burning can not be stored. The energy released from respiration is used to join a phosphate group onto an ADP molecule, making a new molecule called ATP.

ADP + phosphate + energy → ATP

ADP has low energy content while ATP has high energy content, so ATP can be broken down again to release energy when body needs energy.

ATP → ADP + phosphate + energy