Biology · Respiration in Plants · NEET
| Number of steps | Many small stepwise reactions | Single one-step reaction |
| Control | Enzyme controlled | Non-enzymatic (needs a flame/heat) |
| Speed | Slow and gradual | Fast and sudden |
| Temperature | Normal cell temperature | Needs high temperature to start |
| Form of energy | Mostly stored as ATP | Released as heat and light |
| End products | CO2 + H2O (same) | CO2 + H2O (same) |
It is a helpful comparison but not exactly the same. Both oxidise glucose and give CO2 + water + energy. But combustion is a single uncontrolled reaction that dumps all energy as heat and light. Respiration breaks glucose in many small steps using enzymes, so the energy comes out bit by bit and can be stored in ATP. So call it 'controlled, stepwise oxidation', not simple burning.
The end products (CO2 and H2O) and the total energy are the same. What differs is the PATH and the FORM of energy. NCERT says the plant cell oxidises glucose 'not in one step but in several small steps' so that the energy released can be coupled to ATP synthesis instead of escaping as heat. So the same reaction is spread over many controlled steps.
If glucose burned in one step, all the energy would leave as heat and light. A cell cannot use a sudden burst of heat to build molecules, and the heat would damage the cell. By using small steps, some steps release just enough energy to make ATP, which the cell can then use for its work. This is why stepwise release is efficient and safe.
No, respiration does release some heat, but only a part of the energy. Most of the energy is captured in ATP. In combustion almost all of the energy is lost as heat and light. So the difference is the proportion: respiration stores most energy as ATP, combustion wastes it as heat.
No. Combustion is a purely chemical, non-enzymatic reaction and needs a high temperature (like a flame) to start. Respiration is controlled by many enzymes and happens at normal body or cell temperature. This enzyme control is the key reason respiration is slow and step-by-step.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Combustion releases all the energy of glucose at once as heat and light in a single non-enzymatic step. Respiration releases the same energy slowly, in many enzyme-controlled steps, and stores most of it as ATP.
Yes. Both fully oxidise glucose to carbon dioxide and water and release energy. Only the pathway and the form of energy differ.
Because it oxidises glucose like burning does, but in a slow, step-by-step, enzyme-controlled way at normal temperature, so the energy can be captured as ATP instead of lost as a flame.
No. Combustion needs a high temperature to start. Respiration works at normal cell temperature because enzymes lower the energy needed for each step.
Yes. NCERT (Ch 12, Respiration in Plants) directly asks you to differentiate respiration and combustion, and NEET can test the shared products versus the different stepwise, ATP-storing pathway.
