Biology · Respiration in Plants · NEET
When glucose burns in air, it reacts with oxygen in one fast reaction and gives off all its energy at once as heat and light. A living cell cannot catch a big sudden burst of heat and turn it into a usable form, and the heat would also damage the cell. So the cell splits the reaction into many small enzyme-controlled steps, and at some steps it saves the energy in ATP instead of losing it as heat.
Yes. The total energy released from one glucose molecule is the same whether it burns in air or is respired in a cell. The difference is HOW the energy comes out. In burning it all comes out at once as heat. In respiration it comes out in small amounts, step by step, and part of it is trapped in ATP. This is a common NEET point: same energy, different release pattern.
Step-wise means glucose is changed into other molecules through many separate reactions, one after another. Each reaction is run by its own enzyme. In some of these steps a small amount of energy is released, and the cell uses that small amount to make ATP or to form NADH and FADH2. Glycolysis, the Krebs cycle and the electron transport system are all made of many such small steps.
At certain steps the released energy is used right away to attach a phosphate group to ADP, making ATP. Energy is also stored temporarily in reduced coenzymes NADH and FADH2. These carriers later pass energy to the electron transport system, which drives ATP synthase to make more ATP. So the energy is captured in chemical bonds, not lost as a heat flash.
ATP is the energy currency of the cell. Cells cannot directly use heat to do work, but they can use ATP to power reactions, transport and movement. By releasing energy slowly, the cell gets many chances to make ATP. A one-step burn gives zero ATP, so stepwise breakdown is the only way a cell can pay for its life processes.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
In a loose sense yes, because both oxidise glucose using oxygen and both give CO2 and water. But respiration is enzyme-controlled and step-wise, done at body temperature, and it saves energy in ATP. Combustion is fast, uncontrolled, needs high temperature, and loses all energy as heat and light.
A single burst of energy would raise the temperature sharply and could destroy delicate cell parts and enzymes. Releasing energy in small amounts keeps the cell at a safe temperature and lets each bit of energy be captured usefully.
This is from Respiration in Plants. It is the introductory idea before glycolysis, the Krebs cycle and ETS. NCERT states that in respiration the breakdown and oxidation happen in a step-wise, controlled manner and energy is released in small amounts and stored in ATP.
No. Stepwise makes it efficient. Because energy comes out gradually, the cell can trap a large part of it in ATP. A one-step burn would waste all of it as heat, so stepwise is actually the efficient route for the cell.
