Biology · Respiration in Plants · NEET
No. The Krebs cycle happens in the mitochondrial matrix and its job is to release CO2 and load electrons onto NADH and FADH2. The ETS is a separate, later stage. It happens in the inner mitochondrial membrane and its job is to unload those electrons onto oxygen and make ATP. Krebs cycle = fills the carriers; ETS = empties the carriers.
In plants and other cells with mitochondria, the ETS is located on the inner mitochondrial membrane (the folded cristae). This is different from glycolysis, which happens in the cytoplasm. Keep this straight for NEET: glycolysis = cytoplasm, Krebs cycle = matrix, ETS = inner membrane.
NADH and FADH2 are the carriers. They were made in glycolysis, the link reaction, and the Krebs cycle. NADH gives its electrons to Complex I (NADH dehydrogenase). FADH2 gives its electrons through Complex II (succinate dehydrogenase). From there the electrons move to ubiquinone, then cytochrome c, and finally to Complex IV.
No. The ETS itself does not make ATP. As electrons move through the complexes, protons (H+) are pushed across the inner membrane, building a proton gradient. ATP is then made by a separate enzyme, ATP synthase (Complex V), when protons flow back through it. So ETS builds the gradient, ATP synthase makes the ATP.
Oxygen is the final acceptor of electrons and hydrogen at the end of the chain. It combines with electrons and H+ to form water. Its role is only at this terminal stage, but it is vital: by removing hydrogen it keeps the whole chain moving. Without oxygen the electrons have nowhere to go, the chain stops, and aerobic ATP production halts.
By the NCERT count, one NADH gives 3 ATP and one FADH2 gives 2 ATP. FADH2 gives less because it enters later (at Complex II), so it pumps fewer protons. Do not reverse these numbers; that swap is a very common NEET trap.
Which of the following statements is incorrect?
The complex II of mitochondrial electron transport chain is also known as
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Its main function is to make ATP. It passes electrons from NADH and FADH2 down a chain of carriers to oxygen, and the energy released is used to build a proton gradient that drives ATP synthesis. Most of the ATP from respiration is made at this stage.
Oxygen is the final electron acceptor. It combines with electrons and protons to form water. This is why aerobic respiration cannot continue without oxygen.
Because ATP (phosphorylation) is produced using the energy of oxidation-reduction reactions in the electron transport chain. This is different from photophosphorylation, where light energy drives the proton gradient.
NADH gives more: 3 ATP per molecule versus 2 ATP for FADH2. NADH enters at Complex I and pumps more protons, while FADH2 enters later at Complex II.
Yes, the mitochondrial ETS works the same way in plant and animal cells. NCERT describes this common pathway in the Respiration in Plants chapter because plant cells respire using the same electron transport system.
