Question

The last stage of cellular respiration which yields ATP by the oxidation of organic molecules, derived from glucose is
A. Chemiosmosis
B. Citric acid cycle
C. Electron transport chain
D. Glycolysis
E. Oxidative phosphorylation

Answer 1

Hint: Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms. It occurs to convert chemical energy from oxygen molecules or nutrients into adenosine triphosphate (ATP), and then release waste products.
It occurs in presence of oxygen (aerobic) and in absence of oxygen (anaerobic).

Complete answer:
The aerobic respiration occurs in glycolysis → oxidative decarboxylation of pyruvate→ citric acid cycle→ oxidative phosphorylation.
1. In anaerobic respiration, fermentation takes place.
2. Glycolysis is a metabolic pathway that takes place in the cytosol of cells in all living organisms.
In aerobic conditions, glycolysis converts one molecule of glucose into two molecules of pyruvate (pyruvic acid), generating energy in the form of two net molecules of ATP.
3. In oxidative decarboxylation of pyruvate, pyruvate is oxidized to acetyl-CoA and $CO_2$ by the pyruvate dehydrogenase complex (PDC). In the conversion of pyruvate to acetyl-CoA, one molecule of NADH and one molecule of $CO_2$ is formed.
4. The citric acid cycle is also called the Krebs cycle or the tricarboxylic acid cycle (TCA).
Once acetyl-CoA is formed, aerobic or anaerobic respiration can occur.
In the presence of oxygen, when acetyl-CoA is produced, the molecule then enters the citric acid cycle (Krebs cycle) inside the mitochondrial matrix and is oxidized to $CO_2$ while at the same time reducing NAD to NADH.
5. NADH can be used by the electron transport chain to create further ATP as part of oxidative phosphorylation. The total yield from 1 glucose molecule (2 pyruvate molecules) in Kreb’s cycle will give rise to 6 NADH, 2 FADH2, and 2ATP.
6. It releases the chemical energy stored within in order to produce adenosine triphosphate (ATP).
In eukaryotes, the redox reactions are catalyzed by a series of protein complexes within the inner membrane of the cell's mitochondria.
7. In prokaryotes, these proteins are located in the cell's intermembrane space.
These linked sets of proteins are called electron transport chains.
8. The energy transferred by electrons flowing through the electron transport chain is used to transport protons across the inner mitochondrial membrane, in a process called electron transport.
9. Chemiosmosis is the movement of ions across a semipermeable membrane-bound structure, down their electrochemical gradient.

So, the correct answer is “Option E”.

Note: In the early 1940s, the link between the oxidation of sugars and the generation of ATP was firmly established by Herman Kalckar.
The central role of ATP in energy transfer has been confirmed by Fritz Albert Lipmann in 1941.
Later, in 1949, Morris Friedkin and Albert L. Lehninger proved that the coenzyme NADH linked metabolic pathways such as the citric acid cycle and the synthesis of ATP.
The term oxidative phosphorylation was coined by Volodymyr Belitser in 1939.