Glycolysis, Krebs cycle and electron transport system are the three major metabolic pathways involved in the production of ATP, the primary energy currency of the cell. The overall goal of these pathways is to convert the energy stored in glucose into ATP, which can be used for various cellular processes. The correct option is (b) ATP in small stepwise units.

Glycolysis
Glycolysis is the breakdown of glucose into pyruvate, which occurs in the cytoplasm of the cell. It involves a series of ten enzymatic reactions, which convert one molecule of glucose into two molecules of pyruvate. Glycolysis is an anaerobic process, which means it does not require oxygen.

Krebs cycle
The Krebs cycle, also known as the citric acid cycle, occurs in the mitochondria of the cell. It is a series of eight enzymatic reactions that oxidize acetyl-CoA, a product of pyruvate oxidation, into carbon dioxide. The Krebs cycle produces ATP, NADH, and FADH2 molecules, which are used in the electron transport system.

Electron transport system
The electron transport system occurs in the inner membrane of the mitochondria. It is a series of enzymatic reactions that use the NADH and FADH2 molecules produced in the Krebs cycle to generate a proton gradient across the membrane. The energy released from this gradient is used to produce ATP through the process of oxidative phosphorylation.

Formation of ATP
The overall goal of these three metabolic pathways is the production of ATP, which occurs through the process of oxidative phosphorylation in the electron transport system. The energy released from the oxidation of glucose is stored in the form of ATP, which can be used by the cell for various processes.

However, ATP is not formed in one large oxidation reaction, but rather in small stepwise units. The energy released in each step is used to produce ATP, which ensures that the energy is not wasted and is efficiently used by the cell.

In summary, the overall goal of glycolysis, Krebs cycle, and electron transport system is to produce ATP in small stepwise units, which can be used by the cell for various processes.

Glycolysis, Krebs cycle and electron transport system are three interconnected pathways that occur inside the cells for energy production.

Glycolysis:
- It is the first step of cellular respiration that occurs in the cytoplasm of the cell.
- In this process, a molecule of glucose is broken down into two molecules of pyruvate.
- It is a series of reactions that involve the conversion of glucose into pyruvate through a series of enzyme-catalyzed steps.
- ATP is produced in small stepwise units during this process.

Krebs cycle:
- It is also known as the citric acid cycle or the tricarboxylic acid cycle.
- It occurs in the mitochondrial matrix of eukaryotic cells and in the cytoplasm of prokaryotic cells.
- In this process, pyruvate is oxidized to produce carbon dioxide, ATP, and reduced coenzymes such as NADH and FADH2.
- The reduced coenzymes produced in this process carry the electrons to the electron transport system for ATP production.

Electron transport system:
- It is the final step of cellular respiration that occurs in the inner mitochondrial membrane of eukaryotic cells and in the plasma membrane of prokaryotic cells.
- In this process, the reduced coenzymes such as NADH and FADH2 are oxidized to produce ATP.
- The electrons carried by the reduced coenzymes are transferred to a series of electron carriers such as cytochromes and ubiquinone, which pump protons across the membrane.
- The proton gradient generated by the electron transport system is used by ATP synthase to produce ATP.

Overall goal:
- The overall goal of these three interconnected pathways is to produce ATP in small stepwise units.
- The energy released during the oxidation of glucose and other molecules is stored in the form of ATP.
- ATP is the primary source of energy for cellular processes such as muscle contraction, protein synthesis, and active transport.