Assertion: Substrate level phosphorylation is present in glycolysis
Reason: Substrate level phosphorylation causes synthesis of ATP
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C. Assertion is correct but Reason is incorrect
D. Both Assertion and Reason are incorrect

Hint: Glycolysis takes place in the cytoplasm of the cell and is the first step of respiration. Substrate level phosphorylation is the generation of ATP from ADP by transferring phosphate group forms a substrate.

Complete answer: Respiration is not just inhaling oxygen and exhaling out carbon dioxide, it is a chemical process that provides our body with energy in the form of ATP (ATP stands for Adenosine Triphosphate) to perform life processes like protein synthesis, growth and repair of cells, sending nerve impulses, and many more. The equation for respiration is;
${{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}\text{+6}{{\text{O}}_{\text{2}}}\to \text{6C}{{\text{O}}_{\text{2}}}\text{+6}{{\text{H}}_{\text{2}}}\text{O+ATP}$
The process of transferring a phosphate group of substance to the ADP to form ATP is known as substrate-level phosphorylation. Glycolysis is the key mechanism by which ATP is generated. In glycolysis, there are two steps in which ATP is produced which are also known as the pay-off phase. The first reaction of glycolysis where ATP is generated is when 1,3 bisphosphoglycerate is converted into 3-phosphoglycerate. In this step, one phosphate group from 1,3-bisphosphoglycerate is transferred to ADP in order to generate ATP. The second reaction of glycolysis where ATP is generated is when phosphoenolpyruvate is converted into pyruvate. Similarly, the phosphate group from phosphoenolpyruvate is transferred to ADP to generate ATP.
Hence, the correct answer is option A.

Note: The process of glycolysis generated two molecules of ATP, i.e. from substrate-level phosphorylation. One ATP molecule is generated from the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate and one ATP molecule is generated from the conversion of phosphoenolpyruvate to pyruvate.