JAMB 2018 Biology · Question 7

The overall reaction in glycolysis can be summarised as

Options

A.C $_{6}$ H $_{12}$ O $_{6}$ -----> C $_{3}$ H $_{4}$ O $_{3}$ + 4H + ATP
B.C $_{6}$ H $_{12}$ O $_{6}$ -----> 2C $_{3}$ H $_{4}$ O $_{3}$ + 4H + 2ATP
C.C $_{6}$ H $_{12}$ O $_{6}$ -----> 2C $_{3}$ H $_{4}$ O $_{3}$ + 4H + ADP
D.C $_{6}$ H $_{12}$ O $_{6}$ -----> 2C $_{3}$ H $_{4}$ O $_{3}$ + 4H + 2ADP

Answer: B. C $_{6}$ H $_{12}$ O $_{6}$ -----> 2C $_{3}$ H $_{4}$ O $_{3}$ + 4H + 2ATP

Explanation written with AI and checked against the answer key

Analyze the question: It asks for the balanced summary equation of glycolysis, the first stage of respiration, which takes place in the cytoplasm.

Concept: Glycolysis breaks down one molecule of glucose (6C) into two molecules of pyruvic acid (3C each, C₃H₄O₃). Along the way:

2 ATP are used up in the early (investment) phase.
4 ATP are made in the later (pay-off) phase, so the net gain is 2 ATP.
2 NAD⁺ are reduced to 2 NADH, which is the same as 4 hydrogen atoms (4H) removed.

Step-by-step check:

Carbon balance: 6C on the left. Two pyruvate molecules give 2 × 3 = 6C. So we need 2C₃H₄O₃, not one. This eliminates A.
Hydrogen removed: 4H are released (taken up by NAD⁺). This is in all the remaining options.
Energy: glycolysis gives a net gain of 2 ATP. ATP is the product, not ADP. ADP is a reactant that gets converted to ATP. This eliminates C and D, which show ADP as a product.

Overall equation:

C₆H₁₂O₆ → 2C₃H₄O₃ + 4H + 2ATP

Tip: Remember the "2-2-2 rule" for glycolysis: 1 glucose gives 2 pyruvate, a net of 2 ATP, and 2 NADH (4H). Also, ATP is always the energy product, so if you see ADP on the product side, the option is wrong.

AI can make mistakes. Report anything that looks wrong.

The overall reaction in glycolysis can be summarised as

Options

Answer: B. C6_{6}6​H12_{12}12​O6_{6}6​ -----> 2C3_{3}3​H4_{4}4​O3_{3}3​ + 4H + 2ATP

Answer: B. C $_{6}$ H $_{12}$ O $_{6}$ -----> 2C $_{3}$ H $_{4}$ O $_{3}$ + 4H + 2ATP