Glycolysis is a chain of 10 enzyme reactions in the cytoplasm that splits one glucose (6-carbon) into two molecules of pyruvic acid (3-carbon each). ATP is USED at 2 steps early (glucose to glucose-6-phosphate, and fructose-6-phosphate to fructose-1,6-bisphosphate), then ATP and NADH are MADE later. Memory hook: "Glucose Loses Fat, Fructose Gains Two P, Then Payoff Pays Back" — spend 2 ATP first, earn 4 ATP later, keep 2 net.
Glycolysis splits one glucose into two pyruvate through 10 reactions in the cytoplasm: 2 ATP are invested early, then 4 ATP and 2 NADH are made, giving a net gain of 2 ATP.
Your doubts, answered
How many steps and reactions are in glycolysis?
NCERT says glycolysis is a chain of TEN reactions, each controlled by a different enzyme, that produce pyruvate from glucose. You do not need to memorise all 10 for NEET, but you must know the number is 10 and the key steps where ATP or NADH is used or made.
Where in the cell does glycolysis take place?
Glycolysis occurs in the cytoplasm (cytosol) of the cell. It does NOT happen in the mitochondria. This is true for all living organisms, and it is the only respiration process in anaerobic organisms. NEET often asks for the location, so remember: cytoplasm.
At which two steps is ATP used in glycolysis?
ATP is utilised (invested) at exactly two steps. First, glucose is converted to glucose-6-phosphate by hexokinase using 1 ATP. Second, fructose-6-phosphate is converted to fructose-1,6-bisphosphate by phosphofructokinase using 1 ATP. So 2 ATP are spent before any ATP is earned.
Which enzyme catalyses the first step of glycolysis?
Hexokinase phosphorylates glucose to glucose-6-phosphate. This is the first committed and first irreversible step, and it uses one ATP. Do not confuse it with phosphofructokinase (a later step) or aldolase and enolase (still later).
How many pyruvate molecules come from one glucose?
One glucose (6 carbons) is partially oxidised into TWO molecules of pyruvic acid (3 carbons each). So from N glucose you get 2N pyruvate. For example, 206 glucose give 206 x 2 = 412 pyruvate.
Is glycolysis aerobic or anaerobic?
Glycolysis itself does NOT require oxygen, so it runs under both aerobic and anaerobic conditions. In anaerobic organisms it is the only respiratory process. Oxygen is needed only later, in aerobic respiration inside the mitochondria.
⚠️ The NEET trap ✗ Thinking ATP is produced at the glucose to glucose-6-phosphate step because it is the 'first' step. ✓ The first two phosphorylation steps CONSUME 2 ATP (investment phase). ATP is only PRODUCED later in the payoff phase, giving 4 ATP made and a net gain of 2 ATP per glucose. 🧠 Read whether ATP is USED or MADE at each named step — NTA swaps them.
Real NEET questions
2019
Conversion of glucose to glucose-6-phosphate, the first irreversible reaction of glycolysis, is catalyzed by
A · Aldolase
B · Hexokinase ✓
C · Enolase
D · Phosphofructokinase
Solution: In glycolysis, glucose is phosphorylated to glucose-6-phosphate by hexokinase, using one ATP; this is the first committed (irreversible) step. Phosphofructokinase acts later (fructose-6-phosphate to fructose-1,6-bisphosphate), while aldolase splits fructose-1,6-bisphosphate and enolase acts near the end, so none of these phosphorylate glucose itself.
2023
Assertion A: ATP is used at two steps in glycolysis. Reason R: First ATP is used in converting glucose into glucose-6-phosphate and second ATP is used in conversion of fructose-6-phosphate into fructose-1,6-diphosphate. Choose the correct answer.
A · Both A and R are true and R is the correct explanation of A ✓
B · Both A and R are true but R is NOT the correct explanation of A
C · A is true but R is false
D · A is false but R is true
Solution: Assertion is true: ATP is invested at two steps of glycolysis. Reason correctly names those exact steps — the first ATP converts glucose to glucose-6-phosphate (hexokinase) and the second converts fructose-6-phosphate to fructose-1,6-bisphosphate (phosphofructokinase). Since R states precisely these two ATP-investment steps, it correctly explains A.
2026
How many molecules of pyruvic acid are produced at the end of glycolysis from 206 molecules of glucose?
A · 206
B · 309
C · 103
D · 412 ✓
Solution: Glycolysis breaks one glucose (6C) into two molecules of pyruvic acid (3C each). So 206 glucose give 206 x 2 = 412 pyruvic acid molecules. (ReNEET 2026)
Solved Respiration in Plants NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof and J. Parnas, so it is also called the EMP pathway. The word comes from Greek glycos (sugar) and lysis (splitting).
Where does the glucose for glycolysis in plants come from?
In plants, the glucose is derived from sucrose, the end product of photosynthesis, or from stored carbohydrates. Invertase splits sucrose into glucose and fructose, which both enter glycolysis after being phosphorylated by hexokinase.
Is NADH made during glycolysis?
Yes. Two redox equivalents (hydrogen atoms) are removed from PGAL and transferred to NAD+, forming NADH + H+. So glycolysis makes NADH in addition to ATP, while splitting glucose into pyruvate.
What is the net ATP gain of glycolysis?
Four ATP are produced but two are used up early, so the net gain is 2 ATP per glucose, along with 2 NADH and 2 pyruvate.
