2- glycolysis

What is glycolysis?

Glycolysis is the first stage of respiration where glucose is broken down into pyruvate.

Where does glycolysis take place?

In the cytoplasm of the cell.

Is glycolysis aerobic or anaerobic?

Glycolysis is anaerobic and does not require oxygen.

What molecule does glycolysis start with?

Glucose (a 6-carbon hexose sugar).

How does glucose enter cells for glycolysis?

By facilitated diffusion through a specific hexose carrier protein.

How is glucose kept inside the cell once it enters?

It is phosphorylated to glucose phosphate, which cannot diffuse out of the cell.

What is the first step of glycolysis?

Glucose is phosphorylated using ATP to form glucose phosphate.

Why is glucose phosphorylated at the start of glycolysis?

To trap glucose in the cell and activate it for further reactions.

How many ATP molecules are used at the start of glycolysis?

Two ATP molecules.

What happens to glucose phosphate next?

It is phosphorylated again and split into two molecules of glyceraldehyde phosphate (GALP).

What is glyceraldehyde phosphate (GALP)?

A 3-carbon triose phosphate formed during glycolysis.

Why do reactions after GALP happen twice?

Because one glucose molecule produces two GALP molecules.

What happens to GALP during glycolysis?

It is oxidised and converted into glycerate-3-phosphate.

What is oxidation in glycolysis?

The removal of hydrogen from GALP.

Which coenzyme accepts hydrogen during glycolysis?

NAD.

What is NAD reduced to during glycolysis?

NADH + H⁺.

Why is NAD important in glycolysis?

It carries hydrogen to the electron transport chain for ATP production.

How is ATP produced during glycolysis?

By substrate-level phosphorylation.

What is substrate-level phosphorylation?

The direct transfer of a phosphate group to ADP to form ATP.

How many ATP molecules are produced in glycolysis?

Four ATP molecules are produced.

What is the net ATP gain from glycolysis?

A net gain of 2 ATP (4 produced − 2 used).

What is the final product of glycolysis?

Pyruvate (a 3-carbon molecule).

How many pyruvate molecules are produced per glucose?

Two pyruvate molecules.

What happens to pyruvate if oxygen is present?

It enters the mitochondria for aerobic respiration.

What happens to pyruvate if oxygen is absent in animals?

It is converted into lactate.

What happens to pyruvate if oxygen is absent in plants and fungi?

It is converted into ethanol and carbon dioxide.

Why is glycolysis considered a universal pathway?

It occurs in all living organisms.

Why is glycolysis important even in aerobic respiration?

It provides pyruvate and reduced NAD for later stages of respiration.