respiration releases chemical energy in biological processes

What is respiration?

The process by which cells release energy from organic molecules (like glucose) to form ATP

What is the general equation for aerobic respiration?

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy (ATP)

What is the role of ATP in respiration?

ATP stores energy temporarily and provides it for cellular processes like biosynthesis, movement, and active transport

What are the two main types of respiration?

Aerobic (requires oxygen) and anaerobic (does not require oxygen).

Where does glycolysis occur?

In the cytoplasm.

What happens during glycolysis?

Glucose (6C) is broken down into two pyruvate (3C) molecules, producing a net gain of 2 ATP and 2 NADH

Where does the link reaction occur?

In the mitochondrial matrix.

What happens during the link reaction?

Pyruvate is converted into acetyl CoA, producing CO₂ and NADH.

Where does the Krebs (citric acid) cycle occur?

In the mitochondrial matrix.

What are the main products of one turn of the Krebs cycle?

3 NADH, 1 FADH₂, 1 ATP (substrate-level phosphorylation), and 2 CO₂.

Where does oxidative phosphorylation occur?

On the inner mitochondrial membrane (cristae).

How is ATP generated in oxidative phosphorylation?

Electrons from NADH and FADH₂ pass along the electron transport chain, creating a proton gradient; ATP synthase uses this gradient to make ATP (chemiosmosis).

How much ATP is produced per glucose molecule during aerobic respiration?

Approximately 36–38 ATP.

When does anaerobic respiration occur?

When oxygen is absent or insufficient for aerobic respiration.

What happens in anaerobic respiration in animals?

Glucose → lactate + small amount of ATP (2 per glucose)

What happens in anaerobic respiration in plants and yeast?

Glucose → ethanol + CO₂ + small amount of ATP (2 per glucose).

Why is anaerobic respiration less efficient than aerobic?

Because glucose is only partially oxidized, producing much less ATP.

How are mitochondria adapted for respiration?

• Folded inner membrane (cristae) increases surface area for electron transport chain

• Matrix contains enzymes for link reaction and Krebs cycle

• Small and numerous to supply energy to high-demand cells

How is the inner mitochondrial membrane adapted for chemiosmosis?

It contains ATP synthase enzymes and is impermeable to protons, maintaining the proton gradient.

Why is oxygen essential for aerobic respiration?

It acts as the final electron acceptor in the electron transport chain, forming water.

What is the role of NAD and FAD in respiration?

They act as electron carriers, transferring high-energy electrons from glucose to the electron transport chain

What is substrate-level phosphorylation?

Direct synthesis of ATP from ADP and a phosphate group during glycolysis or Krebs cycle.

What is oxidative phosphorylation?

ATP production driven by electrons passing through the electron transport chain and chemiosmosis.

How many ATP are produced per glucose molecule from:

• Glycolysis? →

• Link reaction? →

• Krebs cycle? →

• Oxidative phosphorylation? →

• Glycolysis? → 2 ATP

• Link reaction? → 0 ATP (but 2 NADH per glucose)

• Krebs cycle? → 2 ATP (per glucose)

• Oxidative phosphorylation? → ~32 ATP (from NADH and FADH₂)

Why is the actual ATP yield slightly lower than the theoretical maximum?

Some protons leak across the mitochondrial membrane and some energy is lost as heat.