Respiration

Question 1

Where glycolysis occurs

Answer 1

• Occurs in the cytoplasm of all cells.

Question 2

Glycolysis steps

Answer 2

1. Glucose phosphorylation:
   • Glucose (6C) is phosphorylated by ATP → hexose bisphosphate (6C with two phosphate groups).
   • This uses 2 ATP molecules.
   
   2. Splitting:
      • Hexose bisphosphate is split into two molecules of triose phosphate (TP) (3C each).
   3. Oxidation and ATP production:
      • Each TP is oxidised to pyruvate (3C).
      • During this oxidation, NAD⁺ is reduced to NADH.
      • 4 ATP molecules are produced by substrate-level phosphorylation (net gain of 2 ATP because 2 were used earlier).

Question 3

Where link reaction

Answer 3

Matrix of mitochondria

Question 4

Link reaction steps

Answer 4

1. Pyruvate (3C) from glycolysis is actively transported into the mitochondrial matrix.
   
   2. Pyruvate is oxidatively decarboxylated:
      • One carbon is removed as CO₂ (waste).
      • The remaining 2-carbon molecule is oxidised, reducing NAD⁺ to NADH.
   3. The 2-carbon acetyl group combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA).

Question 5

Where krebs cycle

Answer 5

mitochondrial matrix

Question 6

Krebs cycle process

Answer 6

1. Acetyl CoA (2C) combines with oxaloacetate (4C) to form citrate (6C).
   
   2. Citrate undergoes a series of enzyme-controlled reactions, releasing:
      • 2 CO₂ molecules (waste).
      • 3 NAD⁺ reduced to 3 NADH.
      • 1 FAD reduced to FADH₂.
      • 1 ATP (or GTP) produced via substrate-level phosphorylation.
   3. Oxaloacetate (4C) is regenerated to start the cycle again.

Question 7

Where oxidative phosphorylation

Answer 7

Inner mitochondrial membrane

Question 8

Oxidative phosphorylation steps

Answer 8

1. Electrons from NADH and FADH₂ (produced in glycolysis, link reaction, and Krebs cycle) are passed along the electron transport chain (ETC)—a series of protein complexes.
   
   2. As electrons move along the ETC, energy is released and used to pump protons (H⁺ ions) from the mitochondrial matrix into the intermembrane space, creating a proton gradient (electrochemical gradient).
   3. Protons flow back into the matrix through ATP synthase, driving the synthesis of ATP from ADP + Pi (chemiosmosis).
   4. At the end of the ETC, electrons combine with oxygen (the final electron acceptor) and protons to form water:
      O2 + 4e- + 4H+ = 2 H2O

Question 9

Anaerobic respiration in animals

Answer 9

In Animals (e.g., muscle cells):
• Pyruvate from glycolysis is converted into lactate (lactic acid).
• This reaction is catalysed by lactate dehydrogenase.
• NADH is oxidised back to NAD⁺, allowing glycolysis to continue.
• Lactate can build up, causing muscle fatigue and cramp.
• Later, lactate is transported to the liver and converted back to pyruvate (oxygen debt).

Question 10

Anaerobic respiration In Yeast (and some bacteria):

Answer 10

• Pyruvate is first decarboxylated to ethanol (ethyl alcohol) and CO₂.
• NADH is oxidised back to NAD⁺, allowing glycolysis to continue.
• This is called alcoholic fermentation.