12Class 11 Biology
Respiration in Plants short notes
Short notes on glycolysis, fermentation, the Krebs cycle and the electron transport system. Count the ATP and NADH at each step.
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Glycolysis
- Happens in the cytoplasm of all living cells, and is also called the EMP pathway.
- One glucose becomes two pyruvate, with a net gain of 2 ATP and 2 NADH.
Fermentation
- Without oxygen, yeast makes ethanol and CO₂.
- Muscles and some bacteria make lactic acid.
- It yields far less energy than aerobic respiration.
Aerobic respiration
- Pyruvate enters mitochondria and forms acetyl CoA, giving 1 NADH and 1 CO₂ per pyruvate.
- The Krebs cycle happens in the matrix. Each acetyl CoA gives 3 NADH, 1 FADH₂, 1 GTP and 2 CO₂.
- The electron transport system is on the inner mitochondrial membrane, with oxygen as the final electron acceptor.
- Theoretically, 1 NADH gives 3 ATP and 1 FADH₂ gives 2 ATP.
- The total net yield in the textbook calculation is 38 ATP per glucose.
Respiratory quotient
- RQ = CO₂ released divided by O₂ used.
- It's about 1 for carbohydrates, 0.7 for fats and 0.9 for proteins.
- Respiration is called amphibolic, since it both breaks down and supplies materials for building molecules.
Where students slip up
- Counting Krebs cycle figures per glucose and per acetyl CoA interchangeably. One glucose gives two acetyl CoA.
- Saying glycolysis needs oxygen. It doesn't.
- Calling 38 ATP an exact measured figure. It's a theoretical value.
Try it on your weakest chapter.
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