• Understand the significance of respiration. 
• State the role of ATP in energy transfer. 
• Outline the major steps of glycolysis and aerobic pathways.

• The conversion of oxygen and glucose into carbon dioxide, water and energy - ATP.

👆🏻This photo showing the process of respiration.

• The transformation of energy stored in food into energy used in metabolism which sustains the organism's life.
• Provision of CO₂ for plant's photosynthesis.

Aerobic respiration ➡️Respiration that oxygen is consumed to produce carbon dioxide and water.

👆🏻This photo showing the steps in glycolysis 

1. Energy requirement steps

• Glucose turns into glucose-6-phosphate due to the transfer of phosphate group from ATP.
• Glucose-6-phosphate turns into fructose-6-phosphate ➡️an isomer of glucose-6-phosphate.
• Fructose-6-phosphate turns into fructose-1,6-bisphosphate due to the transfer of phosphate group from ATP.
• Fructose-1,6-bisphosphate splitting into two three-carbon sugars which are dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate.
• DHAP turns into glyceraldehyde-3-phosphate.

2. Energy releasing steps

• Glyceraldehyde-3-phosphate oxidized and NAD⁺ reduced to NADH and H⁺ leads to the formation of 1,3-bisphosphoglycerate.
• 1,3-bisphosphoglycerate turns into 3-phosphoglycerate with the donation of a phosphate group to ADP forming ATP.
• 3-phosphoglycerate turns into 2-phosphoglycerate ➡️an isomer of 3-phosphoglycerate.
• 2-phosphoglycerate turns into phosphoenolpyruvate (PEP) through losing water.
• PEP turns into pyruvate with the donation of a phosphate group to ADP forming ATP.

👆🏻This photo showing the simple version of glycolysis.

• Breakdown of glucose to 3-C compound (triose phosphate).

• Oxidation of triose phosphate to pyruvate.

👆🏻This photo showing the steps in the conversion of pyruvate to acetyl-CoA.

• Pyruvate turns into acetyl-CoA through the removal of carboxyl group to release CO₂, reduction of NAD⁺ to NADH and transfer of acetyl group to conenzyme A.

👆🏻This photo showing the steps in krebs cycle.

• Acetyl CoA turns into a six-carbon molecule (citrate) through joining a four-carbon molecule (oxaloacetate).
• Six-carbon molecules (citrate) turns into isocitrate ➡️an isomer of citrate.
• Isocitrate turns into a five-carbon molecule (α-ketoglutarate) through oxidation of isocitrate releasing CO₂ and NAD⁺ is reduced to NADH.
• Five-carbon molecule (α-ketoglutarate) turns into succinyl CoA through oxidation of α -ketoglutarate releasing CO₂ and NAD⁺ is reduced to NADH.
• Succinyl CoA turns into succinate due to the replacement of CoA with a phosphate group and further used to turn ADP to ATP.
• Succinate turns into a four-carbon molecule (fumarate) that FAD converted to FADH₂ 
• Four-carbon molecule (fumarate) turns into another four-carbon molecule (malate).
• Regeneration of four-carbon molecule (oxaloacetate) via the oxidation of four-carbon molecule (malate) and NAD⁺ is reduced to NADH.

👆🏻This photo showing the simple version of Krebs cycle.

• Combination of acetyl-CoA with a 4-C compound to form a 6-C compound.

• Regeneration of 4-C compound with the release of carbon dioxide.

👆🏻This photo showing the process of oxidation phosphorylation.

• Producing ATP through the electrons transfer from NADH or FADH₂ to O₂ through electron carriers
• NADH converts to 3 ATP
• FADH₂ converts to 2 ATP

Written by Bella | HKDSE Biology Specialist @ TUTTEE

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References 

1. Beck, K. (2019, November 22). Importance of Respiration. Sciencing. https://sciencing.com/importance-respiration-5390615.html.
2. Khan Academy. Glycolysis | Cellular respiration | Biology (article). Khan Academy. https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/glycolysis/a/glycolysis.
3. Khan Academy. The citric acid cycle | Cellular respiration (article). Khan Academy. https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/pyruvate-oxidation-and-the-citric-acid-cycle/a/the-citric-acid-cycle.
4. Khan Academy. Oxidative phosphorylation | Biology (article). Khan Academy. https://www.khanacademy.org/science/biology/cellular-respiration-and-fermentation/oxidative-phosphorylation/a/oxidative-phosphorylation-etc.