Mada za sehemu hiiGaseous Exchange And RespirationMada 4
Respiration is a process by which food substances are oxidised to release energy in the form of ATP, which is needed for metabolic activities in the body.
Respiration takes place within the mitochondria of a cell. Since respiration takes place in a living cell, it is commonly referred to as cellular respiration. There are two types of respiration, namely aerobic respiration and anaerobic respiration.
Aerobic respiration occurs in the presence of oxygen, while anaerobic respiration occurs in the absence of oxygen (therefore, it is sometimes referred to as fermentation). Aerobic respiration involves three main stages or processes, namely glycolysis, Krebs cycle, and oxidative phosphorylation. Respiration is an important process as it yields chemical energy in the form of ATP, which enables organisms to perform life activities such as movement, growth, excretion and reproduction. Respiration process involves oxidation of organic compounds known as respiratory substrates. These are carbohydrates, fats, or proteins.
There are food substances which upon being oxidized yield energy in form of ATP, they include carbohydrates, lipids and proteins. However the most preferred respiratory substrates are the carbohydrate especially glucose.
Glucose is the mostly used respiratory substances. When glucose is completely oxidized aerobically a molecule of glucose yields 38 ATP molecules.
Respiration is completed in the following stages:
a. Glycolysis
Location: Cytoplasm
Process: The breakdown of glucose (a 6-carbon molecule) into two 3-carbon molecules of pyruvate. Occurs in both aerobic and anaerobic respiration.
Products:
- 2 ATP (net gain)
- 2 NADH
- 2 Pyruvate
Oxygen requirement: None (anaerobic)
b. Krebs cycle (Citric Acid Cycle)
Location: Mitochondrial matrix
Process:
- Each pyruvate is converted to Acetyl-CoA and enters the cycle.
- Acetyl-CoA combines with oxaloacetate to form citric acid, and through a series of steps, CO₂ is released, while NADH, FADH₂, and a small amount of ATP are generated.
Products:
- 2 ATP
- 6 NADH
- 2 FADH₂
- 4 CO₂ (released as waste)
Oxygen requirement: Yes (aerobic)
c. Electron Transport System (ETC)
Location: Inner mitochondrial membrane
Process:
- NADH and FADH₂ donate electrons to the electron transport chain.
- Electrons move through a series of protein complexes, releasing energy that pumps protons (H⁺) across the membrane.
- Protons flow back through ATP synthase, generating ATP.
- Oxygen acts as the final electron acceptor and combines with electrons and protons to form water.
Products:
- ~34 ATP (from chemiosmosis)
- Water (H₂O)
Oxygen requirement: Yes (aerobic)
d. Fermentation (only if oxygen is not available)
Location: Cytoplasm
Process: When oxygen is absent, the pyruvate produced from glycolysis is converted into either lactic acid (in animals) or ethanol and CO₂ (in yeast and some plants), regenerating NAD⁺ so that glycolysis can continue.
Products:
- Lactic acid or Ethanol and CO₂
- 2 ATP (from glycolysis)
Oxygen requirement: None (anaerobic)
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