Both heterotrophs and autotrophs take simple organic compounds (such as sugars) and combine them with oxygen to generate energy, CO2 and H2O. What is this process called? (1)
The correct answer and explanation is:
Correct Answer: Cellular Respiration
Explanation (300 words):
Cellular respiration is the process by which both heterotrophs and autotrophs convert simple organic compounds, such as glucose (a type of sugar), into usable energy. This energy is stored in the form of adenosine triphosphate (ATP), the primary energy currency of cells. During this process, oxygen (O₂) is used to break down glucose (C₆H₁₂O₆), and the byproducts of this breakdown are carbon dioxide (CO₂) and water (H₂O).
The overall chemical equation for cellular respiration is:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP (energy)
This process occurs in the mitochondria of eukaryotic cells and involves several stages:
- Glycolysis – This is the first step, which occurs in the cytoplasm. One molecule of glucose is broken down into two molecules of pyruvate, generating a small amount of ATP and NADH (an electron carrier).
- Krebs Cycle (Citric Acid Cycle) – In the mitochondrial matrix, the pyruvate is further broken down, producing CO₂, more NADH, FADH₂ (another electron carrier), and a small amount of ATP.
- Electron Transport Chain (ETC) – This final stage occurs across the inner mitochondrial membrane. NADH and FADH₂ donate electrons to the ETC, and the energy released is used to pump protons and produce a large amount of ATP. Oxygen acts as the final electron acceptor and combines with electrons and protons to form water.
Both autotrophs (like plants) and heterotrophs (like animals) perform cellular respiration. Autotrophs first make glucose via photosynthesis, while heterotrophs obtain it by consuming organic matter. Despite these differences in glucose sourcing, both use cellular respiration to harvest energy from glucose in the presence of oxygen, making this process fundamental to life.