Cellular Respiration and Photosynthesis Explained

Biological Energy Processes

As organisms evolved, their energy requirements became more complex. Fermentation was the appropriate process for simple organisms like yeast, bacteria, and other microorganisms.

Respiration is an oxidation-reduction process: the flow of electrons from hydrogen or high-energy sources (like glucose) to low-energy states (CO2 + H2O). This involves coenzymes and cytochromes (A1, C1, C, A3) that ensure the transfer of electrons through the respiratory chain. Cytochrome A3 (cytochrome oxidase) is the final step in the chain, transferring electrons to molecular oxygen to produce water.

Cellular Respiration

Cellular respiration is the process by which cells oxidize glucose to carbon dioxide and water, releasing energy.

Fermentation: The process during which glucose molecules are broken down by enzymatic action, resulting in simpler compounds and a net gain of 2 ATP molecules.

Mitochondria: These are membrane-bound organelles found in most eukaryotic cells.

Stages of Respiration

• 1. Glycolysis: Does not use oxygen. It involves the transformation of glucose to form pyruvic acid and 4 ATP molecules (net gain of 2 ATP).
• 2. Krebs Cycle: Uses free oxygen. Pyruvic acid is transformed into H2O and CO2, yielding 36 ATP. The process involves: Pyruvic acid + Coenzyme A → Acetyl CoA.
• 3. Respiratory Chain: Coenzymes channel the path of electrons through cytochromes until they reach the final electron acceptor, O2, to form water.

Photosynthesis

Photosynthesis is a process by which plants, algae, cyanobacteria, and some bacteria manufacture their own food using sunlight (light energy).

Chlorophylls: A family of pigments found in cyanobacteria and all organisms containing plastids in their cells, including plants and various groups of protists called algae.

Chloroplasts: Cell organelles in eukaryotic photosynthetic organisms responsible for photosynthesis.