Photosynthesis and Respiration Processes

Photosynthesis and Respiration

Overview

Photosynthesis and respiration are two fundamental processes by which plants and other organisms produce energy and remove waste products. These metabolic activities are interconnected, as photosynthesis converts carbon dioxide into glucose during the daytime, while respiration breaks down the stored glucose into ATP and releases water and CO2 during the night. Both processes involve cellular respiration and require oxygen from the atmosphere.

Stages of Photosynthesis

Light Dependent Reactions

The light-dependent reactions occur in the thylakoid membranes of chloroplasts. They involve the absorption of sunlight by pigments like chlorophyll and carotenoids, which excites electrons and generates high-energy phosphates through photochemistry. This process also produces oxygen gas (O2) as a byproduct.

Calvin Cycle or Dark Reactions

The Calvin cycle, also known as dark reactions, occurs in the stroma of chloroplasts and involves the conversion of atmospheric CO2 into organic compounds. This process uses the energy stored in ATP and NADPH created during the light-dependent reactions. After being fixed as bicarbonate, CO2 is incorporated into organic molecules such as glucose and other sugars.

Stages of Respiration

Cellular Respiration

Cellular respiration occurs in the mitochondria of eukaryotic cells and involves three stages: glycolysis, Krebs cycle (or citric acid cycle), and electron transport chain. It breaks down food molecules to generate ATP for energy and releases CO2 and water as byproducts.

Fermentation

In the absence of oxygen or when oxygen availability is limited, anaerobic fermentation can occur as an alternative pathway to produce small amounts of ATP. This process does not release as much energy as cellular respiration but still generates some ATP while producing ethanol, lactic acid, acetic acid, or other organic compounds.