life science (copy)

Photosynthesis: The process by which green plants, algae, and some bacteria convert light energy into chemical energy, primarily in the form of glucose. It occurs in chloroplasts and involves two main stages:

• Light-dependent reactions:

  • These reactions occur in the thylakoid membranes of the chloroplasts and require light to take place.

  • When sunlight strikes the chlorophyll, it excites electrons, initiating a series of electron transport chains that ultimately lead to the synthesis of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate).

  • Water molecules (H₂O) are split in a process called photolysis, which releases oxygen (O₂) as a byproduct.

  • The primary products of these reactions, ATP and NADPH, serve as energy carriers that are essential for the next phase of photosynthesis.

• Calvin cycle (Light-independent reactions):

  • This cycle occurs in the stroma of the chloroplasts and does not directly require light, although it relies on the ATP and NADPH produced in the light-dependent reactions.

  • During this phase, carbon dioxide (CO₂) is fixed into a stable form through a process known as carbon fixation, mainly facilitated by the enzyme RuBisCO.

  • The fixed carbon is then converted through a series of enzymatic reactions into glucose and other carbohydrates, like ribulose bisphosphate (RuBP) playing a key role in the process.

  • The Calvin cycle can occur at any time of day as long as the necessary substrates are available, making it crucial for plant energy production and growth.

Photosynthesis is essential for life on Earth as it provides oxygen, which is critical for most living organisms, and serves as the foundation of the food chain, forming the basis for energy transfer in ecosystem.