Photosynthesis

Photosynthesis

  • Photosynthesis is a process that converts light energy, usually from the sun, into chemical energy in the form of glucose.
  • This process takes place in the green pigment chlorophyll which is found in the chloroplasts of a plant cell.

The Process of Photosynthesis:

  • Photosynthesis begins when light is absorbed by chlorophyll in the chloroplasts of the plant cell.
  • Water (H2O) is split by light energy to produce hydrogen and oxygen.
  • The oxygen is given off as a by-product and exits the plant via stomata, small openings on leaves.
  • The hydrogen reacts with carbon dioxide (CO2) in a process called the Calvin cycle, resulting in the production of glucose.

The Light-Dependent Reaction:

  • The light-dependent reaction occurs in the thylakoid membranes of the chloroplasts.
  • Light energy is absorbed by chlorophyll and is used to split water molecules into hydrogen ions, electrons, and oxygen.
  • The oxygen is then released as a by-product into the atmosphere.

The Light-Independent Reaction (Calvin Cycle):

  • Known also as the Calvin cycle or carbon fixation, this stage occurs in the stroma of the chloroplasts.
  • It does not directly require light, hence termed ‘light-independent’, but it needs the products of the light-dependent reaction: namely ATP (energy) and NADPH (electron carrier).
  • During the Calvin cycle, CO2 is combined with hydrogen to form glucose.

Importance of Photosynthesis:

  • Photosynthesis is critical for life on Earth as it produces oxygen, an essential component for most organisms’ respiration.
  • It also forms the basis of food chains, as plants are primary producers that utilize photosynthesis to create the energy-rich compounds other organisms need for survival.

Key Terms:

  • Photosynthesis: The process by which green plants and some other organisms use sunlight to synthesize glucose from carbon dioxide and water.
  • Chloroplast: A plastid in green plant cells which contains chlorophyll and in which photosynthesis takes place.
  • Chlorophyll: A green pigment, present in all green plants, responsible for the absorption of light to provide energy for photosynthesis.
  • Stomata: Tiny openings or pores in plant tissue that allow for gas exchange.
  • Thylakoid: A flattened sac within a chloroplast where the light-dependent reaction of photosynthesis takes place.
  • Calvin cycle: The cycle of enzyme-catalysed dark reactions of photosynthesis that convert carbon dioxide and other compounds into glucose.
  • ATP: Adenosine Triphosphate, a molecule which stores and transfers energy within cells.
  • NADPH: Nicotinamide Adenine Dinucleotide Phosphate, an electron carrier used during photosynthesis in the light-independent reactions.