Photosynthesis

Photosynthesis: An Overview

  • Photosynthesis is a process that plants and some other organisms use to convert the energy from sunlight into chemical energy in the form of glucose.
  • It is a vital process for life on Earth, as it contributes to the oxygen cycle, providing oxygen for other organisms to breathe.

The Process of Photosynthesis

  • Photosynthesis happens in two main stages: the light-dependent reactions and the light-independent reactions.
  • The light-dependent reactions occur inside the thylakoids of chloroplasts. Light energy is absorbed by the pigment chlorophyll and is used to produce ATP (energy) and split water into hydrogen and oxygen (a process known as photolysis).
  • Oxygen produced in photolysis is released as a by-product, while the hydrogen and ATP are used in the light-independent reactions.
  • The light-independent reactions (also known as the Calvin cycle) occur in the stroma of chloroplasts. Here, carbon dioxide (CO₂) is reduced by the hydrogen to form glucose.

Factors Affecting Photosynthesis

  • Three main factors affect the rate of photosynthesis: light intensity, temperature, and the concentration of carbon dioxide.
  • As light intensity increases, the rate of photosynthesis increases to a certain point after which it levels off as other factors become limiting.
  • Temperature has an optimum range for photosynthesis – too low, and the reactions slow down; too high, and the enzymes involved in photosynthesis can denature.
  • Higher concentrations of carbon dioxide can increase the rate of photosynthesis to a certain extent, but beyond this, it has no further effect. Again, other factors may become limiting.

Photosynthesis in Food and Ecosystems

  • The glucose produced through photosynthesis is used by the plant in respiration to provide energy.
  • It can also be converted into other forms of carbohydrate like starch for storage or cellulose for structure.
  • Through feeding interactions, the energy stored in plants is transferred through the ecosystem, first to herbivores (that eat plants), and then to carnivores and omnivores.
  • This transfer of energy and nutrients through the ecosystem is what forms a food chain or food web.