Photosynthesis and Plants

Photosynthesis and Plants

Overview of Photosynthesis

  • Photosynthesis is a process by which plants, algae, and some bacteria convert sunlight into chemical energy.
  • The chemical energy is stored in the bonds of glucose, a type of sugar.
  • Overall reaction can be represented as: 6CO2 + 6H2O + light energy → C6H12O6 + 6O2

Stages of Photosynthesis

  • Photosynthesis occurs in two stages: the light-dependent reactions and the light-independent reactions (Calvin Cycle).
  • Light-dependent reactions occur in the thylakoid membrane of the chloroplasts and convert solar energy into ATP and NADPH.
  • The Calvin Cycle uses ATP and NADPH to convert CO2 into glucose.

Role of Chlorophyll

  • Chlorophyll is a green pigment essential for photosynthesis. It is found in the chloroplasts of plant cells.
  • It captures light energy from the sun and initiates the electron transport chain, leading to the creation of ATP and NADPH.

Importance of Photosynthesis to Life on Earth

  • Photosynthesis produces oxygen, crucial for aerobic organisms. This includes most life on earth, like humans.
  • It plays a significant role in the carbon cycle, removing CO2 from the atmosphere and returning oxygen.
  • It is the primary process by which energy enters the ecosystem.

Limiting Factors of Photosynthesis

  • The rate of photosynthesis can be limited by several factors including: light intensity, carbon dioxide concentration, temperature and the amount of water available.

Structure and Function of Leaves

  • Leaves are designed to maximise photosynthesis. They are broad and flat, which increases surface area for light absorption.
  • They have a special structure called stomata (tiny holes on underside of leaf), which allow for gas exchange.

Role of Xylem and Phloem

  • Xylem transports water and minerals from the roots to the rest of the plant.
  • Phloem transports the sugar (glucose) produced during photosynthesis from leaves to other parts of the plant.


  • Transpiration is a process that helps to transport water from roots to leaves, powered by the evaporation of water from the leaves.
  • It cools the plant, provides water for photosynthesis and transports minerals from roots to leaves.
  • Factors affecting the rate of transpiration include temperature, humidity, light intensity, and wind speed.