Photosynthesis and plants

Photosynthesis is an endothermic process that takes part in the chloroplasts (found in leaf cells).

Photosynthesis cycle

Within chloroplasts is chlorophyll, a green pigment responsible for trapping light energy in order to convert carbon dioxide and water into glucose (chemical energy) and oxygen.

Photosynthesis word equation

carbon dioxide + water -> glucose + oxygen

Photosynthesis balanced chemical equation

6CO2 + 6H2O -> C6H12O6 + 6O2

The plant uses the glucose it produces for:

  • Respiration – the glucose is used to provide energy.
  • Storage – the glucose is converted into starch and oils.
  • Useful substances – the glucose is converted into cellulose for cell walls, protein for growth and chlorophyll.

Leaf structure

Leaf structure

Leaves are adapted for:

  • Light absorption.
  • Gas exchange.

Adaptations to maximise light absorption:

  • Each leaf is not in the shade of another.
  • Transparent waxy cuticle – a protective layer that allows light to enter the leaf. It is waterproof in order to prevent water loss by evaporation.
  • Epidermis – transparent, physical defence layer that does not contain chloroplasts. It allows light into the leaf.
  • Palisade mesophyll layer – regularly shaped allowing many to pack together closely at the top of the leaf. These cells also have many chloroplasts in order to trap as much light as possible.
  • Leaves are thin – ensures all cells receive light.
  • Leaves have a large surface area.

Adaptations to maximise gas exchange:

  • Spongy mesophyll – have very few chloroplasts and a large surface area to increase the diffusion of carbon dioxide and oxygen.
  • Intercellular air spaces within the spongy mesophyll layer – they allow the diffusion of carbon dioxide and oxygen.
  • Stomata (small pores usually found on the lower surface of the leaf) – allow carbon dioxide and oxygen to enter and leave the leaf. Each stoma is surrounded by two guard cells that control its opening and closing. Stomata are usually open during the day and closed at night.