Leaves

Leaves

1. Leaves have: -

   • A large surface area - to absorb light rays
   • A thin shape - so gases can diffuse in and out easily
   • Many chloroplasts - to absorb light for the reactions that take place in photosynthesis
   • Veins - to support the structure of the leaf, carry water and ions to the leaf cells, take sucrose and amino acids away from the leaf to all other parts of the plant

2. Inside a Leaf

   • Cuticle : layer of wax that covers the surface of the leaf. The layer prevents water loss by evaporation
   • Upper Epidermis : single layer of cells with no chloroplasts so light goes straight through.
   • Palisade layer : palisade cells contain lots of chloroplasts. Most photosynthesis occurs here.
   • Spongy Layer : more rounded cells, have huge spaces between them for diffusion of gases.
   • Veins : contain xylem vessels that bring water and salt to the leaf, and phoem tube that take dissolved food away.
   • Lower Epidermis : has lots of stomata, these allow gases to diffuse in and out

3. Stomata

   • They are small pores in the lower epidermis. They are there to allow gases diffuse in and out
   • In sunlight
     • Carbon dioxide diffuses in for photosynthesis
     • Oxygen made in photosynthesis diffuses out
     • Water vapour diffuses out
   • Opening and Closing
     • They are opened and closed by guard cells
     • At night the stomata close. They also close in hot, dry weather to help the plant prevent wilting.