Leaf Structure

Leaf Structure and Function

  • Leaves are the main sites for photosynthesis in plants, transforming light energy into chemical energy.
  • The basic structure of a leaf includes the upper epidermis, palisade mesophyll, spongy mesophyll, veins (xylem and phloem), and lower epidermis with stomata.

Upper Epidermis

  • The upper epidermis is a transparent layer that allows sunlight to pass through to the chloroplasts in the cells below.
  • It is covered by a thin layer of waxy cuticle that reduces water loss from the leaf to the atmosphere.

Palisade Mesophyll

  • Under the epidermis lies the palisade mesophyll, which contains most of the chloroplasts.
  • These are closely packed cells, maximising the number of chloroplasts that can be exposed to light so photosynthesis is optimised.

Spongy Mesophyll

  • Below the palisade layer is the spongy mesophyll, comprised of loosely packed cells with large air spaces in between.
  • This facilitates the diffusion of gases (carbon dioxide, oxygen & water vapour) through the leaf.

Veins (Xylem and Phloem)

  • Veins in the leaf contain xylem and phloem tissue.
  • The xylem transports water and minerals from the roots to the leaves.
  • The phloem transports glucose, the product of photosynthesis, around the plant.

Lower Epidermis and Stomata

  • The underside of the leaf, the lower epidermis, contains tiny pores called stomata surrounded by guard cells.
  • The stomata allow for gas exchange, CO2 in and O2 out.
  • The stomata also allow for transpiration, the loss of water vapour, which helps draw more water into the leaf from the roots.
  • The guard cells can open and close the stomata to regulate gas exchange and water loss, depending on environmental conditions.

Importance of Leaf Structure in Photosynthesis

  • The leaf structure supports an efficient process of photosynthesis by allowing for maximum light absorption, efficient gas exchange, and effective water transport.
  • Each leaf’s adaptations, such as the positioning and abundance of chloroplasts or the control of stomatal opening, all serve to optimise photosynthesis.