Gas Exchange in Plants

The leaf

Structure of a typical leaf

Some important structures include:

  • Upper epidermis with waxy cuticle

    • Reduces water loss from leaf surface

  • Air spaces

    • Interconnecting spaces that run throughout the mesophyll layer

  • Palisade mesophyll cells

    • Located beneath the upper epidermis

    • Carry out photosynthesis

  • Spony mesophyll cells

    • Dispersed cells located beteanth the palisade mesophyll

    • Carry out photosynthesis

  • Stomata

    • Small pores surrounded by guard cells on the underside of the leaves that open and close

  • Lower epidermis

    • Bottom layer of cells that contains the stomata and guard cells

  • Vascular tissue (xylem and phloem)

    • Transports water and nutrients

Adaptations of leaf structures for gas exchange:

  • Air spaces

    • Provides a network for gases to quickly diffuse in and out of the leaf and access photosynthesising cells

  • Mesophyll cells

    • Dispersed thoughtout the leaf

    • Provide a large surgacce area across which gases can diffuse

  • Stomata

    • Open when conditions are suitable for photosynthesis

    • Allow inward diffusion of carbon dioxide and outward diffusion of oxygen

    • Close to minimise water loss

How plants limit water loss

Plants require a large leaf surface area for photosynthesis.

But this could lead to lot of water being lost

Plants have teh following to limit water loss:

  • They have a waterproof waxy cuticle on their leaves

  • They have guard cells that can close stomata when needed

Xerophytes

Xerophytes are plants adapted to living in dry environments with limited water availability.

Without adaptations they would become desiccated (dry out) and die

Key adaptations

  • Thick waxy cuticle

    • Reduces wear loss through evaporation

  • Rolling/folding of leaves

    • Encloses the stomata on the lower surface to reduce air flow and evaporation of water

  • Hairs on leaves

    • Trap moist air against the leaf surface to reduce the diffusion gradient of water vapour

  • Sunken stomata in pits

    • Reduces air flow and Evaporation fo water

  • Small, needle-like leaves

    • Reduce the surface across from which water can be lost

  • Water storage organs

    • Conserve water for when it is in low supply