Gas produces in respiration and photosynthesis can be used by eachother

Reduces need of gas exchange with external air

volumes and types of gas exchanged changes

Depends on:

Photosynthesis taking place:

Some CO₂ from respiration but most external air

Some O₂ used in respiration but most diffuses out 

No photosynthesis:

O₂ diffuses into leaf to be used in respiration

CO₂ produced during respiration diffuses out

No living cell far from external air so source of O₂ + CO₂

Diffusion in air so more rapid than in water (in insects)

Short and fast diffusion pathway

Large S.A:Vol ratio

Gas moves in and through plant by diffusion

Thin and flat for large S.A

Many stomata mainly in lower epidermis

Many interconnecting air spaces throughout mesophyll

Minute pores mainly on leaves, especially underside

Each stomata = pair of guard cells that open and close stomatal pore

Control rate of gas exchange

Balance waterloss with gas exchange

Completely/partly close stomata at times when waterloss would be excessive