The majority of the oxygen required diffuses from the atmosphere through stomata and into leaves.

Some of the oxygen produced during photosynthesis diffuses throughout the plant and can be used for aerobic respiration.

The majority of the carbon dioxide required diffuses from the atmosphere through stomata and into leaves.

Some of the carbon dioxide produced during respiration diffuses throughout the plant and can be used for photosynthesis.

In the dark, plants use diffusion to take in oxygen and release carbon dioxide.

This is because photosynthesis cannot occur without light, but aerobic respiration still takes place, requiring oxygen and producing carbon dioxide.

Stomata are pores that can open and/or close to regulate gas exchange and water loss.

Most stomata are located on the lower leaf epidermis and are surrounded by guard cells.

1. Many stomata - ensure short diffusion distances
2. Air spaces throughout the mesophyll - allow rapid diffusion from stomata to photosynthetic cells
3. Large surface area of mesophyll cells - allows rapid gas exchange

1. Waxy cuticle forms a waterproof barrier
2. Guard cells close stomata when needed

Xerophytes are plants adapted to survive in dry conditions with limited water supply.

1. Thick waxy cuticle - reduces water loss by evaporation
2. Small, needle-like leaves - reduce the surface area across which water can be lost
3. Hairs on leaves or rolled-up leaves - trap moist air next to leaf surface reducing the water potential gradient
4. Water storage organs - conserve water
5. Sunken stomata - trap moist air next to leaf surface reducing the water potential gradient

1. Upper epidermis with waxy cuticle - reduces water loss
2. Mesophyll - performs photosynthesis
3. Lower epidermis - has stomata surrounded by guard cells for gas exchange
4. Vascular tissue (xylem and phloem) - transports water and nutrients