Plants

• While plants are complex organisms, they exchange their gases with the atmosphere.
• Water moves through the tissues of aquatic plants and provides the means for the exchange of carbon.
• Air enters the tissues of terrestrial plants, and the gases diffuse through the moisture that bathes the inner cells.
• An abundant supply of carbon dioxide must be available in the leaves of the plant, and oxygen from photosynthesis must be released.
• Gases do not pass through the leaf cuticle; they pass through pores called stomata in the epidermis.
• On the lower surface of the leaf, stomata are numerous and usually open during the day when the rate of photosynthesis is highest.
• The opening and closure of stomata are due to physiological changes in the surrounding guard cells.