<sod>The internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic [[organelles]], the [[chloroplast]]s, to [[light]] and to increase the absorption of [[carbon dioxide]]. Gas exchange is controlled through minute openings ([[stomata]]), about 10&nbsp;μm which open or close to regulate the exchange of carbon dioxide, [[oxygen]], and [[water vapour]] with the [[atmosphere]]. Thir opening is controlled by the [[turgor pressure]] in the cells at the lips of the stomata. In a given square centimeter of a plant leaf there may be from 1,000 to 100,000 stomata.<ref name="Krogh2010">{{citation|author=David Krogh|title=Biology: A Guide to the Natural World|url=http://books.google.com/books?id=Ph7NSAAACAAJ|date=2010|publisher=Benjamin-Cummings Publishing Company|isbn=978-0-321-61655-5|page=463}}</ref><eod>
<sod>The internal organisation of most kinds of leaves has evolved to maximise exposure of the photosynthetic [[organelles]], the [[chloroplast]]s, to [[light]] and to increase the absorption of [[carbon dioxide]]. Gas exchange is controlled through minute openings ([[stomata]]), about 10&nbsp;μm which open or close to regulate the exchange of carbon dioxide, [[oxygen]], and [[water vapour]] with the [[atmosphere]]. Their opening is controlled by the [[turgor pressure]] in a pair of [[guard cell]]s that surround the stomatal opening. In a given square centimeter of a plant leaf there may be from 1,000 to 100,000 stomata.<ref name="Krogh2010">{{citation|author=David Krogh|title=Biology: A Guide to the Natural World|url=http://books.google.com/books?id=Ph7NSAAACAAJ|date=2010|publisher=Benjamin-Cummings Publishing Company|isbn=978-0-321-61655-5|page=463}}</ref><eod>