DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
False-colour scanning electron micrograph of the underside of a leaf from a holly bush, Ilex aquif- olium, found growing in the city, where the air is polluted. E810/152). A number of stomata, pores which allow the exchange of gases, are visible in yellow. The deposit of brown particles comes from the exhaust from motor vehicles; it consists of particles of carbon (soot from the incomplete combustion of fuel), and lead (from leaded petrol). This residue coats the leaf surface, blocking the stomata and reducing the amount of light reaching the cells. Photosynthesis is impaired and hence the health of the plant is affected. Magnification x500 at 6x4.5cm size.
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