Acid rain effect. Light micrograph of a longitudinal section of a spruce leaf (Picea sp) showing the transition between normal tissue (left) and tissue damaged by acid rain (right). The tissue mostly affected is known as spongy mesophyll. It is found underneath the epidermal layer (pink) and has large intercellular spaces which facilitate the gaseous exchange with the atmosphere for photosynthesis. Acid rain contains high levels of sulphuric and nitric acids and is produced by the reaction of sulphur dioxide and nitric oxide in the atmosphere. The burning of fossil fuels such as carbon is thought to be the main cause. Magnification: x30 at 6x7cm size.
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