Lichens are found growing on trees, walls, rocks and soil. Fig. 9.1 shows a lichen of the genus Usnea. Usnea can tolerate only low concentrations of sulfur dioxide and does not grow in places where the air is polluted with sulfur dioxide. Fig. 9.1 Usnea is composed of a mixture of two types of cell: - photosynthetic cells that are classified in the kingdom Protoctista - fungal cells that are classified in the kingdom Fungi. Xanthoria is a lichen that can grow in places where there is a high concentration of sulfur dioxide in the air, for example in towns where homes, factories and vehicles burn fuels. Fig. 9.2 shows a lichen of the genus Xanthoria. Fig. 9.2 (i) A student planned a method to measure the relative abundance of Usnea and Xanthoria on trees along a transect from the town centre at 0 km to unpolluted countryside at 4 km . Suggest why measuring the relative abundance of the two types of lichen gives information that is useful for conservation. … .................................................................................................................................... … .................................................................................................................................... … .................................................................................................................................... … .................................................................................................................................... … .................................................................................................................................... … .................................................................................................................................... ................................................................................................................................. (ii) Although a large biodiversity of lichens can be found in a range of habitats, most people ignore them. Outline why forms of life that are usually ignored, such as lichens, should be conserved. … .................................................................................................................................... … .................................................................................................................................... … .................................................................................................................................... … .................................................................................................................................... .................................................................................................................................

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