Ozone is present in the upper part of the atmosphere called the stratosphere. It is not harmful to animals. It acts as a shield absorbing ultraviolet radiation from the sun. Only the ozone present in the lower part of the atmosphere is harmful. Ozone can destroy certain plant tissues, cause haemorrhages, eye irritation, etc. The greenhouse effect is a natural phenomenon which is responsible for the warming of Earth's surface and atmosphere. But due to the exploitation of nature by humans like the deforestation in tropical areas, the greenhouse effect is aggravated. Eutrophication is the natural ageing of a lake due to biological enrichment of its water. It can be fastened because of the activities of human beings.