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Biology coursework planning - the effect of lead chloride on the growth of cress seeds Aim: To investigate the effect of different concentrations of a heavy metal chloride, namely lead chloride, on the growth of cress seeds. Introduction: Heavy metals compounds, such as lead chloride are able to dissolve in rain and enter the soils surrounding plants. Some sources of such compounds are exhaust fumes from vehicles, additives in gasoline and paints, fertilisers and mining. Lead chloride is able to accumulate in the soil at sufficient concentrations and is easily absorbed by plants. For plants, lead is a toxin and when present in significant amounts, can cause severe decreases in their growth as well as death. The toxicity of heavy metals is seen as the irregularities in the normal functioning of the plant rather than direct toxicity to plant cells. Symptoms include stunted growth and the yellowing of plants (called chlorosis). Heavy...

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