Microplastics are small plastic particles, that are widely distributed in the environment and effect all organisms. Their effects on animals is well known, while there is not a lot of information about their impact on plants. Therefore, the aim of the diploma thesis is to assess the impact of environmentally relevant microplastics on an aquatic plant duckweed Lemna minor. We exposed duckweed to five different types of microplastic particles, that are commonly found in the environment (microplastic from cosmetic, synthetic fibres, pieces of plastic bag, bakelite powder, fragments of plastic bottle), in a seven-day period. We also evaluated the impact of natural particles precisely beech saw dust on plants growth. We determined the specific growth rate, measured the length of roots and calculated the specific concentration of chlorophyll a to make a conclusion if the plant is affected by microplastics. The results showed, that the presence of microplastic (microplastic from cosmetic, pieces of plastic bag, bakelite powder, fragments of plastic bottle) affects the length of roots, while the plants growth and specific concentration of chlorophylls are not affected by any particles.