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Heterocytes are specialized and enlarged cells with thick cell walls . Heterocytes are present in nitrogen fixing cyanobacteria.

Heterocytes lack chlorophyll therefore they are  colourless . They synthesize enzyme nitrogenase . With help of enzyme nitrogenase they perform the function of nitrogen fixation.

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Heterocyst A specialized cell found in nitrogen-fixing cyanobacteria. Heterocysts are enlarged cells with thick cell walls and they lack chlorophyll, giving them a colour less appearance. They are the site of nitrogen fixation, for which they produce the enzyme nitrogenase.