Which of the following is true for heterocysts? 1 . They are formed in blue-green algae. 2 . Heterocysts are nitrogen-fixing cells. 3 . Heterocysts are formed during nitrogen starvation. 4 . Anabaena and Nostoc are examples of heterocyst forming bacteria.

Step-by-step solution

Heterocyst are differentiated cyanobacterial cell that carries out nitrogen fixation when the cells go out of nitrogen, that is during nitrogen starvation these specialized cells are formed for fixing nitrogen under aerobic conditions. Few examples of the same are : Anabaena, Nostoc and Cylindrospermum, these are cyanobacteria which produce heterocyst for nitrogen fixation.