A firm under perfect competition is a price taker because of the following reasons:
(i) A firm under perfect competition is contributing such a small fragment to the market supply that total supply schedule remains unaffected by any change in individual firm's supply.
(ii) All firms are selling homogeneous product. Accordingly, even partial control over price is not possible.
(iii) If any firm tries to fix- its own price, it won't succeed. Higher price would drive the buyers to a large number of other sellers. Lower price would bring so many buyers to a firm that it cannot cope with the demand.