Ddt was harmful to birds because it prevented them from laying eggs.

True.

Explanation:

The statement is true.  

DTT or Dithiothreitol is a redox reagent used to stabilize proteins which possess free sulfhydryl groups. It is used to prevent intramolecular and intermolecular disulfide bonds from forming between cysteine residues of proteins.

DTT is was frequently used as a pesticide and it became very famous for its ability to kill all kinds of unwanted insects. However, species of birds were affected by this pesticide, such as bald eagles, peregrine falcons, and ospreys. The bird's calcium metabolism was altered in a way that resulted in a thin eggshells, due to the administration of DTT. The eggshells was not able to support the weight of the incubating bird.

This led to extinction of many bird species, because with no eggs being layed, then the bird population decreases.

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