Explanation:
The nitrates absorbed by the plant roots are converted into various types of amino acids (about 20 types) which sequences respectively to form polypeptide chains of various protein molecules in the ribosomes. The ribosomes are either free floating in the cell cytoplasm or attached to the endoplasmic reticulum.
Centrosomes present in animal cells involves in spindle and microtubule formation during mitotic cell division; however, in plant cells, centrioles or centrosomes are absent, but still microtubule formation takes place through mitotic phases of cell division.