1. Respiration takes place in the?

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lungs. that is why it is called respiratory system

Explanation:

Mitochondrion.

Explanation:

The enzymatic reactions of cellular respiration begin in the cytoplasm, but most of the reactions occur in the mitochondria. Cellular respiration occurs in the double-membrane organelle called the mitochondrion. The folds in the inner membrane are called cristae.

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.