4. In eukaryotic cells, RNA is copied from DNA in the

Nucleus

Explanation:

In order to form amino acids and proteins, RNA that reflects the DNA found within a cell must be produced. The DNA that is found within cells that is used for gene expression is found in the nucleus of eukaryotic cells, wherein 'RNA transcription' occurs, when the RNA is copied from the DNA.

Let's see what makes the amount of Bi-carbonate ion low in X!

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The question is a bit tricky so read the below points carefully.

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This is what happens inside the Red blood cells:-

At First Hydrogen ion reacts with bicarbonate ion thus forming carbonic acid .

Reaction :

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This bicarbonate in presence of Carbonic anhydrase, converts into carbon-di-oxide and water just before crossing the pulmonary capillary wall! The same happens with the carbaminoharmohlobin!

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Thus the PCO2 is high though the amount of Bi-carbonate ion is low in X!

And just the opposite happens when blood is travelling from alveoli to tissue