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The virus that causes bird flu can attach to the cells of the lower part of the respiratory system i


The virus that causes bird flu can attach to the cells of the lower part of the respiratory system in humans, but not to the cells of the upper part of the respiratory system. The most likely reason for this is that these two groups of cells have different

(1) DNA codes in their nuclei (2) enzymes in their mitochondria (3) amounts of water in their cytoplasm (4) receptor molecules on their membranes