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# Long description

The figure consists of two parts labelled (a) and (b) that illustrate external respiration and cellular respiration. Part (a): a schematic illustration of the respiratory system depicts external respiration, which includes cycles of inspiration and expiration. The respiratory system includes the nasal passage, pharynx, larynx, trachea, bronchi, bronchioles, and lungs. Inspiration involves breathing in oxygen (O2) and expiration involves breathing out carbon dioxide (CO2). Part (b): a schematic illustration of cellular respiration shows a typical eukaryotic cell with cell membrane (outer blue layer), nucleus (brown circle), nucleolus (brown core), endoplasmic reticulum (green tubular network), cytosol (blue environment inside the cell), mitochondrion (orange double-membrane organelle), and Golgi apparatus (stack of red saccules). A magnified view of mitochondrion from the cell shows the exchange of O2 and CO2. O2 moves into the mitochondrion during cellular respiration and CO2 is released out of the mitochondrion.