Fill in all the gaps, then press "Check" to check your answers. Use the "Hint" button to get a free letter if an answer is giving you trouble. You can also click on the "[?]" button if available to get a clue. Note that you will lose points if you ask for hints or clues!
absorbin air alveoli bigger breathe breathing bronch capillaries carbon dioxide cilia ciliated epithelial cells diffusion dirt excretion exhale gas exchange goblet inhale large surface area lots of them mucus Mucus muscles oxygen red blood cells redder sacs size smaller sticky stop sweep tennis court thick thin trachea ventilation very few of them