The structure that prevents food from entering the trachea during swallowing is the:

 # The structure that prevents food from entering the trachea during swallowing is the:

 A. Soft palate

 B. Glottis

 C. Uvula

 D. Epiglottis

The correct answer is D. Epiglottis.

The epiglottis is a flap of cartilage located at the base of the tongue that prevents food and liquids from entering the trachea during swallowing. When you swallow, the epiglottis folds over the glottis (the opening to the trachea), directing food and liquids into the esophagus.

• A. Soft palate: The soft palate helps close off the nasal cavity during swallowing but does not directly prevent food from entering the trachea.
• B. Glottis: The glottis is the opening to the trachea, not a structure that closes it off; it is covered by the epiglottis during swallowing.
• C. Uvula: The uvula helps with speech and directs food toward the esophagus but does not cover the trachea.

The Bohr effect describes the phenomenon where:

 # The Bohr effect describes the phenomenon where:

 A. An increase in CO₂ and H⁺ ions causes hemoglobin to release oxygen more readily.

 B. A decrease in temperature increases hemoglobin's affinity for oxygen.

 C. An increase in O₂ causes hemoglobin to release CO₂ more readily.

 D. An increase in CO₂ causes hemoglobin to bind more oxygen.

The correct answer is A. An increase in CO₂ and H⁺ ions causes hemoglobin to release oxygen more readily.

The Bohr effect describes how hemoglobin's affinity for oxygen decreases in conditions of increased carbon dioxide (CO₂) and hydrogen ion (H⁺) concentration (i.e., lower pH). This occurs in metabolically active tissues, where higher CO₂ and H⁺ levels promote oxygen release from hemoglobin to meet the tissue's oxygen demands. The effect enhances oxygen delivery where it is needed most.

• B. A decrease in temperature increases hemoglobin's affinity for oxygen: While temperature affects hemoglobin's oxygen affinity (lower temperatures increase affinity), this is not the Bohr effect, which specifically involves CO₂ and H⁺.
• C. An increase in O₂ causes hemoglobin to release CO₂ more readily: This describes the Haldane effect, not the Bohr effect.
• D. An increase in CO₂ causes hemoglobin to bind more oxygen: Incorrect, as increased CO₂ reduces hemoglobin's oxygen affinity, promoting oxygen release, not binding.

What is the role of surfactant in the alveoli?

 # What is the role of surfactant in the alveoli?

 A. To increase the surface tension of alveolar fluid

 B. To transport oxygen across the alveolar membrane

 C. To warm the inspired air

 D. To reduce the surface tension of alveolar fluid

The correct answer is D. To reduce the surface tension of alveolar fluid.

Surfactant, produced by type II alveolar cells in the lungs, is a lipoprotein mixture that reduces the surface tension of the fluid lining the alveoli. By lowering surface tension, surfactant prevents the alveoli from collapsing during exhalation, stabilizes alveolar size, and reduces the work of breathing by making it easier for the lungs to expand during inhalation.

• A. To increase the surface tension of alveolar fluid: Incorrect, as surfactant decreases, not increases, surface tension.
• B. To transport oxygen across the alveolar membrane: Incorrect, as oxygen diffusion occurs passively across the alveolar membrane and is not facilitated by surfactant.
• C. To warm the inspired air: Incorrect, as warming inspired air occurs primarily in the upper respiratory tract, not the alveoli, and is unrelated to surfactant function.