Biology 5090/22 — October/November 2012

Walkthrough

The question asks to identify two structures in a sagittal (side) section through a person's head and throat. Structure A is located in the oral cavity, forming the floor of the mouth and pressing against the upper teeth. This is the tongue, which is used to manipulate food and form it into a bolus. Structure B is located in the anterior (front) part of the neck, just below the pharynx. It is the larynx, also known as the voice box, which contains the vocal cords and leads down to the trachea (windpipe).

Key Takeaways

• The tongue is a muscular organ in the mouth used for tasting, manipulating food, and swallowing.
• The larynx (voice box) is the cartilaginous structure at the top of the trachea that houses the vocal cords.

Common Mistakes

• Confusing the larynx with the pharynx (the throat cavity behind the mouth and nose) or the trachea (the tube below the larynx). Label B points specifically to the laryngeal region above the main tracheal rings.
• Writing "throat" for A; the throat is the general region (pharynx), whereas A is specifically the muscular tongue.

Things to Be Careful About

• The mark scheme accepts larynx or voice box. Either is correct, but use precise biological terminology.
• Ensure you match the letter to the correct structure; A is the tongue, B is the larynx.

Walkthrough

Once the bolus of food is swallowed and passes into the oesophagus, it must be transported to the stomach. This is achieved by peristalsis, which is a series of coordinated, wave-like muscular contractions of the oesophageal walls. These contractions squeeze the bolus forward and push it down into the stomach, working against gravity if necessary.

Key Takeaways

• Peristalsis is the involuntary muscular wave that moves food through the alimentary canal, particularly the oesophagus, stomach, and intestines.

Common Mistakes

• Writing "digestion" or "absorption"; these are chemical and uptake processes, not the physical transport mechanism.
• Confusing peristalsis with the action of the diaphragm or intercostal muscles, which are involved in breathing, not swallowing.

Things to Be Careful About

• The question asks for the process name. "Peristalsis" is the exact required term. Do not just describe it; name it.

Walkthrough

Structure C is the epiglottis, a flap of cartilage located at the base of the tongue. When a person swallows, the epiglottis must change its position to protect the airway.

1. Describe what happens: The epiglottis folds down to close or cover the glottis, which is the opening to the trachea (also called the windpipe, air passage, or larynx). This closing is assisted by the raising of the larynx as the whole laryngeal complex is pulled upwards during the swallowing reflex.
2. Explain why this happens: The primary purpose is to prevent food and liquid from entering the respiratory system (trachea and lungs). If food enters the trachea, it causes choking and can lead to aspiration pneumonia. By covering the trachea, the epiglottis ensures the bolus is directed safely into the oesophagus, which leads to the stomach.

Key Takeaways

• The epiglottis acts as a valve during swallowing to prevent aspiration.
• Aspiration (food entering the airway) is dangerous and must be prevented by the mechanical closure of the epiglottis over the trachea.

Common Mistakes

• Naming the epiglottis instead of describing its action; the question asks to describe and explain what happens to structure C, not just name it.
• Saying the epiglottis "blocks the oesophagus"; it blocks the trachea, allowing the oesophagus to remain open for the food.
• Forgetting the explanation part; simply stating "it closes" is not enough, you must explain that it prevents food from going to the lungs.

Things to Be Careful About

• Use precise terms: trachea (not just "windpipe", though both are accepted), oesophagus (not "stomach" directly).
• The mark scheme awards up to 3 marks for: (1) closing/covering, (2) naming the trachea/larynx, (3) preventing food entry to lungs/respiratory system or allowing entry to oesophagus.
• Note the alternative valid point (AWP/AVP): mentioning that the larynx is raised during swallowing is a good additional detail that demonstrates deeper understanding.