1) Nasal congestion can affect the sense of taste. You may have experienced this with a bad cold or severe allergies. Why do you think congestion impairs the sense of taste?

2.   There are many medical conditions that can cause dry mouth. Individuals with dry mouth often experience an impaired ability to taste food. Why do you think dry mouth impairs the sense of taste?

3.   Parosmia describes a condition in which the sense of smell is distorted. Individuals with parosmia experience olfactory hallucinations or phantom smells, where they detect odors that are not truly present. Parosmia has been reported in some COVID-19 patients. What do you imagine could go wrong along the olfactory sensory transduction pathway that might explain these olfactory hallucinations? (HINT: There are many possible answers here.)

1 - A person's sense of smell is driven by certain processes. First, a molecule released from a substance (such as fragrance from a flower) must stimulate special nerve cells (called olfactory cells) found high up in the nose. These nerve cells then send information to the brain, where the specific smell is identified.

Anything that interferes with these processes, such as nasal congestion, nasal blockage, or damage to the nerve cells themselves, can lead to loss of smell.

When one has a cold, flu or sinusitis, or congested nose there is swelling and a lot more mucous in the nose. The mucous and swelling in the nose prevents the smell (odorant) from reaching the top of the nasal cavity. Hence the smell never reaches the smell nerves and the nerves are not stimulated. 

2 - Dry mouth, or xerostomia, refers to a condition in which the salivary glands in your mouth don't make enough saliva to keep your mouth wet. Dry mouth is often due to the side effect of certain medications or aging issues or as a result of radiation therapy for cancer. Less often, dry mouth may be caused by a condition that directly affects the salivary glands.

Saliva has many physiologic functions. Its main role includes transport of taste substances to and protection of the taste receptor. In the initial process of taste perception, saliva acts as a solvent for taste substances; salivary water dissolves taste substances, and the latter diffuse to the taste receptor sites.

Loss of taste is caused by interruption of the transfer of taste sensations to the brain, or by a problem with the way the brain interprets these sensations. Since taste buds can only taste food that is dissolved in saliva, people with dry mouth have trouble tasting their food. 

3 - Parosmia is typically associated with reduced olfactory sensitivity. It can occur after viral infections of the upper respiratory tract or after skull-brain traumas. In rare cases parosmia can be caused by sinusitis by odours which arise in the infected paranasal sinuses.

Olfactory hallucinations may result from disorder almost anywhere along the smell pathway, from the nose to the primary olfactory cortex in the medial aspect of the temporal lobes. Patients with local nasal problems such as infection or trauma may complain of a continuous or intermittent unpleasant smell (phantosmia) in the absence of any external stimulus.

The mechanism by which parosmia and phantosmia occur is not fully understood, but they are thought to result from damage to the olfactory receptor neurons, the cells in our nasal cavity that detect odor molecules. It's quite possible that damage to other areas of the olfactory system, such as the olfactory bulbs, can also cause these conditions.

the above figure shows The location of the olfactory nerves in the nose. When smell is detected by the olfactory nerves, the smell information is carried by signals that are transmitted by the olfactory bulb and olfactory tract to the brain.

2 -

Loss of taste is a common symptom of gastroesophageal reflux disease (GERD), salivary gland infection, sinusitis, poor dental hygiene, or even certain medicines. The medical term for a complete loss of taste is ageusia. A partial loss of taste is called dysgeusia.

Saliva also helps prevent tooth decay by neutralizing acids produced by bacteria, limiting bacterial growth and washing away food particles. Saliva also enhances your ability to taste and makes it easier to chew and swallow. In addition, enzymes in saliva aid in digestion.

Please see the attached file for the complete solution