Which of these statements about taste is true?
a. Sweetness is a measure of the concentration of hydrogen ions in food.
b. Sodium ions from foods can directly depolarize certain taste cells.
c. All bitter-tasting compounds have a similar chemical structure.
d. Sourness is detected when hydrogen ions bind to membrane receptors.

Verified step by step guidance

1. Begin by understanding the basic concepts of taste perception. Taste is one of the five senses and is primarily detected by taste buds located on the tongue. Each taste bud contains taste receptor cells that respond to different taste modalities: sweet, salty, sour, bitter, and umami.
2. Consider the statement about sweetness. Sweetness is typically associated with sugars and certain proteins, not hydrogen ions. Therefore, statement a is incorrect as sweetness is not a measure of hydrogen ion concentration.
3. Examine the statement about sodium ions. Sodium ions are indeed involved in the perception of salty taste. They can directly depolarize taste cells, leading to the sensation of saltiness. Thus, statement b is true.
4. Evaluate the statement about bitter-tasting compounds. Bitter compounds can vary widely in chemical structure, and there is no single structure common to all bitter substances. Therefore, statement c is incorrect.
5. Analyze the statement about sourness. Sour taste is associated with the presence of hydrogen ions, which can bind to specific receptors on taste cells, leading to the perception of sourness. Statement d is true.

Key Concepts

Taste Perception

Taste perception involves the detection of chemical compounds by taste receptor cells located on the tongue. These cells are sensitive to five basic tastes: sweet, sour, salty, bitter, and umami. Each taste is triggered by specific molecules or ions, which bind to receptors or enter taste cells, leading to depolarization and signal transmission to the brain.

Role of Ions in Taste

Ions play a crucial role in taste perception, particularly for salty and sour tastes. Sodium ions (Na+) are responsible for the salty taste by directly entering taste cells and causing depolarization. Similarly, hydrogen ions (H+) are associated with sourness, as they can either enter cells or bind to specific receptors, altering the cell's electrical state and signaling sour taste.

Chemical Structure and Taste

The perception of bitter taste is complex and involves a wide variety of compounds with diverse chemical structures. Unlike sweetness or saltiness, which are often associated with specific ions or molecules, bitter compounds do not share a common structure. Instead, they activate a range of bitter taste receptors, highlighting the diversity in chemical interactions that can result in a bitter taste sensation.