Which statement about olfaction is not true?

Options

A. Dogs are unusual among mammals, in that they depend more on olfaction than on vision, as their dominant sensory modality.
B. olfactory stimuli are recognised by the intersection between the stimulus and a specific macromolecule on olfactory hairs.
C. The greater the number of action potentials generated by an olfactory receptor the greater the intensity of the perceived smell.
D. The perception of different smells results from the activation of different combination of olfactory receptors.

Answer

To determine which statement about olfaction is not true, we can analyze the provided statements step by step.

### Step-by-Step Solution:

1. **Understanding Olfaction**:
- Olfaction refers to the sense of smell. It involves the detection of odor molecules by olfactory receptors in the nasal cavity.

2. **Evaluating the Statements**:
- **Statement 1**: "Dogs are unusual among mammals in that they depend more on olfaction than on vision as their dominant sensory modality."
- This statement is true. Dogs have a highly developed sense of smell and often rely on it more than their vision.

- **Statement 2**: "All olfactory stimuli are recognized by the intersection between the stimulus and specific macromolecules of olfactory hair."
- This statement is misleading. While olfactory receptors do interact with odor molecules, the perception of smell is more complex and involves the processing of signals in the brain. Hence, this statement is not entirely accurate.

- **Statement 3**: "The greater the number of action potentials generated by the affected receptor, the greater the intensity of the perceived smell."
- This statement is true. The intensity of smell is indeed related to the frequency of action potentials generated by olfactory receptors.

- **Statement 4**: "The perception of different smells results from different combinations of olfactory receptors."
- This statement is also true. Different smells are perceived based on the activation of various combinations of olfactory receptors.

3. **Identifying the Incorrect Statement**:
- Based on the evaluations, **Statement 2** is the one that is not true or is misleading regarding the olfactory process.

### Final Answer:
The statement about olfaction that is not true is: "All olfactory stimuli are recognized by the intersection between the stimulus and specific macromolecules of olfactory hair."

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