We feel smell when molecules emanating from flowers, fruits and other things reach the receptors in our nose. The sense of smell is known as olfaction.
The nasal cavity contains special sensory cells that respond to specific smell. Each receptor gets activated only by a specific smell molecule. Thus each receptor is responsible for identifying a particular smell. Many vertebrates, including mammals and reptiles, have two separate systems, main and accessory systems. The main olfactory system, supports the animals living on land and breathing air to detect volatile chemicals. The accessory olfactory system identifies fluid phase chemicals and pheromones.
There are more than thousand receptors in the nasal cavity. When a smell molecule hits a particular receptor, a signal travels to brain informing the presence of a particular smell. Combination of different sets of receptors is capable of identifying other specific smells too.
Now, we have realized that to identify a smell, molecules carrying smell must travel from the object to the receptor. Molecule can diffuse from the object and travel only if the object is volatile like diesel or kerosene. Liquids like petrol, diesel, kerosene etc have the power to evaporate even at normal room temperature. The rate of evaporation, or vapour pressure is dependent on the character of the object. But, the rate of evaporation increases with increase in temperature. When the temperature is higher, the rate of evaporation is also higher. Similarly, when the temperature is low, the rate of evaporation also becomes low.
The fridge lowers the temperature of things kept inside. Thus, when objects are taken out from the fridge, their temperature is much lower than the room temperature. Thus they have lower rate of evaporation. Thus the molecules from them find it difficult to move from the object to the receptor, making it difficult to identify the smell.
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