It's AumSum Time.
Why can't we smell and taste when we have cold?
Because we become lazy.
No.
Our nose has specialized olfactory receptors.
Covered in a thin layer of mucus.
In normal conditions, the odorants released from food or perfume.
Diffuse through the mucus and get transported to the receptors.
Activating them, and thus allowing us to smell.
However, when we have cold, our nose produces excess mucus.
Hence, the odorants are unable to reach the receptors.
Thus making it difficult to smell.
But, why can't we even taste?
When we chew food, specialized gustatory receptors on our tongue.
Tell us whether the food is sweet or salty.
However, at the same time.
Odorants from food travel from back of our mouth.
To the olfactory receptors.
The combination of information from gustatory and olfactory receptors.
Give us the sense of overall flavor.
However, when we have cold.
As the olfactory receptors cannot detect the odors.
We don't get a complete sense of taste and flavor.
Why do old books smell so good?
Because books secretly apply perfume!!
No.
Smell of old books is basically because of paper and ink in those books.
Paper is primarily made up of wood.
Wood is made up of organic compounds like cellulose and lignin.
Over the years, these compounds react to heat, light and moisture.
And begin to breakdown releasing VOCs.
VOCs means vanilla orange cakes, right?
No.
VOCs stand for volatile organic compounds.
These compounds easily vaporize and mix in the air.
Thus forming the smell of old books.
Now, there are different types of VOCs.
A volatile organic compound called vanillin gives vanilla like smell.
Another VOC benzaldehyde gives almond like smell.
Ethyl benzene gives a sweet smell.
In short, the combination of various compounds.
Makes old books smell so good.
Rain.
Why does rain smell?
Maybe it applies a special perfume.
Naahhh.
Rain is just water and water doesn't have any smell.
Ya dude.
So, what's that smell?
The distinctive smell which frequently accompanies the first rain.
After a dry weather is scientifically called petrichor.
It basically comes from plants and bacteria called actinomycetes which live in the soil.
Now during a long dry spell.
The plants release oils into the soil to block other seeds from germinating.
Thus reducing competition for water.
Whereas, the actinomycetes produce a chemical called geosmin.
Now when rain hits the ground, it brings up the oils and geosmin which then mix with air.
The combination of this geosmin along with the plant oils.
Form the smell which we receive after the rain.
How can we smell things?
Dude.
I don't have a nose.
So, how will I know?
Haha.
At the back of our nose, there is a tissue called olfactory epithelium.
It is covered with mucus.
This tissue has specialized neurons called olfactory receptor neurons.
There are about 40 million olfactory receptor neurons.
These neurons are chemoreceptors, that is, neurons which detect chemicals.
Wow.
They have a cool name.
Now, when any substance releases its smell or odor.
The odor consists of chemicals.
When we breathe in, these chemicals enter our nose.
When they reach the olfactory epithelium.
The chemicals get stuck in the mucus, causing them to activate the neurons.
As a result.
These activated neurons send signals through the olfactory tract to the brain.
Informing it about the smell.