The sense of smell
1. Our sense of smell
1.1 Why do we have a sense of smell?
Sight, hearing, touch, taste and smell; we use just these five senses to pick up information about the world around us. Armed with this information, our brain decides how we should behave so that we can survive in our environment. Sights and sounds can warn us of physical dangers, as in crossing the road. Sight, too, plays a major part in helping us find the better things in life, such as food or a partner. We are less conscious, though, of tastes and smells, using them mostly for checking the palatability of food we eat. Other animals take taste and smell far more seriously and use them to recognise territory, find a receptive mate or to help them follow a trail.
Figure 1.1. A cold means that we can't smell the difference between a raspberries and strawberries.
Chemical senses
Taste and smell are both chemical senses in that they give us the ability to detect the molecules of chemicals around us. As life on the planet evolved, it is most likely that organisms developed chemical senses first; even very primitive organisms that exist today have the ability to sense and respond to the chemicals in their surroundings. Our senses of taste and smell are closely connected. In simple terms, smell keeps us in touch with volatile chemicals in our surroundings while taste allows us to sense the non-volatile ones. Since food has volatile and non-volatile components, our experience of eating involves both taste and smell. Often what we think of as the taste of a food comes mainly from its smell. A heavy cold limits our ability to smell food and so reduces its apparent taste. Without our sense of smell, for example, we are unable to distinguish between the tastes of raspberries and strawberries.
Question 1

a) Chemicals that organisms use to communicate with other members of the same species, have a special name. What is it?

b) Find out how a leaf cutter ant (Atta) uses a chemical messenger to help in feeding its colony. (Try looking in the Proteins e-source).