---
title: "The Five Senses"
book: "Primary & Middle School Biology"
subject: biology
language: en
chapter: 5
exercises: 10
source: https://one-course.com/books/biology/1/en/chapter/5-the-five-senses
---

# Chapter 5 — The Five Senses

Close your [eyes](#def-g1-the-five-senses-sense) and the world does not disappear: you still hear the classroom, smell lunch cooking, feel the chair under you. The body has five doors to the world — the senses — and each door is an organ of the body, working for you all day long.

## 5.1 Five senses, five organs

**Definition 5.1 (Sense and sense organ).**

A *sense* is a way the body finds out about the world. Each sense works through a *sense organ*, a part of the body built for that job:

1. *sight* — the *eyes* see light, colors and shapes;
2. *hearing* — the *ears* hear sounds;
3. *smell* — the *nose* smells odors;
4. *taste* — the *tongue* tastes food;
5. *touch* — the *skin* , all over the body, feels rough and smooth, warm and cold.

**Example 5.2 (Breakfast, sense by sense).**

One bowl of hot chocolate uses all five: the [eyes](#def-g1-the-five-senses-sense) see the steam, the nose smells the cocoa, the [skin](#def-g1-the-five-senses-sense) of the hands feels the warm bowl, the [ears](#def-g1-the-five-senses-sense) hear the spoon clink, and the tongue — the best part — tastes it.

![One bowl of hot chocolate, five senses at work before the first sip.](https://one-course.com/images/onecourse/chapters/biology-1/g1-the-five-senses/img-46d276d95c80.jpg)

*One bowl of hot chocolate, five senses at work before the first sip.*

**Remark 5.3 (Touch is everywhere).**

Four [sense organs](#def-g1-the-five-senses-sense) live on the head, but the organ of touch is the [skin](#def-g1-the-five-senses-sense), and the [skin](#def-g1-the-five-senses-sense) covers you from head to toe. That is why you can feel a breeze on your neck, a pebble in your shoe and a ladybug landing on your [arm](https://one-course.com/books/biology/1/en/chapter/4-my-body#def-g1-my-body-parts) — all without looking.

## 5.2 The senses report to the brain

**Proposition 5.4 (Messages to the brain).**

A [sense organ](#def-g1-the-five-senses-sense) does not understand what it senses — it *sends a message*. All the messages travel inside the body to the *brain*, in the head, which puts them together: “that is Grandma’s voice”, “that smell is toast”. Without the brain, the [eyes](#def-g1-the-five-senses-sense) and [ears](#def-g1-the-five-senses-sense) would report to no one.

**Proof.** *Admitted at this level.* ∎

![Each sense organ sends its message to the brain, which makes sense of them all. (The tongue reports too — the picture would just get crowded.)](https://one-course.com/images/onecourse/chapters/biology-1/g1-the-five-senses/fig-e0443d24a12d.svg)

*Each [sense organ](#def-g1-the-five-senses-sense) sends its message to the brain, which makes sense of them all. (The tongue reports too — the picture would just get crowded.)*

**Example 5.5 (Naming things in the dark).**

A friend puts a familiar object in your hands while your [eyes](#def-g1-the-five-senses-sense) are closed: a key, a sponge, a spoon. You name it almost at once. The [skin](#def-g1-the-five-senses-sense) sent its message — cold, hard, jagged — and the brain answered: “a key”. Senses collect; the brain understands.

**Remark 5.6 (Helping each other).**

The senses work as a team. Food “tastes” dull when a cold blocks your nose, because smell was doing half the work of flavor. And when one sense cannot do its job at all, the others learn to do more: people who cannot see read with their fingertips, using touch, and cross the street with their [ears](#def-g1-the-five-senses-sense).

## 5.3 Taking care of the sense organs

**Proposition 5.7 (Fragile doors).**

[Sense organs](#def-g1-the-five-senses-sense) are precious and easy to hurt. Too-loud sound hurts the [ears](#def-g1-the-five-senses-sense); looking at the Sun hurts the [eyes](#def-g1-the-five-senses-sense); a too-hot spoonful burns the tongue. A hurt [sense organ](#def-g1-the-five-senses-sense) may stay hurt — so we protect them.

**Proof.** *Admitted at this level.* ∎

**Method 5.8 (Protecting my senses).**

1. Never look straight at the Sun, not even for a moment;
2. keep sounds gentle: no shouting into [ears](#def-g1-the-five-senses-sense) , headphones at low volume;
3. never push anything into your [ear](#def-g1-the-five-senses-sense) or your nose;
4. blow on hot food before tasting;
5. read and draw with good light.

**Example 5.9 (The concert next door).**

After very loud music, [ears](#def-g1-the-five-senses-sense) sometimes whistle for a while. That whistling is the [ear](#def-g1-the-five-senses-sense) saying “too much!”. People who work with loud machines wear [ear](#def-g1-the-five-senses-sense) covers for exactly this reason — their [ears](#def-g1-the-five-senses-sense) must last them a lifetime.

## 5.4 Exercises

**Exercise 5.1 ★.**

Name the five senses and, for each, its [sense organ](#def-g1-the-five-senses-sense).

**Solution of Exercise 5.1.**

Sight — the [eyes](#def-g1-the-five-senses-sense); hearing — the [ears](#def-g1-the-five-senses-sense); smell — the nose; taste — the tongue; touch — the [skin](#def-g1-the-five-senses-sense).

**Exercise 5.2 ★.**

Which [sense organ](#def-g1-the-five-senses-sense) reports: (a) the color of a balloon? (b) the softness of a blanket? (c) the smell of rain? (d) the sound of a bell?

**Solution of Exercise 5.2.**

(a) The [eyes](#def-g1-the-five-senses-sense). (b) The [skin](#def-g1-the-five-senses-sense). (c) The nose. (d) The [ears](#def-g1-the-five-senses-sense).

**Exercise 5.3 ★.**

Which [sense organ](#def-g1-the-five-senses-sense) is not on the head? How far does it reach?

**Solution of Exercise 5.3.**

The [skin](#def-g1-the-five-senses-sense), the organ of touch. It covers the whole body, from head to toe.

**Exercise 5.4 ★.**

In [Example 5.5](#ex-g1-the-five-senses-dark), the [eyes](#def-g1-the-five-senses-sense) were closed. Which organ sent the message, and which part of the body understood it?

**Solution of Exercise 5.4.**

The [skin](#def-g1-the-five-senses-sense) of the hands sent the message (cold, hard, jagged); the brain understood it and named the object.

**Exercise 5.5 ★.**

With a cold and a blocked nose, food seems to lose its flavor. Which two senses usually team up when you eat?

**Solution of Exercise 5.5.**

Taste and smell. The nose does half the work of flavor, which is why food seems dull when it is blocked.

**Exercise 5.6 ★.**

Give three rules of [Method 5.8](#met-g1-the-five-senses-protect), and say which [sense organ](#def-g1-the-five-senses-sense) each one protects.

**Solution of Exercise 5.6.**

For example: never look straight at the Sun — protects the [eyes](#def-g1-the-five-senses-sense); keep sounds gentle — protects the [ears](#def-g1-the-five-senses-sense); blow on hot food — protects the tongue; nothing pushed into [ear](#def-g1-the-five-senses-sense) or nose — protects [ears](#def-g1-the-five-senses-sense) and nose; good light for reading — protects the [eyes](#def-g1-the-five-senses-sense).

**Exercise 5.7 ★.**

Why do people who work with loud machines wear [ear](#def-g1-the-five-senses-sense) covers? Use [Proposition 5.7](#prop-g1-the-five-senses-fragile).

**Solution of Exercise 5.7.**

Because too-loud sound hurts the [ears](#def-g1-the-five-senses-sense), and a hurt [ear](#def-g1-the-five-senses-sense) may stay hurt. The covers keep the machines’ noise gentle enough for a lifetime of hearing.

**Exercise 5.8 ★.**

Try it: with [eyes](#def-g1-the-five-senses-sense) closed, let a helper hold three foods under your nose — perhaps banana, cheese, orange. How many did your nose name correctly, without the [eyes](#def-g1-the-five-senses-sense)’ help?

**Solution of Exercise 5.8.**

Open answer — most people name two or three out of three. The nose recognizes familiar foods well, even with no help from the [eyes](#def-g1-the-five-senses-sense).

**Exercise 5.9 ★★.**

A friend claims: “The [eye](#def-g1-the-five-senses-sense) understands what it sees.” Correct the sentence using [Proposition 5.4](#prop-g1-the-five-senses-brain): what does the [eye](#def-g1-the-five-senses-sense) really do, and who does the understanding?

**Solution of Exercise 5.9.**

The [eye](#def-g1-the-five-senses-sense) only *sees* — it collects light and sends a message. The brain does the understanding: it receives the message and says “that is Grandma”, “that is my school”. Senses collect; the brain understands.

**Exercise 5.10 ★★.**

How can a person who cannot see “read” a book, and cross a street safely? Say which senses take over which jobs.

**Solution of Exercise 5.10.**

Reading: with the fingertips — touch takes over from sight, feeling raised dots on the page. Crossing the street: with the [ears](#def-g1-the-five-senses-sense) — listening for cars coming and going — often with a cane whose tip lets touch check the ground ahead.