Topic 2: Sense Organs - Science Standard Three (Darasa la Tatu) Notes
What is sense organs?
Sense organs are special organs which help the body to detect and recognise stimuli in the environment and respond to them.
The sense organs receive the stimuli from the environment and send the information to the brain for interpretation.
There are five sense organs
a) Ear
b) Eye
c) Nose
d) skin
e) tongue
A. Eyes
The eyes are used to see and identify things.
They are located on the left and right of the front side of the face.
Parts of the eyes
There are two parts of eyes
(i) The outer
(ii) The inner parts
I. The outer part
The outer part consists of
a) Eyebrows
b) Eyelashes
c) Eyelids
II. The inner part
The inner part includes
a) The pupil
b) Iris
c) Lens
d) Retina
Caring for the eyes
The eyes are cared by:
a) Not wearing glasses without advice from an optician;
b) Reading under enough light;
c) Cleaning your eyes regularly with clean water;
d) Not rubbing or cleaning your eyes with dirty hands or materials.
B. Tongue
The tongue is a sense organ that is used for recognizing tastes of different substances.
The tongue has taste buds which can recognise tastes.
The tongue has five tastes namely:
(i) Sweet
(ii) Sour
(iii) Salty
(iv) Umami
(v) Bitter.
The information on taste is then sent to the brain for interpretation.
Parts of the tongue and their functions
A. The tip of the tongue - To detect sweet taste
B. The two front sides of the tongue - To detect salty taste
C. The middle part of the tongue - To detect umami taste
D. The back sides of the tongue - To detect sour taste
E. The back of the tongue - To detect bitter taste
1. In each group, choose one substance after another for tasting.
2. Write the identified taste in your own prepared table, similar to Table 3.
Exercise
1. Which substances were having similar taste?
Caring for the tongue
The tongue is cared by:
(a) Cleaning your mouth and tongue regularly
(b) Avoiding very hot or cold foods to protect the taste buds of your tongue
(c) Not tasting substances that you do not know because some of them may be poisonous
(d) Not piercing your tongue.
C: The nose
- The nose is the sense organ for smelling.
- Another function of the nose is to allow air into and out of the lungs during breathing.
Caring for the nose
The nose is cared by:
(a) Cleaning your nose using clean water
(b) Not inserting objects into your nose.
The skin
- The skin is a sense organ that covers the whole body of animals, including human beings.
- Its function is to feel or sense different conditions, such as heat, cold, touch, texture, pressure, pain and vibrations.
Layers of the skin
The skin has three major layers which are:
(a) Upper layer or epidermis
(b) Middle layer or dermis
(c) Inner layer or fat layer.
The skin consists of other components such as hair.
Caring for the skin
The skin is cared by:
(a) Keeping it clean by taking bath regularly
(b) Using clean water, sponge or brush and soap when bathing
(c) Drying your body with a clean towel after bath
(d) Applying appropriate body oil or jelly after bath
(e) Eating nutritious food and drinking enough water.
D: The ear
The ear is an organ used for hearing.
It can recognize different sounds.
Parts of the ear
The ear consists of three major parts
(i) Outer ear
(ii) Middle ear
Recognising sounds
(i) The outer ear collects sound waves and directs them into the middle ear through the eardrum.
(ii) The middle ear receives sound waves from eardrum and passes them to the inner ear.
(iii) The inner ear passes the sound waves to the brain where the sound is interpreted.
Caring for the ears
The ears are cared by:
(a) Avoiding loud sound when using a radio or television
(b) Not inserting sharp objects into your ear, as they may damage the eardrum
(c) Ensuring that water does not enter into the ear when bathing or swimming
(d) Not removing the ear wax. The wax prevents things like dust to enter into the ear
(e) Attending the ear clinics regularly for check-up.
Exercise
1. What sense organ will you use to detect or recognize the following?
(a) Smell of a flower
(b) Colour of an orange
(c) Cock crowing sound
(d) Soil texture
(e) Taste of grape juice
2. Match the picture of sense organs with their respective functions.
3. Name two examples of food substances having each of the tastes provided in the following table.
The importance of sense organs
Help us to detect or recognise changes in our environment and respond accordingly.
- Any damage to our sense organs affects the ability to receive or detect the stimuli from the environment.
- For example, defects in the ears can cause deafness and defects in the eyes can cause blindness.
Exercise
Section A: Choose the correct answer.
1. When Rama got up in the morning, he found it was dark and cold. Which sense organs did he use?
(a) Eyes and skin
(b) Ears and eyes
(c) Skin and nose
(d) Nose and ears
2. A pupil ate a ripe banana and said that it was sweet. Which of the following parts of the tongue was responsible for detecting the sweet taste?
(a) Middle part of the tongue
(b) Side parts of the tongue
(c) Tip of the tongue
(d) Side and middle parts of the tongue
3. Which of the following is correct about sense organs?
(a) Ears are used for hearing.
(b) Eyes are used for smelling.
(c) Nose is used for tasting.
(d) Tongue is used for feeling.
4. How many sense organs do human beings have?
(a) Three
(b) Six
(c) Five
(d) Four
5. The sense organ that can be used to detect the green colour of spinach is:
(a) an eye
(b) a nose
(c) a skin
(d) an ear
6. Which of the following represents a group of sense organs?
(a) Nose, legs, ears, skin and tongue
(b) Tongue, ears, skin, nose and mouth
(c) Ears, skin, hands, nose and tongue
(d) Eyes, ears, skin, nose and tongue
Section B: Write TRUE for a correct sentence and FALSE for an incorrect sentence.
7. The skin is a sense organ which is sensitive to heat and cold.
8. The tongue is used for smelling only.
9. The tongue cannot detect the taste of lemon juice.
10. The defects to the ears causes a person to lose the ability to see.
11. The sense organ used for seeing is an eye.
Vocabulary
Organ - part of the body which performs a specific function. Example of organs are ears, nose, tongue, eyes and skin
Taste buds - special cells in the tongue with nerves that collect information about the taste of food
Umami - a combination of tastes which are found in foods such as meat, milk and fish