Page 62 - Biology_Form_3

Biology for Secondary Schools

Tongue or have different taste compared to the
The tongue is a muscular organ in the mouth normal one if held in the mouth while the
that is used to manipulate food for chewing nose is plugged.
and swallowing. The primary function of
the tongue is to taste various substances.
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The lower surface of the tongue is smooth, Bitterness
while the upper surface is rough due to the Sour Sour
presence of stratified squamous epithelium,
with numerous papillae. These are sensory Umami
cells in the upper lining layer of the tongue. Salty
Sensory cells are also called gustatory cells Sweetness Salty
and they have hair like processes projecting Figure 2.28 Taste areas in human tongue
above the surface of the papillae.
Activity 2.8:
A group of sensory cells form taste buds.
When these taste buds are stimulated Investigating the distribution of taste
by chemical stimuli in food or related buds on the tongue
substances they generate a nerve impulse Materials
in the brain through sensory fibre and Spoon, glass, sugar, lemon, common salt,
particular type of taste can be distinguished. coffee, unsalted beef soup and clean and
Taste buds are located on the upper surface safe water
of the tongue. Each taste bud contains about Procedure
25 sensory receptor cells with exposed tiny
taste hairs stimulated by chemical stimuli in 1. Prepare the following: sugar solution
drinks and foods dissolved in saliva. There (sweet), lemon juice (sour), common
are five primary types of taste; sweet, sour, salt solution (salty), coffee solution
salt, bitter and a savoury or meaty taste (bitter), and unsalted beef soup using
(umami). The tip of the tongue is most clean and safe water.
sensitive to sweet foods, the sides of tongue 2. Use a drinking straw to place a drop
are more sensitive to sour and salty foods, of sugar solution on the back, front,
and the back of the tongue is sensitive to sides and middle of the upper surface
bitter foods. The tongue surface senses of the tongue.
the texture of food and its temperature as 3. Repeat step 2 using the other four
shown in Figure 2.28. solutions. Rinse your mouth with
safe and clean water each time you
The senses of smell and taste are closely have completed a test.
related. For example, if a person has a
cold it is difficult to identify both the smell Questions
and taste of food. Some foods that have a 1. Which area of the tongue mostly
characteristic taste become either tasteless sense sweet taste?

55 Student’s Book - Form Three

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