Page 12 - Biology Form Two

Biology for Secondary Schools

Activity 1.1: Classify food items proteins.
according to the nutrients they provide.

Materials A variety of food items

Procedure
FOR ONLINE READING ONLY
1. Collect a variety of food items such as
eggs, maize, beans, carrots, potatoes,
sunflower seeds, groundnuts,
vegetables and tomatoes.
2. Group such food items into Figure 1.3: Sources of protein

different categories based on the Functions of proteins
type of nutrients they contain. Proteins have several functions in the

Question human body including building body
cells, promoting growth, and making
How many food items did you manage
to classify? protoplasm. Proteins also help to repair
damaged tissues such as replacing
damaged or lost cells in wounds,
Proteins
Proteins are organic compounds made skin, and mucus membranes. Since
up of one or more chains of amino acids. proteins are major components of all
Amino acids are made of smaller units cell membranes, they play a role in the
that contain carbon, hydrogen, oxygen, transport of other molecules across the
nitrogen and sulphur. There are two cell membranes. They form part of the
groups of amino acids: essential amino cell structure, and aid in the contraction
acids and non-essential amino acids. of muscles. They are sometimes used
The essential amino acids are obtained as a source of energy, especially when
from foods eaten, while non-essential the body lacks carbohydrates and
amino acids can be made by the body. lipids. Each gram of protein provides
However, the body cannot produce four kilocalories (kcal) of energy.
essential amino acids. Foods like beef, However, proteins are not the major
chicken, fish, termites, eggs, beans, source of energy in the body. Their
lentils, peas, groundnuts, mushrooms, primary function is to promote growth
and milk and its products like cheese and repair worn out body tissues.
are rich in proteins hence provide Proteins are essential for growing
essential amino acids. Figure 1.3 shows children, pregnant women, and people
examples of foods that are sources of recovering from illnesses.

6 Student’s Book - Form Two

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