Nutrition in Mammals – SS1 Biology Lesson Note (Second Term)

Nutrition in mammals is the way animals take in food substances and use them for energy, growth, repair and health. Animals cannot make their own food, so they depend on plants, directly or indirectly. Food is grouped into seven classes: carbohydrates, proteins, fats and oils, mineral salts, vitamins, water and roughages.

Behavioural objectives

By the end of the lesson, students should be able to:

• group animals into carnivores, herbivores and omnivores, with examples;
• list the seven classes of food substances and state the sources and importance of each;
• name the water-soluble and fat-soluble vitamins, with their sources and deficiency symptoms;
• define a balanced diet and state its functions;
• state the characteristics of enzymes and name the classes of digestive enzymes.

How are animals grouped by the food they eat?

Animals generally cannot manufacture their food. Instead, they depend directly or indirectly on plants for their food. Hence they are called heterotrophs. Based on their food types, animals are grouped into three:

1. Carnivores, which feed on the flesh of other animals, e.g. lions.
2. Herbivores, which feed on plants, e.g. goats.
3. Omnivores, which feed on both plants and animals, e.g. man.

What are the classes of food substances?

Foods eaten by animals are generally classified into seven:

1. Carbohydrates
2. Proteins
3. Fats and oils
4. Mineral salts
5. Vitamins
6. Water
7. Roughages

1. Carbohydrates

Carbohydrates are got from foods such as bread, yam and rice. They consist of carbon, hydrogen and oxygen. There are three types:

• Monosaccharides (simple sugars), which include glucose, fructose and galactose.
• Disaccharides (double sugars), which include maltose, sucrose and lactose.
• Polysaccharides (complex sugars), e.g. starch, cellulose and chitin.

Carbohydrates are digested by enzymes such as ptyalin, maltase and lactase, and starch yields glucose as a product of its digestion. Excess carbohydrate is stored in the body as glycogen in the muscles and liver. This can be reconverted to glucose during starvation.

Importance of carbohydrates

• It gives animals energy.
• It provides the heat needed to maintain body temperature.
• It can be used for lubrication, e.g. mucus.
• It provides the body with a strong framework, e.g. the exoskeleton in insects.

2. Proteins

Proteins are complex molecules made up of smaller units called amino acids. They contain carbon, hydrogen, oxygen, nitrogen and sometimes phosphorus and sulphur. Foods such as egg, meat, fish and beans give you protein. Proteins are broken down into amino acids by enzymes such as pepsin, rennin, trypsin and erepsin.

Importance of proteins

• Growth in young ones.
• Repair of worn-out tissues.
• Production of enzymes.
• Production of hormones.
• It supports reproduction.
• It is needed for tissue formation, i.e. body building.

3. Fats and oils (lipids)

Fats are lipids that are solid at room temperature, while oils are liquid. Fats and oils consist of carbon, hydrogen and a little oxygen. Foods such as palm oil, groundnut and soybeans give fat and oil. Lipids are broken down into fatty acids and glycerol by lipase enzymes.

Importance of fats and oils

• They give you more energy than carbohydrates.
• They supply essential fatty acids to the body.
• They help in the maintenance of body temperature.
• They provide the body with fat-soluble vitamins.

4. Mineral salts

Mineral salts are usually taken in very small quantities in the food we eat, except sodium chloride (table salt) and iron tablets, which can be taken directly by man. The lack of these salts results in nutritional deficiency. The minerals include calcium, magnesium, potassium, phosphorus, sulphur, chlorine, iron, iodine, fluorine, manganese, copper, cobalt and sodium.

Importance of mineral salts

• They regulate body metabolism.
• They are components of bones and teeth.
• They aid blood formation.
• They control chemical reactions in the body.
• They aid the formation of enzymes and pigments.

5. Vitamins

Vitamins are organic food substances needed by man and other animals in small quantities for normal growth and development. Lack of, or an inadequate supply of, any of these vitamins results in nutritional deficiency.

Vitamins are grouped into two:

1. Water-soluble vitamins: vitamin B complex and vitamin C. Vitamin B complex includes vitamins B1, B2, B3, B5, B6 and B12.
2. Fat-soluble vitamins: vitamins A, D, E and K.

Vitamins: sources and deficiency symptoms

6. Water

Water is of utmost importance to all organisms. It is made up of two elements, hydrogen and oxygen. Water can be obtained from food, rivers, streams, ponds and so on. Water makes up 75% of the human body.

Importance of water

• Metabolic activities of the body of animals.
• Digestion of food.
• Maintenance of body temperature.
• It is a medium of transportation for all nutrients.
• It helps to maintain the osmotic balance in body tissues.
• It helps in the excretion of metabolic waste from the body, e.g. urine.

7. Roughages

Roughages are indigestible fibrous materials obtained from vegetables, fruit, carbohydrates and proteins. They aid digestion, and a lack of them can lead to constipation.

What is a balanced diet?

A balanced diet is a diet containing the correct proportion of all the food substances. In general, a balanced diet contains 15% protein, 15% fat and oil, 10% vitamins, minerals and water, and 60% carbohydrate. When food is taken in these proportions, there is normal growth and development in the body.

Functions of a balanced diet

1. It makes us healthy.
2. It gives the ability to resist diseases.
3. It makes available the energy needed to carry out all biological activities.
4. It prevents malnutrition and deficiency symptoms. For example, a diet that lacks protein results in a nutritional disease called kwashiorkor in children.

A protein-deficient child has the following features:

1. Retarded growth.
2. Loss of weight.
3. Swollen legs (oedema).
4. Cracked/split stomach and thin legs, etc.

What are digestive enzymes?

Enzymes are organic (protein) catalysts produced by living cells which help to speed up and slow down the rate of chemical reactions. Digestive enzymes aid in the breaking down of complex food substances into simple, soluble and diffusible forms.

Characteristics of enzymes

1. Enzymes are soluble.
2. Enzymes are proteins.
3. They are specific in their actions.
4. Enzymes are sensitive to temperature, i.e. they work best between 35°C and 40°C.
5. Enzymes are pH specific.
6. Enzymes bring about reversible reactions.
7. Enzymes need co-enzymes to activate them and can be inactivated by inhibitors such as mercury and cyanide.

What are the classes and functions of digestive enzymes?

Digestive enzymes are classified by the type of food they act upon:

1. Proteases, e.g. pepsin, rennin, trypsin and erepsin. They act on proteins.
2. Amylases, e.g. ptyalin, lactase, maltase and sucrase. They act on carbohydrates.
3. Lipases, which act on lipids (fats and oils).

Evaluation

1. Name the three groups of animals based on the food they eat, and give one example of each.
2. List the seven classes of food substances.
3. State four ways in which proteins are important to the body.
4. Name two water-soluble vitamins and two fat-soluble vitamins.
5. State two features of a child suffering from kwashiorkor.

Assignment

1. Vitamins are organic food substances required by animals in ____ quantity.
   • A. no
   • B. small
   • C. large
   • D. high
2. The following, except one, are fat-soluble vitamins.
   • A. Vitamin A
   • B. Vitamin B
   • C. Vitamin K
   • D. Vitamin E
3. One of the following food substances is indigestible in man.
   • A. Protein
   • B. Lipids
   • C. Roughages
   • D. Carbohydrates
4. The highest source of energy is ____
   • A. carbohydrates
   • B. proteins
   • C. lipids
   • D. vitamins
5. Rickets (poor bone formation) in children is a deficiency symptom of ____
   • A. potassium
   • B. calcium
   • C. chlorine
   • D. manganese
6. Make a table of food tests showing the columns: food, test, observation and inference.
7. Make a table of important mineral elements in animals, their functions and deficiency symptoms.