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

Nutrition in mammals is the process by which mammals take in food and use it for energy, growth, repair and health.

Behavioural objectives

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

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

How are animals grouped by the food they eat?

Animals are grouped into three: carnivores, herbivores and omnivores.

• Heterotrophs: animals cannot make their own food, so they depend directly or indirectly on plants.
• Carnivores: feed on the flesh of other animals, e.g. lions.
• Herbivores: feed on plants, e.g. goats.
• Omnivores: feed on both plants and animals, e.g. man.

What are the stages of nutrition in mammals?

Mammals feed by holozoic nutrition, which is taking in solid food and digesting it inside the body.

1. Ingestion: food is taken into the mouth.
2. Digestion: complex food is broken down into simple, soluble forms.
3. Absorption: digested food passes into the blood.
4. Assimilation: body cells use the absorbed food for energy, growth and repair.
5. Egestion: undigested food is removed from the body as faeces.

What are the classes of food substances?

There are seven classes of food substances: carbohydrates, proteins, fats and oils, mineral salts, vitamins, water and roughages.

1. Carbohydrates: energy foods such as bread, yam and rice.
2. Proteins: body-building foods such as egg, meat, fish and beans.
3. Fats and oils: energy-rich foods such as palm oil and groundnut.
4. Mineral salts: inorganic substances needed in small amounts.
5. Vitamins: organic substances needed in small amounts.
6. Water: the medium in which body reactions take place.
7. Roughages: fibre that is not digested.

1. What are carbohydrates?

Carbohydrates are food substances made of carbon, hydrogen and oxygen, got from foods such as bread, yam and rice.

There are three types of carbohydrate: monosaccharides, disaccharides and polysaccharides.

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

Digestion and storage of carbohydrates

• Ptyalin: the enzyme in saliva that changes starch to maltose.
• Maltase: changes maltose to glucose, so starch finally yields glucose.
• Lactase: acts on lactose (milk sugar).
• Glycogen: excess carbohydrate is stored as glycogen in the muscles and liver.
• Starvation: glycogen is changed back to glucose.

Importance of carbohydrates

• It gives animals energy.
• It provides the heat needed to maintain body temperature.
• It forms part of mucus, which lubricates body surfaces.
• It provides a strong framework, e.g. the exoskeleton in insects.

2. What are proteins?

Proteins are complex molecules made up of smaller units called amino acids.

• Elements: carbon, hydrogen, oxygen, nitrogen and sometimes phosphorus and sulphur.
• Sources: egg, meat, fish and beans.
• Digestion: pepsin, rennin, trypsin and erepsin break proteins down into amino acids.

Importance of proteins

• Growth in young ones.
• Repair of worn-out tissues.
• Production of enzymes.
• Production of hormones.
• Support for reproduction.
• Tissue formation, i.e. body building.

3. What are fats and oils (lipids)?

Fats and oils are lipids made of carbon, hydrogen and a little oxygen.

• Fats: lipids that are solid at room temperature.
• Oils: lipids that are liquid at room temperature.
• Sources: palm oil, groundnut and soybeans.
• Digestion: lipase enzymes break lipids into fatty acids and glycerol.

Importance of fats and oils

• They give more energy than carbohydrates, gram for gram.
• They supply essential fatty acids to the body.
• They help to maintain body temperature.
• They provide the body with fat-soluble vitamins.

4. What are mineral salts?

Mineral salts are inorganic substances needed in very small quantities for health.

• Minerals: calcium, magnesium, potassium, phosphorus, sulphur, chlorine, iron, iodine, fluorine, manganese, copper, cobalt and sodium.
• Sodium chloride: table salt, added directly to food.
• Iron: can also be taken as tablets.
• Lack of minerals: causes nutritional deficiency.

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.

Some mineral salts: sources, functions and deficiency

5. What are vitamins?

Vitamins are organic food substances needed by man and other animals in small quantities for normal growth and development.

There are two groups of vitamins: water-soluble and fat-soluble.

• Water-soluble vitamins: vitamin B complex and vitamin C.
• Vitamin B complex: includes vitamins B1, B2, B3, B5, B6 and B12.
• Fat-soluble vitamins: vitamins A, D, E and K.
• Lack of any vitamin: results in a deficiency disease.

Vitamins: sources and deficiency symptoms

6. What is the importance of water?

Water is a compound of hydrogen and oxygen that all living things need.

• Sources: food, rivers, streams and ponds.
• Body content: water makes up about 70% of the human body.

Importance of water

• It is needed for the metabolic activities of the body.
• It is needed for the digestion of food.
• It helps to maintain body temperature.
• It is the medium of transport for all nutrients.
• It helps to maintain osmotic balance in body tissues.
• It helps to remove metabolic waste from the body, e.g. in urine.

7. What are roughages?

Roughages are indigestible fibrous materials, mainly cellulose, from plant foods such as vegetables, fruits and whole grains.

• Bulk: they add bulk to food in the gut.
• Movement of food: they help food to move along the gut.
• Constipation: a lack of roughage can lead to constipation.

What is a balanced diet?

A balanced diet is a diet containing the correct proportion of all the food substances.

• Carbohydrate: 60%.
• Protein: 15%.
• Fat and oil: 15%.
• Vitamins, minerals and water: 10%.
• Result: normal growth and development when food is taken in these proportions.

What are the 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 for all biological activities.
4. It prevents malnutrition and deficiency symptoms.

What is kwashiorkor?

Kwashiorkor is a nutritional disease of children caused by a diet that lacks protein.

• Retarded growth: the child grows slowly.
• Loss of weight: the child becomes underweight.
• Oedema: the legs and feet swell with fluid.
• Swollen belly: the abdomen is swollen while the arms and legs are thin.

What are digestive enzymes?

Enzymes are protein catalysts produced by living cells that speed up chemical reactions.

• Digestive enzymes: break down complex food substances into simple, soluble and diffusible forms.

What are the characteristics of enzymes?

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

What are the classes of digestive enzymes?

There are three classes of digestive enzymes: proteases, carbohydrases and lipases.

• Proteases: act on proteins to give amino acids, e.g. pepsin, rennin, trypsin and erepsin.
• Carbohydrases: act on carbohydrates to give simple sugars, e.g. ptyalin (salivary amylase), maltase, sucrase and lactase.
• Lipases: act on lipids (fats and oils) to give fatty acids and glycerol.

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

Answer the five objective questions below.

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