Introduction Animals get their food from plants or other animals. They exhibit a heterotrophic mode of nutrition. In this chapter, we will learn about animal nutrition which include food nutrients. The competences developed will enable you to maintain good eating habits so as to enhance general body health and well-being. This tendency will enable you to avoid the risks of getting nutritional diseases and disorders, as well as other nutritional problems.

Think The life of animals without nutrients.

Concept of nutrition in animals

Task 1.1

Search for information from the library and internet sources on the concept of nutrition in animals. Write short notes on searched information.

Nutrition refers to the study of the relationship between diet, health, and diseases. There are two major types of nutrition based on how organisms obtain their food. These are autotrophic and heterotrophic nutrition Animal nutrition involves nutrient requirement, mode of taking food and its utilisation in the animal body. Animal nutrition also focuses on the dietary nutrient needs of animals. Animals are heterotrophs since they depend on other organisms for their nutritional needs.

Heterotrophic nutrition

Heterotrophs are organisms that cannot make their own food but rely on consuming other organism or organic matter for energy and nutrients. The term ‘hetero’ means different and ‘trophy’ means feeding. Therefore, ‘heterotrophy’ means ‘different feeding’. Heterotrophs feed on either different food substances manufactured by other organisms or feed on other organisms directly. Examples of heterotrophs include all animals, fungi, most bacteria, and protoctists. The mode of feeding in which an organism is unable to make its own food but depends on food already made by other organisms is called heterotrophic nutrition. There are various types of heterotrophic nutrition, including holozoic, saprophytic, and symbiotic nutrition.

Holozoic nutrition

This mode of nutrition involves taking in complex food substances, digesting, absorbing, and assimilating the nutrients into the organism’s body. The undigested and indigestible food remains are finally egested as faeces. This type of nutrition is found in most animals. Holozoic nutrition is divided into three modes of feeding: carnivorous, herbivorous and omnivorous.

Carnivorous: This is a mode of feeding in which an animal feeds on other animals. Examples of animals that practise this type of feeding are driver ants, ground beetles, lions, tigers, and leopards. These animals are called carnivores because they eat other animals, usually of different species. In this kind of feeding relationship, animals that hunt other animals are called predators, while those that are hunted are called preys.

Herbivorous: This is a mode of feeding in which an organism feeds on plants. Animals that undergo this type of feeding are called herbivores because they eat plants or parts of plants. Examples of plant eaters or herbivores include grasshoppers, cattle, rabbits, goats, antelopes, and giraffes.

Omnivorous: This is a mode of feeding in which an organism feeds on both plant and animal food sources. They also feed on other organisms including fungi and algae. They are also known as opportunistic feeders because they feed on a variety of food sources. Examples of omnivorous animals include human beings, bears, chimpanzees, birds, pigs, turtles, lizards, and certain insects such as crickets, ants, and wasps.

Saprophytic nutrition

This is a mode of feeding in which an organism feeds on decaying organic matter. Such decaying matter may originate from plants, animals, and other decomposing materials. Organisms that obtain their food from dead and decaying organic matter are called saprophytes. In this mode of feeding, a saprophyte releases digestive enzymes externally on the substrate. The released enzymes convert complex organic molecules such as starch into simple molecules such as glucose. The glucose can be easily absorbed by body cells and used for various activities. Digestion, which takes place by the release of enzymes outside the cell, is also called extracellular digestion. An example of a saprophyte is a mushroom growing on a log. The mushroom releases enzymes externally through their root-like structures, called rhizoids. The enzymes cause decomposition and decay of the log from which the mushroom gets its nutrients. Another example of a saprophyte is bread mould that grows on the surface of decaying bread to obtain the nutrients, as shown in Figure 1.1.

Figure 1.1: Bread mould growing on decaying bread

Symbiotic nutrition

This is a feeding relationship or an association between two species in which one or both benefit. Symbiosis can be in the form of commensalism, mutualism, or parasitism.

Commensalism:

This is a feeding relationship or an association between individuals of two different species in which one species benefits, while the other is neither harmed nor benefited. In most cases, the host individual is larger than the commensal individual. Commensal organisms benefit in various ways such as in getting nutrients, shelter, support, or transport from the host. For example, small fishes like remora attach to the body of a large fish such as a shark. The shark enables remora to move in different areas without using its own energy, but the shark is not harmed, and it does not benefit from such a relationship. Other examples are epiphytes which are small plants that grow on different trees but do not harm the trees (Figure 1.2). The epiphytes get access to nutrients, exposure to sunlight, and support from the trees while the trees are neither harmed nor benefited by the relationship.

Figure 1.2: Host and epiphytic plants exhibiting commensalism

Mutualism: This is a symbiotic relationship between two species in which both species are mutually benefited. For example, bacteria living in the gut of a goat, sheep, or cow get their nutrients from the food digested by the animals. The bacteria in turn help the animals to digest cellulose, by releasing cellulase enzymes that digest cellulose.

Parasitism: This is a kind of feeding relationship between two species where one species benefits while the other is harmed. For example, the relationship between a tapeworm and human being. The tapeworm lives in the human gut and gets nutrients from the human body while the human being is harmed by getting sick. The organism that benefits is called a parasite while the one that is harmed is called a host. In the human-tapeworm relationship, the human being is a host and the tapeworm is a parasite.

In parasitic mode of nutrition, the parasites depend on nutrients that are found in the body of their hosts. There are two types of parasites, namely ectoparasites and endoparasites. Ectoparasites live outside the body of the host. Examples of ectoparasites include ticks, lice, fleas, and bedbugs. Endoparasites live and obtain their food inside the body of the host. Plasmodium sp., Ascaris sp., and tapeworms are examples of endoparasites.

The importance of nutrition

Nutrition is important in various ways. It encompasses the study of the relationship between diet, health, and diseases. People who study nutrition are called nutritionists or dieticians. They are professionals who advise people on how nutrition affects their health and well-being. Through nutrition, an organism can get the necessary nutrients for the body to get energy and support functioning of various life processes. Such life processes include growth and development of cells, tissues and organs, the repair of damaged parts, and movement. Other processes include ensuring protection against infections and diseases, maintaining body temperature, and reproduction. Through nutrition the body can also synthesise important chemical substances, such as enzymes and hormones.

Moreover, maintaining good nutrition helps to promote general body health so as to reduce the risk of getting chronic diseases such as heart attack, diabetes, stroke, blood pressure, osteoporosis, and certain types of cancer.

Exercise 1.1

1. Using relevant examples, briefly explain the following types of heterotrophic nutrition:

1. holozoic nutrition;
2. saprophytic nutrition; and
3. symbiotic nutrition.

2. Why are omnivores regarded as opportunistic feeders?

3. What is the role of enzymes in the saprophytic mode of feeding?

4. Why are large trees in the forest not harmed by the epiphytes that grow on their bodies?

5. Explain the meaning of the following:

1. commensalism;
2. parasitism; and
3. mutualism.

6. How would you apply the concept of nutrition to improve your diet?

7. What would happen to heterotrophs if there were no autotrophs?

8. Why is proper nutrition essential for maintaining health?

9. Why are human beings, pigs, and bears regarded as omnivorous animals?

Nutrients

Task 1.2 Search for information from the library and internet sources on the concept of nutrients. Summarise important points from what you have researched.

Nutrients are chemical components of foods, which are essential to life and health. They are important for promoting growth and development, as well as regulating chemical processes in the body. Nutrients are obtained from various foods such as cassava, meat, bananas and vegetables.

There are five major types of nutrients, which are carbohydrates, proteins, lipids (fats and oils), vitamins, and minerals. Water and roughage are also important. Nutrients can be divided into two categories depending on the quantity needed by the body. These groups are macronutrients and micronutrients. Macronutrients refer to nutrients that are needed by the body in large amounts. They include proteins, carbohydrates, and lipids. These nutrients contain kilocalories (kcal) which can be burned by the body to produce energy needed for various body functions. A calorie is a unit of measurement of food energy. Micronutrients are those needed by the body in small amounts but are essential for carrying out body functions. They usually assist in many aspects of body functions such as producing energy, digesting food substances, and making macromolecules. Examples of micronutrients are vitamins and minerals. Unlike macronutrients, micronutrients do not contain calories.

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

Materials A variety of food items

Procedure

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 different categories based on the type of nutrients they contain.

Question

How many food items did you manage to classify?

Proteins

Proteins are organic compounds made up of one or more chains of amino acids. Amino acids are made of elements that contain carbon, hydrogen, oxygen, nitrogen and sulphur. There are two groups of amino acids, essential amino acids and non-essential amino acids. The essential amino acids are obtained from foods eaten, while non-essential amino acids can be made by the body. However, the body cannot produce essential amino acids. Foods like beef, chicken, fish, termites, eggs, beans, lentils, peas, groundnuts, mushrooms, and milk and its products like cheese are rich in proteins hence provide essential amino acids. Figure 1.3 shows examples of foods that are sources of proteins.

Figure 1.3: Sources of protein

Functions of proteins

Proteins have several functions in the human body including building body cells, promoting growth, and making hormones. Proteins also help to repair damaged tissues such as replacing damaged or lost cells in wounds, skin, and mucous membranes. Since proteins are major components of all cell membranes, they play a role in the transport of other molecules across the cell membranes. They form part of the cell structure, and aid in the contraction of muscles. They are sometimes used as a source of energy, especially when the body lacks carbohydrates and lipids. Each gram of protein provides four kilocalories (kcal) of energy. However, proteins are not the major source of energy in the body. Their primary function is to promote growth and repair worn out body tissues. Proteins are essential for growing children, pregnant women, and people recovering from illnesses.

When proteins are consumed, they are broken down into amino acids that are absorbed into the bloodstream and used by the body to produce its own proteins. For example, the haemoglobin found in the red blood cells is one of the body proteins. Haemoglobin enables red blood cells to transport oxygen in our bodies. Other examples of body proteins include antibodies which provide body immunity and enzymes which are involved in food digestion. In addition, many hormones are protein in nature. They control various processes in the body.

Lipids

They are organic compounds made of carbon, hydrogen, and oxygen. They are insoluble in water but soluble in organic solvents such as ether and benzene. The main forms of dietary lipids are fats and oils. Fats are solid at room temperature while oils are liquid at room temperature. Lipids are made up of fatty acids and glycerol. Fatty acids can be essential or non-essential. Essential fatty acids are obtained from foods eaten while non-essential fatty acids can be made by the body. The body cannot produce essential fatty acids. It is, therefore, important to eat foods that contain essential fatty acids. Examples of such foods are oily fish, nuts, avocados, oil, and seeds such as sunflower and sesame, as shown in Figure 1.4.

Figure 1.4: Sources of lipids

Functions of lipids

Lipids are a source of energy. They provide more energy than all other food substances. Each gram of lipid provides nine kilocalories (kcal) of energy. They are important components of cell membranes. Fat deposits surround and protect body organs such as the heart and kidneys. Stores of fat in the adipose tissue under the skin help to regulate body temperature by insulating the body against loss of heat. Fat-soluble vitamins are also stored in fatty tissues. Essential fatty acids are important for the formation of substances that help to control blood pressure and activate the body’s immune response.

Carbohydrates

Carbohydrates are organic compounds made up of small repeating units called monosaccharides. The small repeating units form bond with each other to make a larger molecule. Monosaccharides are mainly made up of carbon, hydrogen, and oxygen. Carbohydrates are sugar molecules found in certain foods and drinks. Sources of carbohydrates include maize, sweet potatoes, sugarcane, bananas, cassava, fruits, and yams, as shown in Figure 1.5.

Figure 1.5: Sources of carbohydrates

Functions of carbohydrates

Carbohydrates are a major source of energy in the body. In an ideal situation, we should get two-thirds of our energy from carbohydrates. They are broken down into glucose which acts as fuel for the body. Each gram of carbohydrate produces four kilocalories (kcal) of energy in the body to be used by the cells to perform work. Carbohydrates are also essential for the proper functioning of the nervous system, heart, and kidneys. In addition, carbohydrates form genetic materials, which are DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid) in the cells.

Excess carbohydrates in the body are converted into either glycogen or fats in the liver. The glycogen is stored in the liver and muscles, while fats are stored as fat deposits in the lower abdomen, around kidneys, and under the skin. Glycogen acts as a source of energy when there is short supply of carbohydrates in the body. In the muscles and liver, glycogen is broken down to glucose for provision of energy when required, for example, during a vigorous physical activity. Also, carbohydrates combine with proteins and lipids to form glycoproteins and glycolipids, respectively, which are important components of cell membranes.

Vitamins

Vitamins are complex organic micronutrients that are essential for body growth and survival. Animals need vitamins for proper body functioning and metabolism. Vitamins can be grouped into two categories, which are water-soluble and fat-soluble vitamins.

Fat-soluble vitamins can be stored in the body. Vitamins A, D, E and K are examples of fat-soluble vitamins.

Water-soluble vitamins are not stored in the body. Vitamins B and C are water-soluble. Vitamin B is of various forms namely, vitamin B₁, B₂, B₆, B₁₂, and B₁₂.These can be easily destroyed by heat.

Vitamins are formed by the combination of glucose and some mineral elements. Most of the vitamins are synthesised by autotrophs, particulary green plants. Mammals can synthesise vitamins A and D using plant molecules obtained in their food. Examples of foods containing vitamins are fruits and vegetables, as shown in Figure 1.6.

Figure 1.6: Sources of vitamins

Functions of vitamins

Vitamins play an important role in the metabolic activities of both plants and animals, such as promoting functions of immune enzymes and nervous systems. They are also important in the formation of bone tissue and red blood cells. Deficiency or excess intake of vitamins can cause health problems. Table 1.1 shows examples of vitamins, their sources, functions, and deficiency symptoms.

Table 1.1: Sources, functions, and deficiency symptoms of vitamins

Vitamin	Sources	Functions	Deficiency symptoms
Vitamin A (Retinol)	Liver, milk, eggs, oranges, and yellow vegetables such as carrots and pumpkins	Formation of membranes of the eyes, and the respiratory tract	(i) Night blindness (ii) Increased risk of infections
Vitamin B1(Thiamine)	Lean meat, liver, eggs, mushroom, brown rice, and whole grain cereals	(i) Assists in carbohydrate metabolism (ii) Helps in muscle coordination	Beriberi, a disease characterised by a loss of appetite, muscle cramps, nerve disorder, and heart failure
Vitamin B2(Riboflavin)	Liver, meat, mushroom, and whole grain cereals	Metabolism of all foods, and the release of energy to cells	(i) Cracks and sores around the mouth and nose (ii) Visual problems

Vitamin	Sources	Functions	Deficiency symptoms
Vitamin B3 (Niacin)	Nuts, fish, meat, mushroom, brown rice, and whole grain cereals	Needed by many enzymes that convert food to energy	Pellagra, a disease characterised by skin lesions, loss of appetite, diarrhoea, and muscle weakness
Vitamin B6(Pyridoxine)	Meat, vegetables, mushroom, and whole grain cereals	Protein metabolism	(i) Nerve irritability (ii) Sores in the mouth and eyes (iii) Anaemia
Vitamin B9 (Folic acid)	Liver, fish, green leafy vegetables, legumes, and folate fortified foods	(i) Synthesis of new cells (ii) Metabolism of carbohydrates	(i) Birth defects (ii) Anaemia (iii) Frequent infections
Vitamin B12 (Cyanocobalamin)	Fish, meat, eggs, milk, and liver	(i) Helps in making genetic material (ii) Helps to form red blood cells	(i) Anaemia (ii) Nerve damage (iii) Weight loss
Vitamin C (Ascorbic acid)	Tomatoes, fresh green vegetables, and citrus fruits such as oranges and lemons	(i) Used as Antioxidant (ii) Improves absorption of iron (iii) Used in synthesis of collagen in the bones and gums	(i) Muscle weakness (ii) Easy bruising (iii) Joint pains (iv) Scurvy (bleeding gums) (v) Poor healing of wounds (vi) Frequent infections
Vitamin D (Calciferol)	Egg yolk, milk, oily fish, sunlight, and liver	Helps to build and maintain teeth and bones	(i) Rickets in children (ii) Osteoporosis (soft bones) in adults
Vitamin E (Tocopherol)	Corn or sunflower oil, butter, brown rice, and peanuts	(i) Used as Antioxidant (ii) Prevents damage of cell membranes	(i) Nerve abnormalities (ii) Infertility
Vitamin K	Green vegetables, and liver	Needed for normal blood clotting	Defective blood coagulation resulting in excessive bleeding in case of injury

Minerals

Minerals are inorganic elements that come from the soil and water and are absorbed and used by living organisms. In animal nutrition, minerals fulfill multiple functions in the physiology of all systems. Different types of minerals are needed for different activities in the body. These minerals are called essential minerals. Examples of essential minerals needed by the body include sodium, chlorine, potassium, calcium, phosphorus, magnesium, sulphur, zinc, iodine, copper, manganese and fluoride.

Function of minerals

Most minerals are important for enzyme activities. Some minerals are essential for maintaining balance of body fluids, development of bone tissue, synthesis of hormones, activation of enzymes, transmission of nerve impulses, as well as contraction and relaxation of muscles. Table 1.2 shows examples of minerals, their sources, functions, and deficiency symptoms in the body.

Table 1.2: Examples of minerals, their sources, functions and deficiency symptoms

Mineral	Sources	Functions	Deficiency symptoms
Calcium	Milk, yoghurt, cheese, sardines, eggs, and green vegetables	(i) Helps build strong bones and teeth (ii) Promotes nerve transmission (iii) Helps in muscle contraction (iv) Important in clotting blood	(i) Weak bones and bleeding easily (ii) Impaired nerve activity
Phosphorus	Meat, milk, fish, eggs, and nuts	(i) Builds bones and teeth (ii) Helps maintain acid-base balance (iii) Aids formation of genetic materials	Poor bone and teeth formation
Potassium	Peanuts, bananas, orange juice, meat, and green beans	Helps maintain regular fluid balance needed for nerve and muscle function	(i) Poor muscle contraction (ii) Impaired nerve activity

Mineral	Sources	Functions	Deficiency symptoms
Sodium	Table salt, soy sauce, milk, bread, vegetables, and processed foods	(i) Necessary for nerve transmission (ii) Needed for muscle contraction (iii) Necessary for protein making (iv) Needed for proper fluid balance	(i) Muscle cramps (ii) Poor nerve transmission
Chloride	Table salt, eggs, milk, meat, sea foods, and whole grain foods	Maintenance of water and ionic balance in the body and formation of hydrochloric acid in the stomach	Poor digestion of proteins
Magnesium	Spinach, pumpkin seeds, sesame seeds, beans, nuts, sea foods, and magnesium	(i) Maintaining a healthy immune system (ii) Making proteins (iii) Contraction of muscles (iv) Transmission of nerve impulses (v) Strengthening of bones	(i) Muscle weakness (ii) Irregular heartbeat (iii) Weak bones
Iodine	Sea foods, dairy products, and iodized table salt	Production of thyroid hormone which regulate growth, development, and metabolism	(i) Goitre (enlarged thyroid gland) (ii) Growth retardation (iii) Mental retardation (iv) Still birth
Fluoride	Fish, fluorinated water or water naturally containing fluorine, and most varieties of tea such as green tea	(i) Development of teeth and bones (ii) Helps to prevent tooth decay	(i) Poor development of bones and teeth (ii) Tooth decay
Manganese	Found in most plant foods, kidneys, liver, tea, coffee, nuts, and fruits	(i) Helps in the formation of bones (ii) Activation of enzymes (Coenzyme)	(i) Nausea (ii) Dizziness (iii) Loss of hearing (iv) Loss of bone mass
Copper	Whole grains, meat, drinking water, fish, liver, legumes, nuts, and other seeds	(i) Synthesis of bones and haemoglobin (ii) Activation of enzymes (Coenzyme)	(i) Bleeding under the skin (ii) Easy rupturing of blood vessels (iii) Bones and joints problems (iv) Anaemia
Iron	Liver, lean meat, fish, chicken, egg yolk, legumes, kidney, beans, and green vegetables	(i) Essential for making red pigment in blood (haemoglobin) (ii) Essential for energy production	Anaemia
Zinc	Oysters, shrimp, crab, meat, fish, chicken, whole grains, and vegetables	(i) Necessary for a healthy immune system (ii) Controls normal growth and sexual maturation (iii) Activation of enzymes (iv) Helps in wound healing (v) Helps in taste detection (vi) Promotes protein synthesis and DNA production	(i) Impaired taste (ii) Poor immune response (iii) Skin problems

Roughage

This is dietary fibre that is obtained from the indigestible part of plants (Figure 1.7). Roughage does not have any nutritional value as it is not digested and absorbed in the body. Sources of dietary fibre include cassavas, potatoes, beans, fruits, cabbage, spinach, whole grain cereals.

Functions of roughage

Roughage helps in the passage of food and faeces through the gut by aiding contraction and relaxation of the gut muscles (peristaltic movement). It also helps to control body weight, thus protects the body from diseases such as heart diseases.

Figure 1.7: Sources of roughage

Water

Water is an essential nutrient for the human body as it is a major constituent of body fluids such as blood, tears, and saliva. It forms a large part of the cell cytoplasm and helps to maintain the shape of cells, tissues, and organs. Water helps in the process of breaking down food during digestion. It also lubricates moving parts of the body and prevents friction. Additionally, water helps in the regulation of body temperature. Sweating is one of the means by which water prevents the human body from overheating during hot weather. This is because evaporation of sweat from the surface of the skin helps the body to cool during hot conditions. It is important to drink enough safe water, and eat raw vegetables and fruits to maintain an optimal water content in the body. A lacking of adequate water in the body leads to thirst, dehydration and constipation. Losing more than 10% of water in the body can lead to death.

Balanced diet

Task 1.3

Search for information from the library and internet sources on concept of a balanced diet. Then, summarise your findings.

A balanced diet refers to a meal containing foods from all food groups in the right proportions. A proper diet helps an individual to remain healthy. For young individuals, a balanced diet helps them to grow and develop normally. It also helps them to maintain an ideal body weight. Moreover, it minimises the risk of contracting long lasting diseases like cancer, diabetes, obesity, high blood pressure and others.

Components of a balanced diet include:

1. Carbohydrates (about 60% of daily diet);
2. Proteins (10-35% according to the physiological needs);
3. Fats (about 15% of daily caloric needs);
4. Vitamins and minerals; and
5. Water

Factors for a lack of a balanced diet

A lack of balanced diet comes from various factors, including the following:

(i) Limited access to nutritious food: People living in food desert or areas with inadequate availability of fresh produce may struggle to get a balanced diet

(ii) Economic constraints: Financial limitations can hinder the ability to purchase a variety of healthy foods, leading to an imbalanced diet

(iii) Poor dietary choices: High consumption of highly processed food and convenience foods often result in a diet that is low in essential nutrients

(iv) Lack of knowledge: Insufficient understanding of dietary guidelines can lead to unbalanced food choices. Misinformation about healthy eating can also contribute to poor dietary choices.

(v) Cultural and social influences: Dietary habits influenced by cultural preferences or social norms may not always include a variety of nutrient - dense foods

(vi) Time constraints: Busy lifestyles and competing responsibilities can limit the time available for meal planning and preparation, leading to reliance on less nutritious options

(vii) Health condition: Dietary restrictions due to health conditions or allergies can complicate maintaining a balanced diet if suitable alternatives are not included

(viii) Psychological factors: Emotional eating or eating disorders can disrupt balanced eating patterns and lead to unhealthy food choices.

• To promote a healthy lifestyle, it is important to take in diets containing low fats, sugars and salts but have moderate amounts of proteins, carbohydrates, vitamins, minerals and roughages. It is also important to drink adequate amounts of water and engage in regular physical exercises.

The following should be done to ensure a healthy lifestyle:

(i) Take recommended amounts of proteins, fats or oils, sugars, and salts;

(ii) Take recommended amounts of fruits and vegetables in the diet;

(iii) Eat a variety of foods, including whole grains, fruits, vegetables, and food with roughage to provide the body with the required energy and nutrients;

(iv) Maintain an appropriate body weight to height ratio within the limits recommended by the World Health Organisation (WHO);

(v) Do physical activities daily for 30 to 40 minutes;

(vi) Replace red meat with fish, poultry, or lean meat in your diet;

(vii) Take low fat dairy products and low salt foods;

(viii) Limit consumption of sugary drinks and all sweets; and

(ix) Avoid processed and baked foods, particularly those high in sugars, unhealthy fats and additives.

Nutritional requirements for different groups of people

Task 1.4

Search for information from the library and internet sources on diet requirements for different groups of people. Then, summarise your findings.

The ratio of nutrients needed by the body varies depending on the age, sex, health state, amount of activity, or general state of the body. Therefore, different groups of people such as pregnant women and lactating mothers, children, the elderly, and the sick have different nutritional needs.

Pregnant women and lactating mothers

Pregnant women and lactating mothers need to get enough nutrients in their meals. They should eat a balanced diet because they require enough nutrients for themselves and their developing foetus and babies, respectively. Food rich in protein is needed by pregnant women and lactating mothers to build the muscles, breasts, uterus, blood supply, and for proper functioning of tissues and organs of the foetus and baby.

Pregnant women are advised to eat food rich in folic acid. These help to lower the risk of birth defects such as spina bifida. Spina bifida is a spinal disorder characterised by a hole in the spine. It results from incomplete formation of the spinal cord and the bones of the spine. Often, the spine protrudes through the hole and sometimes a fluid-filled sac may surround the protruding spinal cord.

Calcium helps in the development of the foetus’ and baby’s bones. If the mother’s diet does not contain adequate calcium, this nutrient will be derived from her bones for the foetus or baby. This weakens the mother’s bones.

Zinc is important for the proper progression of labour during delivery. It is also important for proper growth and development of the baby.

The pregnant woman requires iron for her blood supply needs. The foetus also needs to store iron for use during the first few months after birth.

Pregnant women also require adequate amounts of dietary fibre to reduce the likelihood of constipation, which is a common complaint during pregnancy. Their meal should contain adequate vegetables, fruits, and fibre sources. Pregnant women and lactating mothers should also drink plenty of water. Water is a major constituent of breast milk. Some hormones produced during breastfeeding increase thirst. Pregnant women and lactating mothers should avoid alcohol consumption. Alcohol can easily pass from their bodies to the foetus and babies during pregnancy and breastfeeding, respectively, and affect their development.

Nutritional needs for a lactating mother increase during breastfeeding to satisfy the needs of her body and the baby.

Children

Growing children are still growing and they are generally most active. They require diets that provide them with adequate nutrients to ensure proper functioning of their bodies. They need enough proteins for growth and development of the body tissues. Inadequate supply of proteins can lead to stunted growth. Minerals like calcium are necessary for formation of strong bones and teeth. Zinc is important for body growth. It plays an important role in biological processes including cell growth, differentiation, and metabolism. Deficiency in zinc in early childhood can affect growth and decrease resistance to infections. Vitamin B12 is required for the formation of red blood cells since a growing body needs more oxygen and blood. Vitamin B12 is essential for brain development as well as nervous and cognitive functions. Inadequate vitamin B12 during pregnancy and early childhood causes improper cognitive development for children. Vitamin C helps children to build their immunity, and it functions as an antioxidant. An antioxidant is a substance that removes toxins from the body. Children also require enough carbohydrates and lipids because they are active.

The elderly

Elderly people require a balanced diet with adequate amounts of food rich in vitamins, minerals, and roughage to maintain their health. They also need food rich in minerals such as iron, zinc, and calcium. Iron is necessary because it helps to make red blood cells, which carry oxygen around the body. Zinc is required for a healthy immune system and for regulating the healing of wounds. Old age comes with the loss of calcium from bones, leading to soft and weak bones that can break easily. The elderly, therefore, require adequate amounts of calcium to strengthen their bones. They also need vitamin D to improve their mental health and overcome depression.

They often have problems of chewing tough foods because of weakened teeth. Likewise, due to decreased production of saliva, they normally have swallowing problems. It is thus important to ensure the elderly get foods that are nutritious and easy to chew and swallow. For example, they can get proteins from eggs or liver instead of meat.

Sedentary workers

These are individuals who stay in one place for a long time while performing their daily occupational activities. They include office secretaries, tailors, clerks, and receptionists. Sedentary workers are encouraged to balance their daily diets with physical exercise. Due to their lifestyle and occupation, obesity is increasingly becoming common among them. They are also at greater risk of developing non-communicable diseases such as diabetes and disorders of the muscles and skeleton. Therefore, it is recommended that they limit their intake of foods rich in carbohydrates and lipids.

The sick

Sick people require plenty of nutrients to help recover their health. Proper nutrition helps to keep their immune system strong and enables the body to fight against infections and diseases. It also helps the body to withstand strong medication. In addition, a proper diet and exercise help to combat symptoms such as fatigue, nausea, diarrhoea, and high blood sugar. Excess caffeine drinks, sugary foods, fried foods, spicy foods, and alcohol should be avoided because they are harmful to a body whose immune system is already weak. Sick people are supposed to increase the intake of fruits, vegetables, and water. Fruits provide vitamins that are required to fight diseases. Vegetables provide essential minerals for the proper functioning of many body systems. Water replaces the amount of water lost during sickness for example through diarrhoea or vomiting.

It is advisable to use the food guide pyramid in determining what to eat. The food guide pyramid is a chart showing the recommended amounts of variety of foods that dieticians consider as healthy for eating. Figure 1.8 shows an example of a food guide pyramid.

It is not a fixed rule of what to eat each day, but just a general guide that helps to choose the right healthy diet. It helps an individual to eat better every day. The base constitutes foods that are required in larger amounts while the apex constitutes foods that need to be taken in lesser amounts. The food guide pyramid is not universal for all groups of people, it depends on the needs and health status of a person. For example, a diabetic person should not consume a lot of carbohydrates as indicated in the pyramid. Similarly, the elderly require small amounts of carbohydrates but more proteins and vitamins.

Figure 1.8: Food guide pyramid

Activity 1.2: Plan a balanced diet

Materials

Various foods and charts showing different types of food

Procedure

1. Plan a menu consisting of balanced meals for a day considering each of the following special groups of people: pregnant women, lactating mothers, children, the elderly, sedentary workers, and sick people.
2. In your menu, state what your would serve each special group for breakfast, lunch and dinner.
3. Prepare a brief report.

Nutritional deficiencies

These deficiencies arise when the body does not have a sufficient supply of particular food nutrients. Examples of common nutritional deficiencies in humans include marasmus (acute malnutrition), kwashiorkor (acute malnutrition due to oedema), and rickets.

Marasmus

Marasmus is a form of malnutrition in children caused by a lack of adequate amounts of food nutrients (starvation).

Symptoms of marasmus: A child suffering from marasmus shows weight loss, slowed growth, decreased activity and lack of energy. He or she also has wrinkled skin and extreme hunger. The child also cries often.

Prevention of marasmus:

Marasmus is prevented by giving the child adequate amounts of food that contains all the nutrients in the right proportions.

Kwashiorkor

Kwashiorkor is caused by a deficiency of proteins. It affects children, mostly those who are breast-fed or during weaning.

Symptoms of kwashiorkor: The symptoms of kwashiorkor include extremely thin arms and legs, poor growth, swollen abdomen due to enlargement of the liver, and reddish or yellowish thin weak hair. Other symptoms are weakened immunity, diarrhoea, anaemia, dry skin that cracks easily, oedema due to accumulation of excess fluid in the body, and shortness of breath.

Prevention of kwashiorkor: Kwashiorkor can be prevented by providing a child with a diet that has adequate amounts of protein and other food nutrients.

Rickets

Rickets is a condition whereby the bones of a child soften, leading to fractures and deformity. A lack of vitamin D, phosphorus and calcium causes rickets.

Symptoms of rickets: A child suffering from rickets can be identified by observable skeletal deformities such as bow legs, knock knees, and odd-shaped skull, and a deformed spine. The child feels bone pain, experiences dental problems such as weakened or delayed formation of teeth, and develops weak muscles. The child’s bones can easily be fractured and shows slow growth. The child also gets muscle spasms and muscle cramps.

Prevention of rickets: Rickets can be prevented by increasing the amount of vitamin D, phosphorus and calcium in the diet. The condition can also be prevented by ensuring exposure to sufficient amounts of sunlight, and providing the child with enough milk, sardines, and green vegetables.

Nutritional deficiencies and disorders

Task 1.5

Search for information from the library and internet sources on nutritional deficiencies and disorders.

There are different types of nutritional deficiencies and disorders in human beings, which are generally called malnutrition. Malnutrition refers to lack of proper nutrition caused by imbalance of nutrients in the body. It is a result of not having enough nutrients or excess consumption of certain food nutrients.

Nutritional disorders

Nutritional disorders are conditions that occur when a person’s dietary intake does not contain the right amount of nutrients for healthy functioning of the body. They are caused by the imbalance of nutrients in the body due to not having enough nutrients or excess consumption of food. The common nutritional disorders include obesity, anorexia nervosa, and bulimia.

Obesity

Obesity is a nutritional disorder characterised by excess body fat leading to overweight. It mostly results from eating large quantities of high energy foods (carbohydrates and fats) and not exercising enough to sufficiently burn the excess calories produced in the body. A person’s sex, age and level of activity are among other factors that determine his or her ideal body fat. To maintain fertility, women need more body fat than men. Women also store more fat in their breasts, hips and thighs.

Body weight and health risks associated with it are expressed by the Body Mass Index (BMI). It gives the relationship between the estimated body fat and the risk of certain diseases or conditions. Based on height and weight ratio, people can check their Body Mass Index (BMI). The BMI is calculated by dividing a person’s weight in kilograms (kg) by his or her height squared in metres (m).

The World Health Organisation (WHO) recommends the normal level of BMI to be in the range of 18.5–25.4. BMI is calculated using the following formula:

BMI = Body mass/(Person’s height)²

Whereby:

BMI = Body Mass Index in kg/m²

Body mass = Person’s weight in kg

Person’s height = Person’s height in m

For example, if your height is 1.65 metres and your body mass is 60 kilograms, your BMI can be calculated as:

60/(1.65)² = 22.04 kg/m²

If an individual BMI falls in the range of 18.5–25.4, this is considered to be healthy. On the other hand, if the BMI is over 30, one may be at risk of diseases associated with obesity. The following table shows a general guide of how different values of BMI are used to define the condition of the body.

Table 1.3: The BMI guide for adults with 20 years and above

BMI (kg/m²)	Body condition
Below 18.5	Underweight
18.5 to 25.4	Normal weight
25.5 to 29.4	Overweight or pre-obese
29.5 to 34.9	Class 1 obesity
35.0 to 39.9	Class 2 obesity
40 and above	Class 3 obesity (extreme or severe obesity)

Sometimes children may suffer from obesity (childhood obesity) when their body weight is very high in relation to their age and height. The child becomes highly obese due to excessive accumulation of fat in the body.

Causes of obesity

The causes of obesity include overeating, inactivity, eating high amounts of energy foods especially fats and sugars, frequent eating, and genetic makeup. Some people have genes that affect how foods are processed in the body.

Effects of obesity

Obesity is accompanied by several health problems, including shortness of breath and snoring. It also increases the likelihood of conditions such as high blood pressure, heart disease, stroke, diabetes, certain types of cancers, arthritis, and respiratory problems.

Prevention of obesity

Obesity can be prevented by eating properly and engaging in regular exercise. The intake of calories should balance one’s physical activity. It is also important to avoid eating too much fatty foods such as butter, fatty meat, chips, margarine, sausages and sugary foods such as sweets, cakes and chocolates. Eating too much of these foods contributes to obesity.

Anorexia nervosa and Bulimia nervosa

Anorexia nervosa is also called slimming disease or a self-starvation syndrome. It is a nutritional disorder that occurs when a person intentionally refuses to eat enough food, leading to a severe loss of body mass.

The symptoms of Anorexia are:

1. Muscle wasting (including weakening of heart muscle);
2. Excessive loss of body mass;
3. Extreme fear of being fat; and
4. Distorted body image or feeling fat even when one is very thin.

Bulimia nervosa is a nutritional disorder which involves excessive eating followed by an attempt to remove the food from the body. This attempt could involve self-induced vomiting, fasting, excessive exercising or taking drugs that stimulate emptying of the bowels or excessive urination. Bulimics usually have a normal body mass and keep their eating behaviour secret. Hence, it may be difficult to tell that they have it.

Causes of Anorexia nervosa and Bulimia nervosa

Both Bulimia and Anorexia have underlying psychological causes, such as depression, low self-esteem on body image, bottled-up emotions and the need to fit contemporary standards of beauty. Bulimia and Anorexia mostly affect women.

Effects of Anorexia nervosa and Bulimia nervosa

The effects of Anorexia and Bulimia are demonstrated by heart problems due to weak cardiac muscles or an imbalance of mineral salts. They contribute to an impaired mental function because the brain lacks adequate amounts of glucose. Victims also exhibit dehydration. During vomiting, acids present in the stomach come into contact with the teeth and gums. This eventually causes serious damage to the gums and erosion of the teeth. Other effects include anaemia, stomach ulcers, abdominal cramping and inflammation of the gut, irregular or absent menstrual periods and dry skin.

Prevention of Anorexia nervosa and Bulimia nervosa

Anorexia and Bulimia can be prevented by resolving the underlying psychological problems and seeking a medical practitioner who can prescribe a way of getting back to one’s health. They can also be prevented by adhering to the necessary lifestyle and dietary changes.

Activity 1.3: Investigate nutritional deficiencies and disorders

Materials

Notebook, pen and charts showing various nutritional deficiencies and disorders

Procedure

1. Visit a nearby health centre.
2. Ask a health personnel or a dietician about the nutritional deficiencies and disorders that are common in your area.
3. Discuss with the health personnel on the reasons for their prevalence and how they can be prevented.
4. Write short notes on what you have discussed.

Properties of food nutrients

Food nutrients have various properties that help to distinguish them. Such properties can be determined using various laboratory reagents and chemicals such as iodine solution, Benedict’s solution, Sudan III reagent, copper (II) sulphate solution, hydrochloric acid, and sodium hydroxide. Experiments conducted to identify properties of food nutrients are known as food tests.

Food tests

Food tests are used to determine which nutrients are present in a food substance. At this level, you will learn how to test for carbohydrates, proteins and lipids.

When doing a food test, consider the following: the food to be tested, required materials, procedure, observation, and conclusion. For the report to be simple and easy to understand, use a table with four columns. It consists of the following headings: Food sample tested, Procedure, Observation and Inference, as Table 1.4 shows.

Table 1.4: Food testing summary

Food sample tested	Procedure	Observation	Inference

Food sample tested: The food tested can be reducing sugar, non-reducing sugar, starch, lipids or protein. Most substances are mixed with water to make a solution or a mixture before testing. They can also be boiled or heated before testing to make them mix thoroughly with reagents used. The solution or mixture, which is made from food substance, is kept in a container and is referred to as a stock. A small portion of solution or mixture, which is taken from the stock solution for experiment is termed as a food sample.

Procedure: This involves the steps to be followed when carrying out the test for a particular food substance. Steps differ when testing for one food type from another. Failure to follow these steps often results in the wrong conclusion. Therefore, in each step, the procedures to be followed should be stated clearly. The amount of food sample which has been taken from the stock solution in a certain procedure should be stated together with its unit of measurement. The apparatus used should also be stated clearly.

Observation: This refers to the process of carefully watching, monitoring or examining a series of changes that occur when carrying out an experiment. Different changes are experienced as a person attempts one stage after another. These changes can involve colour, smell, sound or heat changes. The changes differ from one experiment to another. During observation, it is important to make sure the colour of the reagent is known to be clear about the new changes.

Inference: It refers to a conclusion that is made following the observation. The conclusion tells whether the type of food tested is present or absent.

Test for carbohydrates

There are three types of carbohydrates, which are monosaccharides, disaccharides and polysaccharides.

Monosaccharides

These are also known as simple sugars (single sugar). They include glucose, fructose (fruit sugar) and galactose (milk sugar). These sugars dissolve in water to form sweet solutions. All monosaccharides can reduce copper (II) in Benedict’s solution from copper (II) (Cu²⁺) which is blue to copper (I) (Cu⁺) which is orange or brick red. Hence, they are named as reducing sugars. During the reduction process, the colour of Benedict’s solution changes from blue, to green, to yellow, and finally to orange or brick red, depending on the concentration of the reducing sugar. If it is high, the colour change can reach to brick red, but if it is low it can end up to the intermediate colours that have been mentioned. Some examples of food sources containing reducing sugars are onions and carrots.

The general formula for monosaccharide is (CH₂O)ₙ, where n represents the number of carbon (C) atoms, and has a value of between 3 and 6. For example, the formula for glucose is C₆H₁₂O₆.

Activity 1.4: Test for the presence of reducing sugars in an onion

Materials

Benedict’s solution, an onion bulb, a knife, mortar and pestle, measuring cylinder (10 ml), test tubes, test tube holder, heat source, water, filter funnel, dropper, test tube brushes and beakers

Procedure

1. Peel an onion and cut it into small pieces using a knife.
2. Grind the pieces of onion using a mortar and pestle. Then, add water to make a mixture.
3. Decant and filter the mixture into a beaker to remove solid particles to get a solution.
4. Put 2 ml of the solution into a clean and dry test tube.
5. Add 2 ml of Benedict’s solution into the test tube.
6. Gently heat the mixture for 2–3 minutes. Observe colour changes while heating.
7. Record the series of colour change occurring.

Safety precautions

Make sure the knife is sharp. Burners should be placed on the bench. Never hold them. Use a test tube holder to hold the test tube. Heat the test tube at the top of the solution, not at the bottom where gas bubbles can cause an explosion.

8. Tabulate your results showing food sample tested, procedures, observation and inference

Food sample tested	Procedures	Observation	Inference

Questions

1. What was the series of colour change observed?
2. What was the final colour?

Disaccharides

These are also known as double sugars. They are formed through condensation when two monosaccharide molecules combine. For example, a glucose molecule and a fructose molecule combine to form sucrose, the sugar found in sugarcane. The general formula for this reaction is:

monosaccharide + monosaccharide → disaccharide + water

For example:

C₆H₁₂O₆ + C₆H₁₂O₆ → C₁₂H₂₂O₁₁ + H₂O

glucose + fructose → sucrose + water

Two glucose molecules combine to form maltose. Maltose is found in germinating seeds. A glucose molecule and a galactose molecule also combine to form lactose, a type of sugar found in milk.

Disaccharides dissolve in water and form sweet solutions. Some disaccharides, for example maltose and lactose can reduce copper (II) ions (Cu²⁺) to copper (I) ions (Cu⁺) like monosaccharides. These are also called reducing sugars. Other disaccharides such as sucrose cannot reduce copper (II) ions to copper (I) ions. These are called non-reducing sugars.

Therefore, non-reducing sugars cannot be tested directly by Benedict’s solution. Instead, it is first converted to reducing sugar by using hydrochloric acid (HCl) in the process called hydrolysis, as shown:

C₁₂H₂₂O₁₁ + H₂O —HCl→ C₆H₁₂O₆ + C₆H₁₂O₆

Sucrose + Water → Glucose + Fructose

The acidic mixture is heated and then left to cool. It is then neutralised by using sodium hydroxide (NaOH) or sodium bicarbonate (NaHCO₃) for the Benedict’s solution to work properly. Thereafter, steps for testing reducing sugars is carried out.

Activity 1.5: Test for non-reducing sugars in sugarcane

Materials

Benedict’s solution, hydrochloric acid, sodium hydroxide solution or sodium bicarbonate solution, a piece of sugarcane, a knife, mortar and pestle, test tubes, test tube holder, heat source, water, filter funnel, dropper, measuring cylinder (10 ml), beakers, and test tube brushes

Procedure

1. Peel the piece of sugarcane and cut it into smaller pieces using a knife.
2. Grind the pieces of sugarcane using a mortar and pestle and add a small amount of water to make a mixture.
3. Decant and filter the mixture to obtain a solution.
4. Pour 2 ml of a sample solution into a clean and dry test tube.
5. Add 1 ml of dilute hydrochloric acid.

Safety precautions

Avoid flammable substances near the heating source. Burners should be placed on the bench, never held in the hands. Use a test tube holder to hold the test tube. Heat the test tube at the top of the solution, not at the bottom where gas bubbles can cause an explosion. Ensure good ventilation for heating safely.

6. Gently heat the mixture for 2–3 minutes.
7. Cool the mixture. Then add 2 ml of sodium bicarbonate solution or sodium hydroxide solution.
8. Add 2 ml of Benedict’s solution to the cooled mixture and heat gently.
9. Record the series of colour change occurring.

Questions

1. What colour changes did you observe?
2. What effect did hydrochloric acid have on sucrose?
3. Why was the sodium hydroxide solution or sodium bicarbonate solution added to the mixture?

Polysaccharides

Polysaccharides are formed by condensation of several monosaccharides. They are commonly used as a storage form of food. Examples of polysaccharides include starch, which is a plant storage compound; glycogen, which is an animal storage compound; cellulose which is a structural material in plant cell walls; and chitin, which is a component of the exoskeleton of arthropods and cell walls of fungi.

Starch: This is a carbohydrate made by the condensation of many glucose molecules. Starch occurs naturally in plant cells as small particles called granules. It is found in abundance in plants. Common starch-containing foods include potato, cassava, maize, rice, and wheat.

Properties of starch

Starch and other polysaccharides have the following properties:

1. they are tasteless, that is, they are not sweet;
2. they are insoluble in water. (When put in water they form a suspension);
3. they coagulate when boiled in water; and
4. when mixed with iodine solution starch changes colour to blue black.

Activity 1.6 (a): Test for the presence of starch in an Irish potato

Materials

Iodine solution, Irish potato, a knife, mortar and pestle, test tubes, test tube holder, heat source, water, sieve, dropper, and a beaker

Procedure

1. Peel the Irish potato and cut it into small pieces using a knife.

Safety precautions

Do not taste any food in the laboratory. Handle all chemicals with care.

2. Grind the pieces of potato and add water to make a mixture.
3. Decant and filter the mixture to make a solution.
4. Put 2 ml of the solution into the test tube.
5. Add 2–3 drops of iodine solution and shake thoroughly.

Question

What is your observation?

Activity 1.6 (b): Investigate the solubility of starch in water

Materials

Maize or wheat flour, heat source, water, stirring rod, measuring cylinder (10 ml), and a beaker

Procedure

1. Take two full spatula of wheat flour and put them in a 100 ml beaker.
2. Add 50 ml of water and stir well to get a uniform mixture.
3. Leave it to settle for 3–4 minutes.
4. Observe and record the findings.

Safety precautions

Ensure proper ventilation for heating safely. Avoid flammable substances near the heating source. Place your burner on the bench, never hold it in the hands.

5. Take the mixture and boil it for 3–4 minutes.
6. Observe and record the findings.

Questions

1. What happened when the unboiled mixture of flour and water was left to settle?
2. Was there any difference when the unboiled mixture was allowed to settle and when it was boiled?

Test for lipids

Lipids are organic food substances consisting of carbon, hydrogen and oxygen just like carbohydrates. A lipid is composed of a glycerol molecule and fatty acids joined through condensation. Unlike carbohydrates, lipids have much less oxygen compared to carbon and hydrogen. For example, the formula of beef fat is C₅₇H₁₁₀O₆. Lipids occur naturally in the protoplasm of all living cells and in adipose tissues of animals. An adipose tissue is a fatty tissue under the skin containing large deposits of lipids.

Lipids can be either solid or liquid at room temperature. Some lipids remain in liquid form at 20°C while others solidify at this temperature. Solid lipids are called fats, and liquid lipids are called oils. Some plant oils and animal oils can be solid or a light at room temperature. Fats and oils are found in various foodstuffs like groundnut, coconut, sunflower, margarine, and butter. Various types of oils are used for cooking.

Properties of lipids

1. Fats are insoluble in water.
2. When oil is shaken in water, the oil breaks down into droplets which disperse in the water. The water and oil separate into two layers after a while.
3. Fats and oils dissolve in organic solvents such as ether, chloroform, acetone, and alcohol.
4. When water is added to a fat or oil that has dissolved in an organic solvent, a white milky suspension is formed. This is called an emulsion.
5. When fat is rubbed against paper, the paper becomes translucent.
6. In a mixture of water and oil, oil takes up Sudan III dye to form a red layer on the top, leaving the water clear.
7. Oils react with osmic acid and stain black.

Activity 1.7 (a): Test for the presence of lipids in groundnuts by the grease spot test

Materials

Groundnut seeds and a piece of white paper

Procedure

1. Peel the groundnuts seeds.
2. Rub the peeled seeds on a piece of paper.
3. Expose the paper to light.
4. Compare the part of the paper rubbed with seeds with the part that was not rubbed.
5. Record what you see.

6. Tabulate your results showing food sample tested, procedures, observation and inference

Food sample tested	Procedures	Observation	Inference

Questions

1. Is the area of the piece of paper rubbed with seeds similar to the unrubbed section of the paper?
2. What did you see after exposing the paper to light?
3. What other seeds can you use to perform the grease spot test?

Activity 1.7 (b): Test for the presence of lipids in cooking oil by using Sudan III reagent

Materials

Sudan III reagent, 5 ml of cooking oil, test tube, measuring cylinder (10 ml), and water

Procedure

1. Pour 3 ml of water in the test tube followed by 2 ml of cooking oil.
2. Add 2 drops of Sudan III reagent in the mixture.
3. Shake well the mixture.
4. Leave the mixture for 3–5 minutes to settle.

Safety precautions

Do not taste any food in the laboratory. Handle all chemicals with care.

5. Observe and record what happens.
6. Tabulate your results showing the food sample tested, procedures, observation and inference.

Food sample tested	Procedures	Observation	Inference

Question

What changes did you observe?

Test for proteins

Protein is a major nutrient that is essential for growth, building body parts and repair damaged cells. It is the major building block of human body responsible for building and maintaining body tissues. The main sources of protein are chicken, fish, milk, beef, eggs, beans, soybeans, and soybean products.

Properties of proteins

(i) Proteins are insoluble in water.

(ii) They coagulate on heating. This means small particles of protein clump together to form bigger particles when a mixture of protein and water is heated. The process is called denaturation.

(iii) Proteins react with sodium hydroxide (NaOH) and copper sulphate (CuSO₄) to produce a violet or purple colour. This is called the Biuret test.

(iv) The Biuret test can be used to identify a protein substance and its presence.

Activity 1.8: Investigate the presence of protein in egg white using the Biuret test

Materials

Egg white, water, test tubes, test tube holder, droppers, measuring cylinder (10 ml), 1M sodium hydroxide solution, and 1% copper sulphate solution

Procedure

1. Pour 3 ml of water into a test tube followed by 2 ml of egg white and shake well.
2. Add 2 ml of 1M sodium hydroxide solution to a test tube containing the mixture of protein and water.

3. Shake the mixture.
4. Drop-wise, add 1% copper (II) sulphate solution to the mixture while shaking.
5. Record your observations.
6. Tabulate your results showing the food sample tested, procedures, observation and inference

Food sample tested	Procedures	Observation	Inference

Question

What colour change did you observe?

Activity 1.9: Investigate the solubility of protein in water and the effect of heat on proteins

Materials

Egg white, water, test tubes, measuring cylinder (10 ml), test tube holder, and heat source

Procedure

1. Pour 3 ml of water into a test tube followed by 2 ml of egg white.
2. Shake the mixture.
3. Record your observations.
4. Heat the mixture for 2–3 minutes.

Safety precautions

Ensure proper ventilation for heating safely. Avoid flammable substances near the heating source. Place your burner on the bench, never hold it in your hands. Use test tube holder to hold the test tube.

5. Observe and record your findings.

Questions

1. What did you observe when the egg white was mixed with cold water?
2. Were there any changes after heating the mixture?

Chapter summary

1. Heterotrophic organisms are incapable of making their own food. Hence, they feed on different kinds of food made by other organisms. Examples of heterotrophs include all animals, fungi, some bacteria, and protists.

2. There are various types of heterotrophic nutrition including holozoic, saprophytic, and symbiotic nutrition or symbiosis. Symbiosis can be in the form of commensalism (a kind of relationship where one organism benefits while the other is neither benefiting nor affected by the relationship); mutualism (a kind of relationship where each of the two organisms benefits from different species); and parasitism (a kind of relationship where one of the two organisms benefits while the other is harmed).

3. Nutrition is important in various ways as it encompasses the study of the relationship between diets, health, and diseases. People who study nutrition are called nutritionists. They are professionals who advise people on how nutrition affects their health and well-being. Through nutrition, an organism can get necessary nutrients needed by the body to produce energy and support the functioning of various life processes. Moreover, maintaining good nutrition helps to promote general body health so as to reduce the risks of chronic diseases such as heart attack, diabetes, stroke, blood pressure, osteoporosis, and certain types of cancer.

4. Various types of nutrients are needed by the human body for its proper functioning. These are proteins, lipids, carbohydrates, vitamins, and minerals.

5. Proteins are obtained from foods like milk, meat, beans, peas, lentils, nuts, mushrooms, and sea foods. They are important for growth, repair, formation of cell membranes, muscle functioning, and production of human protein.

6. Lipids include fats and oils. Lipids are essential sources of energy, provide insulation, store fat-soluble vitamins, and protect internal organs. They are also involved in the formation of cell membranes, regulation of blood pressure in the body, and immune response.

7. Sources of carbohydrates include cassava, maize, potatoes, bananas, rice, and wheat. Carbohydrates are a major source of energy. They also aid in the formation of cell membranes.

8. Vitamins are either fat-soluble (vitamins A, D, E and K) or water-soluble (vitamins B and C). They boost the immunity of the body against diseases.

9. The human body requires minerals such as calcium, phosphorus, magnesium, potassium, sodium, chlorine, iodine, fluorine, manganese and copper.

10. Apart from nutrients, there are other essential constituents of the human diet needed by the body such as roughage and water.

11. Water is important in the formation of body fluids and cell cytoplasm. maintenance of body shape, digestion, lubrication, and cooling the body.

12. A balanced diet constitutes all the nutrients needed by the body in the right proportion.

13. Maintaining a healthy lifestyle is important for normal functioning of the body. Proper diet helps a person to remain healthy.

14. Nutritional requirements for different groups of people vary depending on age, sex, work, and general body condition of a person. For example, pregnant women need a diet that has adequate nutrients necessary to maintain their bodies and help their foetus and babies grow properly.

15. There are different types of nutritional disorders and deficiencies in human beings. These are generally called malnutrition.

16. (a) Examples of nutritional disorders are obesity, anorexia nervosa, and bulimia nervosa.

(b) Examples of nutritional deficiency diseases are marasmus, kwashiorkor, and rickets.

17. There are three types of carbohydrates which are monosaccharides, disaccharides and polysaccharides. Monosaccharides are reducing sugars. They dissolve in water to form sweet solutions. Disaccharides are formed by combining two monosaccharide molecules through condensation. Some disaccharides (like maltose and lactose) are reducing sugars while others are non-reducing sugars (like sucrose). On the other hand, polysaccharides are formed by condensation of several monosaccharides to form a long chain. They are all non-reducing sugars. They do not dissolve in water.

18. Benedict’s solution is used to test for reducing sugars. When testing for non-reducing sugars, hydrochloric acid is used to hydrolyse disaccharides to monosaccharides. Then Benedict’s solution is used to test for any monosaccharides produced. Iodine solution is used to test for starch.

19. Proteins are made of long chains of amino acids. Amino acids contain both acidic carboxyl groups and basic amino groups, so they can act as both bases and acids.

20. Lipids are made up of glycerol and fatty acids. Lipids are insoluble in water but dissolve in organic solvents. The grease spot test, Sudan III test, and emulsion test are used to test for lipids.