Nutrition

Nutrition can be defined as the totality of the processes by which a living thing obtains, and uses food. We have two types of nutrition; plant and animal nutrition.

Plant Nutrition

In plant nutrition, we have photosynthesis and chemosynthesis. The later is a process through which non-green plants use either parasitic or saprophytic modes of nutrition to obtain their food. It can occur in colourless autotrophic bacteria.

Photosynthesis is the process by which green plants make use of raw materials such as carbon (iv) oxide and water to produce sugar and Oxygen in presence of sunlight or solar energy and chlorophyll.

Equation for Photosynthesis

6CO₂     +     6H₂O     →     C₆H₁₂O₆        +    6O₂

Light Reaction

(i) Light energy is captured by chlorophyll

(ii) The energy splits water into hydrogen (H⁺) and hydroxyl (OH^–) ions. The process is called photolysis of water and it is the first step in photosynthesis.

4H₂O    →     4H⁺ +   4(OH^–)   + ATP

(a) The hydroxyl part is reconverted to water and Oxygen is given off as a by-product.

4(OH)   →     2H₂O + O₂ 

(b) The compound (NADH) coenzyme is reduced by hydrogen ion and ATP is formed.[mediator_tech]

With the energy provided by ATP, the reduced compound (NADH) brings about the assimilation of carbon (iv) oxide through series of small steps , each controlled by a specific enzyme to form sugar or starch.

CO₂ + 2H₂    →     CH₂O + H₂O

The overall reaction is below:

CO₂ + 2H₂O      →       CH₂O + H₂O + O₂ 

The Significance of Photosynthesis

1. All living things are supported by the by-products of photosynthesis. For example all animals and non-green plants obtain their energy from green plants.
2. It brings about the purification of the atmosphere by removing excess carbon (iv) oxide (carbon iv oxide)

Materials Necessary for Photosynthesis

These materials are divided into two basic parts: (1) External conditions and (2) Internal conditions.

External conditions:

1. Water
2. Light
3. Carbon (iv) oxide.

Internal conditions:

1. Mineral salts
2. Chlorophyll
3. Enzymes

Some Factors Affecting Photosynthesis:

They include;

1. Temperature,
2. Light intensity,
3. Carbon (iv) oxide,
4. Amount of soil water/moisture

EVALUATION

1. What is nutrition?
2. Define photosynthesis.
3. Explain what happens in light and dark reaction stages of photosynthesis using equations.
4. List materials necessary for photosynthesis in the order of external and internal conditions.
5. Outline some factors that affect photosynthesis.

Micro and Macro Elements

Micro Elements

Micro elements are also known as minor or trace elements or micronutrients. These are elements required by plants in very tiny or very little amounts. Although they are needed in trace amounts, it leads to some deficiency when not available at all.

Some micronutrients include; Boron (B), Cobalt (Co), Copper (Cu), Manganese (Mn), Silicon (Si), Zinc (Zn), Chlorine (Cl).

On other hand, macro or major or macronutrients refer to elements that are required by plants in large amounts. Examples are the seven major elements which include Nitrogen (N), Potassium (K), Calcium (Ca), Magnesium (Mg), Iron (Fe), Phosphorus (P), Sulphur (S).

Micro Nutrients

Macro Nutrients

EVALUATION

1. Define the terms micro and macronutrients
2. List Four (4) each of micro and micro nutrients
3. Write two (2) importance each of macro and micro nutrients
4. Outline two (2) each of the effects of deficiency of micro and macro nutrients.

SUGGESTED PRACTICALS

Carry out an experiment to demonstrate osmosis using a living membrane.

a spirogyra filament and draw a well labeled diagram of 10 – 12c

THE PROPERTIES AND FUNCTIONS OF THE CELL

CONTENT

1. Animal Nutrition
2. Balanced Diet
3. Heterotrophic Nutrition
4. Enzymes
5. Practical Guide on Food Tests

Animal Nutrition

All living things feed in order to obtain energy for their daily activities and also to carry out their metabolic processes. Plants can manufacture their own food (i.e. make complex chemical compounds) from simple raw materials (CO₂ and H₂O) through the process of photosynthesis. Plants need minerals to make some of the complex compounds and these are obtained from the soil as mineral ions. Animals however cannot manufacture their own food, they depend directly or indirectly on plants. Nutrients that animals require are present in their diet.

Hamburger and Fries

One of the meals most associated with the United States is a hamburger and French fries. This burger and fries, a daily special, is accompanied by baked beans and coleslaw.

Food Substances

All food taken in by animals can be divided into six groups of food nutrients namely Carbohydrates, Protein, Fats, Vitamins, Minerals, and Water. Fibre/roughage is also an important component of a diet but it is not a nutrient. All these are needed for a balanced diet, for humans.

Carbohydrates, Protein, Fat & oil, and Water are primary food substances and are necessary for the maintenance of life. Minerals salts and Vitamins are welfare food substances and are essential for the well being of an individual.

Types of Food Substances

A. Carbohydrates

These contain the elements carbon (C), hydrogen (H) and Oxygen (O). The ratio of hydrogen to oxygen is 2:1. Carbohydrates are represented by the formula Cx (H₂O)y. The major sources of carbohydrate are Sugar (e.g. glucose, maltose) and starches (e.g. yam, maize, rice).

Types of Carbohydrates

1. Monosaccharides/Simple sugars: These are made up of only one unit of simple sugar e.g.

(a) Hexose sugars: These consist of six carbon atoms arranged into a ring e.g. glucose, fructose and galactose. They make up the most important energy storage molecules in an organism. Their chemical formula is C₆H₁₂O₆

(b) Pentose sugars: These consist of five carbon atoms e.g. ribose and de-oxyribose. They are used in the formation of nucleic acids.

2. Disaccharides/Complex sugars: These are formed by the condensation (i.e. chemical bonding of two molecules) of two simple sugar molecules. They are represented by the formula C₁₂H₂₂O₁₁ .

Examples are:

(a) Maltose (glucose + glucose – H₂O) found in malted cereals and spouting grains.

(b) Lactose (glucose + galactose – H₂O) found in milk.

(c) Sucrose (glucose + fructose – H₂O) found in sugar cane stems, ripe sweet fruits, sugar – beet and carrot.

NB: All sugars are sweet and soluble and provide energy in a ready-to-use form.

3. Polysaccharides: These are formed by the condensation of hundreds of simple sugar molecules. They are represented by the general formula (C₆ H₁₀O₅) _n where n represents a large number. Examples include starch, cellulose, glycogen (animal starch). Starch and glycogen are insoluble and do not taste sweet.

NB: Condensation is a reaction in which two or more molecules join to form a large molecules with the removal of a molecule of water (H₂O) or some other simple molecule.

Importance of Carbohydrates

(i) They provide us with energy.

(ii) It provides heat during its oxidation which is used in maintaining body temperature.

(iii) It is used in building the exoskeleton of arthropods.

B. Proteins

Proteins are complex molecules made up of carbon, hydrogen, oxygen and nitrogen (N) many also have sulfur (S). They are long – chain molecules made up of smaller molecules called amino–acid. There are 25 types of amino acids and these occur in different numbers and order in different types of protein. Thus one protein is different from the other. Each individual amino acid joins the chain by means of a peptide bond.

During digestion the breakdown of protein occur in the following sequence;

Protein   →    Proteoses  →   Peptones  →   Polypeptides   →   Amino Acids.

Examples of Proteins

Examples of proteins include:

(a) Soluble proteins e.g. haemoglobin (in blood), enzymes (in water/cytoplasm), antibodies, and some hormones (e.g. insulin).

(b) Insoluble proteins e.g. keratin (a fibrous protein found in skin and hair), collagen (found in bones and cartilage), myosin and actin (found in muscle cell). Sources of protein include (a) animal sources such as fish, meat, milk, egg and cheese. (b) Plant sources such as beans, groundnut and soya beans etc.

Uses/Importance of Proteins

1. Protein is used for making body building substances which are necessary for building new cells and replacing old ones.
2. Essential for the repair of cells and worn- out tissues.
3. Essential for formation of enzymes
4. Essential for formation of hormones
5. Essential for formation of antibodies
6. Essential for formation of heamoglobin etc.
7. Essential components of cell membranes
8. It may be required to provide energy.

C. Fats and Oils

These are also called lipids and are composed of carbon, hydrogen and oxygen. Each fat molecule is made up of one molecule of glycerol attached to 3 fatty acids. There are different types of fatty acids and these form different fats with different properties. At room temperature fats are solid while oils are liquid. Lipids are macromolecules and have to be broken down into fatty acids and glycerol before they can be absorbed into the body. Sources of fats include margarine, butter, cheese, fatty meat, melon, groundnuts, palm fruits, castor oil seeds, lard etc.

Importance of Fats and Oils

1. Fats and oil are used for energy storage in the body. They provide more energy to the body than carbohydrate when metabolized.
2. They are solvents for fat soluble vitamins and also for hormones.
3. They are important components of cell membranes.
4. They help in maintaining the body temperature / for thermal insulation in the body. In cold countries, the fat layers under the skins of mammals act as insulators and prevent loss of heat from their bodies.
5. Fats give buoyancy to marine animals e.g. whales have a thick layer of blubber.

D. Mineral Salts

These regulate the metabolic activities within the body. They are also important components of enzymes, pigments and structural parts.

The major source of mineral salts is the diet. Examples of minerals include sodium, potassium, calcium, chlorine, phosphorus, magnesium, iron, copper, cobalt, fluorine and manganese.

Sodium calcium and phosphorus are needed in large quantities in the body while some others like iron and iodine are only needed in small quantities.

A lack of minerals in the diet results to ill health and development of symptoms of deficiency diseases.

Sources, Functions and Deficiency Symptoms of Some Minerals

E. Vitamins

These are organic compounds required by man and other animals in only small quantities for normal growth and healthy development. They are biocatalysts (they promote chemical reactions in the body).

Examples include vitamins A, D, E and K which are water soluble. The main sources are fruits, eggs, milk, palm oil, vegetables and animal organs. Inadequacy or lack of these vitamins leads to nutritional deficiency diseases and ill health.

Sources, Functions and Deficiency Symptoms of Some Vitamins

Apples

The apple tree is widely cultivated throughout temperate regions of the world for its juicy, edible fruit. The many varieties of apples have been popular for centuries and growers have selectively bred certain superior wild varieties for domestication and mass production.

F. Water

This is composed of hydrogen and oxygen and makes up two-thirds (70%) of the body mass of a human being.

Water is taken in when we eat or drink. Sources include metabolic water from food, water from rivers, rain, ponds, springs, etc.

Importance of Water

1. It is required for metabolic activities in the body. It makes up a large part of the protoplasm, thus it is the medium in which chemicals reaction take place in the body.
2. It transfers digested food substances, excretory products (urine & sweat) and hormones.
3. It plays an important role in the regulation of body temperature (sweat cools us down)
4. It helps to maintain the osmotic content of the body tissues.
5. It is an important solvent for food substances during digestion.
6. It constitutes a greater part of the blood.[mediator_tech]
7. It is the main component of plants and animals.

Daily intake of water must equal the loss in urine, faeces, sweat and breath to keep healthy.

G. Roughages/Fibre

This is an indigestible fibrous material derived mainly from vegetables, fruits and seed coats (of carbohydrates and proteinous seed).

Fibre adds bulk to food thus stimulating the movement of the bowel. It passes down the entire gut from mouth to anus and does not provide any energy.

Sources include bran cereals, cabbage, sweet corn, celery, etc.

Papaya Fruit

A view of the interior of the papaya fruit shows the pulp and seeds. This edible fruit, capable of growing as large as 9 kg (20 lb), is widely cultivated in the tropics. The latex of the fruit contains a substance called papain, which can be extracted and used to tenderize meat.

Importance of Roughages/Fabre

1. Fibre helps the movement of food in the alimentary canal by peristalsis so preventing constipation.
2. Fibre absorbs poisonous waste from bacteria in the gut.
3. Many doctors believe a high fibre diet lowers the concentration of cholesterol in the blood.
4. Fibre reduces the risk of heart diseases and bowel cancer.

The Balanced Diet

The intake of a variety of food in the right quantity and proportion that provides the body with all the nutrients and energy needed to sustain the body and ensure good health and growth is referred to as a balanced diet.

A balanced diet must contain the seven food substances i.e Carbohydrates (60%), Proteins (15%), Fats (15%), Vitamins (10%), Minerals, Water and Fibre.

Energy Requirements

Even at rest energy is required for basic functions such as heart beats, working of the lungs and keeping body temperature constant. Also chemical reactions in the body such as those involved in growth & repair are occurring and these need energy. The energy required for these body functions is called the basal metallic rate.

USDA Food Pyramid

The United States Department of Agriculture Food Pyramid provides a practical visual guide to healthful eating, indicating the recommended daily portions of the basic food groups.

(BMR). BMR varies from person to person; an adult needs 7000kg per day, even at rest this energy is still required.

The Importance of a Balanced Diet

1. It is required for normal healthy living.
2. It gives us resistance to diseases.
3. It provides energy required for normal activities.
4. It prevents malnutrition/deficiency diseases e.g. a lack of protein in the diet can cause kwashiorkor and marasmus in children.

EVALUATION

1. Name the constituent element, four food sources and three functions of each of the following (i) Carbohydrates (ii) Protein (iii) Lipid

1. List the sources and functions of four vitamins and minerals.
2. State one deficiency disease/condition associated with each type of nutrient mentioned in 1 and 2 above
3. Define the terms: (a) balanced diet (b) BMR
4. Mention three importance of taking a balanced diet

Heterotrophic Nutrition

This is the type of nutrition in which the organism feeds on complex organic molecules. There are different forms of heterotrophic nutrition.

Types of Heterotrophic Nutrition

1. Holozoic Nutrition:

In this type of nutrition an organism feeds on complex organic materials, usually in solid form. These materials require ingestion, digestion and absorption before assimilation into the body.

Animals that practice holozoic nutrition include herbivores, carnivores and omnivores.

2. Parasitic Nutrition:

In this form of nutrition, one organism (the parasite) lives in or on another organism (the host) causing harm/death to the host. Parasites may be plants or animals.

Parasitic plants attach themselves to the host by means of suckers and send special absorbing organs called haustoria into the tissues of the host’s stem where they absorb water, mineral salts and food substances. Examples are the dodder plant, cassytha and mistletoe (a partial parasite).

Parasitic animals which live outside the host (ectoparasites) have mouth parts that are modified for piercing or boring into the skin of animals or epidermal layer of plants and suck the body fluid of the host. Examples are ticks, aphids, lice, etc. parasitic animals which live within the host (endoparasites) possess attachment organs such as suckers with which they fasten themselves onto the walls of the host’s gut and suck already digested food. Examples are tapeworm, liverfluke, plasmodium and hookworm.

3. Saprophytic Nutrition

This is a form of nutrition in which an organism feeds on dead and decaying organic matter. Examples are Rhizopus, mushroom, mucor, toadstool and bacteria. These organisms have rhizoids through which they secrete enzymes into the substrate extracellularly. The digested portion is then absorbed into the body of the saprophyte.

Feeding Mechanisms In Holozoic Organisms

All animals obtain their food directly from plants or by feeding on other animals. Their nutritional requirements are obtained from ingested food. Various organisms obtain and ingest their food in different ways; this is referred to as their feeding mechanism. The feeding mechanism of an organism depends on the organism’s mode of nutrition and the type of food on which it feeds.

The ingested food is broken down into simple, soluble and diffusible substances through the process of digestion. The digested food is then absorbed into the fluids of the organism and transported to the body cells where it is assimilated (i.e. used). Undigested food is egested from the body.

Feeding mechanism in holozoic organisms include the following;

1. Use of pseudopodia to engulf food e.g. in Amoeba
2. Beating movement of cilia to move food into the oral groove e.g. Paramecium.
3. Sweeping movement of flagella to move food into the mouth e.g. in Euglena.
4. Use of tentacles e.g. Hydra.
5. Filter feeding e.g. Mosquito larvae, whales, oysters, etc.
6. Fluid feeding e.g. Insects, hummingbirds, etc.
7. Saprophytic feeding e.g. mushroom, rhizopus, etc.
8. Parasitic feeding e.g. Dodder plant, Mistletoe, liver fluke, lice, guinea worm, tapeworm, etc.

EVALUATION

1. What are heterotrophs?
2. Give and explain two forms of heterotrophic nutrition
3. Mention two forms of feeding mechanism in holozoic organisms
4. Briefly describe the modification of the mouth parts of a grasshopper to its mode of feeding.

Enzymes

An enzyme is an organic catalyst. A catalyst is a substance which brings about or greatly speeds up a chemical reaction and it is not used up or changed during the reaction. Enzymes speed up metabolic reactions in living cells without changing their composition in the process. Enzymes are protein molecules and are manufactured by an organisms own cells.

Structure and function of an enzyme

Types of Enzymes

Enzymes are classified based on the nature of chemical changes brought about on a substrate. Examples include:

1. Hydrolases: These bring about the decomposition of a substrate by the addition of water molecules to it. This process is called hydrolysis. However, they can also bring about a reverse reaction in which complex substance are synthesized from simple substances by the removal of water (condensation). Most digestive enzymes are hydrolysis enzymes.

2. Oxido-reductase: These bring about oxidation of a substrate by the addition of oxygen or removal of hydrogen. This reaction is usually accompanied by the reduction of another substance. Most respiratory enzymes such as dehydrogenases, oxidases and catalases belong to this group.

3. Transferases: These catalyse reversible reactions

4. Isomerases: These usually change the spatial configuration of a molecule in a living cell. They work on isomers.

5. Lyases: These catalyse the breaking up of bonds by elimination or addition reactions.

6. Ligases: These catalyse the joining of two molecules with accompanying hydrolysis of a high energy bond.

Characteristics of Enzymes

1. They are proteins in nature.
2. They are soluble
3. Some enzymes require the presence of non-proteinous molecules called co-enzymes to activate them.
4. Enzymes are specific in action e.g. amylases will only act on starch.
5. Enzymes are organic catalysts i.e. they speed up chemical reactions in the body but are unchanged at the end of the reaction.[mediator_tech]
6. They are affected by the acidity or alkalinity of their surrounding and will only work in specific pH medium.
7. They have a specific temperature range above or below which they become denatured/ inactive. They work best between 35 to 40ºc.
8. Enzymes can be inactivated by inhibitors like cyanide and mercury.
9. They are usually involved in reversible reactions.
10. Enzymes act in small quantities and catalyses large amount of substrate.
11. They can function outside organisms producing them.

EVALUATION

1. What is an enzyme?
2. What are the functions of enzymes?
3. Enumerate five characteristics of enzymes.

SUGGESTED PRACTICALS

Practical Guide on Food Tests

The materials/nutrients present in food can be identified using various types of tests. These are:

1. Test for carbohydrates

(a) To test for simple sugar e.g. glucose and fructose.

Put a small quantity of glucose solution in a test tube.

Add an equal amount of benedict solution.

Boil the mixture for 4 – 6 minutes. A bricks-red or orange precipitate indicates the presence glucose.

(b) To test for complex sugar e.g. sucrose, maltose or lactose

Put a small quantity of the sucrose solution in a test-tube

Add a few drops of dilute hydrochloric acid to the solution, (This hydrolyses the complex sugar to simple sugar)

Place the test-tube in a boiling water bath for a few minutes.

Add a few drops of dilute caustic soda (to neutralize the excess acid).

Add an equal amount of feeling’s solution and place the test-tube in a boiling bath. An orange-red precipitate/yellow precipitate indicate the presence of sucrose.

(c) To test for starch

1. Boil a sample of the starch material (e.g. yam/rice)
2. Add a few drops of dilute iodine solution to it. A blue-black colouration indicates the presence of starch.

2. To test for proteins

(a) Biuret test

1. Take a small quantity of fresh milk, egg white solution or malt extract in a test-tube.
2. Add a few drops of water and 1cm³ of dilute sodium hydroxide.
3. Carefully add 1% of copper II sulphate solution in drops. Shake the mixture thoroughly after each drop.
4. A violet, purple, violet colour indicates the presence of protein
5. A pink colour indicates the presence of peptones.

(b) Millon’s test

1. Put 3cm³ of egg white/colloidal solution of a protein into a test-tube
2. Add 3cm³ of millon’s reagent and warm the mixture in a water bath for a few minutes.
3. A deep red colour or precipitate shows the presence of protein.

(c) Xanthoproteic test

1. Put 2cm³ of egg white or milk solution in a test-tube.
2. Carefully add about 1cm³ concentrated trioxonitrate (v) acids. A white precipitate forms which turns yellow on heating.
3. Cool the contents and add about 3cm³ of ammonium hydroxide solution. Heat the solution and allow it to cool. The colour of the precipitate deepens to orange indicating the presence of protein.

3. To test for fats and oils

(a) Translucent mark test

1. Drop oil on a spot, on a piece of paper or rub the surface of a fatty food against the surface of a piece of white paper. A translucent mark shows the presence of fat.

(b) Sudan III test

1. Add a few drops of Sudan (iii) solution to some oil in a test-tube. A red colouration is obtained
2. Boil the solution. A black precipitate is formed.

ESSAY QUESTIONS

1. Distinguish between autotrophic and heterotrophic modes of nutrition
2. Describe the symbiotic mode of nutrition
3. Mention three insectivorous plants and discuss one.

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