Sec 3 Bio 1

Chapter 4 – Nutrition

4.1 The Need for Food4.2 Water4.3 Carbohydrates4.4 Fats4.5 Proteins

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Learning ObjectivesCandidates should be able to:• State the roles of water in living organisms• List the chemical elements which make up

carbohydrates, fat, proteins.• Describe tests for starch (iodine solution),

reducing sugars (Benedict’s solution), protein (biuret test), fats (ethanol emulsion).

• State that large molecules are synthesized from smaller basic units– Glycogen from glucose– Polypeptides and proteins from amino

acids– Lipids such as fats from glycerol and fatty

acids

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4.1 The need for food

• Provide energy for the vital activities of the body.

• Synthesis new protoplasm for cell growth, repair of worn-out parts of the body and cell division.

• Stay healthy.

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Nutrients

Definition: Nutrients are chemical substances in food that provide energy and materials needed by the body. They are substances needed by the body for good health.

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How Many Types of Nutrients Are There?

1. Carbohydrates,

2. Fats,

3. Proteins,

4. Vitamins,

5. Minerals,

6. Water.

7. Fibre

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4.2 Water• 60% to 70% of the body weight is water.• Medium or substance in which chemical reactions occur

in an organism.• Regulation of body temperature• Water is needed for transportation of

-digested food ,-Excretory products,-Hormones

• Water is also the key component of :-Protoplasm-lubricants found in joints-digestive juices-blood-tissue fluid

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4.2 Water• In animals:

– Required for certain reactions such as hydrolysis (breakdown of substances in the presence of water)

– Help control body temperature through sweating

• In plants:– Needed for photosynthesis– Helps keep the plant upright through turgor pressure– Needed to transport mineral salts from roots to

leaves– Needed to transport food substances from leaves to

all parts of the body

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4.3 Carbohydrates

• Carbohydrates are organic compounds made up of the elements carbon, hydrogen and oxygen.

• The general formula is: CnH2mOm

• Ratio of hydrogen and oxygen is 2: 1– E.g. glucose: C6H12O6

– E.g. sucrose: C12H22O11

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Types of Carbohydrates

• Monosaccharides (Simple Sugars)-E.g. Glucose, Fructose, Galactose

• Disaccharides (Double Sugars)-E.g. Maltose (malt sugar), Lactose (milk

sugar), Sucrose (cane sugar)Glucose + fructose sucroseGlucose + glucose maltoseGlucose + galactose lactose

• Polysaccharides( Complex Sugars)-E.g. Starch, Cellulose, Glycogen

Fructose Glucose

Galactose

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Formation of disaccharides by condensation

E.g. Maltose (malt sugar)

Definition: A Condensation reaction is a chemical reaction in which two simple molecules are joined together to form a larger molecule with the removal of one molecule of water.

glucose glucose maltose water

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Digestion of disaccharides by hydrolysis

maltose glucose glucose

maltase

Definition: Hydrolysis is a chemical reaction in which a water molecule is needed to break up a complex molecule into small molecules.

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Polysaccharides• Polysaccharides( Complex Sugars): consist

of many monosaccharides (simple sugars)

– Eg. Starch, Cellulose, Glycogen

By which process is polysaccharides formed?

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Test for reducing sugars (Benedict’s Test)

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Results• Blue to orange-redorange-red

precipitate

• Blue to yellow or orange precipitate.

• Blue to green precipitate.

• Large amount of reducing sugar is present.

• Moderate amount of reducing sugar is present.

• Traces of reducing sugar is present.

Conclusion

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This equipment is used to find out nutrients found in food products.

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Applications of Food Test

• In food, dairy and agricultural industries.

• Used by food biotechnologists, nutritionists

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Functions of carbohydrates• A substrate for respiration, to provide

energy for cell activities;• Form supporting structures e.g cell wall• Converted into other organic compounds

such as amino acids and fats• Formation of nucleic acids e.g. DNA• Synthesis lubricants e.g. mucus• Synthesis nectar in some flowers

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Where can we find carbohydrates?

Carbohydrates are found in:

-Starch: Bread, Rice, Pasta, Potatoes

-Sugars: Soft drinks, sweet fruits, sweets

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4.4 Fats• They are organic compounds made up

of the elements carbon, hydrogen and oxygen.

• Fats contain much less oxygen in proportion to hydrogen.– E.g. tristearin C 57 H110 O6

A fat molecule

GLYCEROL FATTY ACIDS

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What make up fats?

Carbon (C) Hydrogen (H) Oxygen (O)

3 fatty acids glycerol

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Fats• It can be broken down into fatty acids and glycerol

by hydrolysis.

+ +

Fat molecule 3 water molecules glycerol three fatty acid molecules

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Differences between saturated fats and unsaturated fats

Saturated fats• Found mostly in

animals• Solid at room

temperature

Eg. Butter• Fatty acid chains are

straight

Unsaturated fats• Found mostly in

vegetables• Liquid at room

temperature

Eg. Olive oil• Fatty acid chains are

bent in some places-A fatty substance called cholesterol is usually found together with polysaturated fats. Too much polysaturated fats and cholesterol in the diet may cause coronary heart disease.

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Test for Fats (Ethanol Emulsion Test)

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Functions of fats

• Source and store of energy• Insulating material preventing excess

heat loss.• A solvent for fat-soluble vitamins and

other vital substances such as hormones.• An essential part of the protoplasm,

especially in cell membrane.• To reduce water loss from skin surface.

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Where can we find fats?• Fats are found in:

– Butter, nuts, certain parts of meat.

• Types of fats:– Saturated

• Found in animals fats• Usually found with cholesterol

– Unsaturated• Found in vegetable fats

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4.5 Proteins• The chemical elements in proteins are carbon, hydrogen, oxygen and nitrogen.

• Often sulphur and phosphorus are present too.

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• Amino acids are the building blocks of proteins.

• There are 2 types of amino acids, essential and non-essential.

• There are 9 essential amino acids that must be supplied by the food you eat.

Proteins

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Proteins

• An amino acid is made up of a amino group (-NH2), and acidic group (-COOH) and a side chain (-R)

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Proteins

• Two amino acids link up in a condensation reaction. The bond formed is called a peptide bond.

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Proteins• Many amino acids linked up by peptide

bond to form a peptone or polypeptide.

• Polypeptides may link up to form long chains of amino acids. Protein molecule is formed when the chains fold together.

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Proteins• Coiled, folded, three-dimensional

shape.

• Coil held by weak hydrogen bonds.

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Test for Proteins (Biuret Test)

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Proteins are needed for:

• growth and repair of tissues

• synthesis of enzymes, antibodies and hormones

• supply of energy

Functions of proteins

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Where can we find proteins?

• Proteins are found in:– Fish, meat, eggs, milk and milk products,

beans

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What is a Balanced Diet?A balanced diet should contain the right amount of:– carbohydrates, – fats,– proteins,– vitamins, – minerals, – water and roughage

to meet the daily requirements of the body.

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Protein deficiency• Leads to Kwashiorkor

• Symptoms: Swollen stomachs, skin crack and become scaly.

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Carbohydrates

NUTRIENTS

may beFunctions of water In animals, water: • is a medium for chemical reactions to occur; • transports digested food products, excretory products, and hormones from one part of the body to another; • is an essential part of protoplasm, lubricants, digestive juices and blood; • is essential for hydrolysis; and • helps to control body temperature.

Monosaccharides (single sugars), e.g. glucose, fructose and galactose

In plants, water: • is essential for photosynthesis; • is needed to keep plant cells turgid; • transports mineral salts from the roots to the leaves; and • transports food substances from the leaves to other parts of the plants.

WaterFats

Organic compounds made up of carbon, hydrogen and oxygen but they contain much less oxygen in proportion to hydrogen.

Organic compounds made up of carbon, hydrogen and oxygen in a ratio of 1 : 2 : 1.

Organic compounds made up of carbon, hydrogen, oxygen and nitrogen. Sulphur may also be present.

Inorganic nutrient. Water does not contain carbon.

Proteins

Disaccharides (double sugars), e.g. maltose, lactose and sucrose

Polysaccharides (complex carbohydrates) made up of many monosaccharides

e.g.

Starch

Glycogen

Cellulose • forms the cell walls in plants; and • cannot be digested by mammals, but is used as fibre in their diet.

Identification Test for reducing sugars: A reducing sugar gives a brick-red precipitate when boiled with Benedict’s solution. Sucrose is a non-reducing sugar.

• serves as the main form of storage for carbohydrates in green plants; and • gives a blue-black colour with iodine (test for starch).

• serves as the main form of storage for carbohydrates in animals and fungi.

Basic units Fats are hydrolysed to form fatty acids and glycerol.

Identification Test for fats: A cloudy white emulsion is formed in the ethanol emulsion test.

Basic units Proteins consist of amino acids linked together by peptide bonds.

Identification Test for proteins: Proteins give a violet colouration with Biuret reagent.

amino acids

polypeptides

proteins