CBSE Class 6 Science Components of Food Exam Notes

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Components of Food

Components of Food

The main components of food are carbohydrates, fats, proteins, vitamins and minerals, these are called nutrients in addition to this, dietary fibres and water are also essential for maintaining the life processes in the human body.


Carbohydrates are the compounds made up carbon, hydrogen and oxygen. Photosynthesis consist of two phase (i) light phase and (ii) dark phase
During the light phase sunlight is absorbed by the photosynthetic pigment present in the green part of the plant, for formation of energy which is used during dark phase for the reduction of carbon dioxide for the formation of carbohydrates.

Carbohydrates are the main and cheapest source of energy for human body there for carbohydrates are called energy giving food,

There are three types of carbohydrates:

i) Sugars: Glucose, fructose, sucrose (cane sugar or sugar), jaggery etc.
ii) Starch: Rice, what, potatoes, maize etc.
iii) Cellulose: Roughage

Sugars: Sugars are the simple carbohydrates and are sweet in taste. These are water soluble main sources of sugar in our food are glucose, can sugar, milk, fruits such as banana, apple, grapes etc. Table sugar is mostly obtained from sugar cane and sugar beet. Refined sugar is a pure carbohydrate. It does not contain any minerals and vitamins.

Starch: Starch is a complex carbohydrate. Starch is tasteless, odourless, white powder. Starch is insoluble in water. Starch molecule contain large number (200 - 1000) of simple sugar (glucose molecules). Major sources of starch in our food are wheat, rice, maize and potatoes.

Cellulose: Cellulose is a complex carbohydrate. Cellulose is tasteless white powder. A molecule of cellulose is made up of large number (100 - 3000) of glucose molecule. Cellulose is present in plants cell wall, wood, cotton etc.

Digestion of carbohydrates: During the process of digestion, starch and sugars get hydrolysed to form glucose. Glucose is then absorbed by blood and transported to various part the body. During respiration, a part of glucose gets oxidized to carbon dioxide (CO2) and water (H2O) and energy is released.


Proper source of fats in our diet include meat, fish, eggs, and nuts.
i) Fats on digestion produce more energy then carbohydrates,
ii) Oils and fats are greasy in nature
iii) Human body stores excess energy in the form of fat.
iv) This stored fat is used by body for producing energy as and when required. That is why fat is considered as energy banned in our body
v) Fat deposit in our body provides cushion to the body organs and protect them from injury. Too much fat deposition in our body leads to obesity.
vi) Animals like whale, camel, polar bear, store fat in their bodies for future use, during winter, the polar bear sleeps for months. During its long sleep it uses the fat sotred in hte body to meat its energy requirements.
vii) Fat gives flavour and taste to our food.
viii) Fats are essential for absorption of vitamins A, D, E and K in the body.

Proteins are complex organic compounds containing carbon, hydrogen, oxygen and nitrogen.
i) A protein molecule is made up as large number of smaller molecules called amino acids.
ii) Proteins are body building food.
iii) Proteins are obtained from both plants and animals, plants contains some proteins but ground nuts, beans, cereals are the best sources of vegetable proteins.
iv) Animal protein contain sufficient quantity of essential amino acids.
v) Proteins helps in – digestion, body growth, tissues repair and catalysing certain biochemical process.

i) Vitamins are essential for growth and maintenance of body.
ii) Vitamins do not provide energy but they help in proper utilization of other nutrients such as carbohydrates and fats.
iii) Our body can synthesize only two vitamins, Vitamin-D and K, therefore, other vitamins should be present in our diet.
iv) The vitamin-B complex is a mixture of several water soluble vitamins. The important vitamins of this group are vitamin-B, B2, B4, B6, B9 and B12.
v) Vitamin-C is destroyed by heat during cooking. Therefore, they should be present in our diet in the form of fruits and half cooked vegetables.

Classification of Vitamins
Vitamin are classified on the basis of their solubility:
i) Water soluble vitamins: Vitamin-B and C
ii) Fat/Oil soluble vitamins : Vitamin-A, D, E and K. Vitamin-A, D, E and K are stored in the body fat 

 CBSE Class 6 Science Components of Food Exam Notes_1

Test for Starch, Proteins and Fats


Plants store glucose as polysaccharide starch. Cereal grains (wheat, rice, corn, oats, barley) as well as tubers such as potatoes are rich in starch.

Starch can be separated into two fractions — amylose and amylopectin. Naturally occuring starch of amylose (10-20%) and amylopectin (80-90%).

Amylose forms a colloidal dispersion in hot water whereas amylopectin is completely insoluble.

Starch Test: Add Iodine-KI reagent to a solution or directly on a potato or other materials such as bread, crackers, or flour. A blue-black color results if starch is present. If starch amylose is not present, then the color will stay orange or yellow. Starch amylopectin does not give the color, not does cellulose, nor do disaccharides such as sucrose in sugar.

Testing for Proteins
Biuret Test: Biuret solution is a blue liquid that changes to purple when proteins are present and to pink in the presence of short chains of polypeptides. The copper atom of the biuret solution reacts with the peptide bonds to cause the color change.

Test for Lipids
♦  Grease spot test/Brown paper test: As we all know from experience, lipids leave translucent spots (grease sports) on unglazed brown paper bags.
♦  Sudan Red Test: Sudan red is a fat-soluble dye that stains lipids red. Using Sudan red can show the amount and the location of lipids.

A balanced diet must contain carbohydrates, protein, fat, vitamins, mineral salts and fibre. It must contain these things in the correct proportions.

i) Carbohydrates: Provide a source of energy.
ii) Proteins: Provide a source of materials for growth and repair.
iii) Fats: Provide a source of energy and contain fat soluble vitamins.
iv) Vitamins: Required in very small quantities to keep us healthy.
v) Mineral Salts: Required for healthy teeth, bones, muscles etc.
vi) Fibre: Required to help our intestines function correctly, it is not digested.

Balanced Diets: We must have the above items in the correct proportion.

Nutritional diseases are diseases in humans that are directly or indirectly caused by lack of one or more essential nutrients in the diet. Nutritional diseases are commonly associated with chronic malnutrition.

Proteins / Fats / Carbohydrates

Protein-energy malnutrition

  1. Kwashiorkor
  2. Marasmus
  3. Mental retardation

Dietary vitamins and minerals


  1. Osteoporosis
  2. Rickets
  3. Tetany

Iodine Deficiency

♦ Keshan disease

Iron deficiency

♦ Iron deficiency anemia


♦ Growth retardation

Thiamine (Vitamin B1)

♦ Beriberi

Niacin (Vitamin B3)

♦ Pellagra

Vitamin C

♦ Scurvy

Vitamin D

♦ Osteoporosis
♦ Rickets

Protein-energy malnutrition (or protein-calorie malnutrition) refers to a form of malnutrition where there is inadequate protein intake.

Types include:

♦ Kwashiorkor (protein malnutrition predominant)

♦ Marasmus (deficiency in both calorie and protein nutrition)

♦ Marasmic Kawashiorkor (both protein deficiency and calorie insufficiency signs present, sometimes referred to as the most severe form of malnutrition).

Note that this may also be secondary to other conditions such as chronic renal disease in which protein energy wasting may occur.

Protein-energy malnutrition affects children the most because they have less protein intake. Few rare cases found in the developed world the almost entirely found in small children as a result of fad diets, or ignorance of the nutritional needs of children, particularly in cases of milk allergy.

Kwashiorkor in an acute form of childhood protein-energy malnutrition characterized by oedema, irritability, anorexia, ulcerating, dermatoses, and an enlarged liver with fatty infiltrates. The presence of oedema caused by poor nutrition defines kawashiorkor. Kwashiorkor was thought to be caused by insufficient protein consumption but with sufficient calorie intake, distinguishing it form marasmus. More recently, micronutrient and antioxidant deficiencies have come to be recognized as contributory. Cases in the developed world are rare.

CBSE Class 6 Science Components of Food Exam Notes_2

More recently, micronutrient and antioxidant deficiencies have come to be recognized as contributory. Cases in the developed world are rare.

Marasmus is a form of severe protein-energy malnutrition characterized by energy deficiency.

Body weight may be reduced to less than 80% of the average weight that corresponds to the height. Marasmus occurrence increases prior to age 1, whereas kwashiorkor occurrence increases after 18 months.

Calcium is an important component of a healthy diet and a mineral necess ary for life. The National Osteoporosis Foundation says, “Calcium plays an important role in building stronger, denser bones early in life and keeping bones strong and healthy later in life”. Approximately 99 percent of the body’s calcium is stored in the bones and teeth. The rest of the calcium in the body has other important uses, such as some exocytosis, especially neurotransmitter release, and muscle contraction.

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Long-term calcium deficiency can lead to rickets and poor blood clotting and in case of a menopausal woman, it can lead to osteoporosis, in which the bone, deteriorates, and there is an increased risk of fractures. While a lifelong deficit can affect bone and tooth formation, over -retent ion can cause hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals.

Vitamin D is needed to absorb calcium.

Selenium deficiency can lead to Keshan disease, which is potentially fatal. Selenium deficiency also contributes (along with iodine deficiency) to Kashin-Beck disease. The primary symptom of Keshan disease is myocardial necrosis, leading to weakening of the heart.

Selenium is also necessary for the conversion of hte thyroid hormone thyroxine (Tr) into its more active counterpart, triiodothyronine.

Iron deficiency (sideropenia or hypoferremia) is one of the most common of hte nutritional deficiencies. Iron is present in all cells in hte human body, and has several vital functions. Examples include as a carrier of oxygen to the tissues from the lungs in the form of hemoglobin, as a transport medium for electrons with ion the cells in the form of cytochromes, and as an integral part of enzyme reactions in various tissues.

The direct consequence of iron deficiency is iron deficiency anemia. Groups that are most prone to developing this disease are children and pre menopausal women.

Iodine is an essential trace element; the thyroid hormones thyroxine and triiodotyronine contain iodine. In areas where there is little iodine in the diet — typically remote inland areas where no marine foods are eaten

— iodine deficiency gives rise to goiter (so-called endemic goiter), as well as cretinism, which results in developmental delays and other health problems.

The no-iodized salt used in these foods also means that people are less likely to obtain iodine from adding salt during cooking.

Goiter is said to be endemic when the prevalence in a population is ?5% and in most cases goiter can be treated with iodine supplementation. If goiter is untreated for around five years iodine supplementation or thyroxine treatment may not reduce the size of the thyroid gland as the thyroid might be permanently damaged.

Zinc deficiency is usually due to insufficient dietary intake, but can be associated with malabsorption, acrodermatitis eteropathica, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses. Symptoms of mild zinc deficiency are diverse. Clinical outcomes include depressed growth, diarrhoea, importance and delayed sexual maturation, alopecia, eye and skin lesions, impaired appetite, altered cognition, impaired host defense properties, defects in carbohydrate utilization and the reproductive teratogenesis.

Thiamine is found in a wide variety of foods at low concentrations. Yeast, extract (e.g. Marmite) and pork are the most highly concentrated sources of thiamine.

Food rich in thiamine are oatmeal, flax, and sunflower seeds, brown rice, whole grain rye, asparagus, kale, cauliflower, potatoes, oranges, liver (beef, pork, and chicken) and eggs.

Beriberi is a neurological and cardiovascular disease. The three major forms of the disorder are dry beriberi, wet beriberi and infantile beriberi.

Niacin (also known as Vitamin B3, nicotinic acid and Vitamin PP) is an organic compound.

This colorless, water-soluble solid is a derivative of pyridine, with carboxyl group (COOH) at the 3-position.

Niacin is involved in both DNA repair, and the production of steroid hormones in the adrenal gland.

Niacin is one of five vitamins associated with a pandemic deficiency disease: niacin deficiency (pellagra), vitamin C deficiency (scurvy), thiamin deficiency (beriberi), vitamin D deficiency (rickets), vitamin A deficiency (night blindness and other symptoms).

Vitamin C or L-ascorbic acid or L-ascorbate is an essential nutrient for humans and certain other animal species. In living organisms ascorbate acts as an antioxidant by protecting the body against oxidative stress.

CBSE Class 6 Science Components of Food Exam Notes_4

Scurvy is an avitatminosis resulting from lack of Vitamin C, since without this vitamin, the synthesized collagen is to unstable to perform its function. Scurvy leads to the formation of brown spots on the skin, spongy gums, and bleeding from all mucous membranes.

In human Vitamin D is unique both because it functions as a parahormone and because when sun exposure is adequate the body can synthesize it (as Vitamin D1),

CBSE Class 6 Science Components of Food Exam Notes_5

Vitamin D prevents rickets in children and osteomalacia in adults, and, together with calcium, helps to protect older adults from osteoporosis. Vitamin D also affects neuromuscular function, inflammation, and influences the action of many genes that regulate the proliferation, differentiation and apoptosis of cells. Deficiency results in impaired bone mineralization, and leads to bone softening diseases including:

Rickets, a childhood disease characterized by impeded growth and deformity of the long bones, can be caused by calcium or phosphorus deficiency as well as a lack of Vitamin D.

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Osteromalacia, a bone-thinning disorder that occurs exclusive in adults and is characterized by proximal muscle weakness and bone fragility. The effects of osteomalacia are though to contribute to chronic musculoskeletal pain.


Salts of metals, non-metals needed by our body for its normal functioning are collectively called minerals.

i) Minerals help in proper utilisation of other nutrients in our body.

ii) Minerals are required by our body in very small quantitie

iii) Copper, Zinc, Magnesium are needed by our body in very small amount.

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i) Water is essential of the life to exist.

ii) About tow-third of our body weight is due to water.

iiii) all fruits, vegetables also contain large quantities of water. Grapes contain more than 50.

Function of Water

i) For transportation of nutrients / chemicals to and from the cell

ii) For maintaining the body temperature.

iii) for extraction of body wastes.

iv) As a medium for biochemical reactions in our body.

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