02. Food & Digestion
Nutrients are chemical substances that keeps the body fit. They provide energy and materials that are
responsible in making cells and other parts of the body.
There are two types of nutrients.
1. Macro Nutrients – the nutrients that are consumed in excess quantities. E.g. – Carbohydrates, Lipids
and proteins
2. Micronutrients – Nutrients that are consumed in very less quantities. E.g. – Vitamins and Minerals
Nutrients
Composition Building
Categories
Uses
Major Source
Elements
Unit
Monosaccharide Carbohydrates Carbon,
Simple
Provides energy Cereal, Whole
Hydrogen,
Sugars
Glucose, Fructose (found in instantly
Wheat, Rice,
Oxygen
fruits), Galactose (Dairy
Yams
Products)
Disaccharides - Lactose
(milk), Sucrose (sugar
Cane)
Polysaccharides - Starch
(plant energy store),
Cellulose (plant fiber),
Glycogen (animal energy
store)
Lipids
Carbon,
Fatty
1. Solid Fats
Formation of cell Chicken Liver,
Hydrogen,
acids and
Animal Fat (Lard)
membranes,
Cheese, Nuts,
Oxygen
Glycerol
2. Liquid Fats
stores excess
Butter, Egg
Plant fats (oils)
amount of fats
Yolk
under the skin as
heat insulation
Proteins
Carbon,
Amino
20 types of amino acids
Building
Egg White,
Hydrogen,
Acids
structures within Soya, Kidney
Oxygen,
the cells,
beans,
Nitrogen, at
Formation of
almonds,
times Sulphur
tissues and
Sesame seeds,
organs, for
cheese, milk,
growth and to
meat, Fish
repair worn out
tissues,
production of
enzymes
Vitamins and minerals – Micro-nutrients, doesn’t provide the body with energy, but required by the
body for other functions of the body activities.
Fiber – Dietary fiber cannot be digested, rather helps the food to be moved along the intestines. As the
fiber moves along the large Intestine, bacteria feed on it and adds bulk to the food along with the fiber.
This helps the muscle to push the food along, as it would have the most amount of water absorbed
within, like a sponge, which makes the undigested foods to form the faeces soft and easy to be
egested.
Water – All the metabolic chemical reaction within the body takes place in the water. Blood is made up
of water 55%, which allows the nutrients and other blood components to be transported throughout the
body. Water also allows the body to maintain its temperature.
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Test for Carbohydrates
1. Benedict’s Test (Test for sugars)
Benedicts solution is composed of Sodium Carbonate, Sodium citrate and copper sulphate.
Obtain a food sample that contains sugars, crush and grind using some amount of water. Filter and
drain the water used to grind, into a test-tube. Add benedicts reagent (Blue in color). Immerse the food
sample into a water bath and heat until the following series of color is been observed.
Blue  Green  yellow  Orange  Red  Brick Red Precipitate
If we are using a sample of sucrose, since it is a disaccharide (non-reducing sugar), it has to be
converted to monosaccharide (Reducing sugar), by adding diluted sulphuric acid and then
neutralizing with an alkaline solution, add benedict’s reagent and then heat it in a water bath.
2. Test for Starch (Iodine Test)
Obtain a food sample that contains starch (E.g. – A piece of bread), add diluted Iodine solution (yellowbrown color). If the bread piece turns into blue-black color, we can conclude that the food sample has
starch in it.
Balanced Diet – A diet that provides all the different nutrients in the appropriate quantities/right
amount is known as balanced diet.
Malnutrition – Malnutrition occurs when a person’s diet contains too many or too few nutrients than
required.
1. Excess amounts of carbohydrates and fats can cause obesity.
2. Excess amounts of proteins, if consumed, part of it would be converted to glycogen and stored in
the liver and the remaining part would be converted to ammonia and be excreted through the
urine.
Deficiency Diseases
Nutrients
Proteins
Lipids
Vitamin A
Vitamin B1
Vitamin C
Vitamin D
Vitamin E
Vitamin K
Iron
Calcium
Iodine
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Function in the body
Growth of cells and tissues
Thermal insulator
Increased resistance to diseases
and for proper visual senses
Prevents digestive disorders and for
proper functioning of nerves and
muscles
To prevent damages caused in the
circulatory system
To prevent weakening of bones and
joints
Protects body tissues from damages
and prevents the person from
aging.
Prevents excess blood flow when
wounded
Helps oxygen to be transported
throughout the body
Buildup of strong bones and joints,
teeth
For production of thyroid hormone
Disease
Marasmus, Kwashiorkor
Anorexia Nervosa
Night blindness, Color Blindness
Beri Beri
Scurvy
Rickets
Less Fertility/hair loss
Leukemia (Bone Marrow Cancer)/ Less blood Clotting
Anemia
Osteoporosis
Goiter
The breakdown of food – 2 major processes.
1. Physical breakdown – food been broken down from larger pieces to smaller pieces using the
teeth is called physical breakdown of food. Human beings have 32 teeth and have 4 types of teeth.
 Incisors – to bite soft foods like fruits.
 Canines – to tear hard food like meat. They are pointed and sharp to carry out the function.
 Molars and premolars – to grind/crush the food into smaller pieces physically.
Part
Function
Enamel
Hard covering, contains Calcium
Dentine
Contains living cells, not hard as
the enamel
Gum
Protects the teeth and the
underlying bone
Pulp cavity
Contains blood vessels and nerves
Fibers
Holds the tooth in the jawbone
Jawbone
Helps in handling the food by
biting, chewing etc.
Blood vessels Supplies blood
What are the causes for holes in your tooth?
 too many sugary or acidic foods and drinks
 a poor oral hygiene routine, such as failing to brush or floss daily
 not getting enough fluoride (Mineral)
 dry mouth (when salivary glands in your mouth don’t produce enough saliva)
 eating disorders, such as anorexia and bulimia (fear of gaining weight)
 acid reflux disease (If the circular muscle is weak or doesn’t tighten properly, the acid from
your stomach can move backward into your oesophagus), which can result in stomach acid
wearing down your tooth enamel.
2. Chemical breakdown of food
Carbohydrates, proteins and lipids are all made up of large molecules which contains of basic
building units. These large molecules cannot be absorbed by the body as it is not soluble in water.
For it to become soluble in water, and be absorbed by the body, it has to be broken down into
smaller molecules by the action of chemical reactions that uses enzymes. Enzymes are chemical
substances that allows a reaction to be fastened, without being used up. Therefore, digestive
enzymes helps the process of chemical breakdown to occur faster.
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.
Digestion begins in your mouth. Saliva plays a major
role in digestion of food, especially carbohydrates.
Saliva is made up of 99% of water, a slimy substance
called mucin and an enzyme called amylase. We
have three pairs of salivary glands named as –
Parotid, Submaxillary and Sublingual.
Muscles can contract but will not be able to lengthen/expand on their own. For this purpose, the
oesophagus is composed of two layers of muscle cells. The outer layer is called longitudinal muscle and
the inner layer is called the circular muscle. The Circular muscles contract in order to squeeze the food
down the gullet, the longitudinal muscles will contract in order to lengthen the circular muscles. This
continuous wave of muscular contraction and expansion is called peristalsis.
Part of the
Digestive
System
Mouth
Oesophagus
Stomach
Small
Intestine
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Name of the
Enzyme
Nutrient
Digested
Type of
Enzyme
Functions (If Any)
Amylase from
Saliva
_
Carbohydrates
Carbohydrase
Carbohydrates  Sugars
_
_
Hydrochloric
Acid
_
_
Pepsin
Bile (from gall
Bladder in liver)
Pancreatic Juice
(from Pancreas)
Proteins
Fats
Protease
Lipase
Passing the food from the mouth
to the stomach by a process
named peristalsis.
Breaks down hard bones into
smaller pieces. Provides an acidic
medium for pepsin to begin its
function.
Protein  Amino Acids
Lipids  Fatty acids + glycerol
Fats
Carbohydrates
Proteins
Lipase
Carbohydrase
Protease
Lipids  Fatty acids + glycerol
Carbohydrates  Sugars
Protein  Amino Acids
Large
Intestine
_
_
_
Absorbs water along with
vitamins and minerals that are
dissolved in it and passes
undigested food through.
Digestion is a chemical reaction, as one substance is changed into a different substance. For this chemical
reaction to occur, enzymes are present within the alimentary canal. Enzymes are substances/chemicals
that speeds up a chemical reaction without
being used up. Enzymes belongs to a larger
category called Catalyst.
Catalyst or biological catalysts usually work in the form of a lock and key model. It can be explained as
follows.
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