Definition of Nutrition

All organisms need nutrients to survive and function. The process of obtaining these nutrients from different types of food is called nutrition.

Types of Nutrition:

Mainly two types:

  1. Autotrophic Nutrition
  2. Heterotrophic Nutrition: 3 types: a) Saprophytic, b) Parasitic, c) Holozoic.

1. Autotrophic Nutrition

In autotrophic nutrition, an organism makes its food from simple inorganic materials like water, minerals, and carbon dioxide in the presence of Sunlight with the help of chlorophyll. This process is called photosynthesis. All green plants examples of autotrophs.

Autotrophic nutrition

2. Heterotrophic Nutrition

In heterotrophic nutrition, organisms take their food from another organism because it cannot prepare their food due to a lack of chlorophyll. There are three types of heterotrophs-

a) Holozoic 
The organisms who take their food in the form of solid or liquid from other organisms are called holozoic. All animals are examples of holozoic. It can be divided into two groups as mentioned below diagram:

Holozoic nutrition

b) Parasite
In parasitic nutrition, an organism lives on the surface or inside of the body of another living organism (known as a host) and take nutrients directly from their host. eg. Tapeworm, Dodders, etc.

Parasitic nutrition

c) Saprozoic
In Saprozoic nutrition, an organism fulfills its own nutrients requirements from the surroundings through the absorption of simple organic materials and dissolved salts in the water. Mainly protozoa and fungi possess this type of Nutrition.

Saprophytic nutrition

The need for Food or Nutrition

There are four reasons to create the need for food or nutrition for an organism as mentioned below-

For Supply of Energy 

All biological activities need the energy to perform this. This need for energy fulfills by nutrients and these nutrients are found in the food intake or prepare by the organism.

For Protection From Diseases

Nutrients develop immunity in the body of organisms for protection from diseases. In the lack of these nutrients, many diseases develop in our bodies.

For Physical Growth 

Without the balanced quantity of nutrients like carbohydrates, proteins, fat, vitamins, etc proper growth of the body is impossible. For perfect development of the body, a well-balanced diet is highly required.

For Regeneration of Body 

In our body, many cells degenerate daily. nutrients play a very important role in the process of regeneration of the body.


Components of Nutrients: Mainly two types-

Components of Nutrients

1. Organic Substances:

There are four main nutrients are found in our food as mentioned below-

a) Carbohydrates:

A carbohydrate is a biomolecular macronutrient of our food consisting mainly of the atoms of carbon, hydrogen, and oxygen. It found in these three forms in our food- monosaccharide, disaccharide, and polysaccharide. Two monosaccharides (like glucose, fructose, etc.) make one disaccharide, and more than two monosaccharides or disaccharides make a polysaccharide.

The main function of carbohydrates is to provide energy to the body for biological and physical activities. according to recent studies carbohydrates are an influence on mood, memory, and decision-making power. Fruits, vegetables, grains, milk, potato, eggs, sugarcane, etc. are rich sources of carbohydrates.

Types and Uses of Carbohydrates

b) Proteins:

Protein is a biomolecular macronutrient of our food composed of amino acids that are organic. It is the compound of carbon, hydrogen, nitrogen, and oxygen or sulfur. According to the national institute of health (NIH), amino acids are the building blocks of protein and proteins are the building blocks of muscles.

The main functions of protein repair and build body tissues of organisms and play some key role in the form of enzymes and hormones. Meet, eggs, milk, almond, broccoli, fish, pulses, etc. are the richest source of proteins.

Uses of Proteins

c) Fats:

Fat is also a biomolecular macronutrient of our food composed of fatty acids and glycerol. Fatty acid and glycerols are compounds of carbon, hydrogen, and oxygen.

The main functions of fat play some important structural and metabolic functions including energy storage, waterproofing, and thermal insulation in many organisms. In the lack condition of the main energy source carbohydrates, our body turns to fat as a backup energy source. Dark chocolate, eggs, fatty fish, flaxseed, nuts, olive oil, etc. are the richest source of fats. Types of fats are mentioned in this image-

Types and Uses Of Fats

e) Nucleic Acids:

Nucleic acids are the most important of all biomolecules which are composed of nucleotides and nucleotides composed of a 5-carbon sugar, a phosphate group, and a nitrogenous base. If the sugar is a compound of ribose, the nucleic acid is RNA (ribonucleic acid) and if the sugar is the compound of deoxyribose, the nucleic acid is DNA (deoxyribonucleic acid). More information about structure are mentioned in this image-

Structure of Nucleic acids

The main functions of nucleic acid are creating, encoding, and storing information of every living cells of organisms. This encoded information is known as genetic code which carries hereditary properties to next-generation also. Green vegetables, meats, eggs, milk products, etc. are rich sources of nucleic acids.

f) Vitamins:

Vitamins are very important organic essential micronutrients of our food. Essential nutrients can not be synthesized in organisms, therefore, must be obtained through the diet. Which an organism needs in small quantities for the proper functioning of its metabolism. On the basis of solubility, vitamins can be divide into two groups-
1: Fat-soluble vitamins- Vitamins A, D, E, and K are fat-soluble vitamins. These can be stored in fat tissue and the liver for a long time.
2: Water-soluble vitamins: Vitamins B-complex and C are water-soluble vitamins. These can not be stored for a long time because excess amount of its with the urine these excrete from the body.
Functions, dietary effects, chemical names,s and food sources of these vitamins are mentioned in this chart.

Water-soluble vitamins:

Vitamins Main Function Main Sources
B1 (Thiamin) • Helps release energy from carbohydrates
• It needed for the proper working of the heart, digestive and nervous systems
• Important for growth
• Yeast extracts
• Wheatgerm and wheat bran
• Nuts and seeds
• Fortified bread and breakfast cereals
• Wholemeal flour and cereals
B2 (Riboflavin • Important for growth and repair of tissues, especially the skin and eyes
• Helps release energy from foo
• Important for growth and repair of tissues, especially the skin and eyes
• Helps release energy from foo
B3 (Niacin) • Helps to release energy from food
• Important for growth
• Helps control cholesterol levels
• Important for the nervous system and digestive health
• Lean meat
• Yeast
• Bran
• Peanuts
• Eggs
• Vegetables
• Milk
B5(Pantothenic acid) • Helps process carbohydrate, fat, and protein for energy
• Involved in the formation of fatty acids and cholesterol
• Yeast extracts
• Fish
• Lean meat
• Legumes
• Nuts
• Eggs
• Green leafy vegetables
B6 (Pyridoxine) • Helps process protein and carbohydrate
• Assists in making red blood cells
• Important for brain function and immune system health
• Lean meat and poultry
• Fish
• Yeast extracts
• Soybeans
• Nuts
• Wholegrains
• Green leafy vegetables
B12 (Cyano-cobalamin) • Works with folate to produce new blood and nerve cells and DNA
• Helps process carbohydrate and fat
• Found only in animal products (lean meat, seafood, eggs, and milk)
• Fortified soy products
Biotin • Helps process fat and protein
• Important for growth and nerve cell function
• Egg yolk
• Oats
• Wholegrains
• Mushrooms
• Nuts
Folate (Folic acid) • Produces red blood cells and DNA
• Keeps the nervous system healthy
• Important in early pregnancy to prevent neural tube defects
• Yeast
• Green leafy vegetables
• Wholegrains
• Peas
• Nuts
C (Ascorbic acid) . Needed for healthy gums, bones, teeth, skin and increase the immunity of the whole body Citrus fruits, vegetables, pineapple, mango, capsicum, spinach.

Fat-soluble vitamins:

A (Retinol) • Essential for eyesight, especially night vision
• Keeps the skin in the mouth, respiratory tract, and urinary tract moist
• Builds immunity
• Full cream dairy products
• Butter and table margarine
• Egg yolk
• Orange, yellow and green fruits and vegetables (carrots, spinach, apricots, mango, pumpkin, broccoli)
D (Cholecalciferol) • Works with calcium and phosphorus to make strong, healthy bones and teeth • Sunlight (about 10 minutes every day)
• Cod liver oil and oily fish (herring, salmon, tuna, and sardines)
• Eggs
E (Tocopherol) • This antioxidant may play a role in preventing cancer and heart disease • Wheatgerm
• Nuts and seeds
• Eggs
• Wholegrains
• Fish
• Fruit and vegetables
K (Phylloquinone or Napthoquinone) • Essential for blood clotting • Green vegetables
• Broccoli and cauliflower
• Eggs
• Cheese
• Wholemeal flour and bread
a) Mineral Salts:

There are some minerals that are found in food and essential micronutrients for a healthy life. Like iron is required for blood formation, calcium for bones, iodine for thyroxine hormones, phosphorous for teeth and bones, sodium and potassium for electrolyte and water balance in the body, etc.

Minerals Main Sources Functions
Calcium Milk and Milk Product Builds and Maintains bone structure, Gives vitality, Heal wounds, Regulates Heartbeats, etc.
Zinc Whole grains, Seafood, Meats, & Eggs Involves in Digestion and Metabolism, Aids in Healing.
Phosphorous Grains, Vegetables, Poultry, & Eggs Bones and Nerve building, and Nourishes brains.
Fluoride Fluorinated water, Marine fish, etc. Stimulates Bone Formation, and Reserves Dental caries.
Iodine Seafood, & Iodized Salts Metabolism normalizes, Prevents Goitre, and Normalizes glands and cells’ action.
Iron Green Vegetables, Grains, & Meats Hemoglobin Formation and increase resistance to stress and diseases
Magnesium Nuts, Green Vegetables, and Whole Grains New cell promotor in the body, Balancing of acid and alkaline, etc.
Chromium Corn Oil, Whole Grains, and Cereals Glucose metabolism, and Increase effectiveness of Insulin.
Copper Nuts, Organ Meats, and Oysters Helps in iron absorption, Synthesis of Hemoglobin, Metabolism of Ascorbic acids, etc
Manganese Fruits, Nuts, and Vegetables Controlling nervous system, enzyme activation, Sex hormone production, etc.
Molybdenum Nuts, Legumes, Whole grains Function as a cofactor of a limited number of enzymes.
Potassium Fruits, Green Vegetables, and Lean Meats Healer in the body, Fluid balancing, control activity of heart muscles, etc.
Selenium Grains, Seafood, and Organ Meats Protect body tissues against oxidative damage from radiation and normal metabolic processing.
Sodium Vegetables, Whole grains, Salts, Alfalfa, Meat, etc. Help in Digestion, Water balancing in the body, Purifies the blood, etc.
Chlorine Milk, Salts, Coconuts, Fish, Cheese, etc. Cleanser in the Body, Purify blood, maintain freshness
b) Water:

Water is a very essential inorganic component of our food. It provides a base for all biochemical reactions in organisms. It regulates the temperature of the body, protects organs and tissues, carries nutrients and oxygen to the cell, helps to excrete waste substances from the body, etc.

Different Stages of Nutrition In Animals:

a) Ingestion:

The process of taking food, drink, or other substances into the body is called ingestion. Different organisms have different organs for this process. Some of them are mentioned below:

Frog: Long sticky tongue- catch its prey.

Paramecium: Stiff- hair-like projections called cilia- for ingestion.

Mosquito: Proboscis- sucks blood.

Housefly: Feeding tube- sucks up food in solution form.

Butterfly: Proboscis- suck nectar from flowers.



The process of changing insoluble complex food into simple soluble form with the help of different enzymes and other digestive juices in the body is called digestion. There are different organs are found for digestion in different animals. For example, the human digestion process performed in the elementary canal while in unicellular organisms it’s performed in vacuoles. Types of digestive systems in some animals are mentioned in this image-

Types of Digestive systems in different animals

c) Absorption:

The process of absorbing nutrients into the body from digested food through the digestive system is called absorption. By this process, the body gets the required nutrients. There are different types of organs are found in different animals for this process. For example in humans, this process performed in the small intestine, and nutrients absorb into lacteal and blood vessels which are situated in the villi of the small intestine.

Absorption of Nutrients in human elementary canal

d) Assimilation:

The process of absorbed nutrients from digested food mixing into the protoplasm of body cells is called assimilation. Transportation means of these nutrients from the digestive system to body cells are different in various organisms. In humans, this means is blood and lymph circulatory system.

Assimilation of food in human

e) Egestion:

After absorption of nutrients from digested food rest waste parts, this food excreting from the body is called egestion. Different organisms have different organs for this process. In human anus and urinal tract are the main excretory organs.

Digestion in Humans: 

Digestion in human is a long process so for the convenience of study it is divided into these 5 steps, as mentioned below-

a) Digestion in Buccal Cavity: 

Structure of buccal cavity-

Structure of Buccal Cavity in Human

In the buccal cavity teeth, tongue and saliva make pulp of ingested food. Lisozym which are found in saliva disinfect food. Ptylin enzymes digest a partial amount of complex or polysaccharide carbohydrates like starch into disaccharides like sucrose.

digestion of starch in buccal cavity

So after a long time chewing food bread give a sweet test. Then it is swallowed in the esophagus.

b) Digestion in Stomach:

Structure of stomach-

Structure of Stomach in Human

When the pulp of food reaches into the stomach from a buccal cavity, gastric glands of the stomach secret gastric juice which contains about-

Composition of gastric juice-

Water- 99.45%,   Inorganic substances- 0.15% (HCl, NaCl, KCl, etc.)
Organic substances- 0.40% (pepsinogen, gastric lipase, prorenin, mucin, etc.)

Here HCl makes medium acidic and disinfects food from the harmful germ.
Pepsinogen is converted by HCl into proteolytic enzyme pepsin which partially digests protein into polypeptide and peptones.

Digestion of Protein in stomach

In infants, HCl converts prorenin into renin enzyme which digests milk protein casein into calcium paracaseinate.

Digestion of Milk Protein(casein) in stomach

Gastric lipase partially digests fat into triglycerides.

Fat digestion in stomach

After 2-3 hours of digestion and mixing food converted into chyme. This form of food is forwarded into the duodenum through the pyloric valve.

c) Digestion in Small Intestine:

It can be divide into three parts-

Parts of Small Intestine

Digestion in the duodenum

When food reaches the duodenum in the form of chyme from the stomach gall bladder releases bile and the pancreas releases pancreatic juice.
Composition of Bile-

Water- 98%,   Bile salts- 0.7%,   Bile pigments- 0.2 (bilirubin & biliverdin)
Fats- 0.51% (cholesterol, fatty acids, & lecithin)
Rest- other substances.

Works of bile

1)-It makes acidic food of stomach alkaline so that pancreatic enzymes act on it.
2)- It emulsified fat particles by this process increased the area of the surface to help pancreatic enzyme action and absorption of it in the small intestine.

Composition of pancreatic juice-
Water- 98.5%
Organic substances-
Proteolytic enzyme( trypsin, chymotrypsin, and carboxypeptidase)
Amylolytic enzyme- pancreatic amylase
Lipolytic enzyme- pancreatic lipase and phospholipase
Neucliolytic enzyme- nucleotidase
Inorganic substances- various ions

Works of pancreatic juice

Pancreatic juice plays a very important role in the process of digestion. It can be considered as mentioned below-

Action of pancreatic enzymes of food in duodenum

Function and Structure of Duodenum in Human
Digestion in jejunum:
Jejunum begins at the duodenojejunal flexure and ends at the ileum. It appears red in color due to a large number of blood vessels. Jejunum makes up about two-fifths of the small intestine.
The main function of the jejunum is the absorption of nutrients like carbohydrates, fatty acids, amino acids, etc. which is an extract of digested food of the duodenum. In this part of the small intestine, the digestion process is negligible.
Digestion in ileum:
It is the final and longest part of the small intestine. First It is specified for the absorption of vitamins B12 and the reabsorption of conjugated bile salts. After that, it also absorbs nutrients gained through final digestion occurs in itself through intestinal juice.
When food reaches in ileum intestinal glands secret digestive juices named succuss enterics. It is an alkaline solution (ph value 7.5-8.3) that contains various enzymes for the digestion of food. These name and functions are mentioned below-
1- Actions of amylolytic enzymes:

Carbohydrates digestion in ileum

2- Action of Lipolytic enzymes-

Fat digestion in ileum

3- Actions of Proteolytic and Nucleolytic enzymes-

Digestion of Protein and Nucleoprotein

Diagram of Human Digestive System

d) Absorption of Nutrients:

the process of absorbing nutrients starts from the duodenum and ends in the large intestine. finger-like structure “villi” are found in the inner surface of the small intestine for the increasing area of absorption. These villi are also segmented microvilli for this purpose. Blood and lacteal vessels are found in these villi and microvillus for the absorption of nutrients.

Internal Structure of Small Intestine in Human
Mainly iron absorb into the duodenum, vitamin B12 and conjugated bile salts absorb in the jejunum and other nutrients like simple carbohydrates (monosaccharides: glucose, fructose, galactose, etc), fatty acids, glycerol, amino acids, phosphate, nitrogenous compounds absorb in the ileum. fatty products absorb in lacteal vessels and all other nutrients absorb in blood vessels.

The large intestine performs the vital functions of converting food into feces, absorbing essential vitamins, minerals, and water.

Absorption of Nutrients in human elementary canal

e) Assimilation of Absorbed Nutrients:

After absorption of nutrients in the blood and lacteal vessels, all of these nutrients carry to the liver through the Hepatic portal vein. Where some of these store in modified form and carry to body cells through the blood and lacteal vessels. Body cells assimilate these nutrients into their protoplasm to execute biochemical activities according to need.

The Process of Assimilation

f) Fecal excretion or Egestion:

After absorption of nutrients and water, the waste parts of the food convert into feces through the large intestine. The anus timely egests this feces.

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