Nutrition in organisms

There are some basic essential activities performed by an organism to survive, these processes are called life processes, or these may be called basic functions performed for the survival of organisms. The life processes are respiration, nutrition, transportation, excretion, control, and coordination.

Life processes are the main criteria to decide whether something is alive or not. If someone is performing life processes can be called alive. i.e. breathing, movement, nutrition, excretion, etc.

Life processes can be categorized as

Some others which are may or may not be seen in some organisms like plants and microscopic organisms as

  • Movement
  • Growth
  • reproduction
Nutrition In Organisms

The process by which organisms obtain and utilize food for their growth, development, and maintenance is called nutrition and the chemical substances present in the food are called nutrients. So, nutrients are the substances used by organisms to survive, grow and reproduce. 

The seven basic components of nutrients are carbohydrates, protein, fat, vitamins, minerals, fiber, and water.

Every organism needs energy to perform its life processes, and these energies are acquired by proteins and ATP formation, for this we need raw material in the form of food.

So food is the source of energy by which we get energy. This is different in plants and animals as Plants manufacture their own food by photosynthesis, but animals including humans have to take in ready-made food.

Types of nutrition

There are two types of nutrition: Autotrophic nutrition and heterotrophic nutrition.

Autotrophic nutrition Heterotrophic nutrition
(AUTO: self, TROPHOS: food)   (Hetero: different, Trophos: food)
Green plants and certain bacteria manufacture their own food (organic substances) from inorganic substances like CO2 and H2O using energy from sunlight Food – Organic and inorganic substances obtained by feeding on other organisms are called heterotrophic. In other words, the organisms cannot produce their food and are dependent on others.
Autotrophic nutrition:

In autotrophic nutrition, the food is synthesized by the organism itself, and in the process of food, production photosynthesis takes place in the presence of sunlight and carbon-di-oxide with the help of chlorophyll.

With the help of chlorophyll, carbohydrates are produced as the product of photosynthesis. The remaining carbohydrates which are not utilized by the plant, are stored in the form of starch. The starch serves as the internal energy reserve to be used as and when required by the plant.

Process of photosynthesis:

These are the events that occur during photosynthesis:

  • Chlorophyll absorbs light energy.
  • Conversion of light energy into chemical energy and water molecules splits into hydrogen and oxygen.
  • Reduction of carbon dioxide to carbohydrates.


In the whole process of photosynthesis chlorophyll, water, carbon-di-oxide, and sunlight are the essential elements. Water for photosynthesis is taken from the soil by the roots in terrestrial plants, from the soil other important materials like nitrogen, phosphorus, iron, and magnesium are taken.

Heterotrophic nutrition

As we know nutrition differs depending on the type and availability of food materials as well as how it organism obtains that food.

  • In single-celled organisms, the food may be taken in by the entire surface. But as the organism becomes complex, different parts become specialized to perform different functions.
  • For example, Amoeba takes food using a temporary finger- Food particles such as minute bacteria are enclosed (caught) by pseudopodia (pseudo = false, podia = feet) to form a food vacuole (Ingestion).
Nutrition in organisms

Nutrition in amoeba

Types of heterotrophic nutrition

Holozoic nutrition: Organisms engulf food in the body, digest it and absorb the soluble products of digestion, e.g. humans.

Saprophytic nutrition: Organisms secrete digestive enzymes onto dead organic material and absorb the products of digestion, e.g. certain bacteria and fungi.

Parasitic nutrition: Food is derived from other living organisms by living on or inside their body e.g., certain bacteria, roundworms, tapeworms, Cuscuta, etc.

Nutrition in human

Human nutrition deals with the provision of essential nutrients in food which are necessary to support good health and life. As we all know, good nutrition is essential for physical and mental growth, so it is highly recommended to take care of it for the whole of humankind.

Nutrients can be divided into two groups:

  1. Macronutrients: These are the components that humans consume in the largest quantities. These are mainly classified into carbohydrates, proteins, and fats. The macronutrients mainly provide energy to organisms.
  2. Micronutrients: These are substances introduced in small quantities, but they are required for adequate growth. eg. Vitamins, minerals
The digestive system in human

The digestive system of humans consists of an alimentary canal which is associated with digestive glands.

The human alimentary canal is a continuous muscular digestive tube that runs through the body. It opens at two ends with openings, which are the mouth at the anterior, and the anus at the posterior end.

  • Digestion in humans takes place through various organs through many processes.

alimentary canal of Human

Organs associated with the human digestive system

1. Mouth

Having associated organs (teeth, tongue)- Minute quantities of water, water-soluble vitamins, and simple sugars like glucose (as in honey) are absorbed in the mouth. Saliva contains only a single enzyme Amylase (old name Ptyalin) which acts on starch.

2. Pharynx (or throat):

 A cavity inside of the mouth. It is a common passage for inhaled air and swallowing food.

3. Oesophagus:

A narrow tube arising from the pharynx, continuing through the thorax and ending in the stomach, food moves in the stomach through the esophagus in the form of the bolus through the movement of peristalsis. These peristaltic movements occur all along the gut.

4. Stomach:

  • An elastic bag-like structure with highly muscular walls, located below the diaphragm.The muscular walls of the stomach help in mixing the food thoroughly with more digestive juices.
  • The stomach churns the food mixing it with gastric juice and thus produces a creamy chyme (partially digested food). It contains Water (98%), some salts, hydrochloric acid (0.5%), lubricant mucin, and two enzymes pepsin. Water, glucose, ethanol (alcohol), certain minerals, vitamins, and certain drugs may be absorbed into the cells lining the stomach.
  • This absorption occurs by osmosis, diffusion (down the concentration gradient), and active transport (against a concentration gradient

5. Small intestine:

  •  It is the longest part of the alimentary canal, a tube about 7 meters long and about 2.5 cm wide.
  • The exit of food from the stomach is regulated by a sphincter muscle which releases it in small amounts into the small intestine. From the stomach, the food now enters the small intestine.
  • The small intestine is the site of the complete digestion of carbohydrates, proteins, and fats. The liver and pancreas help the small intestine with digestion by their juices, pancreatic enzyme makes the food alkaline, as it was acidic from the stomach.
  • Bile juice comes from the liver which acts on fats as, with the help of bile, fat molecules break into small globules, and enzymes work on it effectively.
  • pancreatic juice contains enzymes like trypsin for digesting proteins and lipase for breaking down emulsified fats. The enzymes present in it finally convert the proteins to amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol.
  • Many folds (finger-like projection) in its wall called villi (singular, villus) further increase the surface area of absorption,
  • The epithelial cells have microvilli which are projections of the plasma membrane to further increase the absorptive surface.
  • It is narrow for the slow movement of nutrients allowing absorption.
  • Nutrients absorbed into the blood is carried by veins into the liver, and the nutrients absorbed by the lacteals (small lymph vessels) enter the lymphatic system.

 The three subdivisions of the small intestine are:

(I) DuodenumShort upper part, next to the stomach

(ii) JejunumSlightly longer part, about 2 meters long.

(iii) IleumLongest, about 4 meters long, coiled and twisted.

6. Large Intestine: About 1.5 meters long, It has three parts:

(i) CaecumSmall blind pouch found at the junction of the small and large intestines. A narrow worm-shaped tube (vermiform appendix) projects from the caecum.

(ii) Colon: A little over 1-meter-long, it has three parts termed ascending, transverse, and descending limbs of the colon.

(iii) Rectum: Last part, about 15 cm. long. It has two parts, the rectum proper and the anal canal. The anus is the external opening surrounded by circular muscles (sphincters).

Most of the water present in the food is absorbed in the colon by diffusion. Unabsorbed food is sent here, some mineral ions are absorbed by the colon through active transport, rest material is removed from here through the anus.

Note- The vermiform appendix is a vestigial (functionless) organ in humans, but is large and functional in herbivorous mammals.

Some Glands involved in the digestive system

1. Parotid glands- located in front of and below each ear, produce watery saliva rich in amylase

2. Submaxillary glandsclose to the inner side of the lower jaw, produce water and mucus

3. Sublingual glandsbelow the tongue, produce water and mucus.

4. LiverLiver is the largest gland, located on the upper right side of the abdomen below the diaphragm. It secretes bile.

structure of liver : Nutrition in human

structure of liver

5. Pancreas-located in the bend of the duodenum. Its digestive secretion (pancreatic juice) is poured into the duodenum by the pancreatic duct.

Nutrition in organisms: Pancreas


Endocrine Gland And Hormones

Some enzymes and their role in indigestion-

enzymes, their sources and role

Some enzymes and their role


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