Types of Living Organisms on the Basis of Mode of Nutrition

Types of living organisms on the basis of mode of nutrition

Living organisms can be divided into two groups on the basis of their mode of nutrition.

  1. Autotrophic organisms
  2. Heterotrophic organisms

Autotrophic organisms or autotrophs


Organisms that can prepare their own food from inorganic raw materials taken from their surrounding area known as autotrophic organisms.

Way of nutrition

The molecules of raw materials are small enough to pass through the cell membrane in dissolved form.


Most of the autographs are photosynthetic like plants, algae, and some bacteria, etc.

Heterotrophic organisms


Organisms that are unable to prepare their own from simple inorganic compounds are known as heterotrophic organisms.

Way of nutrition

Heterotrophs obtain food from their environment. Many of the organic molecules found in nature are so large that they cannot be absorbed by the cell membrane. They must first be broken down into smaller and more absorbable molecular units.


Most bacteria, fungi and animals have heterotrophic mode of nutrition.

Basic components of the food

  1. Carbohydrates 2.proteins 3.fats    4.vitamins   5.minerlas   6.water

Main stages of photosynthesis 

The whole process of photosynthesis mainly divided in two stages.

  1. Light reaction
  2. Dark reaction

Light reaction

Definition: light reaction is also known as light dependent reaction, as it requires light in light reaction. Chlorophyll and other molecules capture energy from light and convert some of it into the chemical energy.


  1. Photolysis: in the light reaction, light energy is trapped by chlorophyll. This light energy is used to slit water molecules into oxygen and hydrogen. This splitting of water molecules is known as “photolysis” (photo=light, lysis=to break).
  2. Release of oxygen

Oxygen which is produced during photolysis is released in the environment and hydrogen which is also produced during photolysis is used, together with CO2 in the synthesis of glucose.

  1. Conversion of light energy into chemical energy

Chlorophyll and other pigment molecules within chloroplast, form highly-organized assemblies known as “photo systems”. Conversion of light energy into chemical energy in these photo systems produces two energy rich compounds which are

  • NADPH2 nicotinamide adenine dinucleotide phosphate
  • ATP (adenosine tri- phosphate).

Formation of NADPH2

NADP already exist in the chloroplast reduced into NADPH2.


NADP+H+ +e         ——————> NADPH2

(in cell)  (from H2O)                                                 (reduced form)

Formation of ATP

ADP is another compound which is present in the cell. ADP (adenosine-di-phosphate) reacts with phosphate group by using the light energy to forms ATP.



Dark reaction

Dark reaction is also known as the light independent reaction because light energy is not captured during this phase of photosynthesis.

Mechanism of dark reaction

NADPH2 and ATP are the two energy rich compounds which are formed during the light reaction. These compounds provide for the combination of CO2and H2O to synthesis glucose.

Fixation of CO2  and its conversion into glucose occurs in the chloroplast by means of a series of reaction known as Calvin cycle or dark reactions. At this stage of photosynthesis glucose molecules are formed and stored in the chloroplasts as search.

Dietary fibers

Cell wall of plant cells contains the dietary fibers of roughage, which is taken by us in our food, like fruits vegetables.


  1. Dietary fibers provide bulk to the food in the intestine by retaining water.
  2. It also helps to make the passage of food easier, by stimulating the gut for peristaltic movement.
  3. Intestinal disorders and constipation may be caused by the shortage or absence of dietary fibers in our food.

Tooth decay Definition

Erosion of enamel and the dentine is known as “tooth decay”

Stages of tooth decay

  1. Major reason is dental plaque which is a sticky substance consisting of food remains, mucus and bacteria.
  2. Dental plaque covers the teeth as a hard layer.
  3. Bacteria present in the plaque produce an acid which gradually destroys the enamel and makes a hollow cavity in it.

Causes of tooth decry

  1. Imporper brushing or not cases a hard layer of plaque to develop over tooth.
  2. Eating too much sweets, candies and chocolates also causes the bacteria to grow in the plaque.
  3. The bacteria feed on left over sweets and produce acid that causes tooth decay.
  4. If this decay is ignored, the erosion penetrates deep to destroy the dentine.
  5. After destroying the dentine bacteria infect the pulp which results in tooth ache and tooth is gradually destroyed.


  1. Proper bushing can prevent tooth decay.
  2. Use of a fluoride, based tooth paste makes the tooth strong.
  3. Cutting down sugary diet is also prevention against tooth decay.
  4. Regular dentist ensure the health of teeth.

What are the factors which effect the rate of Photosynthesis?

Some of the factors which effect the rate of Photosynthesis are light intensity

  1. Temperature
  2. CO2 concentration
  3. Light intensity

Light intensity effects the rate of light reaction, in the following ways.

  1. In the bright light water molecules in the chloroplast spilt very fast.
  2. An increase in light intensity speeds up the process of Photosynthesis.


After a particular point, any further increase in light intensity has only a little effect on the process.


This limit on the rate of increase is because all available chloroplasts are fully occupied in light absorption so no more light can be absorbed or used.

  1. Temperature

Temperature has an effect on the dark reaction during Photosynthesis. A rise in temperature increase the rate of ration between CO2 and water molecules to make carbohydrates or glucose hence the rate of Photosynthesis is also increased with the increased in temperature within optimum limits.


Although there is only 0.03% of CO2 in the air, which is absorbed during Photosynthesis but it is a very important factors effecting the rate of Photosynthesis. Shortage of CO2 slows down the rate of Photosynthesis. Increase in the concentration of CO2 also improves the rate of Photosynthesis.

Effect of carbon dioxide concentration of opening of stomata

When the concentration of CO2 inside the leaf cells decreases, the stomata open to allow the entrance of CO2to the leaf cells.

Health problems

Following are some problems related to nutrition.

  • Under-nutrition

When there is a shortage of food or very insufficient food is available the problems of under-nutrition arises.

Effects of under-nutrition

  1. It specially affects the children.
  2. Insufficient food affects the physical growth.
  3. It also affects the mental growth
  4. Such persons reduce to a skeleton only. This condition is known as marasmus.

Affected region

It is a mainly the problem of poor countries, where supply of food is not sufficient. Pamine stricken countries like Ethopia are facing this problem.

  • Mal-nutrition

If one of more basic nutrition are missing from a diet, this condition is known as mal-nutrition.

Affects of mal-nutrition

  1. Person of any age can be affected by mal-nutrition.
  2. Infants and woman are badly affected.
  3. It can cause the retardation in growth.
  4. It can also cause the death.

Affected region

In most of the developing countries mal-nutrition is the major cause of death among the children up to the age of five. In Africa and Asia the diet is usually deficient in proteins and carbohydrates.

  • Over-nutrition

Taking of extra and excess nutrients is referred to as over-nutrition.

Affect of over-nutrition

Obesity is the most common disorder caused by the over-nutrition it is due to the excessive consumption of refined carbohydrates and fats.

Affected regions

It is commonly observed in developed countries where excess supply of food is available.

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