Autotrophic Nutrition in green plants , Mechanism of water & minerals absorption

From Online Sciences - November 15, 2017

Nutrition is one of the characteristics from which the living organism obtains the energy required for all the vital processes of the body , Nutrition is the scientific study of food and various modes of nutrition of the living organisms .


The importance of food for the living organisms that it is a source of the required energy to do all vital processes in the body of the living organism , It constitutes the material needed for the growth and repair of the worn-out tissues .

Types of nutrition

There are two types of nutrition which are Autotrophic nutrition , Heterotrophic nutrition .

Autotrophic nutrition

Autotrophic nutrition is a type ofnutrition in which autotrophs can manufacture their food by themselves .

Examples : The green plants and some types of bacteria can synthesize , inside their cells , the high-energy types of organic food ( such as sugar , starch , fats and proteins ) from the simple , raw and low-energy inorganic materials ( such as CO2 , water and mineral salts ) from the surrounding habitat .

They use these low-energy materials together with the light energy and carry out certain chemical reactions during a process which is celled photosynthesis .

Heterotrophic nutrition

Heterotrophic nutrition is a type of nutrition in which heterotrophs obtain their food from the bodies of other living organisms , They obtain the high-energy food substances either from the green plants or from the animals that have previously fed on plants .

Examples : Heterotrophs can be classified into :

Autotrophic nutrition in green plants

The autotrophic nutrition which is carried out by the green plants includes two important processes which are the process of absorption of water , salts and carbon dioxide , the process of photosynthesis .

Process of absorption of water and salts

The higher green plants absorb water and mineral salts from the soil through the root hairs that present in the root system of plant , then this soil solution is transported from one cell to another , until it finally reaches the ascending vessels .

Root hair is an extension of a single cell of the piliferous layer , It is lined internally with a thin layer of cytoplasm which contains a nucleus and a large sap vacuole , It is about 4 mm .

It doesnt exist for more than a few days or weeks because the epidermal cells are lost from time to time and regenerated continuously from the zone of elongation , Root hair function is fixing the plant into the soil , absorption of water and mineral salts from the soil .

Adaptation of the root hairs to their functions :

Mechanism of water absorption

The mechanism depends on several physical phenomena such as Diffusion phenomenon and Osmosis phenomenon .

Diffusion phenomenon

Diffusion phenomenon is the movement of molecules of ions from a highly concentrated medium to a low-concentrated medium , due the continuous free motion of molecules of the diffused substance , such as the diffusion of a drop of ink when it falls into a beaker containing water .

Osmosis phenomenon

It is the diffusion ( movement ) of water from a medium of high concentration of water ( low concentration of solute molecules ) to another with a low water concentration ( high concentration of solute molecules ) through a semi-permeable membrane , The pressure that causes the water movement is called osmotic pressure .

Osmosis phenomenon is the pressure that causes the diffusion of water through a semi-permeable membrane , due to the difference in concentration of the dissolving substances ( solutes ) in water on the two sides of the membrane .

The relation between the concentration of solutes in the solution and osmotic pressure of the solution is directly proportional , The osmotic pressure increases by increasing in the concentration of solutes in the solution .

Permeability phenomenon

The cell walls and cell membranes differ in their permeability properties , as the following :

Walls and membranes are impermeable , They do not allow water and salts to pass , such as the walls covered by lignin , suberin or cutin .

Walls and membranes are permeable , They allow water and salts to pass , such as cellulose walls .

Imbibition phenomenon

Explanation of water absorption by the root

Absorption of mineral salts


Macro-nutrients importance


Mechanism of minerals absorption


Selective permeability

Active transport

Experiment on Nitella alga


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