biological chemistry

Biological Importance of Water


biological functions of water

Biological Importance of Water

Water is the mother liquid of all forms of life. The essentiality of water for living systems is quite evident as without water, there is no life. No other substance on earth is abundant as water. All aspects of cell structure and functions are adapted to the physical and chemical properties of water. The following are the important biological significance or importance of water in the living system.

(1).  Water is a ‘universal solvent’.

(2).   Water can dissolve most of the biologically important molecules.

(3).  It is the solvent of life. The life originated in water and adapted to survive only in the presence of water.

(4).  About 70 to 90% of a cell occupies water.

(5).  Water acts as a medium for the diffusion of molecules in the cell.

(6).  Osmotic concentration of cell is maintained by water and dissolved solutes.

(7).  The turgidity of the cell is maintained by the water.

(8).  Translocation of inorganic and organic compounds in the living system takes place through the water.

(9).  Carbohydrates, the product of photosynthesis, in plants are transported through the water.

(10).  Water is the source of H+ ions for photosynthesis.

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biological chemistry

Physical and Chemical Properties of Water and its Biological Significance


biological significance of water

Physical and Chemical Properties of Water and its Biological Significance

Water is the most abundant substance in the living system. Water makes up about 70% or more of the weight of almost all organisms. The life has originated in remote past in the aqueous environment. The properties (both physical and chemical) of water enabled it as the ‘solvent of life’. The water possesses some unusual physical and chemical properties. These ‘unusual properties’ are responsible making water as the ‘solvent of life’. The present post describes the Physical, Chemical and Unusual Properties of Water. We will also discuss the importance or significance of these properties of water in the biological system.

The unusual properties of water are mainly due to three factors:

(A).  The small size of water molecules

(B).  The polarity of water molecules

(C).  The formation of hydrogen bonds between adjacent water molecules

Most important physio-chemical and unusual properties of water can be summarized into the following heads:

(1).  Solvent properties of water

(2).  High heat capacity of water

(3).  High heat of vaporization

(4).  High heat of fusion

(5).  Density and freezing properties

(6).  High cohesion, adhesion and surface tension of water

(7).  Water acts as a reactant

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biological chemistry

How Hydrogen Bond is Formed in Water?


biological significance of hydrogen bonds in water

Hydrogen Bond: Formation, Structure and Properties of Hydrogen Bonds in Water

The life was originated and started its evolution in water. Without water, life could not have existed on this planet. The properties of water, both physical and chemical, enabled water as the ‘solvent of life’. The water possesses some unusual physical and chemical properties. These ‘unusual properties’ of water makes water as the solvent of life. The unusual properties of water are due to presence of Hydrogen Bonds in them. The present post describes the method of formation of hydrogen bonds in water its properties.

How Hydrogen Bond is formed in Water?

Ø  Water is a polar solvent.

Ø  The polarity of a molecule due to uneven of distribution charges in them.

Ø  Uneven charge distribution causes a dipole formation.

Ø  One part (pole) of water molecule is slightly positive.

Ø  The other part (pole) of water molecule is slightly negative.

Ø  This type of difference in the distribution of positive and negative charges in a molecule is due to the huge difference in the electronegativity of the atoms in them.

Ø  Electronegativity is the ability of an atom to attract bonded pair of electrons towards its nucleus.

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mcq biology

MCQ on Water: Physical and Chemical Properties; pH and Buffer Systems Part 3 (Biochemistry MCQ-13)


biochemistry MCQ Water Buffer 

(Sample/Model/Practice Questions for CSIR JRF/NET Life Science Examination, ICMR JRF Exam, DBT BET JRF Exam,, GATE BT and XL Exam, ICAR JRF NE Exam, PG Entrance Exam, JAM Exam, GS Biology Exam and Medical Entrance Exam)

(1). What is the molecular weight of water?

a.       10 g/mol
b.      15 g/mol
c.       18 g/mol
d.      20 g/mol

(2). What is the H+ ion concentration in pure water?

a.       1 X 10-7 m
b.      1 X 107 m
c.       1 X 10-14 m
d.      1 X 1014 m

(3). The equilibrium constant of ionization reaction of pure water is:

a.       1.8 X 10-14 M
b.      1.8 X 10-16 M
c.       1.8 X 10-7 M
d.      1.8 X 10-7 M

(4). The pH of pure water is neutral, the best explanation for this is:

a.       The pH of pure water is 7
b.      In pure water the concentration of H+ and OH are same
c.       Water do not contain free H+ or OH ions
d.      What will never ionize

(5). What is the concentration of OH ions in a solution with an H+ ion concentration of 1.3 X 10-4M?

a.       7.7 X 10-11 M
b.      7.7 X 10-10M
c.       1.4 X 10-11M
d.      1.4 X 10-10 M

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biological chemistry

Why the pH of water is 7

Biochemical Principle Behind pH Scale and pH of Water
(The Relationship Between Equilibrium Constant, Ion Product of Water and pH Scale)


pH is defined as the negative logarithm of hydrogen ion concentration in a medium. For example, if you are saying a solution with pH 6.5, it means that the concentration of H+ ions in that solution expressed in negative logarithmic term is 6.5. pH is a scale, a scale to measure the H+ ion concentration in a medium. The pH scale starts from 0 to 14. The middle value in the scale (7) is considered as a neutral pH and any solution with pH below 7 is considered as acidic pH. Similarly any solution with pH above 7 is considered as a basic solution. Like the Celsius temperature scale, the pH scale is also constructed on the basis of water, the universal solvent and also the solvent of life.

pH of water is 7 and it is considered as a neutral pH. The term neutral does not mean that water does not contain H+ ions. In fact the term neutral means water contains equal number of H+ and OH- ions. Everyone knows that the pH of water is 7 and it is a neutral pH. But people often forgot to think why the pH of water is 7; from where the value 7 comes… is it a randomly assigned value to water? No, not at all.., the value 7 is an absolute value derived from the ion product of water. The ion product (the product of ions in water i.e., product of H+ and OH-) of water thus forms the basis of pH scale. The video tutorial explains how water got the pH value 7 and how the ion product of water is related to pH scale.


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