Transport in Plants NEET Notes | EduRev

NEET : Transport in Plants NEET Notes | EduRev

 Page 1


 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
CBSE Quick Revision Notes (Class-11 Biology) 
CHAPTER-11 TRANSPORT IN PLANTS 
 
Plant transport various substance like gases, minerals, water, hormones, photosynthetes 
and organic solutes to short distance (one cell to another) or long distance as water from 
roots to tips of stem.  
• Long distance transport occurs through vascular system, xylem and phloem called 
translocation through mass flow. 
• The direction of translocation may be unidirectional as in case of water and 
multidirectional as in minerals and organic solutes.  
 
Simple Diffusion-  
• Movement by diffusion is passive and slow along the concentration 
gradient through permeable membrane. 
• No energy expenditure takes place. It occurs in liquid and gases. 
• Rate of diffusion are affected by gradient of concentration, permeability 
of membrane, temperature and pressure.  
Facilitated Diffusion- 
• Lipid soluble particles easily pass through cell membrane but the 
hydrophilic solutes movement is facilitated. 
• For facilitated diffusion, membrane possesses aquaporins or water 
channels. Aquaporins are membrane proteins for passive transport 
of water soluble substances without utilization of energy. 
• The protein forms channels in membrane for molecules to pass 
through. The porins are proteins that forms huge pores in the 
outer membrane of the plastids, mitochondria etc. 
• Water channels are made up of eight different types of aquaporins. 
Symport, Antiport and Uniport-  
 In Symport, both molecules cross the membrane in the same 
direction.  
 In Antiport, both molecules moves in opposite direction. 
 When a molecule moves across a membrane independent of other 
molecules, the process is called uniport.  
 
Active Transport 
• Uses energy to pump molecules against the concentration gradient. It is carried out by 
membrane proteins. 
Means of Transport
Simple Diffusion Facilitated Diffusion Active Transport
Page 2


 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
CBSE Quick Revision Notes (Class-11 Biology) 
CHAPTER-11 TRANSPORT IN PLANTS 
 
Plant transport various substance like gases, minerals, water, hormones, photosynthetes 
and organic solutes to short distance (one cell to another) or long distance as water from 
roots to tips of stem.  
• Long distance transport occurs through vascular system, xylem and phloem called 
translocation through mass flow. 
• The direction of translocation may be unidirectional as in case of water and 
multidirectional as in minerals and organic solutes.  
 
Simple Diffusion-  
• Movement by diffusion is passive and slow along the concentration 
gradient through permeable membrane. 
• No energy expenditure takes place. It occurs in liquid and gases. 
• Rate of diffusion are affected by gradient of concentration, permeability 
of membrane, temperature and pressure.  
Facilitated Diffusion- 
• Lipid soluble particles easily pass through cell membrane but the 
hydrophilic solutes movement is facilitated. 
• For facilitated diffusion, membrane possesses aquaporins or water 
channels. Aquaporins are membrane proteins for passive transport 
of water soluble substances without utilization of energy. 
• The protein forms channels in membrane for molecules to pass 
through. The porins are proteins that forms huge pores in the 
outer membrane of the plastids, mitochondria etc. 
• Water channels are made up of eight different types of aquaporins. 
Symport, Antiport and Uniport-  
 In Symport, both molecules cross the membrane in the same 
direction.  
 In Antiport, both molecules moves in opposite direction. 
 When a molecule moves across a membrane independent of other 
molecules, the process is called uniport.  
 
Active Transport 
• Uses energy to pump molecules against the concentration gradient. It is carried out by 
membrane proteins. 
Means of Transport
Simple Diffusion Facilitated Diffusion Active Transport
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
• In active transport movable carrier proteins are called pumps.  
• The pumps can transport substance from low concentration to high concentration. The 
carrier proteins are very specific in what it carries across the membrane. 
Comparison between Transport mechanisms- 
Simple diffusion Facilitated diffusion Active transport 
Special membrane protein 
is not required. 
Special membrane protein 
is required. 
Special membrane protein 
is required. 
Not selective Highly selective Highly selective 
Transport do not saturate Transport saturate Transport saturate  
No uphill transport  Uphill transport  Uphill transport  
No ATP energy is required. No ATP energy is required.  ATP energy is required. 
 
Plant Water Relationship 
 Water is essential for all physiological activities of plants along with all living organisms. It 
provide medium for most substances to dissolve in it. 
 Protoplasm of cells contains water in which different molecules are dissolved and 
suspended. 
 Terrestrial plants take lot of water and release most of it in form of water vapour by the 
process of transpiration.  
 Water is the limiting factor for plant growth and productivity in both agricultural and 
natural environments.  
Water Potential (? w)- is a concept fundamental to the understanding water movement. 
Water potential is determined by solute potential (? s) and pressure potential (? p). 
 Water molecules possess kinetic energy. The greater the concentration of water in the 
system, the greater is its kinetic energy or water potential. So pure water has greatest 
water potential. 
 Water potential is denoted by Greek symbol Psi (?) and is expressed in pressure unit 
Pascal (Pa).  
 Water pressure of pure water is taken as zero at standard temperature and pressure. A 
solution has less water potential due to less water concentration. 
 The magnitude of lowering of water potential due to dissolution of solute is called solute 
potential (? s ). Solute potential is always negative. More the solute molecules in the 
solution lesser the solute potential.  
 If a pressure greater than atmospheric pressure is applied to pure water or solution, its 
water potential decreases. Pressure potential is usually positive. Pressure potential is 
denoted by (? p).  
 Water potential of a cell is affected by both solute and pressure potential. The relationship 
is as follows. 
 
 
 
Page 3


 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
CBSE Quick Revision Notes (Class-11 Biology) 
CHAPTER-11 TRANSPORT IN PLANTS 
 
Plant transport various substance like gases, minerals, water, hormones, photosynthetes 
and organic solutes to short distance (one cell to another) or long distance as water from 
roots to tips of stem.  
• Long distance transport occurs through vascular system, xylem and phloem called 
translocation through mass flow. 
• The direction of translocation may be unidirectional as in case of water and 
multidirectional as in minerals and organic solutes.  
 
Simple Diffusion-  
• Movement by diffusion is passive and slow along the concentration 
gradient through permeable membrane. 
• No energy expenditure takes place. It occurs in liquid and gases. 
• Rate of diffusion are affected by gradient of concentration, permeability 
of membrane, temperature and pressure.  
Facilitated Diffusion- 
• Lipid soluble particles easily pass through cell membrane but the 
hydrophilic solutes movement is facilitated. 
• For facilitated diffusion, membrane possesses aquaporins or water 
channels. Aquaporins are membrane proteins for passive transport 
of water soluble substances without utilization of energy. 
• The protein forms channels in membrane for molecules to pass 
through. The porins are proteins that forms huge pores in the 
outer membrane of the plastids, mitochondria etc. 
• Water channels are made up of eight different types of aquaporins. 
Symport, Antiport and Uniport-  
 In Symport, both molecules cross the membrane in the same 
direction.  
 In Antiport, both molecules moves in opposite direction. 
 When a molecule moves across a membrane independent of other 
molecules, the process is called uniport.  
 
Active Transport 
• Uses energy to pump molecules against the concentration gradient. It is carried out by 
membrane proteins. 
Means of Transport
Simple Diffusion Facilitated Diffusion Active Transport
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
• In active transport movable carrier proteins are called pumps.  
• The pumps can transport substance from low concentration to high concentration. The 
carrier proteins are very specific in what it carries across the membrane. 
Comparison between Transport mechanisms- 
Simple diffusion Facilitated diffusion Active transport 
Special membrane protein 
is not required. 
Special membrane protein 
is required. 
Special membrane protein 
is required. 
Not selective Highly selective Highly selective 
Transport do not saturate Transport saturate Transport saturate  
No uphill transport  Uphill transport  Uphill transport  
No ATP energy is required. No ATP energy is required.  ATP energy is required. 
 
Plant Water Relationship 
 Water is essential for all physiological activities of plants along with all living organisms. It 
provide medium for most substances to dissolve in it. 
 Protoplasm of cells contains water in which different molecules are dissolved and 
suspended. 
 Terrestrial plants take lot of water and release most of it in form of water vapour by the 
process of transpiration.  
 Water is the limiting factor for plant growth and productivity in both agricultural and 
natural environments.  
Water Potential (? w)- is a concept fundamental to the understanding water movement. 
Water potential is determined by solute potential (? s) and pressure potential (? p). 
 Water molecules possess kinetic energy. The greater the concentration of water in the 
system, the greater is its kinetic energy or water potential. So pure water has greatest 
water potential. 
 Water potential is denoted by Greek symbol Psi (?) and is expressed in pressure unit 
Pascal (Pa).  
 Water pressure of pure water is taken as zero at standard temperature and pressure. A 
solution has less water potential due to less water concentration. 
 The magnitude of lowering of water potential due to dissolution of solute is called solute 
potential (? s ). Solute potential is always negative. More the solute molecules in the 
solution lesser the solute potential.  
 If a pressure greater than atmospheric pressure is applied to pure water or solution, its 
water potential decreases. Pressure potential is usually positive. Pressure potential is 
denoted by (? p).  
 Water potential of a cell is affected by both solute and pressure potential. The relationship 
is as follows. 
 
 
 
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
 
? w = ? s + ? p 
Osmosis is the diffusion of water across a semi-
permeable membrane. The net direction and rate of 
osmosis depends upon the pressure gradient and 
concentration gradient. Water will move from its 
region of higher concentration to region of lower 
concentration until equilibrium is reached. 
 
• Solute A has more water and less water so high water potential in comparison the solution 
in B container.  
• Osmotic potential is the pressure required to prevent water from diffusing. More the 
solute concentration greater will be the pressure required to prevent water from diffusing 
it. 
• Numerically osmotic pressure is equal to osmotic potential but sign is opposite. Osmotic 
pressure is the positive pressure while osmotic potential is negative. 
• If the surrounding solution balances the osmotic pressure of cytoplasm, the solution is 
called isotonic. 
• If the external solution is more dilute than cytoplasm, it is hypotonic. The cells swell up 
when placed in hypotonic solution. 
• If the external solution is more concentrated than cytoplasm, it is hypertonic. Cell will 
shrink in hypertonic solution.  
• Plasmolysis is the shrinkage of the cytoplasm of the cell from its cell wall under the 
influence of hypertonic solution. The pressure of plasmolysis is usually reversible when 
the cell is placed in hypotonic solution. 
• The pressure build up against the wall due to movement of water inside is called turgor 
pressure. It is responsible for enlargement and extension growth of cells.  
• Imbibition is a special type of diffusion when water is absorbed by solid colloids causing 
them to increase in volume. For example absorption of water by seeds and dry woods. 
Imbibition is also a kind of diffusion because movement of water is from higher 
concentration to lower concentration. 
• Water potential gradient between the absorbent and liquid imbibed is essential for 
imbibition. 
 Long distance transport of water in plants takes place by mass or bulk flow system. It is 
the movement of substance in bulk from one point to another as a result of pressure 
difference between two points. 
 The bulk movement of substances through the conducting or vascular tissue of plants is 
called Translocation. Xylem is associated with translocation of water and mineral salts, 
some organic nitrogen and hormone from roots to aerial parts of plants. 
 Phloem transport organic and inorganic solutes from leaves to other part of plants. 
 
Page 4


 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
CBSE Quick Revision Notes (Class-11 Biology) 
CHAPTER-11 TRANSPORT IN PLANTS 
 
Plant transport various substance like gases, minerals, water, hormones, photosynthetes 
and organic solutes to short distance (one cell to another) or long distance as water from 
roots to tips of stem.  
• Long distance transport occurs through vascular system, xylem and phloem called 
translocation through mass flow. 
• The direction of translocation may be unidirectional as in case of water and 
multidirectional as in minerals and organic solutes.  
 
Simple Diffusion-  
• Movement by diffusion is passive and slow along the concentration 
gradient through permeable membrane. 
• No energy expenditure takes place. It occurs in liquid and gases. 
• Rate of diffusion are affected by gradient of concentration, permeability 
of membrane, temperature and pressure.  
Facilitated Diffusion- 
• Lipid soluble particles easily pass through cell membrane but the 
hydrophilic solutes movement is facilitated. 
• For facilitated diffusion, membrane possesses aquaporins or water 
channels. Aquaporins are membrane proteins for passive transport 
of water soluble substances without utilization of energy. 
• The protein forms channels in membrane for molecules to pass 
through. The porins are proteins that forms huge pores in the 
outer membrane of the plastids, mitochondria etc. 
• Water channels are made up of eight different types of aquaporins. 
Symport, Antiport and Uniport-  
 In Symport, both molecules cross the membrane in the same 
direction.  
 In Antiport, both molecules moves in opposite direction. 
 When a molecule moves across a membrane independent of other 
molecules, the process is called uniport.  
 
Active Transport 
• Uses energy to pump molecules against the concentration gradient. It is carried out by 
membrane proteins. 
Means of Transport
Simple Diffusion Facilitated Diffusion Active Transport
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
• In active transport movable carrier proteins are called pumps.  
• The pumps can transport substance from low concentration to high concentration. The 
carrier proteins are very specific in what it carries across the membrane. 
Comparison between Transport mechanisms- 
Simple diffusion Facilitated diffusion Active transport 
Special membrane protein 
is not required. 
Special membrane protein 
is required. 
Special membrane protein 
is required. 
Not selective Highly selective Highly selective 
Transport do not saturate Transport saturate Transport saturate  
No uphill transport  Uphill transport  Uphill transport  
No ATP energy is required. No ATP energy is required.  ATP energy is required. 
 
Plant Water Relationship 
 Water is essential for all physiological activities of plants along with all living organisms. It 
provide medium for most substances to dissolve in it. 
 Protoplasm of cells contains water in which different molecules are dissolved and 
suspended. 
 Terrestrial plants take lot of water and release most of it in form of water vapour by the 
process of transpiration.  
 Water is the limiting factor for plant growth and productivity in both agricultural and 
natural environments.  
Water Potential (? w)- is a concept fundamental to the understanding water movement. 
Water potential is determined by solute potential (? s) and pressure potential (? p). 
 Water molecules possess kinetic energy. The greater the concentration of water in the 
system, the greater is its kinetic energy or water potential. So pure water has greatest 
water potential. 
 Water potential is denoted by Greek symbol Psi (?) and is expressed in pressure unit 
Pascal (Pa).  
 Water pressure of pure water is taken as zero at standard temperature and pressure. A 
solution has less water potential due to less water concentration. 
 The magnitude of lowering of water potential due to dissolution of solute is called solute 
potential (? s ). Solute potential is always negative. More the solute molecules in the 
solution lesser the solute potential.  
 If a pressure greater than atmospheric pressure is applied to pure water or solution, its 
water potential decreases. Pressure potential is usually positive. Pressure potential is 
denoted by (? p).  
 Water potential of a cell is affected by both solute and pressure potential. The relationship 
is as follows. 
 
 
 
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
 
? w = ? s + ? p 
Osmosis is the diffusion of water across a semi-
permeable membrane. The net direction and rate of 
osmosis depends upon the pressure gradient and 
concentration gradient. Water will move from its 
region of higher concentration to region of lower 
concentration until equilibrium is reached. 
 
• Solute A has more water and less water so high water potential in comparison the solution 
in B container.  
• Osmotic potential is the pressure required to prevent water from diffusing. More the 
solute concentration greater will be the pressure required to prevent water from diffusing 
it. 
• Numerically osmotic pressure is equal to osmotic potential but sign is opposite. Osmotic 
pressure is the positive pressure while osmotic potential is negative. 
• If the surrounding solution balances the osmotic pressure of cytoplasm, the solution is 
called isotonic. 
• If the external solution is more dilute than cytoplasm, it is hypotonic. The cells swell up 
when placed in hypotonic solution. 
• If the external solution is more concentrated than cytoplasm, it is hypertonic. Cell will 
shrink in hypertonic solution.  
• Plasmolysis is the shrinkage of the cytoplasm of the cell from its cell wall under the 
influence of hypertonic solution. The pressure of plasmolysis is usually reversible when 
the cell is placed in hypotonic solution. 
• The pressure build up against the wall due to movement of water inside is called turgor 
pressure. It is responsible for enlargement and extension growth of cells.  
• Imbibition is a special type of diffusion when water is absorbed by solid colloids causing 
them to increase in volume. For example absorption of water by seeds and dry woods. 
Imbibition is also a kind of diffusion because movement of water is from higher 
concentration to lower concentration. 
• Water potential gradient between the absorbent and liquid imbibed is essential for 
imbibition. 
 Long distance transport of water in plants takes place by mass or bulk flow system. It is 
the movement of substance in bulk from one point to another as a result of pressure 
difference between two points. 
 The bulk movement of substances through the conducting or vascular tissue of plants is 
called Translocation. Xylem is associated with translocation of water and mineral salts, 
some organic nitrogen and hormone from roots to aerial parts of plants. 
 Phloem transport organic and inorganic solutes from leaves to other part of plants. 
 
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
Absorption of water by plants 
• Water is absorbed along with mineral solutes by roots hairs by diffusion. The absorbed 
water passes to deeper layer of by two pathways. 
Apoplast pathway Symplast pathway 
a. It consists of nonliving parts of 
plants body such as cell wall and 
intercellular spaces.   
b. There is little resistance in 
movement of water. 
c. It is faster. 
d. Metabolic state of root does not 
affect apoplast pathway.  
a. It consists of living parts of plant 
body such as protoplast connected to 
plasmodesmata. 
b. Some resistance occurs in the 
movement of water. 
c. It is slightly slower. 
d. Metabolic state of root directly affect 
symplast pathway.  
   
• Most of the water flows in 
roots via apoplast pathway 
because cortical cells are 
loosely packed and offers no 
resistance to water movement.  
• The inner boundary of cortex, 
endodermis is impervious to 
water due to suberized matrix 
called Casperian strip. Water molecules are directed 
through wall regions that are not suberized.  
• Water flows through the different layers of roots to 
reach the xylem tissues as follows- 
 
• A mycorrhiza is the symbiotic association between a 
fungus and angiosperic roots. The fungal filaments 
forms a network around the young root to have large 
surface area that mineral ions and water from the soil. The fungus provide minerals and 
waters and roots in turn provide organic and nitrogen containing compounds. 
 Ascent of saps (Translocation of water) 
The upward movement of water from roots towards the tips of stem branches and their 
leaves is called ascent of sap.  
 
Theories of ascent of sap
Vital Force 
Theory
Root Pressure 
Theory
Theory of 
Capillarity
Cohesion 
TensionTheory
Page 5


 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
CBSE Quick Revision Notes (Class-11 Biology) 
CHAPTER-11 TRANSPORT IN PLANTS 
 
Plant transport various substance like gases, minerals, water, hormones, photosynthetes 
and organic solutes to short distance (one cell to another) or long distance as water from 
roots to tips of stem.  
• Long distance transport occurs through vascular system, xylem and phloem called 
translocation through mass flow. 
• The direction of translocation may be unidirectional as in case of water and 
multidirectional as in minerals and organic solutes.  
 
Simple Diffusion-  
• Movement by diffusion is passive and slow along the concentration 
gradient through permeable membrane. 
• No energy expenditure takes place. It occurs in liquid and gases. 
• Rate of diffusion are affected by gradient of concentration, permeability 
of membrane, temperature and pressure.  
Facilitated Diffusion- 
• Lipid soluble particles easily pass through cell membrane but the 
hydrophilic solutes movement is facilitated. 
• For facilitated diffusion, membrane possesses aquaporins or water 
channels. Aquaporins are membrane proteins for passive transport 
of water soluble substances without utilization of energy. 
• The protein forms channels in membrane for molecules to pass 
through. The porins are proteins that forms huge pores in the 
outer membrane of the plastids, mitochondria etc. 
• Water channels are made up of eight different types of aquaporins. 
Symport, Antiport and Uniport-  
 In Symport, both molecules cross the membrane in the same 
direction.  
 In Antiport, both molecules moves in opposite direction. 
 When a molecule moves across a membrane independent of other 
molecules, the process is called uniport.  
 
Active Transport 
• Uses energy to pump molecules against the concentration gradient. It is carried out by 
membrane proteins. 
Means of Transport
Simple Diffusion Facilitated Diffusion Active Transport
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
• In active transport movable carrier proteins are called pumps.  
• The pumps can transport substance from low concentration to high concentration. The 
carrier proteins are very specific in what it carries across the membrane. 
Comparison between Transport mechanisms- 
Simple diffusion Facilitated diffusion Active transport 
Special membrane protein 
is not required. 
Special membrane protein 
is required. 
Special membrane protein 
is required. 
Not selective Highly selective Highly selective 
Transport do not saturate Transport saturate Transport saturate  
No uphill transport  Uphill transport  Uphill transport  
No ATP energy is required. No ATP energy is required.  ATP energy is required. 
 
Plant Water Relationship 
 Water is essential for all physiological activities of plants along with all living organisms. It 
provide medium for most substances to dissolve in it. 
 Protoplasm of cells contains water in which different molecules are dissolved and 
suspended. 
 Terrestrial plants take lot of water and release most of it in form of water vapour by the 
process of transpiration.  
 Water is the limiting factor for plant growth and productivity in both agricultural and 
natural environments.  
Water Potential (? w)- is a concept fundamental to the understanding water movement. 
Water potential is determined by solute potential (? s) and pressure potential (? p). 
 Water molecules possess kinetic energy. The greater the concentration of water in the 
system, the greater is its kinetic energy or water potential. So pure water has greatest 
water potential. 
 Water potential is denoted by Greek symbol Psi (?) and is expressed in pressure unit 
Pascal (Pa).  
 Water pressure of pure water is taken as zero at standard temperature and pressure. A 
solution has less water potential due to less water concentration. 
 The magnitude of lowering of water potential due to dissolution of solute is called solute 
potential (? s ). Solute potential is always negative. More the solute molecules in the 
solution lesser the solute potential.  
 If a pressure greater than atmospheric pressure is applied to pure water or solution, its 
water potential decreases. Pressure potential is usually positive. Pressure potential is 
denoted by (? p).  
 Water potential of a cell is affected by both solute and pressure potential. The relationship 
is as follows. 
 
 
 
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
 
? w = ? s + ? p 
Osmosis is the diffusion of water across a semi-
permeable membrane. The net direction and rate of 
osmosis depends upon the pressure gradient and 
concentration gradient. Water will move from its 
region of higher concentration to region of lower 
concentration until equilibrium is reached. 
 
• Solute A has more water and less water so high water potential in comparison the solution 
in B container.  
• Osmotic potential is the pressure required to prevent water from diffusing. More the 
solute concentration greater will be the pressure required to prevent water from diffusing 
it. 
• Numerically osmotic pressure is equal to osmotic potential but sign is opposite. Osmotic 
pressure is the positive pressure while osmotic potential is negative. 
• If the surrounding solution balances the osmotic pressure of cytoplasm, the solution is 
called isotonic. 
• If the external solution is more dilute than cytoplasm, it is hypotonic. The cells swell up 
when placed in hypotonic solution. 
• If the external solution is more concentrated than cytoplasm, it is hypertonic. Cell will 
shrink in hypertonic solution.  
• Plasmolysis is the shrinkage of the cytoplasm of the cell from its cell wall under the 
influence of hypertonic solution. The pressure of plasmolysis is usually reversible when 
the cell is placed in hypotonic solution. 
• The pressure build up against the wall due to movement of water inside is called turgor 
pressure. It is responsible for enlargement and extension growth of cells.  
• Imbibition is a special type of diffusion when water is absorbed by solid colloids causing 
them to increase in volume. For example absorption of water by seeds and dry woods. 
Imbibition is also a kind of diffusion because movement of water is from higher 
concentration to lower concentration. 
• Water potential gradient between the absorbent and liquid imbibed is essential for 
imbibition. 
 Long distance transport of water in plants takes place by mass or bulk flow system. It is 
the movement of substance in bulk from one point to another as a result of pressure 
difference between two points. 
 The bulk movement of substances through the conducting or vascular tissue of plants is 
called Translocation. Xylem is associated with translocation of water and mineral salts, 
some organic nitrogen and hormone from roots to aerial parts of plants. 
 Phloem transport organic and inorganic solutes from leaves to other part of plants. 
 
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
Absorption of water by plants 
• Water is absorbed along with mineral solutes by roots hairs by diffusion. The absorbed 
water passes to deeper layer of by two pathways. 
Apoplast pathway Symplast pathway 
a. It consists of nonliving parts of 
plants body such as cell wall and 
intercellular spaces.   
b. There is little resistance in 
movement of water. 
c. It is faster. 
d. Metabolic state of root does not 
affect apoplast pathway.  
a. It consists of living parts of plant 
body such as protoplast connected to 
plasmodesmata. 
b. Some resistance occurs in the 
movement of water. 
c. It is slightly slower. 
d. Metabolic state of root directly affect 
symplast pathway.  
   
• Most of the water flows in 
roots via apoplast pathway 
because cortical cells are 
loosely packed and offers no 
resistance to water movement.  
• The inner boundary of cortex, 
endodermis is impervious to 
water due to suberized matrix 
called Casperian strip. Water molecules are directed 
through wall regions that are not suberized.  
• Water flows through the different layers of roots to 
reach the xylem tissues as follows- 
 
• A mycorrhiza is the symbiotic association between a 
fungus and angiosperic roots. The fungal filaments 
forms a network around the young root to have large 
surface area that mineral ions and water from the soil. The fungus provide minerals and 
waters and roots in turn provide organic and nitrogen containing compounds. 
 Ascent of saps (Translocation of water) 
The upward movement of water from roots towards the tips of stem branches and their 
leaves is called ascent of sap.  
 
Theories of ascent of sap
Vital Force 
Theory
Root Pressure 
Theory
Theory of 
Capillarity
Cohesion 
TensionTheory
 
 
 
Material downloaded from http://myCBSEguide.com and http://onlineteachers.co.in 
Portal for CBSE Notes, Test Papers, Sample Papers, Tips and Tricks 
 Vital force theory was forwarded by J.C.Bose in 1923. This theory believes that the 
innermost cortical cells of the root absorb water from the outer side and pump the same 
into xylem channels.  
 Root pressure theory was forwarded by Priestley in 1916. Root pressure is positive 
pressure that develops in the xylem sap of the root of plants. It can be responsible for 
pushing up water to small heights in plants. 
 Loss of water in liquid phase by herbaceous plants from the tips of leaf blades is known as 
guttation.   
 Water rises in tubes of small diameters, kept in vessels having water due to force of 
surface tension. Similarly water rises up in the walls of xylem channels due to adhesion 
and cohesion. This theory is called Theory of Capillarity. 
 Cohesion Tension theory was put forwarded by Dixon and Joly in 1894. According to this 
theory water is mostly pulled due to driving force of transpiration from the leaves. The 
water molecules remain attached with one another by cohesion force. The water molecule 
does not breaks in vessels and tracheid due to adhesive force between their walls and 
water molecules.  On account of tension crated by transpiration, the water column of plant 
is pulled up passively from roots to great heights.  
 Transpiration is the loss of water in form of water vapour from aerial parts of plants. The 
following purpose is fulfilled by transpiration- 
a. Creates transpirational pull for absorption and transports in plants. 
b. Supplies water for photosynthesis. 
c. Transport minerals and salts from soil to other parts of plant. 
d. Cool the leaves and maintain their shape and size. 
 Photosynthesis is limited by available water. C 4 plants are twice as efficient as C 3 plants in 
term of fixing carbon. Although C 4 plants uses half as much water as C 3 plants for the same 
amount of CO 2 fixed. 
Uptake and transport of mineral nutrients 
• Most of the minerals enter the roots by active absorption into the cytoplasm of epidermal 
cells because- 
(i) Minerals are present in the soil as charged particles (ions) which cannot move across cell 
membranes. 
(ii) The concentration of ions in soil is usually lower than concentration in roots. 
• Active absorption needs energy in form of ATP. Active uptake of ions is also responsible 
for water potential gradient in roots.  
• Transport proteins of epidermal cells are control point where quantity and type of solutes 
that reach the xylem is adjusted. 
• The ions that reaches to xylem by active or passive transport moves further upward along 
with transpirational pull. 
• The chief sink of mineral elements are growing region of plants like apical meristem, 
young leaves, growing flower and fruit, and the storage organs. 
• Minerals are frequently remobilized from older senescing part of plants to young growing 
parts of plant. 
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