Transport in Plants Class 11 Notes Biology

 Page 1


Points To Remember
Translocation (Long distance transport) : Transport of substances in 
plants over longer distances through the vascular tissue (Xylem and Phloem) 
The transport of water and mineral in Xylem is unidirectional while transport of 
organic and mineral nutrients in phloem is multi-directional.
Means of transport (Short distance transport) : The transport of material 
into and out of the cells is carried out by a number of methods. These are diffusion, 
facilitated diffusion and active transport.
(i) Diffusion : Diffusion occurs from region of higher concentration to region 
of lower concentration across the permeable membrane. It is passive and slow 
process. No energy expenditure takes place.
Factors affecting diffusion : Permeability of membrane, Temperature, 
pressure, gradient of concentration and the size of substances.
(ii) Facilitated diffusion : The diffusion of hydrophilic substances along 
the concentration gradient through fixed membrane transport protein without 
involving energy expenditure. For this the membrane possess aquarporins and 
ion channels. No ATP energy is utilized in this process.
Porins—The proteins that form huge pores in the outer membranes of the 
plastids, mitochondria and some bacteria which allow the small size molecules 
to pass through.
Aquaporins—Proteins that facilitate diffusion of water molecules through/
across the plasma membrane of cell.
Methods of Facilitated Diffusion
           Symport Antiport Uniport
(Two molecules cross the (Two molecules move (Single molecule moves
membrane in the same in opposite direction at across membrane indpen-
direction at the same time.) the same time.) dent of other molecules.)
Page 2


Points To Remember
Translocation (Long distance transport) : Transport of substances in 
plants over longer distances through the vascular tissue (Xylem and Phloem) 
The transport of water and mineral in Xylem is unidirectional while transport of 
organic and mineral nutrients in phloem is multi-directional.
Means of transport (Short distance transport) : The transport of material 
into and out of the cells is carried out by a number of methods. These are diffusion, 
facilitated diffusion and active transport.
(i) Diffusion : Diffusion occurs from region of higher concentration to region 
of lower concentration across the permeable membrane. It is passive and slow 
process. No energy expenditure takes place.
Factors affecting diffusion : Permeability of membrane, Temperature, 
pressure, gradient of concentration and the size of substances.
(ii) Facilitated diffusion : The diffusion of hydrophilic substances along 
the concentration gradient through fixed membrane transport protein without 
involving energy expenditure. For this the membrane possess aquarporins and 
ion channels. No ATP energy is utilized in this process.
Porins—The proteins that form huge pores in the outer membranes of the 
plastids, mitochondria and some bacteria which allow the small size molecules 
to pass through.
Aquaporins—Proteins that facilitate diffusion of water molecules through/
across the plasma membrane of cell.
Methods of Facilitated Diffusion
           Symport Antiport Uniport
(Two molecules cross the (Two molecules move (Single molecule moves
membrane in the same in opposite direction at across membrane indpen-
direction at the same time.) the same time.) dent of other molecules.)
Transport Proteins—They are present in the membrane. They allow the 
passage of substances through membrane.
(i) Carrier Proteins—They bind to the particular solute particle to be 
transported and deliver these to other side of membrane.
(ii) Channel Proteins—Ion Channel—They are specific for different ions like  
K
+
, Cl
–
, 
Water Channel—Surrounded by eight proteins called aqua protein and 
allow passage of water or water soluble substance.
(iii) Active transport : Active transport is carried by the movable carrier 
proteins (pumps) of membrane. Active transport uses energy to pump molecules 
against a concentration gradient from a low concentration to high concentration 
(uphill-transport). It is faster than passive transport.
Different Transport Mechanisms
 S. Property Simple Faciliated Active
 No. Diffusion Transport Transport
1. Required Special No Yes Yes
membrane protein
2. Uphill transport No No Yes
3. Requires A TP Energy No No No
? Water potential—( ?
w
)–Greater the concentration of water in a system,
greater is its kinetic energy and greater is the water potential. It is measured
in pascal (Pa). or mega pascal.
? If two systems are in contact, then there is movement of water from the
solution with higher potential to lower water potential.
? Solute potential—( ?
s
)–Magnitude of lowering of water potential, when a
solute is added to the water.
? Pressure Potential—( ?
p
)—Magnitude of increase of water potential, when
pressure greater than atmospheric pressure is applied to pure water or a
solution.
? Water potential of pure water is zero (0).
? Solute potential is always negative (–) and pressure potential is always
positive (+).
?
w = 
?
s + 
?
p
Page 3


Points To Remember
Translocation (Long distance transport) : Transport of substances in 
plants over longer distances through the vascular tissue (Xylem and Phloem) 
The transport of water and mineral in Xylem is unidirectional while transport of 
organic and mineral nutrients in phloem is multi-directional.
Means of transport (Short distance transport) : The transport of material 
into and out of the cells is carried out by a number of methods. These are diffusion, 
facilitated diffusion and active transport.
(i) Diffusion : Diffusion occurs from region of higher concentration to region 
of lower concentration across the permeable membrane. It is passive and slow 
process. No energy expenditure takes place.
Factors affecting diffusion : Permeability of membrane, Temperature, 
pressure, gradient of concentration and the size of substances.
(ii) Facilitated diffusion : The diffusion of hydrophilic substances along 
the concentration gradient through fixed membrane transport protein without 
involving energy expenditure. For this the membrane possess aquarporins and 
ion channels. No ATP energy is utilized in this process.
Porins—The proteins that form huge pores in the outer membranes of the 
plastids, mitochondria and some bacteria which allow the small size molecules 
to pass through.
Aquaporins—Proteins that facilitate diffusion of water molecules through/
across the plasma membrane of cell.
Methods of Facilitated Diffusion
           Symport Antiport Uniport
(Two molecules cross the (Two molecules move (Single molecule moves
membrane in the same in opposite direction at across membrane indpen-
direction at the same time.) the same time.) dent of other molecules.)
Transport Proteins—They are present in the membrane. They allow the 
passage of substances through membrane.
(i) Carrier Proteins—They bind to the particular solute particle to be 
transported and deliver these to other side of membrane.
(ii) Channel Proteins—Ion Channel—They are specific for different ions like  
K
+
, Cl
–
, 
Water Channel—Surrounded by eight proteins called aqua protein and 
allow passage of water or water soluble substance.
(iii) Active transport : Active transport is carried by the movable carrier 
proteins (pumps) of membrane. Active transport uses energy to pump molecules 
against a concentration gradient from a low concentration to high concentration 
(uphill-transport). It is faster than passive transport.
Different Transport Mechanisms
 S. Property Simple Faciliated Active
 No. Diffusion Transport Transport
1. Required Special No Yes Yes
membrane protein
2. Uphill transport No No Yes
3. Requires A TP Energy No No No
? Water potential—( ?
w
)–Greater the concentration of water in a system,
greater is its kinetic energy and greater is the water potential. It is measured
in pascal (Pa). or mega pascal.
? If two systems are in contact, then there is movement of water from the
solution with higher potential to lower water potential.
? Solute potential—( ?
s
)–Magnitude of lowering of water potential, when a
solute is added to the water.
? Pressure Potential—( ?
p
)—Magnitude of increase of water potential, when
pressure greater than atmospheric pressure is applied to pure water or a
solution.
? Water potential of pure water is zero (0).
? Solute potential is always negative (–) and pressure potential is always
positive (+).
?
w = 
?
s + 
?
p
? Osmotic Pressure—External pressure applied to prevent the diffusion of
water. It depends upon solute concentration.
? Numerically, osmotic pressure is equal to osmotic potential. Osmotic pressure
has positive (+) sign. Osmotic potential has negative (–) sign.
Turgor Pressure—Due to osmotic entry of water, the protoplasm of a plant
cell presses the cell wall towards the outside with a force, it is called Turgor 
Pressure.
Diffusion Pressure—The pressure exerted by the tendency of the particles to 
diffuse from the area of higher concentration to lower concentration. It is directly 
proportional to the concentration of particles of diffusing substance.
Osmosis : Osmosis is movement of solvent or water molecules from the 
region of their higher diffusion pressure or free energy to the region of their lower 
diffusion pressure of free energy across a semipermeable membrane.
Water molecules move from higher water potential to lower water potential 
until equilibrium is reached.
Plasmolysis : Process of shrinkage of protoplast in a cell due to exosmosis 
in hypertonic solution. If a plasmolysed cell is placed in water or a hypotonic 
solution it becomes turgid.
Hypotonic solution : The external solution which is more dilute than the 
cytoplasm.
Hypertonic solution : The external solution, which is more concentrated 
than the cytoplasm.
Isotonic solution : When the external solution balances the osmotic pressure 
of the cytoplasm.
Casparian strip : It is the tangential as well as radial walls of endodermal 
cells having the deposition of water impermeable suberin.
Imbibition : Imbibition is the phenomenon of absorption of water by the 
solid particles of an adsorbent causing it to enormously increase in volume without 
forming a solution.
Some examples of Imbibition :
(i) If a dry piece of wood is placed in water, it swells and increases in its volume.
(ii) If dry gum or pieces of agar-agar are placed in water, they swell and their 
volume increases.
 (iii) When seeds are placed in water they swell up.
 (iv) Swelling of wooden door during rainy season.
Conditions essential for imbibition
1. W ater potential gradient between the surface of the adsorbent and  the imbibed
liquid, is essential.
2. Affinity between the adsorbent and the imbibed liquid.
Page 4


Points To Remember
Translocation (Long distance transport) : Transport of substances in 
plants over longer distances through the vascular tissue (Xylem and Phloem) 
The transport of water and mineral in Xylem is unidirectional while transport of 
organic and mineral nutrients in phloem is multi-directional.
Means of transport (Short distance transport) : The transport of material 
into and out of the cells is carried out by a number of methods. These are diffusion, 
facilitated diffusion and active transport.
(i) Diffusion : Diffusion occurs from region of higher concentration to region 
of lower concentration across the permeable membrane. It is passive and slow 
process. No energy expenditure takes place.
Factors affecting diffusion : Permeability of membrane, Temperature, 
pressure, gradient of concentration and the size of substances.
(ii) Facilitated diffusion : The diffusion of hydrophilic substances along 
the concentration gradient through fixed membrane transport protein without 
involving energy expenditure. For this the membrane possess aquarporins and 
ion channels. No ATP energy is utilized in this process.
Porins—The proteins that form huge pores in the outer membranes of the 
plastids, mitochondria and some bacteria which allow the small size molecules 
to pass through.
Aquaporins—Proteins that facilitate diffusion of water molecules through/
across the plasma membrane of cell.
Methods of Facilitated Diffusion
           Symport Antiport Uniport
(Two molecules cross the (Two molecules move (Single molecule moves
membrane in the same in opposite direction at across membrane indpen-
direction at the same time.) the same time.) dent of other molecules.)
Transport Proteins—They are present in the membrane. They allow the 
passage of substances through membrane.
(i) Carrier Proteins—They bind to the particular solute particle to be 
transported and deliver these to other side of membrane.
(ii) Channel Proteins—Ion Channel—They are specific for different ions like  
K
+
, Cl
–
, 
Water Channel—Surrounded by eight proteins called aqua protein and 
allow passage of water or water soluble substance.
(iii) Active transport : Active transport is carried by the movable carrier 
proteins (pumps) of membrane. Active transport uses energy to pump molecules 
against a concentration gradient from a low concentration to high concentration 
(uphill-transport). It is faster than passive transport.
Different Transport Mechanisms
 S. Property Simple Faciliated Active
 No. Diffusion Transport Transport
1. Required Special No Yes Yes
membrane protein
2. Uphill transport No No Yes
3. Requires A TP Energy No No No
? Water potential—( ?
w
)–Greater the concentration of water in a system,
greater is its kinetic energy and greater is the water potential. It is measured
in pascal (Pa). or mega pascal.
? If two systems are in contact, then there is movement of water from the
solution with higher potential to lower water potential.
? Solute potential—( ?
s
)–Magnitude of lowering of water potential, when a
solute is added to the water.
? Pressure Potential—( ?
p
)—Magnitude of increase of water potential, when
pressure greater than atmospheric pressure is applied to pure water or a
solution.
? Water potential of pure water is zero (0).
? Solute potential is always negative (–) and pressure potential is always
positive (+).
?
w = 
?
s + 
?
p
? Osmotic Pressure—External pressure applied to prevent the diffusion of
water. It depends upon solute concentration.
? Numerically, osmotic pressure is equal to osmotic potential. Osmotic pressure
has positive (+) sign. Osmotic potential has negative (–) sign.
Turgor Pressure—Due to osmotic entry of water, the protoplasm of a plant
cell presses the cell wall towards the outside with a force, it is called Turgor 
Pressure.
Diffusion Pressure—The pressure exerted by the tendency of the particles to 
diffuse from the area of higher concentration to lower concentration. It is directly 
proportional to the concentration of particles of diffusing substance.
Osmosis : Osmosis is movement of solvent or water molecules from the 
region of their higher diffusion pressure or free energy to the region of their lower 
diffusion pressure of free energy across a semipermeable membrane.
Water molecules move from higher water potential to lower water potential 
until equilibrium is reached.
Plasmolysis : Process of shrinkage of protoplast in a cell due to exosmosis 
in hypertonic solution. If a plasmolysed cell is placed in water or a hypotonic 
solution it becomes turgid.
Hypotonic solution : The external solution which is more dilute than the 
cytoplasm.
Hypertonic solution : The external solution, which is more concentrated 
than the cytoplasm.
Isotonic solution : When the external solution balances the osmotic pressure 
of the cytoplasm.
Casparian strip : It is the tangential as well as radial walls of endodermal 
cells having the deposition of water impermeable suberin.
Imbibition : Imbibition is the phenomenon of absorption of water by the 
solid particles of an adsorbent causing it to enormously increase in volume without 
forming a solution.
Some examples of Imbibition :
(i) If a dry piece of wood is placed in water, it swells and increases in its volume.
(ii) If dry gum or pieces of agar-agar are placed in water, they swell and their 
volume increases.
 (iii) When seeds are placed in water they swell up.
 (iv) Swelling of wooden door during rainy season.
Conditions essential for imbibition
1. W ater potential gradient between the surface of the adsorbent and  the imbibed
liquid, is essential.
2. Affinity between the adsorbent and the imbibed liquid.
112
Transport of water in plants : Water is absorbed by root hairs by diffusion. 
Then water moves upto xylem by two pathways–apoplast and symplast pathway.
Apoplast Pathway—Movement occurs through the intercellular spaces or 
walls of the cell, without entering the cytoplasm. This movement is fast. In roots, 
movement of water occurs via apoplast except at the carparian strip, most of water 
enters through apoplast.
Symplast Pathway—W ater enters the cell through cell membrane and travels 
intercellularly through plasmodesmata. This movement is slow. At casparian strip 
region water moves through symplast.
Root Hair
Cortex
Endodermis
Phloem
Xylem
Pericycle
Casparian Strip
Epidermis
Apoplastic Pathway
(through cell wall only)
Symplastic Pathway (through cells)
Apoplastic And Symplastic Pathways of Water Transport
Ascent of Sap—Upward movement of water in the form of dilute solution of 
mineral ions from roots to the top aerial parts of plants through tracheary elements 
of xylem against the gravitational force is called ascent of sap. It involves two 
theories—
(i) Cohesion—Tension-transpirtation pull theory.
(ii) Root pressure theory.
(1) Cohesion-Tension-transpiration pull theory—
(i) Continuity of water column—The transport of water to the top of trees 
occurs through xylem vessels. The forces of adhesion and cohesion maintain a 
thin and unbroken column of water in the capillaries of xylem vessels through 
which it travels which is travels upward. Water is mainly pulled by transpiration 
from leaves.
(ii) Transpiration Pull—Transpiration accounts for loss of 99% of water in 
the form of water vapours the surface of leaves. The loss is mainly through stomata.
? Pull of water as a result of tension created by transpiration is the major diving
force of water movement upward in a plant.
 Three physical properties of water which affect the ascent of xylem sap due 
to transpiration pull.
Page 5


Points To Remember
Translocation (Long distance transport) : Transport of substances in 
plants over longer distances through the vascular tissue (Xylem and Phloem) 
The transport of water and mineral in Xylem is unidirectional while transport of 
organic and mineral nutrients in phloem is multi-directional.
Means of transport (Short distance transport) : The transport of material 
into and out of the cells is carried out by a number of methods. These are diffusion, 
facilitated diffusion and active transport.
(i) Diffusion : Diffusion occurs from region of higher concentration to region 
of lower concentration across the permeable membrane. It is passive and slow 
process. No energy expenditure takes place.
Factors affecting diffusion : Permeability of membrane, Temperature, 
pressure, gradient of concentration and the size of substances.
(ii) Facilitated diffusion : The diffusion of hydrophilic substances along 
the concentration gradient through fixed membrane transport protein without 
involving energy expenditure. For this the membrane possess aquarporins and 
ion channels. No ATP energy is utilized in this process.
Porins—The proteins that form huge pores in the outer membranes of the 
plastids, mitochondria and some bacteria which allow the small size molecules 
to pass through.
Aquaporins—Proteins that facilitate diffusion of water molecules through/
across the plasma membrane of cell.
Methods of Facilitated Diffusion
           Symport Antiport Uniport
(Two molecules cross the (Two molecules move (Single molecule moves
membrane in the same in opposite direction at across membrane indpen-
direction at the same time.) the same time.) dent of other molecules.)
Transport Proteins—They are present in the membrane. They allow the 
passage of substances through membrane.
(i) Carrier Proteins—They bind to the particular solute particle to be 
transported and deliver these to other side of membrane.
(ii) Channel Proteins—Ion Channel—They are specific for different ions like  
K
+
, Cl
–
, 
Water Channel—Surrounded by eight proteins called aqua protein and 
allow passage of water or water soluble substance.
(iii) Active transport : Active transport is carried by the movable carrier 
proteins (pumps) of membrane. Active transport uses energy to pump molecules 
against a concentration gradient from a low concentration to high concentration 
(uphill-transport). It is faster than passive transport.
Different Transport Mechanisms
 S. Property Simple Faciliated Active
 No. Diffusion Transport Transport
1. Required Special No Yes Yes
membrane protein
2. Uphill transport No No Yes
3. Requires A TP Energy No No No
? Water potential—( ?
w
)–Greater the concentration of water in a system,
greater is its kinetic energy and greater is the water potential. It is measured
in pascal (Pa). or mega pascal.
? If two systems are in contact, then there is movement of water from the
solution with higher potential to lower water potential.
? Solute potential—( ?
s
)–Magnitude of lowering of water potential, when a
solute is added to the water.
? Pressure Potential—( ?
p
)—Magnitude of increase of water potential, when
pressure greater than atmospheric pressure is applied to pure water or a
solution.
? Water potential of pure water is zero (0).
? Solute potential is always negative (–) and pressure potential is always
positive (+).
?
w = 
?
s + 
?
p
? Osmotic Pressure—External pressure applied to prevent the diffusion of
water. It depends upon solute concentration.
? Numerically, osmotic pressure is equal to osmotic potential. Osmotic pressure
has positive (+) sign. Osmotic potential has negative (–) sign.
Turgor Pressure—Due to osmotic entry of water, the protoplasm of a plant
cell presses the cell wall towards the outside with a force, it is called Turgor 
Pressure.
Diffusion Pressure—The pressure exerted by the tendency of the particles to 
diffuse from the area of higher concentration to lower concentration. It is directly 
proportional to the concentration of particles of diffusing substance.
Osmosis : Osmosis is movement of solvent or water molecules from the 
region of their higher diffusion pressure or free energy to the region of their lower 
diffusion pressure of free energy across a semipermeable membrane.
Water molecules move from higher water potential to lower water potential 
until equilibrium is reached.
Plasmolysis : Process of shrinkage of protoplast in a cell due to exosmosis 
in hypertonic solution. If a plasmolysed cell is placed in water or a hypotonic 
solution it becomes turgid.
Hypotonic solution : The external solution which is more dilute than the 
cytoplasm.
Hypertonic solution : The external solution, which is more concentrated 
than the cytoplasm.
Isotonic solution : When the external solution balances the osmotic pressure 
of the cytoplasm.
Casparian strip : It is the tangential as well as radial walls of endodermal 
cells having the deposition of water impermeable suberin.
Imbibition : Imbibition is the phenomenon of absorption of water by the 
solid particles of an adsorbent causing it to enormously increase in volume without 
forming a solution.
Some examples of Imbibition :
(i) If a dry piece of wood is placed in water, it swells and increases in its volume.
(ii) If dry gum or pieces of agar-agar are placed in water, they swell and their 
volume increases.
 (iii) When seeds are placed in water they swell up.
 (iv) Swelling of wooden door during rainy season.
Conditions essential for imbibition
1. W ater potential gradient between the surface of the adsorbent and  the imbibed
liquid, is essential.
2. Affinity between the adsorbent and the imbibed liquid.
112
Transport of water in plants : Water is absorbed by root hairs by diffusion. 
Then water moves upto xylem by two pathways–apoplast and symplast pathway.
Apoplast Pathway—Movement occurs through the intercellular spaces or 
walls of the cell, without entering the cytoplasm. This movement is fast. In roots, 
movement of water occurs via apoplast except at the carparian strip, most of water 
enters through apoplast.
Symplast Pathway—W ater enters the cell through cell membrane and travels 
intercellularly through plasmodesmata. This movement is slow. At casparian strip 
region water moves through symplast.
Root Hair
Cortex
Endodermis
Phloem
Xylem
Pericycle
Casparian Strip
Epidermis
Apoplastic Pathway
(through cell wall only)
Symplastic Pathway (through cells)
Apoplastic And Symplastic Pathways of Water Transport
Ascent of Sap—Upward movement of water in the form of dilute solution of 
mineral ions from roots to the top aerial parts of plants through tracheary elements 
of xylem against the gravitational force is called ascent of sap. It involves two 
theories—
(i) Cohesion—Tension-transpirtation pull theory.
(ii) Root pressure theory.
(1) Cohesion-Tension-transpiration pull theory—
(i) Continuity of water column—The transport of water to the top of trees 
occurs through xylem vessels. The forces of adhesion and cohesion maintain a 
thin and unbroken column of water in the capillaries of xylem vessels through 
which it travels which is travels upward. Water is mainly pulled by transpiration 
from leaves.
(ii) Transpiration Pull—Transpiration accounts for loss of 99% of water in 
the form of water vapours the surface of leaves. The loss is mainly through stomata.
? Pull of water as a result of tension created by transpiration is the major diving
force of water movement upward in a plant.
 Three physical properties of water which affect the ascent of xylem sap due 
to transpiration pull.
 (iii) Cohesion force or Tensile strength of water—
? Cohesion—Mutual attraction between water molecules.
? Adhesion—Attraction of water molecules to polar surface.
? Surface tension—Attraction of water to each other in liquid phase to a
greater extent than to water in gaseous phase.
(2) Root pressure Theory : A hydrostatic pressure existing in roots which
pushes the water up in xylem vessels  upto certain height to herbaceons plant.
Guttation : The water loss in its liquid phase in the form of water droplets at
night and early morning  through special openings of vein near the tip of leaves. 
These opening are called hydathodes.
Transpiration : The loss of water through stomata of leaves and other aerial 
parts of plants in form of water vapours.
Factors affecting transpiration : Temperature, light, relative humidity, wind 
speed, number and distribution of stomata, water status of plant, canopy structure.
Significance of transpiration —Advantages—Helps in ascent of sap removal 
of excess water, cooling effect, distribution of mineral salts, supply water for 
photosynthesis.
Disadvantages—May cause reduced growth, wilting (loss of turgidity), 
reduced yield and waste of energy.
Since there are advantages as well as disadvantages of transpiration so—
‘Transpiration is called a necessary evil’.
Opening and closing of stomata—Mechanism of opening and closing of 
stomata involves  two steps—
(i) Change to the turgidity of gaurd cells.
(ii) Orientation of cellulose microfibrils in the cell wall of gaurd cells.
Endosmosis—When a cell is placed in water or hypotonic solution, water 
enters into the cell. This in called endosmosis. Due to it the volume of cell increases 
and it creates turgor pressure.
Exosmosis—When a cell is placed in hypertonic solution, water comes out 
of the cell, this is called exosmosis. It decreases volume of the cell.
Uptake and transport of mineral nutrients—Ions are absorbed by the roots 
by passive and active transport. The active uptake of ions require ATP energy. 
Specific proteins in membranes of root hair cells activity pump ions from the soil 
into the cytoplasm of epidermal cells and then xylem. The further transport of ions 
to all parts of the plant is carried through the water stream. Older dying leaves 
export much of their mineral content to younger leaves. Elements phosphorus,  
sulphur, nitrogen and potassium are most readily mobilised.