TRANSPORT IN PLANTS
In plants, the substances that need to be transported are water, mineral nutrients, organic
nutrients and plant growth regulators.
Long distance transport occurs through vascular system, xylem and phloem is called
translocation. The direction of translocation may be unidirectional as in case of water and
multidirectional as in minerals and organic solutes. Plants can transport various substances
like minerals, water, hormone and organic solutes to short distance (one cell to another) by
Diffusion or by cytoplasmic streaming supplemented by Active transport.
MEANS OF TRANSPORT:
1. Cellular level transport- uptake and release of substances within a cell.
2. Short distance transport- transport of substances from one cell to another.
3. Long distance transport- transport of water and sugar via xylem and phloem.
PASSIVE TRANSPORT
In this type, a molecule is transported along the concentration gradient through permeable
membrane. No energy expenditure takes place. It occurs in liquid and gases.
Diffusion:
It is the movement of molecules/ions/particles from higher to lower concentration . It
requires no energy expenditure and remains unaffected by the concentration gradient of other
molecules. Example:
a)Exchange of gases
b)Absorption of ions
c)Stomatal transpiration
d)Fragrance of flower
Diffusion pressure:
It is the pressure developed by the movement of diffusible particles of a substance as they
move from higher to low concentration.
*Diffusion pressure of pure water is maximum.
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:
1
,When a molecule moves across a membrane independent of other molecules, the process is
called Uniport. It helps in transport of Ca2+ across the membrane.
In Symport, both molecules cross the membrane in the same direction. It helps in the
transport of K+ and Na+ across the membrane.
In Antiport, both molecule moves in opposite direction. It helps in the transport of glucose,
Na+ across the membrane.
Osmosis:
It is the diffusion of water molecules through a semi permeable membrane from higher
concentration to lower concentration. This process is responsible for: absorption of water by
roots, turgidity of plant organs, cell to cell movement of water, opening and closing of
stomata, resistance of plants to drought.
2
,Osmotic pressure:
It is the actual pressure which develops in a solution when it is separated from pure water by
means of semi permeable membrane.
*Osmotic pressure of solution is always higher than its pure solvent.
*Highest osmotic pressure is seen in a xerophytic plant, Atriplex confertalia.
Solutions can be of three types depending upon the solution around cell sap:
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:
Plasmolysis is the shrinkage of the cytoplasm of the cell away from its cell wall under the
influence of hypertonic solution. When a cell is placed in hypertonic solution, the protoplasm
shrinks and leaves the cell wall due to exosmosis and cell becomes flaccid. This cell is called
Plasmolysed cell.
3
, The pressure of plasmolysis is usually reversible when the cell is placed in hypotonic
solution. The cell again becomes turgid due to endosmosis and the phenomenon is called
Deplasmolysis.
*Bacteria get plasmolysed in salty pickles and sugary jams. Common salt also kills
weeds by plasmolysis.
IMBIBITION:
Imbibition is a special type of diffusion when water is absorbed by solid colloids causing
them to increase in volume. Eg- 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.
ACTIVE TRANSPORT:
It uses energy to pump molecules against the concentration gradient. It is carried out by
membrane proteins. 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.
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In plants, the substances that need to be transported are water, mineral nutrients, organic
nutrients and plant growth regulators.
Long distance transport occurs through vascular system, xylem and phloem is called
translocation. The direction of translocation may be unidirectional as in case of water and
multidirectional as in minerals and organic solutes. Plants can transport various substances
like minerals, water, hormone and organic solutes to short distance (one cell to another) by
Diffusion or by cytoplasmic streaming supplemented by Active transport.
MEANS OF TRANSPORT:
1. Cellular level transport- uptake and release of substances within a cell.
2. Short distance transport- transport of substances from one cell to another.
3. Long distance transport- transport of water and sugar via xylem and phloem.
PASSIVE TRANSPORT
In this type, a molecule is transported along the concentration gradient through permeable
membrane. No energy expenditure takes place. It occurs in liquid and gases.
Diffusion:
It is the movement of molecules/ions/particles from higher to lower concentration . It
requires no energy expenditure and remains unaffected by the concentration gradient of other
molecules. Example:
a)Exchange of gases
b)Absorption of ions
c)Stomatal transpiration
d)Fragrance of flower
Diffusion pressure:
It is the pressure developed by the movement of diffusible particles of a substance as they
move from higher to low concentration.
*Diffusion pressure of pure water is maximum.
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:
1
,When a molecule moves across a membrane independent of other molecules, the process is
called Uniport. It helps in transport of Ca2+ across the membrane.
In Symport, both molecules cross the membrane in the same direction. It helps in the
transport of K+ and Na+ across the membrane.
In Antiport, both molecule moves in opposite direction. It helps in the transport of glucose,
Na+ across the membrane.
Osmosis:
It is the diffusion of water molecules through a semi permeable membrane from higher
concentration to lower concentration. This process is responsible for: absorption of water by
roots, turgidity of plant organs, cell to cell movement of water, opening and closing of
stomata, resistance of plants to drought.
2
,Osmotic pressure:
It is the actual pressure which develops in a solution when it is separated from pure water by
means of semi permeable membrane.
*Osmotic pressure of solution is always higher than its pure solvent.
*Highest osmotic pressure is seen in a xerophytic plant, Atriplex confertalia.
Solutions can be of three types depending upon the solution around cell sap:
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:
Plasmolysis is the shrinkage of the cytoplasm of the cell away from its cell wall under the
influence of hypertonic solution. When a cell is placed in hypertonic solution, the protoplasm
shrinks and leaves the cell wall due to exosmosis and cell becomes flaccid. This cell is called
Plasmolysed cell.
3
, The pressure of plasmolysis is usually reversible when the cell is placed in hypotonic
solution. The cell again becomes turgid due to endosmosis and the phenomenon is called
Deplasmolysis.
*Bacteria get plasmolysed in salty pickles and sugary jams. Common salt also kills
weeds by plasmolysis.
IMBIBITION:
Imbibition is a special type of diffusion when water is absorbed by solid colloids causing
them to increase in volume. Eg- 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.
ACTIVE TRANSPORT:
It uses energy to pump molecules against the concentration gradient. It is carried out by
membrane proteins. 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.
4
