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CHAPTER-11 TRANSPORT IN PLANTS
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CHAPTER-11 TRANSPORT IN PLANTS
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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.
Means of Transport
Simple Diffusion Facilitated Diffusion Active Transport
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.
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, • 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 Special membrane protein Special membrane protein
is not required. is required. 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 (Ψw)- is a concept fundamental to the understanding water movement.
Water potential is determined by solute potential (Ψs) and pressure potential (Ψp).
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 (Ψ) 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 (Ψs ). 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 (Ψp).
Water potential of a cell is affected by both solute and pressure potential. The relationship
is as follows.
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