Bachelor’s Degree Programme (BSCG) – Plant Physiology and Metabolism Assig. Answer | BBYCT–137(Q-1)
Q-1) Differentiate between:
i) Apoplastic and symplastic pathway
ii) Diffusion and osmosis
iii) Stomatal index and stomatal frequency
iv) Water potential and matrix potential
v) Primary and secondary active transport
i) Apoplast pathway – water is transported from root hair to xylem through the cell wall of intervening cells. Apoplastic water movement beyond the cortex is blocked by the Casparian strip of endodermal cells.
– Symplastic pathway – The pathways of ion and water created by symplast are known as the symplastic pathway. This pathway offers resistance to the flow of water since the selective plasma membrane of the root cells handles the intake of ions and water.
ii) Diffusion – The process of moving of solvent particles across a semipermeable membrane from a dilute solution into a concentrated solution to equalize concentration. The complete process does not require energy in order to take place.
– Osmosis – The process of moving particles from a region of higher concentration to the region of lower concentration until equilibrium is reached. Simple diffusion does not require energy in order to take place; however, facilitated diffusion requires ATP.
iii) Stomatal frequency – The number of stomata present per unit area of a leaf.
– Stomatal frequency – The total area of stomata covered in a leaf are the essential prerequisite to assess the rate of water loss through stomata.
iv) Water potential – a) Water potential is a measure of the concentration of free water molecules.
b) Free water molecules are the water molecules that are free to move. Therefore, it is the potential energy in water.
c) The Greek letter ψ (psi) is used to denote water potential,
d) It is measured from the unit of pressure: megapascals (MPa).
Matric potential – a) The matric potential is the amount of the water which is bound to the matrix of a plant and it is always value zero to negative.
b) The cell wall of the plant is cellulosic in nature so it is hydrophilic and so it can acts as a matrix for the adhesion of water so it is known as the matrix potential.
c) Matrix potential cannot be manipulated by the plants.
d) The matrix potential value is usually between 0 – 20.
v) Primary active transport – a) Primary active transport is the transport of molecules against a concentration gradient by the use of energy from ATP.
b) Primary active transport uses energy from ATP.
c) A single molecule is transported in primary active transport.
Secondary Active Transport – a) Secondary active transport is the transport of two different molecules across a transport membrane using energy in other forms than ATP.
b) The concentration gradient of the driving ion provides the energy for the transport of the driven ion/molecule against its concentration gradient in secondary active transport.
c) Two types of molecules are transported at once in secondary active transport.