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Class 10 Class 12
Is there a general mechanism to explain opening and closing of stomata? Justify your answer.

The opening and closing of stomata is operated by turgor changes in guard cells. When the guard cell absorb water they become turgid and the stomata opens. The opening and closing of stomatal pore is aided by the differential thickening of the guard cell's inner and outer membrane and the orientation of the microfibrils in the cell. 
When the guard cell absorb water then the 
thin outer walls bulge out and force the inner walls into a crescent shape, thus opening the stomatal pore. The radial orientation of cellulose microfibrils rather than longitudinally enable the stoma to open. When the lose water they lose turgidity , the elastic inner walls regain their original shape, the guard cells become flaccid and the stoma closes.


Who introduced the apoplast—symplast concept ?

E. Munch (1930).

What is transmembrane pathway ?

The movement of water through cell membranes is called trans membrane pathway.

Why the water is forced to move through cell membrane beyond endodermis ?

Water is forced to move through cell membranes beyond endodermis because of the suberin (waxy substance) present on radial walls of endodermal cells blocks water and solute movement through cell walls of endodermis. 

Why the cortex produces no resistance to movement of water ?

The cortical cells are loosely packed and produce no resistance to movement of water via cell walls or apoplast.

Give the term for the ability to resist a pulling force.

Tensile strength