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Class 10 Class 12
Describe the external factors affecting transpiration.

Extermal factors affecting transpiration are :

1. Temperature : Rate of transpiration is directly proportional to the temperature. Transpiration rate increases with increase in temperature.

2. Light : More light closes the stomata.

3. Relative humidity : Rate of transpiration is inversely proportional to the relative humidity.

4. Velocity of the wind : The rate of transpiration is directly proportional to the velocity of wind. However, the wind of 40-50 km/hr brings closing of stomata and thus decreases the rate of transpiration.

5. Atmospheric pressure : Rate of transpiration is inversely proportional to the atmospheric pressure.

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

Tensile strength
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Who introduced the apoplast—symplast concept ?

E. Munch (1930).
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What is transmembrane pathway ?

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