Introductory Crop Physiology (1+1)

Differences between active and passive water absorption

Permanent wilting percentage or wilting coefficient

	Active water absorption		Passive water absorption
1.	It is due to the activity of the roots and particularly root hairs	1.	It is due to the activity of the upper part of the plant such as shoot system.
2.	Osmotic and non osmotic mechanisms are involved	2.	Passive absorption is due to transpiration in the upper part
3.	In active absorption, the osmotic process involves diffusion pressure deficit (DPD) of the cells. The root hairs have more DPD as compared to soil solution.	3.	It occurs due to the tension created in the xylem sap by transpiration pull
4.	Active absorption involves symplastic movement of water in root hairs. The water first enters the cell sap and then passes from one cell to another. Such type of movement, where living protoplasm involved is called as symplast	4.	In passive absorption, water moves probably through the free spaces or apoplast of root. The apoplastic movement of water includes cell wall and intercellular spaces, which are fully permeable. The water can reach up to endodermis through apoplast but it moves through the endodermis by symplast.
5.	The evidences for active absorption are root pressure, bleeding and guttation.	5.	The evidence for passive absorption can be given by cutting the roots under water. The absorption of water continued even if all the roots are removed.