Tag: biology

The respiratory quotient (R.Q) is the ration of the volume of the CO$ _{2}$ released to the volume of the O$ _{2}$ utilized by a substrate during the process of respiration. It solely depends on the nature of the substrate. The R.Q. reflect the nature of the substrate, for example, R.Q. 1 indicated that glucose is the respiratory substrate.

Guttation is a loss of water from plants in liquid form through hydathodes. The force responsible for guttation is positive root pressure. Guttation is easily observed when transpiration rate is low and soil is well watered.

Root pressure helps to pull the cell sap through a plant stem to the leaves. It occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when transpiration is low during the day.

When transpiration is low and soil is generally well watered, a positive root pressure develops. Under the influence of positive root, pressure water oozes out from ends of xylary elements in plants. The main reason for the development of positive root pressure is the active absorption of minerals and water by roots.

Transpiration is defined as loss of water as gas or vapors from aerial parts, like leaves through the stomatal pore. If there is less of transpiration as due to high atmospheric humidity and the soil is well watered; there will be an increase in root pressure. The increased root pressure leads to oozing out of a solution of minerals from hydathodes (called as guttation) and other openings (called as bleeding). 

Root pressure can be defined as the pressure exerted by the cortical cells of the root upon the sap in the xylem vessels which pushes the sap upward if the stem of the plant is cut just above the root water seeps or exudes out of the cut end of the stem for a considerable period of time. This indicates that there is a force pushing water up the stem from the roots.

One atmospheric pressure can raise water to a height of more than $32$ feet. so a pressure of about $13$ atmospheres would be required to raise water at the top of a $416$ feet high tree. The tension developed in the xylem sap of trees that are actively transpiring can be measured only indirectly and has been found to be high as $-77$ bars.

One atmospheric pressure can raise water to a height of more than $32$ feet. So a pressure of about $13$ atmospheres would be required to raise water at the top of a $416$ feet high tree. The tension developed in the xylem sap of trees that are actively transpiring can be measured only indirectly and has been found to be high as $-77$ bars.